W 71' 1 2 5 7 OR 111577 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Technical Report 32-1436 A Systematic Review of Heat-Shieid Tectinology for Extraterrestfi$l Atmosptieric Entry mBKBm 11 Robert G. Nagler JET PROPULSION LABORATORY CAliFORNIA INSTITUTE OF TiCHN0i06Y PASADENA, CALIFORNIA March 15, 1970 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Technical Report 32-1436 A Systematic Review of Heat-Sliieid Tectinoiogy for Extraterrestrial Atmospiieric Entry Robert G. Nagler JET PROPULSION LABORATORY CAliFORNIA iNST!TUTE OF TECHNOLOGY PASADENA, CAliFORNIA March 1 5, 1 970 I Prepared Under Contract No. NAS 7-100 National Aeronautics and Space Administration Preface The work described in this report was performed by the Engineering Mechanics Division of the Jet Propulsion Laboratory. JPL TECHNICAL REPORT 32-1436 iii Contents I. Introduction 1 II. The Review Process 1 A. Technology Outline 3 B. Technology Rating 3 C. Task Definition 7 D. Task Magnitude Assignment 7 E. Program Plans 7 III. Venus-Entry Heat-Shield Development Program 7 A. Typical Spread of Venus-Entry Missions 7 B. Critical Tasks From Review 9 C. Proof-Test Feasibility 10 D. R&D Support Plan for 1973 Mission Alternatives 11 E. R&D Support Plan for 1975 Mission Alternatives 12 Appendix A. An Outline of Heat-Shield Technology for Extraterrestriol Atmospheric-Entry Missions 15 Appendix B. A List of Heat-Shield R&D Tasks for Extraterrestrial Atmospheric-Entry Missions 64 Tables 1. Contents of technology outline (Appendix A) 3 2. Entry environment definition 5 3. Rating scale 5 4. NASA ground test-simulation facilities for nominal Venus-entry trajectories . . 12 5. Typical preproject fund projections for 1973 mission 12 6. Typical preproject fund projections for 1975 mission 12 Figures 1. A technology review process for planning heat-shield technology 2 2. Technology rating chart for planetary entry 4 JPL TECHNICAL REPORT 32-1436 Contents (contd) Figures (contd) 3. Summary sheet for comparing company technology ratings and for emphasis rating 6 4. Task resource summary 8 5. Representative Venus-entry missions 9 6. NASA ground test-simulation capability compared to typical Venus-entry trajectories 11 7. Flow diagram for preproject heat-shield R&D support of a Venus 1973 spacecraft mission 13 8. Flow diagram for preproject heat-shield R&D support of a Venus 1975 spacecraft mission 14 vi JPL TECHNICAL REPORT 32-1436 Abstract Heat-shield technology is reviewed systematically by considering individually each parameter that contributes to heat-shield design. These parameters range from ablation models to pyrometer calibration, from the effects of adding fluorine to polymeric molecules to nondestructive testing of finished heat-shield subsys- tems. Each parameter has been rated as to its effect upon mission success and heat-shield design, and tasks have been formulated to investigate the most im- portant parameters analytically or experimentally. As an example of the utility of the review methodology, alternative research and development support activi- ties have been delineated for typical Venus-entry missions based upon the formu- lated tasks and their criticality ratings. JPL TECHNICAL REPORT 32-1436 vii A Systematic Review of Heat-Shield Technology for Extraterrestrial Atmospheric Entry I. Introduction In 1965, NASA began seriously to consider a Mars-entry mission. An informal NASA heat-shield coordination group was formed, at the urging of the Jet Propulsion Laboratory (JPL), to investigate the special problems of extraterrestrial planetary entry. The membership of this group included Ames Research Center (ARC), Langley Research Center (LaRC), Lewis Research Center (LeRC), Manned Spacecraft Center (MSC), and JPL. This group has met informally one or more times a year since 1965 to review current research and development (R&D) pro- grams and to provide coordinated direction to the NASA programs in the heat-shield area. Based upon the extensive information exchange set up by these meetings, a myriad of new problems in extra- terrestrial atmospheric entry have been uncovered. In the planetary exploration program, vast funding to solve these problems is not likely. To make the best use of available funds, it is necessary to investigate the antici- pated problem areas systematically, and to fund only those efforts that are critical to mission success. The remainder of this report describes such a review. A Venus-entry heat-shield development program is delin- eated as an example of the program plans that use of the review makes possible. II. The Review Process Various approaches to carrying out a technology review of heat shields or thermal-protection systems were con- sidered. A flow chart of the methodology actually used in the review is provided in Fig. 1. The conceptual basis for the review process is shown on the left of the figure. First, all parameters of any importance to heat-shield technology are examined and listed. Each parameter is then rated as to its importance to particular problem areas in each of the missions under consideration. The importance ratings are used to define specific tasks, grouping the related parameters and delineating specific areas that warrant effort. Each of these tasks is then assigned manpower and funding requirements. The avail- ability of both facilities and applicable experience in each area is also estimated. The importance ratings and resource information may be used to construct specific programs that match the stated funding emphasis of each NASA Headquarters agency, and yet provide a balanced technology advance in each area. JPL TECHNICAL REPORT 32-1436 CO >- 00 > LU a: U Z o u 00 1— z LU ai 2o lo So- 1— ./,Z z SPO < ?^ p z z 5lo OS- UJ o o cc 1 xSk U O N z ^ LU UJ m O 1- 5 o ?z§ Q O °- U ^-i z ^ Ll_ Zp5 o z O z ^ -■ 9J u. LU Q O <=" u LU 1— >- T^ Z U. 1 is LU •- o oo o. U 00 ^ < < Z a: Z o oo ;i U. o LU z —1 ►- o o O _l O z X u LU 1- Q r 1 LU " O- LU Li. LU Ox 00 U 1° > u m oo O oo §u 5 <^ O zS o 1 1 I z 3 LI. '^ >- o o ^ i2i f o< ozsi -T' X LU oy"' r! \=. zS Otii X z yo *-. z 1=1 >- u. z 00 Z5 < Qi 2^ 1^ o< z < o ?^ (J oo ir< z < LU 5 9 ^ 00 < SI s: oo 5 u. — O tii z < o« Et; z> t^ ^o 1— oo >■ LU <■ 3 < 2> <^=! LU CO 1 z L^< Olo So GEMENT INTO SPECIFIC PROGRAM PLANS D ON VARYING FUNDING INCREMENTS AND RATED IMPORTANCE ri J" LU in ^ po z 2 ^ << y OO 1- LU a: >- CD 0£ oo 7 LU 2- s O) -C ic o c o i c c a> 1 S 8. i o> a c '± c 0) 2 8. £ i o LU 4- c 1) £ 0) 8L 1 c «> 1 5 c 1 0) o i 15 o c c C 1 0) !^ a 8. c « o "5 c _o a O c O) o JPl TECHNICAL REPORT 32-1436 Table 2. Entry environment definition Parameter Mart Venus Jupiter Out of orbit Direct entry Earth similar High energy Low energy High energy Peak convective heat- ing, Btu/ftVs Peak radiative heat- ing, Btu/ftVs Peak pressure, atm 50 0.5 500 50 1.0 1000 1000 3.0 3000 14 X 10' 100 6000 6000 20 10 X 10* 10 X 10' 200 specified for high-energy Jupiter entry. With heating- rate ranges from to 10" Btu/ft^/s, all earth-entry mis- sions are also included (at least as to degree of severity) because differences in atmospheric composition have some effect. The two columns under each mission in Fig. 2 (impor- tance and potential) are filled in according to the five- point rating scale given in Table 3. The importance rating is essentially a measure of the effect of the indi- vidual parameter upon mission feasibility or success. Therefore, an item may be key (*); may have a very large effect (1); could be of long-range significance only, with the magnitude and timing of an output that is not immediately obvious (2); could be needed as a computer input, but without significant accuracy requirements (3); or could be without relative merit (4). The ratings for potential or probability of achieving an improvement in reliability, weight, or cost— given reasonable funding— is a more difficult scale. Two attempts at quantification are shown in Table 3; however, it really comes to a per- sonal feeling of potential rather than any real, definable break between categories. The following 14 organizations have been contacted, at one stage or another, to participate in the rating: (1) Ames Research Center, Moffett Field, Calif. (NASA). (2) Langley Research Center, Langley Station, Hampton, Va. (NASA). (3) Lewis Research Center, Cleveland, Ohio (NASA). (4) Manned Spacecraft Center, Houston, Tex. (NASA). (5) Jet Propulsion Laboratory, Pasadena, Calif. (NASA). (6) Air Force Materials Laboratory (Department of Defense). Table 3. Rating scale Raring Importance Potential (reliability, cost, weight) * Key Key 1 High Large (>50%) 2 Long range Significant (10-50%) 3 Needed, but small effect Refinements (1-10%) 4 Minor Insignificant (<1%) (7) Aerotherm Corp., Mountain View, Calif. (8) Avco Corp., Lowell, Mass. (9) Boeing Co., Seattle, Wash. (10) General Electric Co., Valley Forge, Pa. (11) Lockheed Corp., Sunnyvale, Calif. (12) Martin Co., Denver, Colo. (13) McDonnell Douglas Corp., St. Louis, Mo. (14) McDonnell Douglas Corp., Santa Monica, Calif. A sample summary sheet to provide cross-company comparison of the individual ratings for a particular mission is shown in Fig. 3. This sheet can be used not only to make a consensus of the relative importance of each parameter, but also to provide NASA with a guide to the biases in the various organizations active in the field. Up to the time of this writing, only the Avco Corporation, the General Electric Company, JPL, the Martin Company, and the St. Louis division of the McDonnell Douglas Corporation had submitted a full response to the rating activity. Most of the other orga- nizations aided in making the technology outline (Appendix A) complete, but had not yet responded on the rating sheets. JPL TECHNICAL RfPORT 32-1436 JPL ARC LaRC LeRC MSC AFML AERT AVCO BOEG DOUG GE LOCK MART McD Fig. 3. Summary sheet for comparing company technology ratings and for emphasis rating JPL TECHNICAL REPORT 32-1436 C. Task Definition The available ratings from participants were used to compile a list of over 350 tasks covering the first three rating categories only. This list is included as Appendix B. Each task contains one or more parameters from the technology outline, grouped together in such a way as to take advantage of particular analytical techniques or experimental facilities. The list of tasks is organized as shown in Table 1. Some of the task listings have (*), (1), or (2) following the task number. These symbols represent the composite rating of the participants for the two nominal Venus missions. Tasks listed without a symbol in parentheses are peculiar to Mars or Jupiter, but not to Venus. In each subcategory, tasks are listed according to their Venus priority. Of the 335 tasks with some Venus priority, only 6% were given the critical priority rating. Another 30% were given the next priority rating, which means that they could have a large effect upon weight, cost, reliability, and mission success. The remaining tasks are all tasks with long-range research implications. A number of these should always be funded as a link to the future, but specific selection is normally dependent upon individual interest in the NASA research centers rather than upon realizeable immediate benefit. Aiajor lunuing eriipiiasis, on tiie otner hanu, siiouiu go to the critical or key tasks. D. Task Magnitude Assignment To establish plans for an R&D program, some esti- mates of funding requirements are desirable. Beginning with the form shown in Fig. 4, and based upon discus- sions held with representatives of the various NASA research centers and industry, each of the tasks listed in Appendix B can be assigned an estimated resource re- quirement. It is important to know (1) the length of time the effort will take, (2) the average manpower require- ment per year, (3) the type of manpower needed, (4) the typical support personnel requirements (e.g., technicians or computer operators) needed for each technical man- year, (5) any facility cost, and (6) where the capability exists (in NASA or in industry). At this point, only the critical tasks discussed below have been assigned an esti- mated resource requirement. Although information is readily available for most of the other tasks, it has not been systematically reviewed and incorporated. E. Program Plans At this stage, with the tasks identified, priorities as- signed, and estimates of necessary resource allocations defined, specific programs can be structured to solve the problems of particular missions or groups of missions to Mars, Venus, or Jupiter. Funding responsibility can be assumed by each NASA agency according to the stated interests and desires of that agency. Tasks without nat- ural funding sources can be identified, and action taken to relieve the obvious gaps. For each funding agency, different incremental levels of funding can be delineated, with a description of the gains and losses inherent in each level. It is important to create a balance among specific project or mission needs, exploratory studies, technolo- gies or facihties requiring long lead times, advanced development, and long-range technology research. A program plan for a variety of Venus-entry missions is provided as an example. III. Venus-Entry Heat-Shield Development Program Recent exploratory studies of 1973 or 1975 Venus-entry probe missions, with 1971 or 1973 project-funding starts, have provided an example to verify the utility of such a technology review. Because design normally freezes after the first 6 mo of a 2-yr project of this type, some preliminary heat-shield advanced development must be accomplished before the project begins if the new ablation-regime experience of Venus entry is to be fea- sible. A look at the Venus-entry envirorunent for a spread of typical missions provides some rationale for the criticality of the key tasks selected from the review, with special emphasis upon ground proof-test feasibility. If these critical tasks are then placed in a time perspec- tive, R&D support plans can be delineated. A. Typical Spread of Venus-Entry Missions Three representative missions can be examined as ex- amples of various degrees of severity in the entry-heating pulse for Venus. These missions are shown in Fig. 5. The most severe heating condition is shown as mis- sion A, which represents a 44,000-ft/s entry at —45 deg to the planet from a 1973 Venus-Mercury flyby. With a ballistic coefficient of 0.6 slug/ft^, this mission provides an extreme radiative-heating rate at the nose of approxi- mately 10,000 Btu/ftVs— even after the tradeoffs between nose bluntness, dynamic stability, etc., have been made. This magnitude of heating on blunt bodies exceeds earth experience, and provides considerable uncertainty in heat-shield weight calculations. Mission B represents a limitation chosen to keep the heating and pressure pulse within ground test-facility JPL TECHNICAL REPORT 32-7436 Emphasis rating Time scope Effort scope Manpower type Support ratio Facility cost, 10*^ dollars Existing NASA capability Industry capability Years Man -years Analy Exper Support <0.01 <0.1 <1 >1 Year Prof Fig. 4. Task resource summary JPL TECHNICAL REPORT 32-1436 ■N^ 10 o z < UJ u UJ > z o o I— z o a. I Z o I— < Z o < < Q I o 10 - 10 10 MISSION A V = 44, 000 ft/s = 0.6 slug/ft'' y^= -45 deg 2/ - ^^ — q^ = 13,600 Btu/ft /s • q = 4000 Btu/ftVs f MISSION B Vp = 40,000 ft/s 4= 0.6 slug/ft = -45 deg = 350 Btu/ft^s MISSION C Vg = 36,000 ft/s 4= 0.3 slug/ft^ L y^ = 45 deg 2 - _L 10 10 ' 10 ' 10" STAGNATION PRESSURE, atm Fig. 5. Representative Venus-entry missions 10 10 capability. (This comparison is discussed below.) The mission consists of a 40,000-ft/s entry at a — 45-deg angle to the planet and with a ballistic coefficient of 0.6 slug/ft^. Mission C is typical of a low-energy Venus entry, either direct or out of orbit, with Apollo technology pro- viding sufficient heat-shield qualification. In this case, the initial entry velocity is held below 36,000 ft/s, at the same —45-deg entry angle to the planet, and the ballistic coefficient is reduced to 0.3 slug/ft^. B. Critical Tasks From Review TV./.. .^..Cfir^/^l ^ ,1.-.- 1,.^:„ i.„„Ur. *.„1^,^« £«^ — t-'U^ ±^x\^ ^AiUCai ^^tjiiipiiici-rtiiiiiyaia iciSKS lai^cii iiOiii ili^^ review are summarized as follows: (1) Establish credence limits on available computer pro- grams for Venus-entry material-response analysis. (2) Carry out parametric studies of Venus-entry heat- shield requirement, using best available program. (3) Make minimal modifications to best available pro- grams to make them more representative of true state of art for Venus entry. (4) Develop improved mathematical models to empir- ically represent critical uncertainty areas: (a) Internal flow processes, including degree of equilibrium, cracking and redeposition, chem- ical erosion, etc. (b) Internal degradation processes under high heating rates. (c) High-blowing-rate effects. (d) CO2 atmosphere radiative heating. (e) Rough surface-radiation balance. (f ) Turbulent transition on cone. The input-data-measurement tasks taken from the re- view are summarized as follows: (1) With existing capabilities, measure thermal, opti- cal, mechanical, and degradation properties of heat-shield materials of interest to Venus entry (where not already available). JPL TECHNICAL REPORT 32-1436 (2) Establish brittle transition criteria for Venus-entry heat-shield materials. (3) Ensure that ground, launch, and transit environ- ments introduce no catastrophic failure mecha- nisms by making judicious material selections and carrying out simple supplemental tests. The test-facility-development tasks taken from the re- view are summarized as follows: (1) Establish a minimum-acceptable calibration proce- dure for existing ablation-test facilities. (2) Establish applicability of monochromatic laser radiation to high-heating-rate material-response measurements. (3) Build a large laser test facility (required only for Venus-entry velocities greater than 40,000 ft/s). The ablation-test-program tasks taken from the review are summarized as follows: (1) Establish constraints on Venus-entry mission choice due to ground test-simulation limitations. (2) Screen ground-testable Venus-entry environments for ablation-mechanism definition, using standard ablative composites. (3) Screen a variety of readily available improved ma- terials, using standard critical environments, and loop with material development. (4) Characterize ablative performance of final candi- date materials. The material-development tasks taken from the review are summarized as follows: (1) Tailor available resins and fillers into a composite that more closely satisfies transit and entry re- quirements for Venus. (2) Investigate applicability of easily fabricable dual- density composites (high-density, high-ablation- efficiency surface layer with a low-density, high- insulation-efficiency sublayer) . Accurate input data are not generally available on the materials of interest, and must be measured, along with some evaluation of the effect of environmental prehistory upon the Venus-entry performance. The same historical testing problem exists of inade- quate facility definition. High-energy radiant-heating facilities (if applicable) will be necessary to produce the 10,000-Btu/ft^/s radiative-heating rate typical of mis- sion A. The available facilities must then be used to best advantage, within funding constraints, to qualify the heat-shield candidates and furnish data for analysis. Polymer-chemistry advances allow better resin systems and better processing control than those generally used in the ablation industry. Some of these materials and techniques could be incorporated in any development program to increase ablator reliability. Composites with a hard outer layer and a low-density insulating inner layer are one form with great promise of weight savings for missions with longer entry times. C. Proof-Test