Heat Sink Versus Ablation

Since the peak heating rates for this blunt-body, high-drag configuration were expected to be one whole order of magnitude less than those experienced by ballistic missiles, no one competent to judge the issue now considered the "thermal barrier" problem insoluble. Rather, it had been proven to be no more than a "thermal thicket." Since the mid-fifties, various civilian and military experimental teams had studied the reentry problems for ballistic missile warheads, but only part of this research data was applicable to the different case of the spacecraft. Army and Vitro Corporation reentry experiments using ablation materials (such as graphite, teflon, nylon, or lucite) had already demonstrated that Jupiter nose cones worked quite well as ablators. But NACA preferred to rely on the successful prior experience of the Air Force with heat-sink metals, particularly copper, for early Thor nose cones. The results of these thermodynamic studies in materials science were contradictory, or at least inconclusive. So the manned satellite project began life officially in October without a commitment to either method of heat shielding, but with a definite preference for Faget's prejudice.44

Gilruth, Faget, and other members of the Space Task Group since March 1958 had been leaning toward the heat sink. A 600-pound metallic heat sponge might be a little heavier but it would be more reliable than a ceramic heat dissipator, for the simple reason that there was more industrial experience with fabricating refractory metals than with molding and bonding ablation materials. Some officials were convinced by the Navy's successful use of a lightweight beryllium heat sink on Polaris flight tests that beryllium was the answer. The heat sink method also was thought to have the considerable advantage over ablating materials of creating less of a "plasma sheath" - the envelope of ionized air [128] generated by the friction of atmospheric braking. Telemetry and communications blackouts from this phenomenon might be troublesome. Pending further study, the Task Group and Silverstein decided to retain the original specification that a beryllium heatshield be provided by the capsule contractor. Requiring all the bidders to assume a beryllium shield should give a fairer evaluation of their proposals. Until Big Joe could test the ablation technique, no final decision would be made.45

Ablation technology, imprecise by nature, was neither well understood nor very highly sophisticated as yet, whereas the metallography of heat sink materials was straightforward, and the thermodynamics of metals was deducible. Faget believed there would be no intrinsic weight penalty for using a metal shield; the difficulty of ditching a hot shield without danger had yet to be solved. There was no disposition to ignore ablation in favor of heat sink. Big Joe was conceived to resolve the problem. By late November, when Aleck Bond took charge of it, his presumption was that Big Joe would provide the definitive test of an ablation heatshield.

Rocketry was not the only means considered for accomplishing high-altitude qualification tests at the beginning of the program. On their own initiative in the summer of 1958, Jerome Hammack, John B. Lee, Joe W. Dodson, and other Langley engineers had begun a modest program of parachute and stability trials by dropping boilerplate capsule models from C-130 transports provided by the Air Force. Balloon flights, however, seemed to promise even more effective and economical means of qualifying by "space-soaking" the complete capsule and its associated systems. From the Montgolfier brothers in the 1780s to David G. Simons' Manhigh ascents in 1957 and the contemporary Strato-Lab project of the Navy, ballooning had always been an attractive way to pierce the vertical dimension.46

Believing that the environmental conditions at extreme altitude could be experienced more easily than they could be simulated in vacuum chambers on Earth, the Space Task Group proceeded with plans to launch balloons carrying ballistic capsules as gondolas. Tests of instrumentation, retrorockets, drogue and main parachute systems, and recovery procedures, plus pilot orientation and training, might be done within a year's time by lighter-than-air ascents. Contracts were let to the Weather Bureau, the Office of Naval Research, and the Air Force Cambridge Research Center for planning this flight support program.47

No sooner had these feasibility studies been started than the Space Task Group discovered how intricate, vast, and expensive had become stratospheric sounding technology in recent years. The popular craze over Unidentified Flying Objects during the fifties had been caused partly by atmospheric and cosmic-ray research with floating objects, enormous Mylar plastic gas bags drifting around at high altitudes. Preliminary balloon flights for the manned satellite project threatened to become much more expensive than had been originally anticipated.48

Contract planning, booster procurement, and the need for specialized help [129] from the military services were central concerns of NASA and the Space Task Group during their first three months of existence. The possibility of friction in management relations between NASA and the Defense Department was also recognized as a potential problem. To facilitate coordinated work and plans, STG needed in-house representatives in uniform. Efficient administration demanded liaison officers to serve as single points of contact between STG and each of the military services. So in December orders were cut for Lieutenant Colonel Keith G. Lindell of the Air Force, Lieutenant Colonel Martin L. Raines of the Army, and Commander Paul L. Havenstein of the Navy to report to the Space Task Group for this function.