Feasibility A comparison of proof-test feasibility is made in Fig. 6 for the three missions shown in Fig. 5 and the four major NASA entry-heating test-facility operations. The key to specific facilities is provided in Table 4. All of the facili- ties cover the Apo/Zo-similar mission, as expected, because these facilities were primarily developed to support the Apollo program. The Structures Division at LaRC ap- pears to provide the best simulation of the early portion of the trajectory, whereas ARC and the MSC appear to provide better high-pressure simulation for the later por- tion of the trajectory. The MSC facility designated QJ) on Fig. 6 does not actually provide the testing capability shown. The nozzle exit for these conditions is only 1.5 in. Therefore, the heating rates quoted for a flat-faced 1.25-in. sample are, for the most part, not really possible. Even with this in mind, extrapolation to the 40,000-ft/s trajectory is probably reasonable. The 44,000-ft/s trajec- tory, on the other hand, represents a questionable extrapolation. These conclusions are further complicated by the nec- essary radiative-heating simulation (see Fig. 5). On a 1-in. sample, ARC can superimpose 1000 Btu/ft-/s with 14 arc lamps, MSC can superimpose 500 Btu/ft^/s with four arc lamps, and JPL can superimpose 300 Btu/ft-/s with two arc lamps. Although the ARC, MSC, and JPL facili- ties are sufficient for the Apo??o-similar mission, only the ARC facility gives a sufficient indication of extrapolation for the 40,000-ft/s entry case. To investigate the material compatibility with radiative- heating rates of the order of magnitude of 10,000 Btu/ftVs, a high-energy radiant-heating facility is needed. One such 10 JPL TECHNICAL REPORT 32-1436 10 3 CO < O z u uj > z o u \— z o a. Z O 1— < z o < 10^ 10 3 10 NORMALIZED TO 1 .25-in. FLAT-FACED TEST CONFIGURATION IN FACILITIES NUMBERS REFER TO KEY IN TABLE 4 LaRC STRUCTURES DIV MSC -ARC AMPD = APPLIED MATERIALS AND PHYSICS DIVISION 10 10 10 ■ 10" STAGNATION PRESSURE, atm 10' 10' Fig. 6. NASA ground test-simulation capability compared to typical Venus-entry trajectories facility is being constructed by ARC at present, and JPL is investigating the possibility of achieving even higher- energy densities. All of this indicates that (1) the high- energy radiant-heating facility is needed for mission A, (2) existing facilities provide adequate extrapolation for mission B, and (3) existing data will suffice, for the most part, for mission C. D. R&D Support Plan for 1 973 Mission Alternatives A typical flow diagram for the preproject R&D sup- port on a 1973 Venus spacecraft mission at 44,000 ft/s from a Venus-Mercury flyby is shown in Fig. 7. Most of the FY 69 tasks have been funded. To carry out the remainder of the tasks in FY 70, the NASA organization with project managership would have to assume direc- tion and coordination leadership. Most of the activities within NASA already exist as tasks; only direction for a specific mission is needed. The extra funds needed for industry to manufacture and characterize materials, to build facility components, and to carry out supplemental tests are estimated in a gross sense in Table 5. For the mission A assumption (the Venus-Mercury flyby), about $1.5 million is needed. For the mission B assumption, the need for a laser facility is eliminated; therefore, the funding requirement drops. For the mis- sion C assumption, Apollo technology eliminates some of the analysis and testing, further reducing the total. Assumption D provides a heavy heat shield (15% or more of the entire vehicle weight), which contains a high enough factor of safety in relation to heat-absorption capability for reliability to be assured without more than superficial tests after the project begins. Detailed calcu- lations of heat-shield requirements, with the limited analysis techniques available at present, indicate that approximately 3-10% of the vehicle should be heat shield. The percentage is dependent upon the trajectory and statistically estimated factors of safety, which are calculated from uncertain inputs. Under assumption D, JPL TECHNICAL REPORT 32-1436 11 Table 4. NASA ground test-simulation facilities for nominal Venus-entry trajectories Number (Fig. 6) Facility 1 Ames Research Center* 2.5-cm constricted arc: 2-in. exit 2 Ames Research Center 1.25-cm constricted arc: 2.75-in. exit 3 Ames Research Center Linde N~4001: 2-, 7-, 12-, and 24-in. exits 4 Ames Research Center Linde N-4000: 2-, 7-, 12-, and 24-in. exits 5 Langley Research Center, Linde N-4001: 2-, 4.6-, and AMPD 7.6-in. exits 6 Langley Research Center, Rotating arc: 2-, 3.3-, 6.6-, AMPD and 20-in. exits 7 Langley Research Center, AMPD Ceramic tunnel 8 Langley Research Center, Linde N-4001: 2-, 4-, and Structures Division 6-in. exits 9 langley Research Center, 3-phase ac arc: 2.75-, 4-, Structures Division and 6-in. exits 10 Langley Research Center, TD double-end arc: 2- and Structures Division 6-in. exits n Manned Spacecraft Center" ARMSEF: 5-, 10-, 15-, and 20-in. exits 12 Manned Spacecraft Center DCA; 1.5-in. exit 13 Manned Spacecraft Center MRA: 1.5-in. exit — Jet Propulsion Laboratory*^ PG500 arc: 2- and 3-in. exits "Superimpc Radiative energy rac sed radiative heating of 1000 heating up to 10,000 Blu/ftVs iation system. Stu/ftVs is available at present, is proiected with the new high- ''Superimpc sed radiative heating of 500 E tu/ftV> is available at present. *^Superimpc sed radiative heating of 300 E tu/ftVs is available at present. no preproject funds are required in the heat-shield tech- nology area, and reliability is achieved by an overweight condition. E. R&D Support Plan for 1 975 Mission Alternatives Missions projected for 1975 are less severe than the comparative 1973 examples. A 38,0(X)-ft/s mission in 1973 is replaced by a 36,000-ft/s mission with the same general launch-energy requirements. The comparison is made on a similar basis, however, with the maximum- entry-velocity mission still above the present groimd test-facility capability and requiring development of a high-energy radiant-heating test facility. A typical flow diagram for the preproject support of a 1975 Venus-entry spacecraft mission, with a maximum entry velocity of 42,0(X) ft/s, is shown in Fig. 8. Again, most of the FY 69 tasks have been funded. The other tasks are essentially the same as those for the 1973 mis- sion; they are spread out in time, however, and more opportunity is provided for the development of material improvements and unique testing capabilities within the framework of the critical tasks listed in Section III-B, above. Typical fund projections (Table 6) show about half again as much as those estimated for the 1973 mis- sion (see Table 5). Most of this increase is due to addi- tional effort towards increasing the confidence level in the heat shield that will finally be chosen for the mission. It should be remembered that these estimates are for the items the review has designated as critical. Other, or looser, interpretation of the review could add a consid- erable number of additional tasks, with the inherent need for additional funds. Assumption D still eliminates the need for any preproject R&D. Table 5. Typical preproject fund projections for 1973 mission Astumpfion Fiscal Year funding, 10' dollars Total preproject funding, 10' dollars 1969 1970 Mission A 600 900 1.5 Mission B 300 700 1.0 Mission C 100 400 0.5 D Table 6. Typical preproject fund projections for 1975 mission Assumption Fiscal Year funding, 10' •*• in O 0) 2 = I .£ ^ Ic o in » J. I o 2 r. « o c 5. .2 £ » o E o 0) o l/L Is JPl TECHNICAL REPORT 32-7436 13 o w » w a a. O 0) 8: * 2 « «> «: 0) d ■c o a..S 0> lA E o a o eo D) 14 JPL TECHNICAL REPORT 32-1436 Appendix A Contents I. Ablation Theory 16 II. Computer Program Development 21 III. Characterization ond Physical Properties 22 IV. Thermal and Optical Properties 23 V. Mechanical Properties 28 VI. Electrical Properties 33 VII. Degradation Kinetics Investigations 34 VIII. Pre-entry Environmental Compatibility Tests 38 IX. Entry-Simulator Development 40 X. Entry-Simulator Testing 46 XI. Diagnostic Instrumentation Development 47 Xll. Flight Test 50 XIII. Rocket-Nozzle Testing 51 XIV. Resin Development 52 XV. Filler Development 54 XVI. Composite Development and Fabricability Investigations 56 XVII. Nondestructive Testing 60 XVIII. Design Criteria and Parametric Studies for Design 62 JPL TECHNICAL REPORT 32-1436 15 Appendix A An Outline of Heat-Shield Technology for Extraterrestrial Atmospheric-Entry Missions Survival of an entry vehicle during the atmospheric- deceleration portion of an extraterrestrial scientific mis- sion is an important part of the total mission reliability. Rocket-nozzle performance provides a similar contribu- tion. On a flight vehicle, these heat shields may appear to be reasonably simple coatings over a structure; how- ever, many disciplines are involved in providing that simplicity (see Table 1). Chemistry evolves a material. Numerous thermal, optical, physical, chemical, mechani- cal, and electrical properties are measured to charac- terize the material and allow analysis. Aerothermal, thermal, and structural analysis techniques are combined to predict performance. Complicated and expensive facilities are evolved and operated to simulate as much as possible of the ground-storage, launch, transit, and entry environments. Finally, an attempt is made to manufacture this somewhat idealized material in large, reproducible quantities; then to apply it to real vehicle shapes, without inhomogeneities or significant manufac- turing errors. I. Ablation Theory Ablation has been defined by the American Society for Testing Materials (ASTM) as "a self regulating heat and mass transfer process in which incident energy is ex- pended by sacrificial loss of material." As outlined here, ablation theory covers the mathematical models believed to represent the physical processes actually occurring during this sacrificial loss of material. The items listed in the outline that follows are those parameters or effects that actually influence each of the physical processes under consideration. Any particular parameter may or may not be incorporated in any mathematical model that exists at present. Both solutions in which material re- sponse is coupled to the flow field and those with vari- ous forms and degrees of empiricism are considered, without more than superficial separation, to emphasize the individual physical processes. Heat sinks, reradiators, transpiration cooling, etc., are taken to be simplified cases of this theory. The various kinds of computer pro- grams that might be developed out of these theories are discussed in Section II of this appendix. A. Internal Heat-Transfer Processes 1. Solid conduction. a. Temperature effects. (1) Low-temperature dropoff. (2) Degradation layer transition. (3) High-temperature variation. (4) Hysteresis. b. Virgin material structure. (1) Anisotropy. (2) Filler material (oxide, carbon, etc.). (3) Filler form (fiber, powder, cloth, microbal- loon, etc.). (4) Honeycomb. (5) Permeability. c. Char structure. (1) Char solid structure (geometric form). (2) Porosity. (3) Ordering. (4) Swelling or shrinkage. (5) Anisotropy. (6) Pyrolytic or nonpyrolytic deposition. (7) Sublimation. (8) Micro- or macrocracking. (9) Sihcone oxides and carbides. (10) Filler material and form. 2. Caseous conduction. a. High-temperature effects. (1) High-temperature variations. (2) Species variations. 16 JPL TECHNICAL REPORT 32-1436 b. Pressure effects. (1) Vacuum. (2) Pressure gradient. (3) Pore structure (size and geometric form). 3. Radiation conduction or transfer. a. Temperature effects— high-temperature variation. b. Char structure. (1) Pore structure (size and geometric form). (2) Pore optical properties. (3) Micro- or macrocracking. (4) Filler material and form. 4. Transmittance of surface radiation, a. Optical effects. (1) Absorption coefficient. (2) Internal reflectance. b. Geometry effects. (1) Surface roughness. (2) Pore geometry. (3) Cracks in char. 5. Mass transfer. a. Thermochemical state. (1) Equilibrium. (2) Nonequilibrium. (3) Frozen. (4) Cracking. (5) Rcdeposition. b. Flou) phenomena. (1) Pressure and pressure gradient. (2) Flow velocity. (3) Diffusion. (a) Darcy's law. (b) Other. (4) Pore structure (size and geometry). (5) Species. (6) Solid entrainment. B. Internal Heat Absorption 1. Specific energy absorption. a. Solid phase. (1) Swelling or shrinkage effects, (2) Specific heat. (3) Multiple constituents. b. Liquid phase. (1) Density variation. (2) Specific heat. (3) Blowing or flow. (4) Multiple constituents. c. Gas phase. (1) Pressure-density relation. (2) Specific heat of individual species. (3) Species identification. (4) Flow. 2. Thermal degradation of polymers. a. Form of mathematical representation. (1) Arrhenius. (2) Polynomial. (3) Other. b. Control parameters. (1) Temperature. (2) Heating rate. (3) Atmospheric species. (4) Pressure. (5) Geometric size or shape. c. Order of reaction. 3. Phase change. a. Melting and vaporization. (1) Organic. (2) Inorganic. JPL TECHNICAL REPORT 32-1436 17 (3) Blowing or flow. (4) Char interaction. (5) Structural vs nonstructural phases. b. Sublimation. (!) Vapor pressure. (2) Temperature. (3) Diffusion from surface. (4) Pressure or velocity gradient. c. Crystalline transformations. (1) Carbon. (2) SiO^. (3) Other. 4. Thermochemical reactions. a. Cracking of gases. (1) Temperature. (2) Pressure. (3) Species. (4) Char catalysis. b. Chemical erosion and internal oxidation. (1) Temperature. (2) Pressure. (3) Species. (4) Char composition. c. Pyrolytic or nonpyrolytic deposition. (1) Temperature. (2) Pressure. (3) Species. (4) Char catalysis. d. Silicon carbide formation. (1) Temperature. (2) Pressure. e. Char-reinforcement reactions. f. Photochemical reactions from incident radiation. g. Mixing and friction. C. External or Surface Heat-Transfer Processes J. Convective heat transfer. a. Planetary gases. (1) Mars: CO2, N2, Ar. (2) Venus: CO2, N„ H2O, O2, Ar. (3) Jupiter: H2, He, CU,, NH3. (4) Monatomic theory. b. Continuum flow. (1) Transition from free molecular. (2) Deviations. c. Chemical state of boundary layer. (1) Equilibrium. (2) Nonequilibrium. (3) Frozen. (4) Other. d. Pressure. (1) Level. (2) Gradient. e. Surface effects. (1) Catalysity. (2) Roughness. (3) Protuberances, holes, or slits. /. Velocity effects. (1) <30,000ft/s. (2) < 50,000 ft/s. (3) >50,000ft/s. (4) > 100,000 ft/s. g. Distribution around body. (1) Flow field, two- and three-dimensional. (2) Vehicle shape. (3) Heat-transfer theory, two- and three- dimensional. (4) Angle-of-attack effects. (5) Base heating. 18 JPL TECHNICAL REPORT 32-1436 h. Transition criteria. (1) Reynolds number. (2) Enthalpy ratio. (3) Velocity (pu) ratio. (4) Molecular weight of species. (5) a. (6) Surface roughness. i. Turbulence. (1) Model development. (2) Vorticity interaction. /. Mass injection coupling (see I-C-3, below), k. Boundary layer suction. 2. Radiative heat transfer. a. Planetary gases. (1) Mars: CO,, N^, Ar. (2) Venus: CO^, N^, H2O, O^, Ar. /o\ T :t. — ti xj„ i\.T„ cvi ■\-'/ j"iJl!-Ci. 1.1.2, ll'^, i'lC, VJXJ.4. (4) Monatomic. b. Surface absorptance at low wavelengths. c. Equilibrium. (1) Level. (2) Pressure. (3) Nonablative inviscid flow. d. Nonequilibrium. (1) Level. (2) Pressure. (3) Collision-limiting effects. '4' Trunca*"ion. e. Distribution around body. (1) Equilibrium. (2) Nonequilibrium. (3) Vehicle shape. (4) Angle-of-attack effects. /. Entropy layer. g. Precursor. h. Reynolds-number effects. i. Self-absorption. j. Ablative species absorption. (1) Gross. (2) Spectral. k. Blackout. I. Velocity effects. (1) <30,000ft/s. (2) <50,000ft/s. (3) >50,000ft/s. m. Turbulence effects. 3. Blocking or mass addition. a. Coupling with external flow. (1) Effective velocity vector of evolved gases. (2) Change in boundary-layer dimensions. (3) Change in shock-layer dimensions. (4) Temperature-gradient changes. (5) Pressure-gradient changes. (6) Upstream effects. b. High-blowing-rate theory. (1) Laminar. (2) Turbulent. c. Radiative-heating coupling. (1) Absorption. (2) Molecular weight of injected species. d. Convective-heating coupling. (1) Effective velocity vector of evolved gases. (2) Molecular weight of injected species. e. Transpiration coefficient. 4. Reradiation from surface. a. Emittance. (1) Level. (2) Change during ablation or mechanical erosion. JPL TECHNICAL REPORT 32-1436 19 (3) Spectral distribution. (4) View angle. b. Surface effects. (1) Surface porosity. (2) Superheating at the surface. (3) Temperature gradient (in depth). (4) Temperature gradient (laterally). c. Reabsorption in gas—convective-radiative coupling. 5. Combustion processes in boundary-layer gas and at char surface, a. Reaction-rate-limited oxidation. b. Dijfusion-role-limited oxidation. c. Gaseous combustion. d. CO^ equivalent oxidation. e. Reactions with nitrogen. f. Pressure effects. g. Combustion cutoff, h. Impurities. i. Oxidation inhibitors. /'. Combustion heating. k. Mass-transfer cooling from combustion species. 6. Sublimation. a. Rate equations. (1) Arrhenius form. (2) Knudsen-Langmuir equation. (3) Other. b. Pressure effects. (1) Partial-pressure equation. (2) Vapor-pressure data. c. Diffusion effects. (1) Escape (out) from surface. (2) Collision with .species moving toward surface. (3) Pick's law. (4) Diffusion limit. (5) Superheating at surface. d. Species properties. (1) C„, Si, SiO, etc. (2) Free energy functions. (3) Heats of formation. (4) Entropy. (5) Sublimation point. (6) Triple point. (7) Vaporization coefficient. (8) Micro- vs macrocrystallites. e. Impurities. 7. Vaporization. a. Oxides. (1) Silica. (2) Glass. (3) Other. b. Rlowing by subvaporizing species or lateral flow. c. Sublimation (see I-C-6, above). 8. Solid-mass removal processes. a. Liquid layer. (1) From glassy fillers. (2) From silicone elastomers. (3) Flow processes. (4) In-depth melting. (5) Viscosity dependence. b. Shear removal. (1) Pressure gradient. (2) Upstream transpiration. c. External-pressure effects. (1) Crushing. (2) Movement of boundary layer into char. 20 JPL TECHNICAL REPORT 32-1436 d. Porosity effects. (1) Pressure failure from confining of evolved gases. (2) Internal lateral gas flow. e. Thermal stress effects. (1) Char failure. (2) Bond-line failure. f. Coupling turbulent boundary layer with ablator response. g. Cross-hatching. h. All of the above (a-g) superimposed. D. Sublayer Heat-Transfer Mechanisms 1. Thin superconducting layers or sublayer heat sinks. 2. Foam conductance. 3. Honeycomb-sandwich conductance. (!) Metallic. /C^\ XT _ . 11 • {Z) iNonmcraiuc. 4. Multilayer-insulation conductance. (1) Normal temperatures. (2) High temperatures. 5. Unlike interfaces. (1) Contact resistance. (2) Thermostructural compatibility. 6. Rear surface cooling. (1) Active. (2) Passive. 7. Joints, windows, feedthroughs, etc, II. Computer Program Development To decrease costs and improve accuracy and under- standing, computer program development includes both the formulation of total programs— to analyze ablation theory or reduce ablation-related data— and the investi- gation of computation processes and data handling. A. Computer Usage Techniques 1. Numerical processes. a. Node selection. (1) Variable size. (2) Change with time. (3) Material property dependence. b. Numerical method. (1) Explicit. (2) Implicit. (3) Implicit/explicit. (4) Other methods. c. Differences between theory and numerical method. (1) Form. (2) Range of validity. (3) Biases. (4) Truncation errors. d. Time shortcuts. (1) Numerical method. (2) Computing-interval optimization. e. Simplification of calculation matrix. f. Time-integrating techniques. g. Multidimensional techniques. 