In general, relations between NASA and the Department of Defense had proceeded quite amicably since the drafting of a "Memorandum of Understanding" in September by the Joint Manned Satellite Panel.49 However, with so much initiative being taken by the Space Task Group, there was danger that the concurrent actions of NASA Headquarters and STG might cause some frustrations and confusions in the Pentagon and among military contractors. NASA was still too young for its STG to be known. At this stage most of the planning for budgeting, procurement, tracking, and recovery operations had to be done in Washington; NASA Headquarters was carefully guarding its prerogative of conducting interagency business.50 Cooperation between Defense and NASA, and between STG and its own Headquarters, was good, if not idyllic, during the first 100 days. Nowhere was this more obvious than in astronaut selection.

44 Message, Commanding Officer, Wright Air Dev. Center, to C.O., Air Research and Development Command, July 9, 1958. On Army Ballistic Missile Agency's successes with ablative Jupiter nosecones in 1957 and 1958, see Reentry Studies, 2 vols., Vitro Corp. report no. 2331-25, Nov. 25, 1958; Sarah S. Whitaker, "Bibliography - Jupiter Nose Cones," MSFC, Sept. 14, 1962; and W. R. Lucas and J. E. Kingsbury, "The ABMA Reinforced Plastics Ablation Program," reprinted from Modern Plastics (Oct. 1960).

45 Memo, Wood to Office of Space Flight Development, "Background on Letter of October 22, 1958, Covering 'Ablation/Heat Sink Investigation - Manned Reentry,'" Nov. 7, 1958. Cf. memo, Low to Newell Saunders, Nov. 28, 1958; "Specifications for Manned Space Capsule"; Faget (interview) said "Ablation was ruled out as a material in the competition for the simple reason that it would prove to be too much of a 'wild card' in the technical assessment." In other words, said George Low, Oct. 5, 1965, "we wanted to select the best spacecraft manufacturer and not only the best heat shield inventor."

46 Jack C. Heberlig, interview, Houston, Feb. 20, 1964; Hammack, interview, Houston, Feb. 13, 1964. See pp. 50-52. For a convenient overview of the Manhigh, Excelsior, and Strato-Lab projects, see "Report on Manned Space Flight," session VII of Proceedings of the Second National Conference on the Peaceful Uses of Space, Seattle, Washington, May 8-10, 1962, NASA SP-8 (Washington, 1962), 241-261.

47 "Project Mercury Status Report No. 1 for Period Ending Jan. 31, 1959," STG. See also, Emme, Aeronautics and Astronautics 1915-1960, appendix C, 161-165.

48 Careful study of the "half proposal" by Winzen Research, Inc., described in "Technical Proposal for NASA Man-in-Space Capsule Program," No. 1160-P, Dec. 8, 1958, for a balloon-hoisted sealed cabin similar to those used in the Air Force Project Manhigh and the Navy Strato-Lab continued within STG for several more months and was instrumental in determining that this kind of "space soak" would not justify its cost.

49 Low, "Status Report No. 2 - Manned Satellite Project," Dec. 17, 1958. The danger of friction was probably greatest in the anomalous relationship between the Advanced Research Projects Agency of the Department of Defense and the military services' own advanced research groups. Memorandum of understanding, NASA-ARPA Manned Satellite Panel, "Principles for the Conduct by NASA and the Department of Defense of a Joint Program for a Manned Orbital Vehicle," Sept. 19, 1958. See also memo, Gilruth for all concerned, "Organization of Space Task Group," Jan. 26, 1959.

50 Letter, Silverstein to Lt. Gen. Roscoe E. Wilson, U.S. Air Force, Nov. 20, 1958; NASA-Army joint news release, "NASA-Army Agreement," Dec. 3, 1958; DeMarquis Wyatt, interview, Washington, Sept. 1, 1965.

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