2. Standardization. a. Notation. b. Units. c. Common subroutines. d. Input techniques. e. Output techniques. (1) Listing. (2) Plotting. (3) Punched card. /. Coordinate system reference. JPL TECHNICAL REPORT 32-1436 21 3. Data storage and retrieval. a. Storage techniques, h. Retrieval access. c. Graphical output. d. Punched-card output. B. Heat Shield Design Programs 1. Preliminary design. a. Simplified model. b. Sophisticated one-dimensional model for checkpoints. c. Simplified multidimensional singularity model. 2. Final design. a. Sophisticated one-dimensional uncoupled model. b. Fully-coupled model for checkpoints. c. Sophisticated multidimensional uncoupled model. d. Specialized sophisticated singularity models. C. Data Reduction and Analysis Programs 1. Plasma-jet data reduction. a. Flow-field analysis. (1) Definition of stream parameters. (2) Including mass addition. (3) Including specimen shape change. b. Correlation of ablation test data with facility parameters. c. Conversion of digital output data to diagnostic tables and plots and to ablation records. d. Correlation of flight environments with facility parameters. e. Derivation of ablation properties from ground test data. (1) Extensive. (2) Limited. 2. Material properties (per property where applicable). a. Derivation of property from laboratory test data. (1) Extensive. (2) Limited. b. Derivation of property from thermocouple data. (1) Nonhnear regression. (2) Parameter optimization. (3) Other. III. Characterization and Physical Properties The measurements outlined in this section are those that are used— to a greater or a lesser degree— to charac- terize ablative specimens before testing them for some other property. These measurements are essentially used to define the instantaneous state of the material after exposure to a particular environment and before the changes inherent in the next form of property measure- ment are initiated. Hence, undegraded ablative compos- ites have specific component and elemental distributions, and have density, permeability, and porosity. Chars may be similarly defined, but also require a measurement of their micro-ordering. A. Elemental Analysis 1. C, H, O, N, Si, F, CI, S, P, etc. a. Microcombustion. 2. Alkali metals. a. An electron-beam microprobe. 3. Relative accuracy of experimental techniques. B. Component Distribution J. Virgin material. a. Volume or weight percent of original materials. b. Additives. c. Cross-linking density. d. Infrared spectrum. e. Thin sectioning. (1) Cutting problems. (2) Mounting problems. 22 JPL TECHNICAL REPORT 32-1436 /. Photomicrographs. (1) Filler distribution. (2) Mixing efficiency. 2. Char. a. Carbon content. h. SiOg and other oxide contents. c. SiC content. d. X-ray diffraction pattern. (1) Diffraction intensities. (2) Crystal spacings. e. Thin sectioning. (1) Cutting problems. (2) Mounting problems. /. Photomicrographs. (1) Pore shape and size. (2) Filler structure. (3) Char structure. (4) Pyrolytic deposition. C. Permeability 1. As a measure of low-temperature diffusion of species out of or through an undegraded ablative composite. 2. Adequate experimental setup needed. 3. Permeability factors. a. Temperature dependence. (1) Activation energy. (2) Freauencv factor. b. Flow factors. (1) Area. (2) Time. (3) Quantity of permeant. (4) Natural porosity. (5) Open vs closed cell foam. D. Specific Volume (or Density) and Porosity 1. Measurement techniques. a. Micrometer. (1) Surface roughness. (2) Repeatability. (3) Applicability to partially charred samples. b. Photomicrograph. (1) Thin sectioning. (2) Area summation. (3) Representativeness. c. Fluid displacement. (1) Water. (2) Mercury. (3) Nitrogen (B.E.T.). (4) Apparent vs true density. (5) Open vs closed cells. (6) Two levels of porosity. (7) Shape effects. d. Grinding and weighing. e. Dye penetrant. f. X-ray. 2. Special problems. a. Variation with temperature. b. Cracking and pyrolytic deposition. c. Swelling or shrinkage. E. Vapor Pressures J, Equipment development. a. High temperature. h, Hign pre.ssure. 2. Special problems. a. Carbon triple point. IV. Thermal and Optical Properties Thermal properties, as outlined below, are primarily nonkinetically controlled, specific-energy-absorption- process constants and intemal-energy-transfer constants JPL TECHNICAL REPORT 32-1436 23 for solids and fluids. Emphasis is upon low-density, polymeric-based materials and porous derivatives such as chars. Optical properties, as outlined below, consist of sur- face phenomena or reactions to external radiation sources only. Emittance and reflectance techniques are basically well established, and require only adaptation to particu- lar situations or materials. Transmittance measurements and absorption-coefficient concepts on low-density heat- shield materials and their porous derivatives are both less available and less understood. Thermal expansion is also outlined in this section, although it could as well be located under Mechanical Properties (Section V). A. Thermal Expansion 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure. (3) Gas species. (4) Heating rates. c. Accuracy. (1) Temperature measurements. (2) Heat losses. (3) Expansion measurement. (4) Sample distortion. (5) Window distortion. d. Biases. (1) Equipment. (2) Analytical model. e. Standardization. 2. Equipment development, a. Dilatometer. (1) Increase useful temperature range. (2) Improve sensing mechanism. (3) Improve environmental compatibility. b. Optical comparators. (1) Increase useful temperature range. (2) Define sensitivity limit. (3) Minimize optical distortions. c. Interferometer. (!) Increase useful temperature range. (2) Define sensitivity limit. (3) Minimize optical distortions. d. Diffraction. (1) Increase useful temperature range. (2) Define sensitivity limit. (3) Minimize distortions. e. Other. 3. Special problems. a. Temperature. (1) Low (to -200''F). (2) High (to 7000 "F). (3) Time at temperature. b. Surrounding atmosphere. (1) Vacuum. (2) Extreme pressure. (3) Chemically active gaseous species. c. High heating rate. (1) Experimental approach needed. d. Sample representativeness. (1) Shape. (2) Ablation state. (3) Fabrication. B. Specific Heat of Solids 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure. (3) Gas species. 24 JPL TECHNICAL REPORT 32-1436 c. Accuracy. (1) Temperature measurements. (2) Heat losses. (3) Sample weight and shape. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. 2. Equipment development. a. Method of mixtures (drop method). (1) Expand temperature limits. (2) Automate operation and data recording. (3) Minimize oxidation and shock effects at high temperature. (4) Investigate environmental effects. b. Adiabatic calorimeter. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Investigate environmental effects. c. Bunsen ice calorimeter. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Investigate environmental effects. d. Differential scan calorimeter. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Investigate heating-rate effect. (5) Investigate representativeness of spcci xiii\-'Xi>ji e. Other. 3. Special problems, a. Temperature. (1) Low (to -200"?). (2) High (to 7000 "F). (3) Time at temperature. b. Surrounding atmosphere. (1) Extreme pressure. (2) Trapped internal gases. (3) Chemically active gaseous species. c. Sample representativeness. (1) Shape. (2) Ablation state. (3) Fabrication. C. Specific Heat of Evolved Gases 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure. (3) Species. c. Accuracy. (1) Temperature measurements. (2) Heat losses. d. Biases. (1) Calculation technique. (2) Equipment limits. e. Standardization. 2. Equipment development. a. Calculation from basic principles. (1) Availability of applicable data. b. Differential scan calorimeter. (1) Increase temperature limit. (2) Automate operation and data recording. (3) Adapt for liquid or gas measurements. c. Other. 3. Special problems. a. High temperature (to 7000" F). b. Surrounding atmosphere. JPL TECHNICAL REPORT 32-1436 25 (1) Extreme pressure. (2) Ionization and dissociation. D. Thermal Conductance 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure or vacuum. (3) Gas species. c. Accuracy. (1) Temperature measurements. (a) Surface. (b) In depth. (c) Along an interface. (2) Heat losses. (3) Sample configuration. (4) Anisotropy. (5) Surface contact. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. (1) Equipment. (2) Sample materials. 2. Equipment or technique development, a. Guarded hot plate. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Adapt for honeycomb sandwich or similar composite materials. (5) Adapt for superinsulation. h. Radial measuring techniques. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Improve sample configuration; set size and shape limits. (5) Improve measurement precision. (6) Adapt to nonhomogeneous material. c. Cut bar. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Adapt to absolute rather than comparative measurement. (5) Adapt to low-conductivity materials. (6) Adapt to anisotropic materials. d. Reverse calculation from internal temperature response. (1) Define accuracy in temperature-response data. (2) Investigate other factors lumped under conductance. e. Pulse methods. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental capability. (4) Investigate applicability of laser source. (5) Improve measurement precision. (6) Investigate radiation interaction. (a) With porous material. (b) With glassy reinforcements. (7) Investigate analytical model of interaction of a high-energy, short-time pulse on a porous surface. /. Other. 3. Special problems. a. Temperature. (1) Low (to- 200° F). (2) High (to 7000° F). (3) Time at temperature. 26 JPL TECHNICAL REPORT 32-1436 b. Surrounding atmosphere. (1) Vacuum. (2) Extreme-pressure gaseous conduction. (3) Chemically active gaseous species. c. Sample representativeness. (1) Geometrical shape. (2) Pore structure. (a) Open. (b) Closed. (c) Shape. (3) "Graphitization." (4) Ablation state. (5) Inhomogeneity. d. Anisotropy. e. Core-sandwich configurations. f. Superinsulation configurations. s. Joint, feedthrough, window, etc., conductances, h. Geometric limitations. (1) Flat plate vs radial. (2) Sample size. i. Internal radiative heat-transfer mechanisms. j. Differences between steady-state and transient techniques. E. Optical Properties 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure or vacuum. (3) Gas species. (4) Wavelength. (5) Angle of incidence. c. Accuracy. (1) Temperature level. (2) In-depth gradient. (3) Laterial gradient. (4) Heat losses. (5) Sample configuration. (a) Shape. (b) Anisotropy. (c) Surface roughness. (6) Optics. (a) Wavelength. (b) Beam spreading. (c) Beam distortion. d. Biases. (1) Equipment. (2) Emittance model. (3) Reflectance model. (4) Sample. e. Standardization. (1) Equipment. (2) Sample materials. 2. Equipment or technique development. a. Hemispherical emittance. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Increase wavelength range for both spectral and total measurements. b. Directiorml emittance. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Increase wavelength range for both spectral and total measurements. c. Parallel-beam source /hemispherical readout. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. JPL TECHNICAL REPORT 32-7436 27 (4) Increase wavelength range for both spectral and total measurements. (5) Improve source. (6) Improve optics (lens, filters, etc.). d. Hemispherical source/ parallel-beam readout. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Increase wavelength range for both spectral and total measurements. (5) Improve source. (6) Improve optics (lens, filters, etc.). 3, Special problems, a. Temperature. (1) Low (to -200°F). (2) High(to7000''F). (3) Time at temperature. (4) Lateral temperature gradient. (5) Internal temperature gradient. 6. Surrounding atmosphere. (1) Vacuum. (2) Extreme pressure. (3) Chemically active gaseous species. c. Sample representativeness. (1) Geometric shape. (2) Surface roughness. (3) Pore configuration. (4) Inhomogeneity. (5) Fillers. (6) Anisotropy. (7) Spectral vs diffuse. (8) Angle of incidence and lobing. (9) Laboratory specimens vs true samples. d. Apparent inequality of spectral emittance to spectral absorptance for ablative chars. e. Source development. (1) Higher temperatures. (2) Wider range of wavelengths. /. Optics development. (1) Diffraction gratings. (2) Prisms. (3) Filters for lower wavelengths. g. Absorptance coefficient. (1) Define adequately in relationship to porous surfaces. h. Transmittance. (1) Development of measuring equipment. (2) Total vs diffuse. i. Char profiling with reflectance measurements. /. Hot-gas optical properties, k. Light-pipe effects. V. Mechanical Properties As outlined below, mechanical properties cover all of the common properties used in structural analysis plus many of the structurally oriented tests investigating spe- cial failure mechanisms, e.g., shock, impact, etc. A. Tensile and Compressive Strength and Modulus 1. Evaluation of measurement techniques. a. Appropriateness to analysis requirements. b. Environmental factors. (1) Temperature. (2) Pressure. (3) Gaseous species. (4) Heating rate. c. Accuracy. (1) Temperature level. (2) Uniformity. (3) Sample configuration. (4) Loading. (a) Rate. 28 iPL TECHNICAL REPORT 32-143^ (b) Load-cell sensitivity. (c) Cell mounting. (5) Strain measurement. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. (1) Equipment. (2) Sample materials. (3) Specimen shape. 2. Equipment or technique development. a. Expand temperature limits. h. Automate operation and data recording c. Adapt for high-heating-rate tests. d. Expand loading-rate capability. e. Adapt for pyrolyzed samples. L lltiJI ulyC' ^ iouu-ccii senxitwity . g. Adapt for bidirectional-loading techniques. h. Adapt for vacuum testing. i. Adapt for testing during pyrolysis. j. Improve strain-measuring devices. 3. Special problems. a. High heating rate. b. High loading rate. c. In situ test. (1) In vacuum. (2) During pyrolysis. d. Temperature. (1) Low (to -200°F). (2) High(to7000°F). (3) Creep during time at temperature. (4) Cycling. e. Stress concentration. f. Investigation of flow and fracture behavior. g. Investigation of bidirectional loading, h. Material. (1) Ablative state. (2) Sample configuration. (3) Strain sensitivity at high compensation. (4) Ordering and pyrolytic deposition effects. (5) Directional properties or anisotropy. (6) Composites. i. Investigation of applicability of normal analyti- cal concepts. (1) Relationship between yield strength and ultimate strength. (2) Relationship between Young's, secant, and tangent modulus. (3) Poisson's ratio. (4) Elongation to failure. B. Flexure Strength and Modulus 1. Evaluation of measurement techniques. a. Appropriateness to analysis requirements. b. Environmental factors. (1) Temperature. (2) Pressure. (3) Heating rate. c. Accuracy. (1) Temperature level. (2) Uniformity. (3) Sample configuration. (4) Loading. (a) Rate. (b) Sensitivity'. (5) Strain measurement. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. (I) Equipment. JPL TECHNICAL REPORT 32-1436 29 (2) Specimen configuration. (3) Sample materials. 2. Equipment or technical development. a. Expand temperature limits. b. Adapt for temperature gradient through thickness. c. Automate operation and data recording. d. Adapt for high-heating-rate tests. e. Adapt for prepyrolyzed or partially pyrolyzed samples. f. Adapt for vacuum testing. g. Improve strain-measuring device, h. Adapt for high loading rate. 3. Special problems. a. Temperature. (1) Low(to-200°F). (2) High (to 7000° F). (3) Cycling. (4) Creep. (5) Test with temperature gradient through thickness. b. High heating rate. c. High loading rate. d. Material. (1) Pyrolyzed level. (2) Anisotropy. (3) Composites. e. In situ tests. (1) Vacuum. /. Sample configuration. (1) Three- vs four-point loading. (2) Beam length. (3) Beam width. (4) Span-to-depth ratio. C. Shear Strength and Modulus 1. Evaluation of measurement technique. a. Appropriateness to analysis requirements. b. Environmental factors. (1) Temperature. (2) Vacuum. c. Accuracy. (1) Temperature level. (2) Uniformity. (3) Sample configuration. (4) Loading. (5) Strain measurement. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. (1) Equipment. (2) Specimen configuration. (3) Sample materials. 2. Equipment or technique development. a. Short beam. b. Torsion. c. Plate shear. d. Pin shear. e. Aerodynamic shear. f. Sandwich shear. g. New techniques. (1) Char shear. (2) During aerodynamic ablation. 3. Special problems. a. Identity of true shear test without tensile or compressive components. b. Temperature. (1) Low (to- 200"" F). 30 JPL TECHNICAL REPORT 32-1436 (2) High (to 7000 -F). (3) Cycling. c. Shear application. (1) High rate. (2) Aerodynamic. d. Material. (1) Pyrolyzed level. (2) During ablation or after cooldown. (3) Anisotropy. (4) Composites. e. In vacuum. f. Relation of shear modulus to Young's modulus and Poisson's ratio. D. Brittle Transition Temperature 1. Evaluation of measurement techniques. a. Appropriateness to analysis requirements. }y. Environmental "factots. (1) Pressure. (2) Rate of loading. c. Accuracy. (1) Temperature level. (2) Uniformity. (3) Sample configuration. (4) Loading. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. 2. Equipment or technique development. a. Differential thermal arwlysis. b. Differential scanning calorimeter. c. Expansion. d. Torsional pendulum. e. Penetration. f. Electrical properties. g. Thermal properties. 3. Special problems. a. Physical identity of brittle transition temperature. b. What brittle transition temperature measures. (1) Change in polymer morphology. (2) Cohesive energy density. (3) Hindered rotation. (4) Chain stiffness. (5) Geometry variations. (6) Toughness. c. Material. (1) Fillers and reinforcements. (2) Pores. (3) Internal lubricants. d. Kinetics of transition. E. Thermai Shock I. Evaluation of alternate methods. a. Appropriateness to arudysis requirements. b. Environmental factors. (1) Heat. (2) Cold. (3) Pressure. c. Accuracy. (1) Initial temperature. (2) Shock temperature. (3) Rate of shock. d. Biases. (1) Equipment. (2) Inherent method. e. Standardization. 2. Equipment or technical development. a. Extreme heating rates. b. Extreme cooling rates. JPL TECHNICAL REPORT 32-1436 31 3. Special problems. a. Meaningfulness of any test. b. Relationship of results. (1) To tensile strength and modulus. (2) To thermal expansion. (3) To thermal conductance. (4) To specific heat. c. Trapped volatiles. F. Impact and Micrometeoroid Penetration 1. Evaluation of measurement techniques. a. Appropriateness to analysis requirements. b. Environmental factors. (1) Temperature. (2) Pressure. (3) Fluid contact. (a) Gas. (b) Full oxidizer. c. Accuracy. (1) Ability to define sample dimensions. (2) Temperature. (3) Ability to measure loading. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. 2. Equipment development. a. Izod. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Adapt for vacuum testing. (4) Increase impact rate. b. Charpy. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Adapt for vacuum testing. (4) Increase impact rate. c. Falling ball. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Adapt for vacuum testing. (4) Increase impact rate. d. Projectile guns. (1) Expand temperature limits. (2) Automate operation and data recording. (3) Adapt for vacuum testing. (4) Increase impact rate. e. Mass accelerators. 3. Special problems. a. Temperature. (1) Low (to -200°F). (2) Cycling. b. Impacting rate. c. Material. (1) Pore structure. (2) Filler. (3) Reinforcement. (4) Backup structure. d. Relationship to area under stress-strain curve. e. Fuel sensitivity. (1) Liquid oxygen. (2) Nitrogen oxides. /. In situ testing. (1) Vacuum. (2) Other transit environments. g. Angle-of-incidence effects. h. Ablator contamination. i. Effect of penetration on thermal performance. /'. Shielding requirements. 32 JPL TBCHNICAL REPORT 32-1436 G. Peel Strength at Ablator-Structure Interface 1. Evaluation of measurement techniques, a. Appropriateness to analysis requirements. b. Environmental factors— temperature. c. Accuracy. (1) Temperature level. (2) Uniformity. (3) Measure of strains from all sources. d. Biases. (1) Equipment. (2) Prestresses. (3) Inherent model. e. Standardization. 2. Equipment or technique development needed. 3. Special problems. a. Nature of structure. ^1) Metallic vs nonmetallic. (2) Original surface roughness. (3) Surface preparation. (4) Primer. b. Nature of adhesive. (1) Thickness and uniformity. (2) Reinforcement. (3) Rigidity. c. Nature of ablator. (1) Porous. (2) Rigidity. d. Temperature. (1) Low (to -200°F). (2) High (to 1000-F). H. Virgin-Char-Interface Strength I. Equipment or technique development. a. During ablation. b. After cooldown. 2. Special problems. a. In situ testing. b. Combined stress sources. c. Reinforcement contributions. 1. Combined Strength of Ablator-Structure Composite 1. Equipment or technique development. a. Flexure test with superimposed thermal gra- dients and pressure. 2. Special problems. a. Material considerations. (1) Flexibility. (2) Interface compatibility. (3) Charring. (4) Structure selection. b. Dynamic damping effects. c. Structural deformations. d. Temperature gradients across thickness. J. Fatigue J. Equipment or technique development. a. Low cycle— high strain. b. High cycle— low strain. VI. Electrical Properties The electrical properties of ablators are primarily concerned with signal transmission for altimeters or communications systems. For certain types of missions, staging operations and subsystem complication are de- creased if antermas are built into the ablator-structure subsystem or look through it at the planet. To do this, the structure and heat shield must either be entirely transparent to the signal wavelength or must have com- palible Iraiisparent windows built mto tiie fligut config- uration. Signal attenuation before, during, and after ablation thus becomes important. A method of predicting this attenuation from basic composite electric properties is also desirable. A. Signal Attenuation 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. JPL TECHNICAL REPORT 32-1436 33 b. Environmental limitations. (1) Temperature. (2) Vacuiim. (3) Gas species. (4) Heating rate. (5) Continuity of exposure. c. Accuracy. (1) Sample distortion. (2) Waveguide design. (3) Hot-gas attenuation. (4) Contamination. d. Biases. (1) Equipment. (2) Analytical model. e. Standardization. 2. Equipment development. a. Rotating disk with point or line heater. (1) Expand heating-rate limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Increase frequency and wavelength range. (5) Decrease exposure time per rotation. b. Wedge in plasma arc. (1) Expand heating-rate limits. (2) Investigate other sample configurations. (3) Improve sending-receiving units. (4) Allow wider range of sources, (a) G planar arrays, etc. (5) Automate operation and data recording. (6) Increase environmental-simulation capability. c. Other. 3. Special problems. a. Temperature. (1) High(to7000°F). (2) Time at temperature. b. Surrounding atmosphere. (1) Vacuum and vacuum breakdowm. (2) Contamination. c. Sample representativeness. (1) Geometric shape. (2) Ablation state. (a) Virgin material. (b) Partially pyrolyzed. (c) Fully pyrolyzed. (3) Thickness effects. d. Optical. (1) Wavelength. (2) Incident angle. e. Analytical determination of transmission proper- ties from temperature profile and dielectric data as a function of temperature. f. Develop facilities for microwave transmission under simulated ablation conditions. g. Flight test. B. Dielectric Properties 1. Dielectric strength and dielectric constant. a. Short time vs step by step. b. Frequency— to kilomegacycle region. c. Temperature. d. Vacuum. e. Gaseous species. 2. Volume and surface resistivity. 3. Power factor. 4. Loss tangent — less than 0.001. 5. Electirical conductance. VII. Degradation Kinetics Investigations This section emphasizes the basic chemical processes involved in the degradation of pure and filled polymer systems. Mechanisms are stressed, and quantitative data 34 JPL TECHNICAL REPORT 32-1436 may or may not be directly applicable to real ablative systems on reentry vehicles or in rocket nozzles. A. Reaction-Energy Studies 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure or vacuum. (3) Gas species. (4) Heating rate. (5) Gas flov*' rate. c. Accuracy. (1) Temperature measurements. (2) Sample mass and configuration. (3) Heat losses. (4) Endo- vs exothermal changes. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. 2. Equipment or technique development. a. Differential thermal analysis (DTA). (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Investigate heating-rate effects. (5) Investigate representativeness of specimens, b. Differential scanning calorimeter (DSC). (1) Expand temperature limits. (2) Automate operation and data recording. (3) Increase environmental-simulation capability. (4) Investigate heating-rate effects. (5) Investigate representativeness of specimens. 3, Special problems. a. Temperature. (1) Low (to -200"^). (2) High (to degradation temperature or tem- perature range). (3) Time at temperature. (4) Rate of temperature change. b. Surrounding atmosphere. (1) Vacuum. (2) Extreme pressure. (3) Chemically active gaseous species. (4) Gas flow rate. c. Sample representativeness. (1) Geometrical shape. (2) Mass. (3) Pretreatment. (4) Inhomogeneity. heat. e. Variations due to change in thermocouple to sample thermal conductance. f. Derivation of heat of pyrolysis from data. (1) Identification of baseline. (2) Standards. (3) Area under exo- or endotherm. g. Sublimation-energy studies, h. Liquid and gas studies. B. Reaction-Rate Studies— Thernfjogravimetric Analysis (TGA) J. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Temperature. (2) Pressure or vacuum. (3) Heating rate. JPL TECHNICAL REPORT 32-1436 35 (4) Gaseous species. (5) Gas flow rate. c. Accuracy. (1) Temperature measurement. (2) Heat balance. (3) Furnace temperature gradients. (4) Sample configuration. (5) Sample-holder configuration. (6) Buoyancy effect. (7) Humidity effect. (8) Weight-loss measurement. (9) Time identification. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. 2. Equipment or technique development. a. Establish differences. (1) Isothermal. (2) Constant temperature rise. (3) Constant heating rate. b. Automate operation and data recording. c. Adapt for high-heating-rate investigations. d. Investigate effect on kinetics of specimen seeing hot wall vs specimen seeing cold wall. e. Investigate furnace-configuration effects. 3. Special problems. a. Difference between isothermal, constant- temperature-rise, and constant-heating- rate methods. b. Rate mechanisms under high heating rates. c. Specimen representativeness. (1) Size and shape effects. (2) Powder vs film vs block. (3) Diffusion dependence. (4) View temperature. (5) Pretreatment. d. Comparison with DTA and DSC. e. Correlation with char elemental analysis. f. Correlation with electrical conductance. C. Species and Reaction Identification J. Evaluation of techniques. a. Appropriateness to analysis requirement. (1) Gas chromatograph. (2) Mass spectrometer. (3) Time-of -flight mass spectrometer. (4) Infrared spectrometry. h. Environmental limitations. (1) Temperature. (2) Pressure. (3) Species. c. Accuracy. (1) Discrimination. (2) Area under curves. (3) Pyrolysis representativeness. (4) Second reactions or effects. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. 2. Equipment or technique development, a. Gas chromatograph. (1) Evaluate control parameters. (a) Carrier gas and flow rate. (b) New column materials and column length. (2) Improve pyrolysis method. (3) Compare detection systems. (a) Flame ionization. (b) Conductivity cell. 36 JPL TECHNICAL REPORT 32-1436 (4) Develop elevated temperature columns. (5) Improve discrimination. (6) Investigate H2 and H2O detectability. (7) Automate operation and data recording. b. Mass spectrometer. (1) Evaluate control parameters. (a) Carrier gas and flow rate. (b) Ionization voltage. (c) Pressure. (2) Improve pyrolysis method. (a) Wire. (b) Knudesen cell. (c) Other. (3) Improve quantitative identification. (4) Automate operation and data recording. c. Infrared spectrometry. 3, jpecuU pvooisms. a. Postcracking of gases on adjacent hot walls. b. Re polymerization transients. c. Condensation of evolved gases in cooler regions. d. Pyrolysis representativeness. (1) Heating-rate effects. (2) Specimen-configuration effects. (3) Heating-method effects. e. Mass balance. f. Coupling of gas chromato graph and mass spectrometer. D. Secondary Reactions 1. Cracking and pyrolytic deposition, a. Equipment development. (1) Temperature dependence. (a) Gas. (b) Surface. (c) Rise rate. (2) Pressure dependence. (3) Leakage limitations. (4) Species-handling capability. (a) Inertness. (b) Tagged. (5) Porosity effects (choking). (6) Cas flow rate. (7) Definition of adequate facility. (8) Weight pickup. (9) Analysis of deposited material. (10) Mass balance. b. Special problems. (1) Establishment of magnitude of cracking ef- fect on heat balance. (2) Investigation of interaction of cracking with porosity. (3) Investigation of interaction of cracking with conductance. (4) Pyrolysis-product-mixture cracking vs crack- ing of individual species. (5) Cracking in porous carbon or graphite chars vs cracking in porous-silica chars. (6) Test representativeness. (a) Temperature gradient. (b) Species. (c) Gas flow rate. (d) Catalysity. (e) Path length. (7) Mechanism and kinetics of cracking process. (8) Investigation of interaction of cracking with mechanical strength. (9) Development of computer model. 2. Carhon~-silica reactions, a. Equipment development. (1) Temperature dependence. (2) Definition of adequate facility. JPL TECHNICAL REPORT 32-1436 37 b. Special problems. (1) Establish effect on char conductance. (2) Estabhsh effect on char mechanical strength. (3) Establish mechanism of reaction and further vaporization. (4) Catalysis by presence of transition-metal compounds. 3. Carborv-COi and carbon^HgO reactions. a. Special problems. (1) Meaningful facility. (2) Magnitude of effect on heat balance. E. Heat of Combustion 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. 2. Equipment or technique development, a. Parr bomb calorimeter. 3. Special problems. a. Analysis of char variations. b. Analysis of variations in effective heat of com- bustion using simulated planetary atmospheres. c. Combustion of reinforced plastics. d. Ash analysis (from combustion products). F. Flammability 1. Comparison of alternate techniques. a. Appropriateness to analysis technique. 2. Equipment or technique development. a. ASTM methods. b. Radiant heaters. c. Plasma-arc adaptation. 3. Special problems. a. Investigate control parameters. (1) Temperature. (2) Pressure. (3) Atmospheric species. (4) Evolved species. (5) Catalysis. (6) Gas phase vs surface. (7) Stream velocity. (8) Diffusion. (9) Convective cooling. b. Establish flammability criteria. (1) Burning rate. (2) Self-extinguishing. G. Diffusion Constants for Gases 1. Equipment or technique development. 2. Special problems. a. Temperature. b. Use in ablation analysis. c. Thermal diffusion vs gas diffusion. VIII. Pre-entry Environmental Compatibility Tests Tests to evaluate the performance degradation in ablative composites caused by pre-entry enviroiunental exposure are especially important in planetary-entry missions. Exposure to foreign chemicals and long expo- sure to vacuum and space radiation greatly affect some polymeric materials and composites. A. Chemical Resistance J. Definition of problem. a. Fuels and oxidizers spilled during tank filling. (1) N^O,. (2) Hydrazine and derivatives. (3) Diborane BaHe. b. Vapor leakage during long-time storage for a propulsive lander. 2. Test development. a. Change in chemical nature. b. Change in properties required at a later time. 38 JPL TECHNICAL REPORT 32-1435 B. Sterilization 1. Comparison of alternate methods. a. Appropriateness to analysis requirements. 2. Equipment or technique development. a. Chemical surface decontamination. (1) Decontaminate. (a) Ethylene oxide. (b) Other. (2) Carrier gas. (a) Freonl2. (b) CO2. (c) Other. (3) Temperature control. (4) Humidity control. (5) Concentration control. b. Dry-heat sterilization. (1) Effluent. (a) Nitrogen. (b) Other. (2) Temperature control. (3) Heatup and cooldown ramps. 3. Special problems. a. Long-term degradation by retained chemical decontaminant. b. Effect of dry-heat sterilization on retained chem- ical decontaminant. c. Redeposition of volatiles during cooldown phase. d. Explosive hazard. e. Sterile assembly. f. Biological vents or feedthroughs. g. Freon 12 a solvent for fluorocarbons. C. Vibration 1. Special problems. a. Brittle behavior at launch conditions. b. Brittle behavior while cold in space under mid- course propulsion correction or injection into planet. D. Rapid Pumpdown I. Special problems. a. Ability of low-density ablators to withstand a sudden decrease in external pressure without ex- ploding or cracking because of entrapped gases. E. Vacuum Compatibility J. Comparison of alternate techniques. a. Appropriateness to analysis requirements. b. Environmental limitations. (1) Vacuum level. (2) Temperature. (3) Time. c. Accuracy. (1) Weight-change sensitivity. (2) Temperature rise rate and level control. (3) Vapor pressure. (4) Vacuum level. (5) Diffusion rate. (6) Prior conditioning. d. Biases. (1) Equipment. (2) Inherent model. e. Standardization. (1) Equipment. (2) Samples. 2. Equipment or technique development. a. Vacuum balance. (1) Quartz-crystal balance. (2) Dimensional-change monitoring. (3) Coupling with species identifiers. b. Microvolatile condensible material tests. (1) Screening only. JPL TECHNICAL REPORT 32-1436 39 (2) Establish prior temperature level for sample and plate. (3) Establish proper pressure level for standard materials. (4) Lower vacuum-level capability. c. Macrovolatile condemible material tests. (1) Establish proper sample size and shape. (2) Investigate diffusion dependence. (3) Investigate secondary evaporation from cold plate. (4) Establish proper temperature level for sam- ple and plate. (5) Lower vacuum-level capability. 3. Special problems. a. Investigate effects of condensibles. (1) On optical properties. (2) On electrical properties. b. Investigate vacuum-loss effects. (1) On mechanical properties. (2) On conductance. F. Radiation Resistance 1. Comparison of alternate techniques. a. Appropriateness to analysis requirements. 2. Equipment or technique development. a. Source development. 3. Special problems, a. Space radiation. (1) Particle vs ultraviolet. (2) Synergistic effects. (3) Temperature at radiation. (4) Kinetics of radiation degradation. (5) Effects of additives and protective agents. (6) Combined with TGA. (7) With in situ mechanical properties. b. Nuclear radiation. (1) Dose requirement. (2) Temperature. (3) Additives and protective agents. (4) With in situ mechanical properties. iX. Entry-Simulator Development To simulate entry, the time histories of pressure, heat- ing rate, and enthalpy must be matched in the specific planetary gaseous composition. These must be matched on a specimen that has been both exposed to an identical pre-environment and so manufactured that flight shape and size are directly simulated. Radiant heaters are needed that span heating ranges from 1 to 10'' Btu/ftVs (for certain Jupiter entries). Convective heaters are needed to produce a wide range of heating rates, pres- sures, and enthalpies. Combinations of these two types of heat source must be coupled with each other and with various degrees of exposure to pre-entry environments. A. Plasma-Arc Facility Development 1. Arc-configuration development. a. Types of arc. (1) Ring. (2) Constricted. (3) AC. (4) Gerdien. (5) Vortex or aerodynamically stabilized. (6) Magnetically stabilized. (7) Regenerative. (8) Transpiration cooled. (9) Inductive. (10) Other. b. Limitations. (1) Electrode materials. (2) Electrode shape and location. (3) Flow. (4) Power: towards 300 MW. (5) Size. 40 JPL TECHNICAL REPORT 32-1436 (6) Cooling system. (7) Energy-transfer efficiency: 1000 to 100,000 Btu/lb. (8) Pressure: lO* torr to 200 atm. (9) Working fluid species: air, CO2, N2, O2, H2, Ar, CH4, He, etc. (10) Calibration. c. Starting techniques. (1) Jumpwire. (2) Vacuum. (3) Touch. (4) High frequency. (5) Capacitive discharge. d. Special problems. (1) Energy-transfer mechanisms. (2) Transport properties of gases. (3) Radiation loading. (4) Arc-column studies. (5) Size scaling. (6) Reactive working fluid. (7) High enthalpy in high-working-fluid flow rates. (8) Difference in energy distribution in induc- tive arc vs other arcs. (9) Enthalpy pulsing. (a) Power. (b) Flow. (10) Simultaneous increase in heating rate and pressure. 2. Fotver source development, a. DC types. (1) Batteries, (2) Dynamo. (3) Moving-coil or core-controlled rectifier. (4) Saturable-core-reactor-controlled rectifiers. (5) Silicon-controlled rectifiers. h. Special problems. (1) Ripple. (2) Power-factor correction. (3) Control speed and flexibility. (4) Component life. (5) Control for multiple arcs. (6) Control feedback for pulsing enthalpy. 3. Exhaust configuration. a. Types. (1) Sonic nozzles. (2) Supersonic nozzles. (3) Mixing chambers. (4) Multiple-arc mixing. (5) Dual ducts. (6) Turbulent ducts. (7) Shrouding. (8) Two-dimensional shear nozzles. (9) Rectangular nozzles. b. Special problems. (1) Mixing uniformity. (2) Reproducibility. (3) Coring. (a) Central. (b) Donut. (4) Mach-number control: 1 to 20. (5) Shock-diamond location and control. (6) Turbulence. (a) Intensity level. (b) Initiation control. (c) Test-specimen meaningfulness. (7) Stream contamination. (8) Arc radiation. (9) Coupling plasma heads to produce high shear (to 300 lb/ft==). JPL TECHNICAL REPORT 32-1436 41 4. Exhaust-species removal and static-pressure control. a. Pumping system development. (1) Mechanical pump— booster systems. (2) Steam-ejector systems. (3) Control-valve sensitivity improvement. (4) Diffusers. (5) Heat exchangers. (6) Air-ejector systems. h. Special problems. (1) Backfilling without changing exhaust uniformity. (2) Pressure balance between nozzle exit and chamber. (3) Pressure pulsing at sample surface. 5. Sample-injection-mechanism development. a. Types. (1) Linear. (2) Angular. h. Limitations. (1) Speed of entrance and exit. (2) Oscillations. (3) Recession compensation. (4) Scanning speed and sensitivity. c. Special problems. (1) Three-dimensional scanning. (2) Easy-access and simple model switching methods. (3) Multiple-precision insertion. (4) Recession compensation and rate-measuring system. (5) Protection of model in stowed position. 6. Sample configuration development. a. Types. (1) Flat-faced probe. (2) Isothermal-surface probe. (3) Hemispherical probe. (4) Special-curvature probe with shroud. (5) Flat plate. (6) Cone. (7) Wedge. (8) Cylindrical pipe. (9) Channel. (10) Complex combinations. b. Limitations. (1) Size. (2) Guarding. (a) Side. (b) Rear. c. Special problems. (1) Temperature measurement and sensor mounting. (a) Rear surface. (b) Internal. (2) Subsonic vs supersonic configurations. 7. Readout instrumentation development, a. Recorder-computer-plotter system. b. Special problems. (1) Recorder speed. (2) Shortening return time on plots. B. Radiant-Heater Facility Development 1. Filament lamps. a. Types. (1) Tungsten-filament tubes. (2) Quartz. b. Limitations. (1) Filament life. (2) Low heating rates (less than 200 Btu/ftVs). (3) Time limitation on pulsing. (4) Venetian-blind effect of heating distribution. 42 JPL TECHNICAL REPORT 32-1436 c. Special problems. (1) Lamp arrangement for large specimens. (2) Integration into coupled system. 2. Carbon-arc imaging furnace. a. Types. (1) By mirrors. (a) Parabolic. (b) Ellipsoidal. (c) Spherical. (2) By electrodes. (a) Opposing dc. (b) Carbon-vapor-lamp ac. b. Limitations. (1) Carbon-electrode lifetime. (2) Mirror imperfections. (3) Electrode splatter. (4) Source-shape irregularity. (5) Time fluctuations. (6) Shadowing. (7) Low heat fluxes. c. Special problems. (1) Degradation kinetics in a controlled environment. 3. Solar-furnace limitations. (1) Sun dependence and time fluctuations. (2) Mirror imperfections. (3) Tracking accuracy. 4. High-pressure compact arcs. a. Types. (1) Clear-glass spherical or ellipsoidal envelope. (2) Metal cavity. (3) Mercury, xenon, CO2, or combinations. b. Limitations. (1) Poor flux distribution. (2) Inefficiency. (3) Low flux. c. Special problem. (1) Defining useful range. 5. High-pressure vortex-stabilized plasma arcs. a. Types. (1) By working fluid. (a) Xenon. (b) Neon. (c) Argon. (d) N,. (e) CO2. (2) By electrode configuration. (a) Opposing. (b) Concentric. (3) By optics. b. Limitations. (1) Electrode configuration and lifetime. (2) Mirror. (a) Lifetime. (b) Imperfections. (c) Clouding. (d) Cooling. (3) Pressure efficiency. (4) Container strength. (a) Body. (b) Window. (5) Focusing lens or window. (a) Imperfections. (b) Stirength. (c) Clouding. (d) Transmission characteristics. (e) Cooling. JPL TECHNICAL REPORT 32-1436 43 (6) Size. (a) Arc. (b) Optics. (7) Heat flux (maximum). (8) Spectral characteristics. (a) Wavelength. (b) Distribution. (c) Blockage. (9) Starting. (a) Touch. (b) High frequency. (10) Power. c. Special problems. (1) Optical materials. (2) Column efficiency vs brightness. (3) Shape vs brightness. (4) Dousing. (5) Remote calibration. 6, Laser. a. Limitations. (1) Preheater. (a) Size. (b) Fuel. (2) Power. (a) Capability. (b) Efficiency. (3) Optics. (a) Focusing. (b) Mirrors and lenses (to four decimal points). (4) Wavelength - CO,. (5) Sample size and shape. (6) Time stability. (7) Lateral flux gradient. 44 b. Special problems. (1) Extension to other wavelengths. (2) Scaling size. 7. Peripheral equipment development for low-shear environment. a. Species removal and static-pressure control. (See IX-A-4, above.) b. Sample configuration development. (See IX-A-6, above.) c. Readout instrumentation. (See lX-A-7, above.) 8. General problem areas. a. Heat flux. (1) Uniformity with time. (2) Uniformity over surface. (3) Accurate calorimetry. b. Pressure and evolved-gas removal. (1) Control at sample surface from 10 "^ torr to 100 atm. (2) Surface blowing or splatter. (3) Window fogging. c. Specimen temperature. (1) Internal and lateral gradients. (2) Surface-temperature determination. (3) Optical-property changes. d. Surface recession. (1) Irregularities. (2) Subsurface vaporization. (3) Change in calibration from splatter. e. Radiation transfer. (1) Wavelength distribution of source. (2) Attenuation by pyrolysis-production absorp- tion. (3) Subsurface vaporization. /. Optics. (1) Mirrors. JPL TECHNICAL REPORT 32-1436 (2) Lenses. (3) Windows. C. Radiant Heater Coupled With Cold-Gas Flow for Shear Simulations J. Validity of aerothermalrsimulation concept. a. Heating rate. (1) Radiative simulation of convective heating. (2) Wavelength effects. (3) Variations caused by local erosion. b. Flow field. (1) Inequivalence of local pressure gradients. (2) Inequivalence of local temperature gradients. (3) Local erosion effects. 2. Need for development and verification of an ana- lytical model. D. Convective— Radiative Heater Coupling 1. Plasma arc — arc-imaging furnace, a. Special problems. (1) Optics. (a) Donut effect in radiant image. (b) Clouding and splatter. (c) Focusing quality. (2) Specimen. (a) Size limitations. (b) Shape limitations. (3) Diagnostics. (a) Heating-rate determination. (b) Surface-temperature determination. (4) Pulsing control. 2. Plasma arc — high-pressure plasma-arc radiators, a. Special problems. (1) Optics. (a) Focusing quality. (b) Clouding and splatter of mirrors and lenses. (c) Wide incident angle. (2) Specimen. (a) Size limitations. (b) Shape limitations. (3) Diagnostics. (a) Heating-rate determinations. (b) Surface-temperature determination. (4) Pulsing control. 3. Plasma arc — plasma-arc radiant source. a. Special problems. (1) Ratio of one heating rate to the other diffi- cult to control. (2) Specimen size and shape limitations. (3) Diagnostics. E. Other Heater Sources 1. Oxyacetylene torch. a. Limitations. (1) Low enthalpy. (2) Chemical-reactivity differences. b. Special problems. (1) Evaluation of thermostructural compatibility. (2) Shear tests. (3) Comparison with plasma-arc data. (4) Validity of simulation. 2. Pebble-bed heater and porous-resist-ance heaters. a. Limitations. (1) Low enthalpy. (2) Time-variant enthalpy. b. Special problems. (1) Long-time, low-heating-rate tests on com- paratively large specimens. JPL TECHNICAL MPORT 32-1436 45 3. Rocket test facility. a. Limitations. (1) Low enthalpy. (2) Pressure control coupled. (3) Lack of gas-composition simulation. b. Special problems. (1) Evaluation of thermostructural compatibility. (2) Scaling to larger sizes possible. 4. Wave superheater. a. Limitations. (1) Small specimen size. (2) Poorly defined environment (discontinuous heat pulses). (3) Uninterpretable surface gradients. b. Special problems. (1) High-pressure effects. 5. Magneto accelerators in combiruition with plasma arcs. a. Limitations. (1) Acceleration not uniformly applied. (2) Inefficiency. 6. Shock tunnels. a. Limitations. (1) Short test duration. (2) Small specimen size for Reynolds-number simulation. (3) Pressure range not simulated. b. Special problems. (1) Validity of simulation. (2) Transient model behavior. 7. Free-flight range. a. Limitations. (1) Small specimen size. (2) Short test duration. b. Special problems. (1) Impact destruction of model for postanalysis instrumentation. 8. Nuclear explosions. a. Limitations. (I) Short test duration. b. Special problems. (1) Jupiter entry. X. Entry-Simulator Testing If suitable entry simulators are available, much can be done to delineate theoretical concepts in ablation tech- nology, as well as to provide specific information on material performance in simulated missions. Mars, Venus, and Jupiter each presents individual problems in simu- lation. A. General Studies /. Boundary layer. a. Boundary-layer structure. b. Interaction with ablation recession. c. Gaseous combustion with evolved ablation prod- ucts. 2. Surface oxidation. a. Reaction-rate limited. (1) Air. (2) CO^. b. Diffusion-rate limited— air. c. COj-ZVj equivalent to air. d. Effect of other species. (1) Argon. (2) Water. 3. Other reactions. a. Nitration. b. CHi, NHs, He, and Hi atmospheres. c. Other gases. 46 iPL TECHNICAL REPORT 32-1436 4. SubUmation. a. Heating-rate limits. b. Pressure effects. 5. Blocking. a. Blowing studies— concentric calorimeters and specimens. b. Radiation-absorption studies. 6. Standardization. a. Inierfacility correlation. b. Shape standardization. c. Definition of minimum stream and specimen calibration. 7. Radiation effects. a. Gas-cap emittance and absorption. (1) Various gases. (2) Ablation uroducts, b. Gas-cap spectral distribution effects on ablator response. 8. Scaling studies. 9. Surface-roughness effects. a. Turbulence tripping. b. Surface-temperature determination. 10. RF transparency during ablation. 11. In situ testing. a. After long exposure to vacuum. b. After sterilization. c. With simulated micrometeoroid damage. d. With cold models. e. After exposure to nuclear radiation. 12. Effects of joints, cracks, protuberances, holes, and erosion on ablative heat transfer with radiation. B. Specific Studies 1. Mara. a. Material response to integrated Mars transit and entry environment. (1) Out of orbit (peak heating <100 Btu/ftVs). (2) Direct entry (peak heating <500 Btu/ftVs). b. Scaling tests. (1) Plasma arc to 24-in. diam. (2) Radiant heaters to 20-ft diam. c. COt combustion equivalence. 2. Venus. a. Material response to Venus entry. (1) Low angle, low ballistic coefficient, low velocity. (2) High-energy entry. b. COi combustion equivalence. c. Sublimation regime. (1) CO, effects. (2) Pressure effects. d. Laser applicability. e. Applicability of direct-arc exposure. f. Ground test-simulation limits. 3. Jupiter. a. Correlation of atomic-blast data with entry- material response. b. Development of analytical model spanning heat- ing rates from 10,000 to 60,000,000 Btu/ft'/s. XI. Diagnostic Instrumentation Development Exotic test equipment is only as good as the ability to define the environment produced by the equipment and the response of the test material to that environment. A. Calorimetry 1. Types. a. Absolute. b. Slug. JPL TECHNICAL REPORT 32-1436 47 c. Thin foil. d. Gardon. e. Null. f. Bimetal-wafer stacks. g. Radiometer, h. Other. 2. Limitations. a. Reads average of a distributed flux. h. Window transmission and contamination. c. Two- and three-dimensional effects. (1) Shape. (2) Lateral heat flow. d. Heating-rate maximums. e. Surface-temperature differences. f. Catalytic behavior. g. Electrical interaction. h. Calibration. i. Response time. 3. Special problems. a. Stream property influence. (1) Velocity gradients. (2) Contaminants. (3) Thermal distribution. (4) Gas composition. b. Calibration technique. (1) Measurement standard. (2) Validity of analytical technique. (3) Reproducibility. c. Blocking effects. d. Contamination probe. e. Concentric calorimeters. f. Wall calorimeters. B. Stream Pressure 1. Sensor type. a. Transducer. b. Manometer. c. Other. 2. Limitations. a. Response time. b. Orifice size and shape. c. Probe configuration. d. Temperature-gradient effects. e. Frequency. f. Noise. 3. Special problems. a. Separation of static and dynamic pressure. b. Pitch and yaw effects. c. Pressure on ablating models. C. Stream Enthalpy 1. Methods and limitations. a. Energy balance. 1) Small temperature rises magnify importance of measurement errors. b. c. 2) Average enthalpy only. Fay-Riddell reverse calculation. 1) Model inaccurate for highly ionized flows. 2) Must have accurate pressure and heating- rate measurements. Sonic flow. 1) Basic and equilibrium method. 2) Extrapolatible to frozen and nonequilibrium flow. 3) Requires plenum chamber. 4) Rotational flow negates pressure measurements. Total collection. 1) Unwieldy. 2) Inaccurate. 48 JPL TECHNICAL REPORT 32-1436 e. Tare probes. (1) Good for high enthalpies. (2) Split flow vs standard. (3) Guarding techniques critical. (4) Analytical model questionable. (5) Measurement tolerances large. (6) Interjacket heat transfer. (7) Equal heating outside and inside. /. High-sensitivity, stagnation-point probe. (1) Two mutually insulated jackets. (2) Comparatively large size. g. Shock-stvallowing probe— low-density, low-heat- flux only. h. Transient fast-response probe. 2. Special problems. a. Coring and enthalpy distribution. b. Very high entlialpies and pressures. c. Difference in needs for super- and subsonic probes. D. Flow-Field Analysis 1. Measurement techniques. a. Probes. (1) Langmuir. (2) Electrostatic. (3) Hall effect. (4) Magnetic. h. Optical. (1) Spectroscopy. (2) Electron beam. (3) Microwave. (4) Ultrasonics. (5) Schlieren. (6) Interferometer. (7) Laser. (8) Optical and nuclear tracers. 2. Important parameters. a. Mack number. b. Local density and pressure distribution. c. Mass-flow distribution. d. Ionization level and distribution. e. Temperature distribution. f. Electrical conductivity. 3. Limitations. a. Measurement tolerances, h. Validity of analytical model. 4. Special problems. a. Shock interactions. b. Chemical state. (1) Frozen. (2) Equilibrium. (3) Nonequilibrium. c. Tank and probe interference. d. Rotational flow and vorticity. e. Imbalance of energy states relative to equilibrium. (1) Translational. (2) Rotational. (3) Vibrational. (4) Electronic. E. Material-Response Data J. Internal temperature. a. Thermocouples. (1) Initial calibration and drift. (2) Cold junction. (3) Connections to external components. (4) Sensitivity to stray currents or magnetic fields. b. Resistance thermometers. (1) Thin film. (2) Location along isothermal surface. JPL TECHNICAL REPORT 32-1436 49 (3) Size disruption of local temperature field. (4) Contact resistance. 2, Internal density. a. Postanalysis. (1) Thin-slice representativeness. (2) Loss of transient nature. b. X-ray. (1) Averages over thickness. (2) Flat isothermal surfaces necessary in depth. 3, Surface temperature. a. Methods. (1) One-color pyrometry. (2) Two-color pyrometry. (3) Total-radiation pyrometry. (4) Spectrographic. b. Limitations. (1) Optical properties must be known. (2) Model assumes nonrough surface. (3) Gas-cap contributions. (4) Arc reflections. (5) Readout sensitivity. c. Special problems. (1) Surface-roughness effects. (2) Relationship to computer-node model. 4, Surface recession and mass-loss rate. a. Methods. (1) Tare weights and dimensions. (2) Camera. (3) X-ray. b. Limitations. (1) Isothermal surfaces not flat. (2) Transient effects. c. Special problems. (1) Model drive system. (2) Contamination effects from electrode and gas. (3) Lateral motion of material along surface. 5. Photographic records of surface phenomena. (1) Roughness effects. (2) Lateral flow. (3) Erosion-irregularity records. XII. Flight Test Earth flight tests can hardly ever be made to com- pletely duplicate planetary-entry flight trajectories. Dif- ferences in atmospheric-universe scale height could be adequately handled, except that atmospheric-composition variations make it impossible to duplicate the actual chemical kinetics of the material response. Mars out-of- orbit entry is an exception to this because heat loads are low and combustion kinetics do not play a significant part. On the other hand, the degree (or range) of sever- ity can mostly be simulated without regard to the rela- tive balance of energy-absorbing mechanisms (except in the case of direct Jupiter entry). In this way, the analytical techniques can be exercised to increase con- fidence in their use for predicting performance in severe, nonearth-simulatible environments without an exact simulation of the hypothesized flight. A. Earth Simulation of Mars Entry 1. Out of orbit. a. Matching of all parameters possible. 2. Direct entry. a. Convective heating and pressure good. b. Radiative duplication possible with shape manipulation. c. Combustion duplication poor. B. Earth Simulation of Venus Entry 1. Lower-energy entries. These are not simulated be- cause of the large dependence of material performance upon combustion. 2. Higher-energy entries. These are somewhat more simulatible because most of the ablation response is in the sublimation regime, which is not greatly dependent upon external species. 50 iPL TECHNICAL REPORT 32-1436 3. Degree of severity. This can always be tested to exercise analytical techniques and to increase confidence. C. Earth Simulation of Jupiter Entry 1. Difficult to impossible at this time. D. Special Problems 1. Scale vs full size. a. Size contribution. b. Shape contribution. 2. Flight instrumentation. a. Thermocouples and thermistors. b. Heat pipes. c. Break wires. d. Radioactive recession gages. e. Calorimeter. f. Pressure transducers. XIII. Rockei-Nozzle Testing This area is discussed primarily because of the close relationship in technology utilization between entry heat shields and rocket-nozzle heat shields. Planetary uses of the rocket-nozzle heat shield are primarily centered around smaller systems for midcourse guidance, orbital or planetary injection, attitude control, or soft-landing touchdown. This section is not nearly as complete as the other sections, and is not intended to be. Its inclusion is meant, again, to emphasize the technology application to both fields. A. Motor Liner or Combustion Chamber 1. Material systems. a. Structures for solids. (1) Molded. (2) Tape-wrapped. (3) Filament-wound. b. Structures for liquids. (1) Metallic. (2) Molded carbon. (3) Composite. c. Insulations. (1) Foam. (2) Multilayer. (3) Powder with container. 2. Performance limits. a. Total heat load. b. Pressure containment. 3. Special problems. a. Injector-erosion pattern. b. Chamber-design effects. (1) Standard. (2) Submerged nozzle. (3) Solid-hole pattern. B. Throat and Throat Inlet 1. Material systems. a. Ablative. (1) Molded-glass or carbon-cloth laminate. (2) Tape-wrapped laminate. (3) Graphite. (4) Prepyrolyzed composites. (5) Special fillers. (6) Silica-impurities effects. (7) High and low silica-carbon ratios. (8) Three-dimensional reinforcements. b. Metallic. (1) Coated or uncoated. (2) Filled porous. 2. Performance limits. a. High pressures. b. Long times. c. Fuel dependence. 3. Special problems. a. Minimizing shape changes. JPL TECHNICAL REPORT 32-1436 51 b. Restart. c. Submerged nozzles. C. Exit Cone 1. Materials. a. Metallic or graphite, radiation cooled, h. Ablative. (1) Molded. (2) Tape-wrapped. 2. Special problems. a. 'Nozzle-expansion ratio, h. Turbulent tripping. D. Test Stands 1. Liquid. a. Dimensions. b. Fuel-to-oxidizer ratio. c. Chamber-pressure control. d. Injector pattern. e. Run duration and restart. 2. Solid. a. Dimensions. b. Fuel. (1) Polymeric. (2) Metallized. c. Chamber-pressure control. d. Propellant configuration. e. Run duration. 3. Plasma arc. a. Working fluid simulates combustion-produced gases. XIV. Resin Development Resin systems can be tailored to a wide variety of requirements by combining complementary systems or by building molecules to provide specific properties. Although it is possible to use existing polymers, new resin systems can potentially provide a wider variety of design solutions for future needs. A. Clean-Characterized Polymer Standards 1. Polymers. a. Silicone elastomer. b. Phenolic. c. Epoxy. d. Epoxy Novalac. e. Polyimide. f. Polybenzimidazole. 2. Characteristics. a. Variations. Two or three variations of each type are desirable, as follows: (1) One should be the simplest, most reproduc- ible molecule possible of its type. (2) One should be representative of a common- usage variety. (3) One should be representative of a high- temperature, high-performance variety. b. Reproducibility in time should be stressed. c. Amount of testing necessary to characterize each resin must be determined rigorously. B. New High-Temperature Resin 1. Improved phenolics, a. 2,7-Naphthdlenediol: Formaldehyde. b. p-Phenylphenol: Formaldehyde. c. o,o'-Biphenol: Formaldehyde. d. Other. 2. Silicones. a. Glass resins. b. Metacarborane: dimethyl silane. c. Rigid silicones— phenyl T related. d. Quinone based. e. Epoxy: Siloxane. f. Phenolic: Siloxane. 52 JPL TECHNICAL REPORT 32-1436 g. Polysilphenylene Stloxanes. h. Polyarylorysilanes. i. Fluorinated silicones, j. Others. 3. Polyimides. a. Flexibilized. h. Other. 4. Polybenzimidazoles. a. Low-volatile version. b. Flow control at high temperatures. 5. Ladder polymers. a. Pyrrones. b. Other. 6. Polyperfluoroalkyltriazine. 7. Polybenzothiazole. 8. Polyquinoxaline. 9. Polyphenyl oxides. 10. Semiorganic or inorganic polymers. 11. Other. C. New Fpams J. Polymeric systems. a. Polytetrafluorethylene. b. Cross-linked polycarbonate. c. Polyur ethanes. d. Polyphenylene oxide. e. Polyethylene. f. Diphenyl oxide. g. Polyimide. h. Epoxy. i. Isocyanurate. j. Other. 2. Characteristics. a. Low density. b. Rigidity. (1) Stiff with reasonable structural strength. (2) Flexible. c. Homogeneous and fine void distribution. d. Tough. D. Tailoring Resin Systems for Particular Needs 1. Good low-temperature flexibility. a. High chemorheological temperature. b. High heat-distortion temperature. c. Low brittle temperature. 2. Good low-temperature toughness. 3. Good high-temperature toughness. 4. High char yield. a. High char strength. b. High degradation-zone strength. c. Uniform char surface. d. High emittance and absorptance. e. Chemically unreactive. f. Low shrinkage. 5. High-temperature stability. 6. No unreacted or reactive sites after cure. a. Stoichiometric balance of reactive components. b. Capping of chain ends. 7. RF transparency. a. Virgin state. b. Char. (1) Nonconductive. (2) Hot or cold. 8. Single or multiple degradation reactions. 9. Endothermic decomposition. JPL TECHNICAL REPORT 32-1436 53 10. Specific specie concentration in evolved gas. a. Low molecular weight. b. Wake quenching. 11. High specific heat. 12. Low conductance. 13. Thermally stable char in presence of fillers. 14. Easy processing. a. A liquid system in uncured state. b. Low-temperature and low-pressure processing. c. Good filler wetting and bonding. d. Addition polymerization rather than condensa- tion polymerization. e. Low cure shrinkage. 15. Low thermal expansion coefficient. a. Isotropic. b. Anisotropic. 16. Space stable. 17. Ground-storage stability. a. Fungus. b. Humidity. c. Sunlight. d. Smog. 18. High strain capability, a. Elastomers. 19. Controlled Poisson's ratio. 20. Good adhesion. 21. Impact-energy absorption. 22. Inertness to sterilization. a. Chemical. b. Dry heat. XV. Filler Development Filler development is important to widen the scope of design solutions for capsule heat-shield problems. A. Clean-Characterized Filler Standards J. Filler materials. a. Glass, silica, and quartz. (1) Fiber. (2) Yam. (3) Eccospheres. b. Carbonaceous. (1) Fiber. (2) Yam. (3) Powder. c. Organic. (1) Nylon. (a) Powder. (b) Fiber. (2) Phenolic— microballoon. d. Cork. 2. Characterization. a. Uniformity. b. Cleanliness. c. Reproducibility. B. New Filler Development 1. Materials. a. Oxides. (1) Aluminum. (2) Titania. (3) Zirconia. (4) Aluminum, silica, and chromia. b. Other refractories. (1) Nitrides— boron nitride. (2) Borides. (3) Silicates. (4) Carbides. 54 JPL TBCHNICAL REPORT 32-1436 c. High-temperature metals. d. Organic. (1) Nomex powder. (2) PBI. (a) Fiber. (b) Microballoons. (3) PI. (a) Fiber. (b) Microballoons. (4) BBB. (a) Fiber. e. Wood. (1) Baka. /. Asbestos. 2. Special additives, a. Antioxidants. b. Decomposing salts. c. Fire retardants. d. Additives to control chemical cracking. 3. New forms. a. Submicron particles. C. Improved Fabrication Techniques 1. Fiber. a. Drawing. b. Controlled fiber lengths. c. Single crystal. d. Finishes. e. Diameter control—small diameters. f. Size distribution. g. Placing additives in spinning dope prior to fiber formation. 2. Yam. / V. Mechanical Properties 69 V(. Electrical Properties 70 VII. Degradation Kinetics Investigations 70 VIII. Pre-entry Environmental Compatibility Tests 71 IX. Entry-Simulator Development 72 X. Entry-Simulator Testing 73 XI. Diagnostic Instrumentation Development 74 XII. Flight Test 7(, XIII. Rocket-Nozzle Testing 76 XIV. Resin Development 76 XV. Filler Development 79 XVI. Composite Development and Fabricabiiity Investigations 81 XVII. Nondestructive Testing 82 XVIII. Design Criteria and Parametric Studies for Design 82 64 iPl TECHNICAL REPORT 32-1436 Appendix B A List of Heat-Shield R&D Tasks for Extraterrestrial Atmospheric-Entry Missions The R&D tasks outlined in this appendix were pro- duced from a systematic review of heat-shield technol- ogy; they represent the total scope of effort possible with a reasonable expectation of successful advancement of this technology. It is unlikely that any one agency could or would desire to fund all of these tasks. Within each sub- category, the listed tasks are preceded by a symbol in parentheses to indicate their estimated relative value. Starred items (*) are considered key or critical. Items marked (1) are expected to have a large effect on mission success, reliability, weight, or cost. Items marked (2) have implications towards technology growth or long-range re- search, whereby the magnitude or timing of the output is not immediately obvious. (Some funding in this latter area is important, but the selection is arbitrary.) i. Ablation Theory A. Internal Processes 1. (*) Develop a new mathematical model for inter- nal degradation processes, accounting for heat- ing rate as well as temperature, pressure, spe- cies, and shape factors. 2. (*) Develop an internal flow model that accounts for the actual thermochemical state of the gases with the accompanying pressure gradients, diffusion coefficients, chemical erosion, etc. 3. (I) Develop a char-conductance model as a func- tion of temperature, temperature history, micro- ordering, and density changes (relate to IV-H and IV-I). 4. (1) Develop a new mathematical model for phase- cfiaiige arm negrauation processes, accountmg for volume changes. 5. (1) Develop a conductance model that differenti- ates between conduction and internal radiation transfer in porous materials (relate to IV-J). 6. (1) Develop a diffusion model to replace the model based on Darcy's law. 7. (1) Develop a conductance model for nonhomo- geneous and anisotropic materials with filler. porosity, and honeycomb reinforcements (re- late to IV-K). 8. (1) Develop an internal flow model that represents cracking and redeposition reactions. 9. (2) Develop a conductance model as a function of pressure and gas species— air, N2, CO2, CO, CH4, H2, and He (relate to IV-G). 10. (2) Develop a silicone-elastomer liquid-layer model with vaporization. 11. (2) Develop a silica or glass reinforcement liquid- layer model with vaporization. 12. (2) Develop a conductance model representing the changes caused by cracking and pyrolytic depo- sition (relate to IV-C-4). 13. (2) Develop a m_odel for silicone-carbide forma- tion and other char-reinforcement reactions. 14. Investigate photochemical reactions from inci- dent radiation. B. External Processes or Surface Interactions 1. (*) Develop an absorptance, emittance, and trans- mittance model that accounts for surface roughness, pore geometry, temperature gradi- ents, and wavelength. 2. (*) Develop a high-blowing-rate model. 3. (*) Develop a radiative-heating model for repre- sentative combinations and pressures of N2, O2, Ar, H2O, H2, He, LHj, and NH3 in various equi- librium and nonequilibrium states and with self-absorption. 4. (*) Develop an improved turbulent-heating model with turbulent transition on the cone. 5. (1) Develop a model for mass-addition changes in shock shape and radiative heating, accounting for absorption in the evolved gaseous species (including upstream effects). 6. (1) Develop a boundary-layer-combustion model, including upstream influences and effects on heating. JPL TECHNICAL REPORT 32- J 436 65 7. (1) 8. (1) 9. (1) 10. (1) 11. (1) 12. (1) Develop a combustion model for CO2-C. Develop a combustion model for H2-C. Develop a sublimation model accounting for temperature, pressure, species, diffusion, and vapor-pressure effects. Develop a shear and thermomechanical erosion model, accounting for aerodynamic shear, ex- ternal pressures, internal pressures, thermal stresses, inertial stresses, and pre-stresses (up- stream transpiration). Develop a model for surface roughness and cat- alysity effects on convective and radiative heat- ing. Develop a laminar convective-heating model for representative combinations and pressures of N2, O2, CO2, Ar, H2O, H2, He, CH4, and NH3 in various equilibrium and frozen states and for free molecular and continuum flow. Develop a model for convective- and radiative- heating distribution around an entry body, in- cluding base heating, angle-of-attack effects, and improved transition criteria. Develop an improved model for mass-addition changes in flow-field and convective heating, including upstream effects. Develop a combustion model for N2-C. Develop a ^vaporization model for oxide rein- forcements that is consistent with the sublima- tion model (I-B-9). Develop a combustion model with inhibitors. Investigate turbulence effects on radiation-heat transfer. C. General 1. (2) Develop a model for joints, windows, and feed- throughs (geometrical discontinuities). 2. (2) Develop a conductance model for honeycomb- sandwich materials. II. Computer Program Development A. Computer Processes 1. (1) Establish techniques for feeding entry- simulator calibration and test data directlv 13. (1) 14. (1) 15. (2) 16. (2) 17. (2) 18. (2) into, and getting finished plots directly out of the computer. 2. (1) Establish techniques for computer reduction of basic material-property data. 3. (2) Investigate computer processes in depth to im- prove accuracy, decrease computer time, and provide multidimensional capability. 4. (2) Establish standards for notation, coordinate systems, units, common subroutines, and input and output handling. 5. (2) Establish a practical data-storage and -retrieval system. B. Computer Programs 1. (1) Establish a set of preliminary design programs for a Venus-entry heat shield. 2. (1) Establish a set of preliminary design programs for a Jupiter-entry heat shield. 3. (1) Develop a sophisticated, one-dimensional, uncoupled-ablation computer program includ- ing: a. An improved conductance model with hys- teresis, pressure, and radiation effects. b. An improved radiation-absorptance model with surface-roughness effects. c. An improved internal-degradation model. d. Allowance for swelling and shrinking. e. An improved internal-flow model with real- istic diffusion, thermochemical equilibrium, cracking, redeposition, and silicon-carbide formation. f. An improved combustion model for oxygen and carbon dioxide. g. Nitration reactions in the proper tempera- ture regime. h. An improved sublimation model. i. A combustion model for hydrogen. j. An improved thermomechanical-erosion model with pressure, shear, thermal gradi- ent, and evolved gas stresses. k. An improved liquid-layer model. 4. (2) Develop a fully coupled boundary-layer- ablation-response computer program. 66 JPL TECHNICAL REPORT 32-1436 5. (2) Develop a multidimensional uncoupled-ablation computer program. 6. (2) Establish a set of preliminary design programs for a Mars-entry heat shield. 7. (2) Establish a standard program for back- calculating materials properties from thermocouple-response data. III. Characterization and Physical Properties A. Characterization 1. (1) Adapt specific-density model to account for deposition. 2. (1) Investigate sample representativeness for any laboratory testing. 3. (1/2) Adapt specific-density model to account for swelling and shrinkage. 4.(l/2)Develop methods of determining percent of each major component in virgin materials and chars. 5. (2) Develop elemental-analysis techniques that al- low identification of full realm of species an- ticipated. 6. (2) Develop a method of measuring permeability in typical porous heat-shield material. 7. (2) Measure permeability of representative heat- shield materials as a function of temperature, permeant, and porosity. 8. (2) Compare methods of measuring specific den- sity and porosity; establish density and porosity model that should actually be used in compu- tations. 9. (2) Investigate application of reflectance measure- ments to char profiling. B. Physical Properties 1. (2) Develop a method of measuring vapor pres- sures under extreme temperature and pressures. 2. (2) Measure vapor pressures of carbon through its triple point. IV. Thermal and Optical Properties A. Thermal Expansion 1. (*) Measure thermal-expansion coefficients of typical ablation materials. 2. (1) Develop a high-temperature (to 7000° F) thermal-expansion apparatus suitable for graph- ites and chars with and without exotic fillers or reinforcements. a. Determine thermal-expansion model that is used by each of the existing expansion fa- cilities. b. Determine biases that remain in expansion measurements, providing that care is taken to minimize facility error, from the different facilities. c. Determine facility that best represents ex- pansion for use in computer modeling and provides the best accuracy in obtaining ex- perimental data. d. Determine how this facility can be modified or replaced to improve accuracy and computer-model representation. e. Make the modifications and automate the operation. 3. (2) Develop a low-temperature thermal-expansion technique (-200 to +800*^) to handle in- homogeneous ablative composites. 4. (2) Investigate effects of high heating rates on thermal expansion of ablative materials. B. Specific Heat 1. (*) Measure specific heat of typical ablation ma- terials. 2. (2) Compare alternate methods of measuring spe- cific heat of solids from -200 to +7000°F and select the simplest, most accurate, most repro- ducible method for each temperature range. 3. (2) Establish methods of measuring specific heat of evolved ablation gases. C. Thermal Conductance 1. (*) Measure conductance of typical ablation m_a- terials. 2. (1) Develop a high-temperature conductance ap- paratus suitable for graphites and chars. JPL TECHNICAL REPORT 32-1436 67 a. Determine conductance form that is mod- eled by each of the existing conductance facilities. b. Determine biases that remain in conduc- tance measurements, providing that care is taken to minimize facility error, from the different facilities. c. Determine facility that best represents con- ductance, as used in computer models, and provides the best accuracy in obtaining ex- perimental data. d. Determine how this facility can be modi- fied or replaced to improve accuracy and computer-model representation. e. Make the modifications and automate the operation. 3. (1) Investigate conductance from- 200 to -t- 7000 °F of carbonaceous chars varied in known fashion as to char structure, time at temperature, and pyrolytic deposition; establish a standard char- conductance-characterization test matrix. 4. (1) Investigate conductance from - 200 to + 7000 ° F of silaceous chars (from silicone elastomer resins or silica or glass reinforcements) and es- tablish a standard char-conductance- characterization test matrix. 5.(l/2)Devise an experiment to separate out the radiative-transfer component in high- temperature conductance and establish a realis- tic mathematical model for its representation (may or may not be attached to the study in IV-C-8, above). 6. (2) Investigate effect of pressure or vacuum on conductance of porous ablators. 7. (2) Develop an apparatus for accurately measuring conductance of honeycomb-sandwich compos- ites in both directions. 8. (2) Devise an experiment to determine conductance anisotropy in ablative materials caused by fill- ers, porosity, reinforcements, or honeycomb. 9. (2) Develop an apparatus for accurately measuring conductance of superinsulation with joints and attachments. 10. (2) Develop an apparatus to measure the effects on composite conductance of joints, feedthroughs, windows, etc., in ablators. D. Optical Properties 1. (*) Measure optical properties of typical ablation materials. 2. (1) Investigate absorption coefficient and trans- mittance of chars as functions of char structure, surface roughness, and temperature (may or may not be attached to the study in IV-D-7, below). 3.(l/2)Develop a high-temperature reflectance or emittance apparatus suitable for graphites and chars. a. Determine optical theory that is modeled by each of the existing conductance facilities. b. Determine biases that remain in optical measurements, providing that care is taken to minimize facility error, from the different facilities. c. Determine facility that best represents ab- sorptance and emittance as they are used in the numerical processes of computer models and provides the best accuracy in obtain- ing experimental data. d. Determine how this facility can be modi- fied or replaced to improve accuracy and computer-model representation. e. Make the modifications and automate the operation. 4.(l/2)Develop a technique to measure reflectance or absorptance at lower (<0.2 fim) wavelengths (may or may not be attached toIV-D-3, above). 5.(l/2)Investigate effects of lateral and in-depth tem- perature gradients on surface temperature and optical-property measurements as functions of surface roughness and temperature level. 6.(l/2)Develop higher temperature sources for reflec- tance measurement plus sources with a wider range of wavelength capability. 7. (2) Investigate reflectance and emittance of car- bonaceous and silaceous carbon chars as func- tions of char structure, time at temperature, surface roughness, pressure, wavelength, and pyrolytic deposition. 8. (2) Develop an apparatus for measuring optical properties of hot gases. 68 JPL TECHNICAL REPORT 32-1436 9. (2) Investigate why three quite different emit- tance facihties give the same emittance value, and three quite different reflectance facilities give the same absorptance value, but— for the same wavelength— emittance can appear to be unequal to absorptance for chars while show- ing adequate equivalence for high-density carbons or graphites. 10. (2) Identify spectral and diffuse components of reflectance and delineate lobing. 11. (2) Investigate light-pipe effects in porous chars. V. Mechanical Properties A. General Mechanical Properties 1. (*) Measure tensile, compressive, flexure, and shear strength of typical ablation materials. 2. (1) Develop a high-temperature (room tempera- ture to 7000 °F) tensile-compressive apparatus, suitable for graphites and chars, with auto- mated operation and data recording, improved load-cell sensitivity, and adaptations for con- trolled atmosphere testing and hish-heatinff- rate— high-loading-rate testing. 3. (1) Develop a high- temperature (room tempera- ture to 7000 °F) shear apparatus, suitable for graphites and chars, with automated operation and data recording and with adaptations for testing under controlled atmospheres, high loading rates, and high heating rates. 4. (1) Investigate effect of inert gases and vacuum on tensile, compressive, flexure, and shear strength of heat-shield materials and their chars. 5. (2) Develop a low-temperature ( -200 to -I- 1000 °F) tensile-compressive apparatus suitable for both rigid and elastomeric heat-shield mate- rials, with automated operation and data recording and adaptations for testing in con- trolled atmospheres and at high loading rates. 6. (2) Develop a low-temperature (-200 to H- 1000 °F) flexure apparatus suitable for both rigid and elastomeric heat-shield materials, v^dth auto- mated operation and data recording and with adaptations for testing in controlled atmos- pheres, under high loading rates, and for fa- tigue under cycling. 7. (2) Develop a low-temperature (-200 to +1000° F) shear apparatus suitable for both rigid and elastomeric heat-shield materials, with auto- mated operation and data recording and adaptations for testing under controlled atmos- pheres. 8. (2) Investigate applicability of normal analytical concepts for representing the mechanical be- havior of heat-shield materials and their chars. 9. (2) Investigate effect of high heating rates and temperature gradient through the thickness on the tensile, compressive, flexure, and shear strength of heat-shield materials and their chars. 10. (2) Investigate flow and fracture behavior of heat- shield materials, including such factors as high loading rate, strain sensitivity under high com- pensation, creep at high and low temperatures, cycling loads, stress concentrations, and ani- sotropy. 11. (2) Investigate effect of bidirectional loading on tensile, compressive, and shear strength of heat- shield materials. B. Special Mechanical Properties 1. (*) Develop a simple method of determining low- temperature brittle transition of nonhomogene- ous heat-shield composites that will be a true indicator of low-temperature mechanical per- formance. 2. (1) Develop a simple method of determining re- sistance of heat-shield materials to thermal shock, using both sudden cooldown of a hot specimen and sudden heating of a cold speci- men. 3. (1) Determine micrometeoroid-penetration resis- tance of typical heat-shield materials as a func- tion of temperature, pressure, impact rate, im.pact direction, material density, reinforce- ment, and previous history. 4. (1) Develop a method of measuring mechanical properties of ablator-structure composites with superimposed temperature gradients and pres- sure forces for development of better analyti- cal models of combined performance. 5. (1) Develop a meaningful thermal-stress measure- ment technique. JPL TECHNICAL REPORT 32-1436 69 6. (2) Establish appropriateness of standard notch- impact tests for analyzing performance of heat- shield materials. 7. (2) Develop a micrometeoroid-penetration appa- ratus with a wide variation of particle size and velocity, low-vacuum capability, and capability of bombarding reasonably large specimen areas with simulated interplanetary radiation. 8. (2) Investigate relationship between impact re- sistance of typical heat-shield materials and the area under the stress-strain curve. 9. (2) Investigate effect of penetrations on thermal performance of typical heat-shield materials as a function of hole size and shape. 10. (2) Develop a method of determining peel strength of an ablator-structure interface that will be meaningful in relation to the singly and doubly curved shapes typical of real fabrications. 11. (2) Investigate methods of improving peel strength at both high and low temperatures. 12. (2) Develop a method of measuring strength of a virgin-char interface both during ablation and after cooldown. 13. (2) Develop a meaningful set of fatigue tests for ablators, including both low-cycle-high-strain and high-cycle-low-strain tests. VI. Electrical Properties A. Signal Attenuation l.(l/2)Measure signal attenuation of typical heat- shield materials before, during, and after ablation to determine the effects of pressure, atmospheric species, ablator thickness, pyro- lyzed thickness, heating rate, shape, wave- length, incident angle, and time at temperature. 2. (2) Develop an improved apparatus for determin- ing attenuation of various signals passing through typical classes of heat-shield materials before, during, and after ablation. 3. (2) Evaluate possibility of calculating transmission properties from temperature profiles and di- electric data as a function of temperature. B. Dielectric Properties 1. (2) Measure dielectric properties of typical heat- shield materials. VII. Degradation Kinetics Investigations A. Primary Degradation Kinetics 1. (1) Identify exo- and endothermic processes inher- ent in different classes of heat-shield compos- ites as a function of temperature, temperature change rate, pressure, gaseous species, sample size and state, and thermocouple biases. 2. (1) Adapt TGA methods for high heating rates and measure differences in kinetics for typical heat- shield materials. 3. (2) Improve DTA facility capabilities by expanding temperature limits, increasing environmental- simulation capabilities, and automating opera- tion and data recording. 4. (2) Improve DSC capabilities by expanding tem- perature limits, increasing environmental- simulation capabilities, expanding heating-rate capability, and automating operation and data recording. 5. (2) Improve TGA facility capabilities by minimiz- ing control deviations, providing better atmo- sphere control, and automating operation and data handling. 6. (2) Investigate differences between isothermal, constant-temperature-rise, and constant- heating-rate TGA methods for deriving kinetic parameters. 7. (2) Investigate effects of size, shape, form, holder, buoyancy, diffusion, pretreatment, and view temperature of sample on TGA kinetic constants. 8. (2) Compare TGA data with DTA and DSC results. 9. (2) Investigate appropriateness of gas chromato- graphs, mass spectrometers, time-of-flight mass spectrometers, and infrared spectrometers for identifying evolved species and specific reac- tions during polymer degradation and their representativeness in relation to species actu- ally evolved during entry or in rocket nozzles, including: a. Postcracking on adjacent hot wall. b. Repolymerization transients. c. Condensation. d. Heating-rate effects. 70 JPL TECHNICAL REPORT 32-I43(S e. Specimen-configuration effects. f . Heating-method effects. 10. (2) Improve gas-chromatograph capabilities. 11. (2) Improve mass-spectrometer capabilities. 12. (2) Improve infrared-spectrometer capabilities. B. Secondary Reactions 1. (1) Develop equipment to investigate cracking and deposition of gases in graphites and chars. 2. (1) Investigate effect of cracking and deposition on conductance. 3. (1) Investigate cracking in silica-reinforced chars as compared with completely carbonaceous chars. 4. (1) Investigate mechanisms and kinetics of crack- ing and deposition, including temperature and pressure effects, species, gas-flow rate, porosity, facility biases, specimen representativeness, and catalysity. 5. (1) Develop a computer model for cracking and deposition. 6. (2) Establish magnitude of the effect of cracking on heat balance. 7. (2) Investigate effect of cracking and deposition on porosity of typical chars. 8. (2) Investigate effect of cracking and deposition on mechanical strength. 9. (2) Develop equipment to study carbon-silica re- actions in chars. 10. (2) Investigate carbon-silica reactions in chars as to their effect on material removal, mechanical strength, and conductance. 11. (2) Develop equipment to study carbon-COa and carbon-H:.0 reactions in chars, and investigate their effect on ablator performance. C. Other Porameters 1. (1) Measure heat of combustion for typical heat- shield materials. 2. (2) Develop an apparatus to measure heat of com- bustion of graphites and chars, using different planetary atmospheres. 3. (2) Develop a technique to determine flammability of ablative materials in planetary atmospheres. 4. (2) Measure flammability of different heat-shield materials. 5. (2) Develop equipment for measuring diffusion constants of typical ablation gases and plane- tary atmospheres, and measure the constants. VIII. Pre-entry Environmental Compatibility Tests A. Preiaunch Environments 1. (1) Carry out a test program to determine effect of spilled fuel or long-time exposure to fuel vapors on thermal and mechanical performance of typical ablation materials. 2. (1) Investigate effect of chemical surface decon- tamination and dry-heat sterilization on ther- mal and mechanical performance of typical heat-shield materials. 3. (1) Investigate alternate carrier gases to replace Freon 12 in chemical surface decontamination. B. Launch Environments 1. (1) Shake and shock typical heat-shield materials at different temperatures. 2. (1) Investigate compatibility of low-density mate- rials with rapid evacuation. C. Transit Environments 1. (1) Determine vacuum stability of typical heat- shield materials. 2. (1) Determine volatile condensable material con- tent of typical heat-shield materials. 3. (2) Investigate effect of space radiation on typical heat-shield materials. 4. (2) Investigate effect of nuclear power plant radia- tion on typical heat-shield materials. D. Combined Environments 1. (2) Measure flexure and tensile strength of typical ablators after consecutive in situ exposure to sterilization, launch vibration, launch pump- down, and long-time exposure to vacuum. JPL TECHNICAL REPORT 32-1436 71 IX. Entry-Simulator Development A. Plasma-Arc Facilities 1. (1) Investigate control systems capable of pulsing both power and working-fluid flow rate simultaneously. 2.(l/2)Investigate methods of increasing heating rate and pressure simultaneously. 3. (2) Investigate arc processes such as energy- transfer mechanisms, arc-column studies, radi- ation loading, and transport properties of gases. 4. (2) Develop arc heads for high-flow-rate, high- pressure, high-power systems. 5. (2) Develop arc heads for reactive working fluids such as oxygen, carbon dioxide, hydrogen, and methane. 6. (2) Develop scaling techniques for increasing the sizes of various classes of arcs toward 500-MW capabihty. 7. (2) Investigate differences in energy distribution in gases heated by dc current, ac current, and inductive coils, respectively. 8. (2) Develop improved electrode materials and configurations. 9. (2) Develop simple starting techniques. 10. (2) Develop power sources with low ripple, low power-factor correction, wide power range, in- stantaneous control response, and rapid control- change capability for large short-time power pulses. 11. (2) Develop power-source controls for multiple-arc systems. 12. (2) Develop diodes and rectifiers with longer life. 13. (2) Develop nozzles for higher supersonic-flow capability at high pressures. 14. (2) Develop arc-chamber, plenum-chamber, and exhaust-nozzle systems that will maximize ex- haust uniformity, without contamination, while minimizing power loss. 15. (2) Develop turbulent-duct techniques. 16. (2) Develop rectangular supersonic-nozzle techniques. 17. (2) Develop high-shear exhaust systems. 18. (2) Develop high-sensitivity exhaust-pumping sys- tems capable of fine-tuning exhaust-shock pat- terns and capable of varying static pressure over a wide range of pressures. 19. (2) Couple exhaust-pumping system pulsing con- trol to the enthalpy and working-fluid pulsing controls mentioned above. 20. (2) Develop high-velocity, high-location-accuracy sample injection mechanisms with three- dimensional scanning. 21. (2) Develop a recession-compensation and rate- measuring system. 22. (2) Develop a probing system for injecting gas- sampling probes into the boundary layer of an ablating sample in an arc exhaust. 23. (2) Investigate and delineate merits and limitations of various sample configurations. 24. (2) Develop recorder-computer-plotter systems for direct conversion of diagnostic and test data to graphical or tabular results. B. Radiant Heaters 1. (*) Develop a continuous CO^ laser capable of pro- ducing heating rates in the 10,000-Btu/ft^/s range. 2. (1) Investigate similar laser systems with other gas carriers. 3. (1) Investigate extension of the laser system to large sample sizes. 4. (2) Develop filament-lamp heater systems for Mars-entry simulation on large shapes. 5. (2) Develop high-pressure, vortex-stabilized, plasma-arc, radiant-heater systems with longer life, more efficient optics, brighter and larger- view-angle sources, and capability of handling a variety of working fluids. 6. (2) Develop better lens, window, and mirror mate- rials for radiant heaters. 7. Develop high-pressure, compact-arc heater sys- tems for Mars-entry simulation. C. Combined Facilities 1. (1) Develop an entry-simulator system using ra- diant heaters and cold-gas flow for shear simulation. 72 JPL TECHNICAL REPORT 32-1436 2. (1) Investigate validity of using the radiant-heater cold-gas system as to wavelength effects, heating-distribution effects, surface-roughness and transmittance effects, inequivalence of local pressure and temperature gradients, and local erosion effects. 3. (1) Develop an analytical model for the flow field and surface interaction of the radiant-heater cold-gas system. 4. (1) Investigate differences and limitations in simu- lation between convective-radiative facilities, comparing: a. Plasma-arc-arc-imaging-furnace facilities. b. Plasma-arc-plasma-arc radiant-heater facilities. c. Plasma-arc facilities with specimens mounted near the arc. d. Plasma-arc-focused-laser facilities. 5. (1) Develop the most suitable facility (from IX-C- 4) into a larger Venus-direct-entry simulator with pulsed-convective heating, radiative heat- ing, anu pressure. 6. (2) Investigate applicability and limitations of the Cornell Aeronautical Laboratory wave super- heater for Venus-entry simulation. Develop the most suitable facility (from IX-C- 4) into a small Mars-direct-entry simulator with pulsed-convective heating, radiative heating, and pressure. Investigate concepts of pebble-bed and porous- resistance heaters for Mars-entry simulation in CO2-N2 atmospheres. Investigate applicability and limitations of nuclear-explosion data to simulation of high- energy Jupiter entry. X. Entry-Simulator Testing A. General Studies 1. (1) Investigate comparative oxidation capability of air and CO2-N2 combinations as to the CO2-N2 equivalent of air, reaction-rate and diffusion- rate processes, and potential effects of low- percentage contaminants; e.g., argon and water. /. 8. 2. (1) Investigate sublimation processes in graphites and chars at high temperature, including heating-rate limits and pressure effects. 3. (1) Investigate dynamic blocking effects using calorimeter-ablator combinations in concentric- probe, wedge, and circular- or square-tube configurations. 4. (1) Develop techniques for scaling plasma-arc abla- tion results to larger body sizes. 5. (1) Investigate effects of joints, cracks, protuber- ances, holes, and erosion on ablation response. 6. (2) Develop an equilibrium-chemistry and boundary-layer flow model that will adequately represent boundary layers in planetary atmo- spheres, and compare it to the boundary layer in plasma-generator studies. 7. (2) Investigate changes in boundary-layer condi- tions in a plasma arc caused by surface reces- sion in different model configurations. 8. (2) Investigate gaseous-combustion processes in a plasma-arc system by injecting separated evolved gas species into the planetary- atmosphere-simuiated exhaust gas. 9. (2) Investigate nitration reactions with graphite and chars in high-temperature plasma-arc ex- hausts with and without the presence of oxy- gen or carbon dioxide. 10. (2) Develop standards in specimen shape and in minimum acceptable stream and specimen calibration. 11. (2) Investigate gas emittance and absorptance for various planetary-atmospheric species and typ- ical ablation products. 12. (2) Investigate effects of spectral distribution on ablator response. 13. (2) Investigate radiation absorption in the bound- ary layers of specimens in a plasma-arc exhaust. 14. (2) Investigate contribution of regular surface roughness to ablation response in chars. 15. (2) Investigate ablation response to turbulent heat- ing, comparing pipe, plate, and wedge flow. 16. (2) Investigate mechanisms of tripping laminar flow to turbulent flow. JPL TECHNICAL REPORT 32- T 436 73 17. (2) Using an arc-heated charring sample, investi- gate surface-roughness effects on surface- temperature measurements. 18. (2) Develop techniques for making RF-attenuation measurements during ablation. 19. (2) Investigate RF-attenuation characteristics of typical ablation materials during ablation. 20. (2) Develop techniques for ablation testing of typ- ical heat-shield materials in situ: a. After long-time exposure to vacuum. b. After sterilization. c. After simulated micrometeoroid damage. d. After exposure to nuclear radiation. e. On cold models. 21. Investigate reactions of CH,,, NHs, and He with graphites and chars at high temperatures. B. Specific Mars Studies 1. Screen new low-density foams and composites relative to earlier materials for out-of-orbit Mars entry (heating rates <100 Btu/ftVs). 2. Test best materials from out-of-orbit Mars entry, screening for complete definition of ma- terial response within heating range, including transient effects of actual pulses. 3. Test large samples of best Mars out-of-orbit materials combined with structural members in integrated facilities, with both transit and entry environments, using radiant bulbs to heat the samples. 4. On typical classes of heat-shield materials, in- vestigate the Mars direct-entry environment (heating rates less than 400 Btu/ft-/s in CO,,- Na) in depth, including CO2 combustion equiv- alence, blocking effects, and pressure effects. Using critical environments (defined in X-B-4, above), screen a variety of candidate low- density ablation materials for relative performance as RF-transparent and non-RF- tran.sparent ablators. Test large samples of the best Mars direct- entry materials combined with structural mem- bers in integrated facilities, with both transit and entry environments, using radiant bulbs to heat the samples. 5. 7. Investigate scaling effects on Mars direct-entry materials in plasma-arc facilities with model sizes up to 24 in. in diameter. C. Specific Venus Studies 1. (*) For suitable classes of heat-shield materials, in- vestigate the Venus low-energy-entry environ- ment (heating rates <2000-Btu/ftVs convective and 1000-Btu/ftVs radiative in CO-^-Na), in- cluding CO2 combustion equivalence, CO2 combustion processes, sublimation processes, pressure effects, blocking contributions, and material response. 2. (*) Using critical environments (defined in X-C-4, above), screen a variety of candidate ablation materials. 3. (*) Investigate applicability of laser systems to sim- ulate high-energy Venus-entry environment. 4. (*) Using available facilities, identify ground-test simulation limits for high-energy Venus-entry simulation, and test typical candidate ablative materials for their relative performance in these environments. 5. (2) Investigate applicability of direct-arc exposure to simulate the high heating rates and pressure of a high-energy Venus entry. D. Specific Jupiter Studies 1. Correlate atomic-blast-container ablation data with Jupiter-entry material response (heating rates on the order of 1,000,000 Btu/ftVs). 2. Use these data to infer analytical ablation models for high-heating-rate environments on a first-cut basis. XI. Diagnostic Instrumentation Development A. Environmental Instrumentation 1. (*) Investigate and establish minimum environ- mental calibration for testing ablative samples in entry-simulation facilities. 2. (1) Establish accuracy of heating-rate limits and surf ace-catalysity effects for various calorimeter types, and develop standard configurations for calorimeters showing greatest promise in each convective and radiative heating-rate range. 74 JPL TECHNICAL REPORT 32-1436 3. (1) Establish pressure limits and accuracy of vari- ous pressure-probe concepts for plasma-arc facilities, and develop standard configurations for probes showing greatest promise for each pressure range. 4. (1) Establish enthalpy limits, accuracy, and ionized- flow biases for various enthalpy-measuring techniques, and develop standard techniques for methods showing greatest promise for plasma-arc exhaust definition. 5. (1) Develop enthalpy probes for very high enthal- pies and pressures. 6. (1) Develop enthalpy probes for accurately deter- mining coring effects. 7. (2) Investigate window-transmission limitations on radiative-heating-rate measurements. 8. (2) Investigate the difference in stream-property influence of nonablating and ablating models in plasma-arc exhaust streams and their influence on measured heating rates. 9. (2) Develop and investigate concentric-calorimeter probes wherein ablative materials could be used to replace any of the individual calorim- eters for inference of blocking effects. 10. (2) Develop a contamination probe for analyzing stream contamination and its influence on heating-rate measurements. 11. (2) Investigate wall-calorimeter designs and de- velop standard calorimeters for insertion in nonablating and ablating systems. 12. (2) Develop methods for accurately separating static and dynamic pressure. 13. (2) Investigate pitch and yaw effects on pressure measurements. 14. (2) Develop methods for measuring pressure on ablating models. 15. (2) Differentiate between problems for subsonic and supersonic enthalpy probes. 16. (2) Establish usefulness limits, accuracy, and ap- propriateness of the various probe and optical techniques for analyzing plasma-arc exhaust- flow fields for velocity, temperature, and elec- trical distributions. Consider chemical state, shock interactions, tank and probe interference, rotational flow and vorticity, and energy state in equilibriums. 17. (2) Develop a class of wedge models with a de- fined and useful range of environments for ablation testing. 18. (2) Develop a class of pipe- or square-channel models with a defined and useful range of en- vironments for ablation testing. B. Material-Response Instrumentation 1. (1) Investigate applicability of thermocouples to measurement of internal temperatures of abla- tive materials, establishing the criticality of various readout parameters (e.g., wire calibra- tion and drift, cold-junction drift, nonisothermal connections to external equipment, and sensi- tivity to stray currents and magnetic fields), as well as the more familiar location problems. 2. (1) Establish limitations, accuracy, surface- roughness effects, and gas-cap or arc-radiation effects on the various surface-temperature- measurement techniques, and develop standard techniques for various sample-configuration and exposure environments. 3. (1) Investigate surface-temperature measurements as they relate to surface roughness of chars and to alternate computer-node models near or at the svurface. 4. (2) Develop reliable techniques to manufacture and install 1-mil or smaller thermocouples in abla- tion samples. 5. (2) Investigate measurement problems of using thin films to estabhsh back-surface or interface tem- peratures on ablation materials. 6. (2) Develop techniques and quantify the problems of measuring internal temperatures in ablative chars. 7. (2) Investigate differences between postanalysis and transient techniques (e.g.. X-rays) to mea- sure variations in internal density during abla- tion, and establish the reasonableness of using these techniques to derive transient ablation models. 8. (2) Compare surface-recession and mass-loss-rate calculations from tare weights and dimensions vs transient camera or X-ray techniques for dif- ferent environmental-exposure regimes. JPL TECHNICAL REPORT 32-1436 75 9, (2) Establish standard techniques of measuring surface-recession and mass-loss rate for different ablative-material test configurations. 10. (2) Establish standard photographic techniques for recording surface phenomena of ablating specimens in different brightness regimes, in- cluding narrow-wavelength-regime filters, po- larization, etc. 11. (2) Use photographic techniques to study the lateral surface flow of glassy fillers in ablative ma- terials. XII. Flight Test A. Earth Flight-Test Simulations 1. (1) Venus low-energy-entry severity can be simu- lated by earth-flight test, and is desirable to prove out the high-performance heat-shield sys- tems necessary to provide payloads on the anticipated missions. 2. (1) Venus high-energy-entry severity can be better simulated by earth-flight tests because combus- tion or available gaseous species play a lesser role in the overall ablation response, and such a test is desirable for the reason given in XII-A-1, above. 3. Mars out-of-orbit entry can be fully qualified by an earth-flight test, which is desirable to decrease conservatism in heat-shield and struc- tural requirement estimates in the extremely weight-sensitive, low-ballistic-coefficient cap- sules under consideration. 4. Mars direct-entry severity can be closely matched in an earth-flight test, depending upon the importance of combustion processes, and is desirable for the reason given in XII-A-3, above. 5. Jupiter lower-energy-entry conditions are simi- lar to the Venus conditions discussed in XII-A-1 and -2, above. B. Flight Instrumentation 1, (1) Investigate available flight heat-shield-diagnostic instrumentation in depth, and establish instru- ment limitations, accuracy, and meaningfulness to performance diagnostics. 2. (1) Develop better temperature-history measuring systems. 3. (I) Develop better dynamic calorimeters and pres- sure probes. 4. (1) Develop better surface-recession indicators. XIII. Rocket-Nozzle Testing A. Small Rocket Tests 1. Test specific selected materials in specific sub- systems of interest to particular missions. 2. Test a variety of materials with the new special high-performance propellants. 3. Investigate restart problems in nozzle-throat performance. 4. Improve and automate solid and liquid test- stand operation. 5. Investigate plasma-arc simulation of rocket- nozzle performance in depth. XIV. Resin Development A. Clean-Characterized Polymer Standards 1. (1) Establish phenolic standards. 2. (2) Establish silicone-elastomer standards. 3. (2) Establish epoxy and epoxy-novalac standards. 4. (2) Establish polyimides standards. 5. (2) Establish polybenzimidazole standards. B. New High-Temperature Resins 1. (1) Investigate, theoretically and experimentally, the probable limitations or potential improve- ments in phenolic and epoxy resins, and es- tablish their relative contribution to thermal stability, char properties, and low-temperature toughness. 2. (1) Repeat XIV-B-1 for polyimides and polybenzi- midazoles, as well as some of the more exotic ladder and other polymers, to establish poten- tial limitations of basic carbonaceous polymeric structures. 3. (2) Investigate contribution of fluorination on XIV- B-1 and -2. 4. (2) Repeat XIV-B-1 for silicone-elastomer-based polymers to establish potential limitations of basic siliceous polymeric structures. 76 JPL TECHNICAL REPORT 32-1436 5. Investigate the following: a. (1) Silicone-glass resins. b. (1) Flexibilized polyimides. c. (1) Noncondensation polymers of any kind. d. (2) Rigid silicones. e. (2) Aromatic silicones. i. (2) Fluorinated silicones. g. (2) New phenolic systems. h. (2) Ladder polymers. i. (2) Thiazole- and quinone-based polymers. j. (2) Polyphenyl oxides. k. (2) Fluorinated versions of carbonaceous polymers. 1. (2) Semiorganic polymers. m. (2) Inorganic polyiners. C. New Foams 1. Establish density, hom.ogeneity, toughness, rigidity, high-temperature stabilitv, and limita- tions of the following: a. (1) Polyphenylene oxide. b. (1) Diphenyl oxide. c. (1) Polyimide. d. (1) FBI. e. (2) Polyethylene. f. (2) Polytetrafluoroethylene. g. (2) Cross-linked polycarbonate, h. (2) Epoxy. i. (2) Isocyanurate. j. (2) Polyurethanes. D. Tailoring Resin Systems for Particular Needs 1. Consider a resin system for Mars out-of-orbit entry that provides the following properties or the best compromise possible within the limits of the potential catastrophic failures that are not avoidable through design (high- performance— low-density ablator): a. Good low-temperature flexibihty or tough- ness. b. Good high-temperature stability and rea- sonable char-residue strength. c. Low conductance. d. Inert to fillers or strengthened by their pres- ence. e. Good processability (with or without fillers) to densities in the range of 10 Ib/ff or lower. f. Easy fabrication and application to complex shapes. g. Low thermal-expansion coefficients. h. Low volatile and recondensable-volatile content in space vacuums. i. Space-vacuum and radiation stability. j. Ground-storage inertness. k. Compatible with reasonable adhesive sys- tems. 1. Inert to sterilization and surface decontami- nation. m. Low volume change during degradation. Consider a resin system for Mars direct entry that provides the following properties or the best compromise possible within the limits of the potential catastrophic failures that are not avoidable through design (high-performance- low-density ablator): a. Good low-temperature flexibility or tough- ness. b. Good high-temperature stability and rea- sonably strong. c. Low conductance. d. Inert to fillers or strengthened by their pres- ence. e. Good processability (with or without fillers) to densities in the range of 20 Ib/ft^ or lower. f. Easy fabrication and application to complex shapes. g. Low thermal-expansion coefficients. h. Low volatile and recondensable-volatile content in space vacuums. JPL TECHNICAL REPORT 32-1436 77 i. Space-vacuum and radiation stability. j. Ground-storage inertness. k. Compatible with reasonable adhesive sys- tems. 1. Inert to sterilization and surface decontami- nation. m. Low volume change during degradation. 3. Consider an RF-transparent resin system for Mars direct or out-of-orbit entry that provides the following properties or the best compro- mise possible within the limits of the potential catastrophic failures that are not avoidable through design (high-performance-RF- transparent-low-density ablator) : a. Good low-temperature flexibility or tough- ness. b. Good high-temperature stability and either no char or a nonconductive char residue. c. Low conductance. d. Inert to fillers or strengthened by their pres- ence. e. Good processability (with or without fillers) to densities in the range of 20 Ib/ft^ or lower. f. Easy fabrication and application to com- plex shapes. g. Low thermal-expansion coefficients. h. Low volatile and recondensable-volatile content in space vacuums. i. Space-vacuum and radiation stability. j. Ground-storage inertness. k. Compatible with reasonable adhesive sys- tems. 1. Inert to sterilization and surface decontami- nation. m. Low volume change during degradation. 4. (*) Consider a resin system for Venus low-energy entry that provides the following properties or the best compromise possible within the limits of potential catastrophic failures that are not avoidable through design (high-performance- medium-density ablator): a. Good low-temperature toughness or flexi- bility. b. Good high-temperature stability. c. Low volume change during degradation. d. Good char or residue strength. e. Reasonable resistance to combustion by planetary gases. f. Reasonable resistance to combined aerodynamic-shear pressure and thermal- stress forces. g. Low thermal-expansion coefficients, h. Low conductance. i. High emittance. j. Good processability (with or without fillers) to densities in the range of 20 to 50 Ib/ft^. k. Easy fabrication and application to complex shapes. 1. Compatible with reasonable adhesive sys- tems. m. Inert to fillers or strengthened by their pres- ence. n. Space-vacuum and radiation stability. o. Low volatile and recondensable-volatile content in space vacuum. p. Ground-storage inertness. q. Inert to sterilization and surface decontami- nation. 5. (*) Consider a resin system for Venus low-energy entry that provides the following properties or the best compromise possible within the limits of potential catastrophic failures that are not avoidable through design (high-performance- high-density ablator): a. Good low-temperature toughness or flexi- bility. b. Good high-temperature stability. c. Low volume change during degradation. 78 JPL TECHNICAL REPORT 32-1436 d. High char or residue strength under high- temperature, high-pressure, high-shear con- ditions. e. Reasonable resistance to combustion by planetary gases. f. Reasonable resistance to combined aerodynamic-shear pressure and thermal- stress forces. g. Low thermal-expansion coefficients, h. Low conductance. i. High emittance. j. Good procrasability with or without fillers. k. Easy fabrication and apphcation to complex shapes. 1. Compatible with reasonable adhesive sys- tems. m. Inert to fillers or strengthened by their presence. n. Space-vacuum and radiation stability. o. Low volatile and recondensable-volatile content in space vacuum. p. Ground-storage inertness. q. Inert to sterilization and surface decontami- nation. Consider a resin system for small control- or injection-motor nozzles that provides the fol- lowing properties or the best compromise possible within the constraint of potential catastrophic failvires that are not avoidable through design (high-performance-high-density ablator): a. Good low-temperature toughness or flexi- bility. b. Good high-temperature stability. c. Low volume change during degradation. d. High char or residue strength under high- temperature, high-pressure, high-shear con- ditions. e. High resistance to combustion by oxidizer- rich environments. f . High resistance to failure from internal dis- tortions. g. Low thermal-expansion coefficients. h. Low conductance. i. High emittance. j. Good processability witii or without fillers. k. Easy fabrication and application to complrac shapes. 1, Compatible with reasonable adhesive sys- tems. m. Inert to fillers or strengthened by their presence. n. Space-vacuum and radiation stability. o. Low volatile and recondensable-volatile content in space vacuum. p. Ground-storage inertness. q. Inert to sterilization and surface decontami- nation. 7. (2) Develop resin systems with high endothermic decomposition. 8. (2) Investigate alternates for XIV-D-1 through -5 with high strain capability and controlled Pois- son's ratio. 9. (2) Investigate alternates for XIV-D-1 through -6 with good impact-energy absorption. XV. Filler Development A. Clean-Characterized Reproducible Filler Standards 1. (2) Establish fiber, yam, and eccosphere standards for glass, silica, and quartz. 2. (2) Establish fiber, yam, and powder standards for carbon and graphite. 3. (2) Estabhsh fiber and powder standards for nylon. 4. (2) Establish microballoon standards for phenolic resins. 5. (2) Establish standards for cork. B. New Filler Development 1. (I) Investigate wetting and bonding additives. 2. (2) Investigate usefulness of nitrides, borides, car- bides, and high-temperature metals as filler materials in high-temperature ablative com- posites. JPL TECHNICAL REPORT 32-1436 79 3. (2) Investigate alternate organic-fiber reinforce- ments to replace nylon. 4. (2) Investigate higher-temperature microballoon systems than phenolic systems. 5. (2) Investigate submicron particles as fillers. 6. (2) Investigate limitations and potential improve- ments of special additives such as antioxidants, fire retardants, and chemical-cracking controls. 7. (2) Investigate salts that decompose endothermi- cally yet are resistant to space vacuum and radiation. 8. (2) Investigate fiber-production techniques and methods to control the nature of the fiber, its size, and its surface properties. 9. (2) Investigate yarn-production techniques and methods to control the nature of the yam, its size, and its surface properties. 10. (2) Investigate three-dimensional (3D) weaving techniques. 11. (2) Investigate powder-production techniques and methods to control uniformity and size distri- bution. 12. (2) Investigate microballoon-production techniques and methods to control uniformity and size dis- tribution. 13. (2) Investigate eccosphere-production techniques and methods to control uniformity and size dis- tribution. C. Tailoring Filler Properties to Needs 1. Consider a filler system for Mars entry that provides the following properties or the best compromise possible within the limits of the potential catastrophic failures that are not avoidable through design: a. High temperature. b. Resin stabilization. c. High-temperature strength, modulus, and toughness. d. Low-temperature strength, flexibility, and toughness. e. Low density. f. Strengthens char and is highly resistant to char erosion. g. Endothermic decomposition. h. Low volume change. i. High specific heat. j. Low conductance. k. Char-combustion protection. 1. Inert to space, sterilization, and ground storage. m. Good dispersion; wetting and adhesion with resin. 2. (1) Consider a filler system for Venus entry that provides the following properties or the best compromise possible within the limits of the potential catastrophic failures that are not avoidable through design: a. High temperature. b. Resin stabilization. c. High-temperature strength, modulus, and toughness. d. Low- temperature strength, flexibility, and toughness. e. Reasonable density. f. Strengthens char and is highly resistant to char erosion. g. Endothermic decomposition, h. Low volume change. i. High specific heat. j. Low conductance. k. Char-combustion protection. 1. Inert to space, sterilization, and ground storage. m. Good dispersion; wetting and adhesion with resin. n. High sublimation energy. 3. Consider a filler system for small control- or injection-motor nozzles that provides the fol- lowing properties or the best compromise possible within the limits of the potential catas- trophic failures that are not avoidable through design: a. High temperature. 80 JPL TECHNICAL REPORT 32-1436 b. Resin stabilization. c. High-temperature strength, modulus, and toughness. d. Low-temperature strength, flexibility, and toughness. e. Reasonable density. f. Strengthens char and is highly resistant to char erosion. g. Endothermic decomposition, h. Low volume change. i. High specific heat. j. Low conductance. k. Char-combustion protection. 1. Inert to space, sterilization, and ground storage. m. Good dispersion; wetting and adhesion with resin. n. High sublimation energy. o. High vaporization energy. p. High melting temperature. q. Low viscosity at high temperatures. XVI. Composite Development and Fabricability Investigations A. Standard Ablative Composites l.(l/2)Establish a high-density phenolic carbon stan- dard. 2.(l/2)Establish a high-density phenolic nylon stan- dard. 3. (2) Establish a high-density phenolic silica stan- dard. 4. (2) Establish a high-density polyimide carbon stan- dard. 5. (2) Establish a low-density phenolic nylon stan- dard. 6. (2) Establish a low-density foam standard. 7. (2) Establish a low-density silicone-elastomer composite standard. B. Component Preparations 1. (2) Investigate viscosity control, wettability con- trol, and low-molecular-weight fragment- removal techniques for resin systems. 2. (2) Investigate filler-reinforcement pretreatments. 3. (2) Investigate low-density filler processing. 4. (2) Investigate unidirectional and bias-cut tape production. 5. (2) Investigate cloth-weaving techniques. C. Fabricability Studies l.(*/l)Develop dual-density ablator concept. 2. (1) Each resin system and filler combination that passes gross early screening should be sub- jected to an extensive fabricability investiga- tion, including: a. Mixing problems. b. Alternate application techniques. c. Use of honeycomb reinforcement. ■J * n . __• ^«4.;U;l;#-»r a. iVUIleSiVC ■v-UllJpaiiuilliy. e. Optimum cure cycle with each application technique. f. Machining methods. g. Repair and refurbishment. 3. (1) Special studies should be made of the kindx)f resin and filler variations necessary to im- prove fabricability, along with their relative effect on performance for each application technique: a. Foaming. b. Vacuum-bag or compression molding with fibers. c. Vacuum-bag or compression molding with microballoons or eccospheres. d. Spraying. e. Extrusion. f. Rollcrcoating. g. Trowelling with or without honeycomb, h. Gumming honeycomb. JPL TECHNICAL REPORT 32-1436 81 i. Cloth layup with vacuum-bag or compres- sion molding. j. Tape wrapping. k. Filament winding. 1. Three-dimensional weaves. 4. (1) Adhesive studies. 5. (1) Coating development for temperature control during transit. 6. (1) Establishment of process-control procedures. 7. (2) Continuous processing and scale-up studies. 8. (2) Joint problems. 9. (2) Radar cross-section studies for tracking in transit. 10. (2) Abrasion-resistance studies. 11. (2) Studies of compatibility with active transpiration-cooling systems. XVII. Nondestructive Testing A. Methods Development 1. (1) Alternate methods, along with their limitations for various classes of ablation materials, should be studied in depth. 2. (1) New techniques with theoretical promise should be pursued with vigor. B. Applications 1. (1) The best available methods should be applied to each class of material surviving early Mars and Venus environmental screening. XVIII. Design Criteria and Parametric Studies for Design A. Design Criteria 1. (1) Reasonable listings of heat-protection system requirements and constraints (and their most plausible alternates) plus the best available def- inition of anticipated environments should be openly published following approval by NASA Headquarters, updated at standard intervals, and widely distributed. B. Parametric Studies for Design 1. Using nominal conditions and properties, com- bined uncertainties, safety factors, and realistic updating procedures for reduced uncertainties, parametric studies should be made of the fol- lowing: a. Mars out-of-orbit entry. b. Mars direct entry. c. (*) Venus low-energy entry. d. (*) Venus high-energy entry. e. Jupiter lower-energy entry. f . Jupiter higher-energy entry. 82 JPL TECHNICAL REPORT 32-1436 NASA - JPL - Coml., LA., Gilif.