Quest 10.3, July 3

T ECHNOLOGY Heated Debates A History of the Development of the Space ShuttleÕs Thermal Protection System: 1970-1981 By BRIAN WOODS tioners may strive to create order, sys- intense heat induced by atmospheric tem and control, through rational deci- drag on re-entry attracted such visible sion-making, technological develop- controversy because its solution was INTRODUCTION ment is a diverse, capricious, contradic- inextricably bound-up with the design tory and messy process. Authors in the of other major elements of the Shuttle. A documentary on the Columbia dis- both the history and sociology of sci- Airframe configuration, structure and aster, recently aired on British ence and technology have shown that materials could not be divorced from Television, concluded that the accident scientific knowledge and technological the selection of materials and structure was the result of Òflawed design.Ó In a artifacts and systems have to be treated of the thermal protection system. similar vein to commentary that fol- as socio-historical products: that the Equally, the weight and distribution of a lowed the Challenger disaster in 1986, definition and creation of an object is thermal protection system could have Nigel Henbest and Heather CouperÕs also the definition and creation of its adverse effects on the design of the documentary located the causes of this socio-technical context. To build and propulsion system.3 Òflawed designÓ and so by implication operate large complex technologies like NASA and its contractors explored the accident itself, in the technical com- the Shuttle, the protagonists have to four principal thermal protection design promises that emerged from the politi- enroll a variety of things, organizations concepts in early 1970: replaceable cal battles between NASA and the and individuals into a range of associa- ablator panels; metallic heat shields; Nixon Administration during the 1969 tions and negotiations that are continu- non-metallic materials; and carbon-car- to 1972 period. ally being enacted and re-enacted.2 The bon hot structures. Although pertinent, Henbest and aim of this paper then, is not to find Ablator technologies had been CouperÕs mistake was to separate poli- fault or to lay blame, but in light of the developed and utilized on the Mercury, tics from technology: to place politics recent Columbia disaster and as a guide Gemini and Apollo programmes. on the outside where it impinged on and to future commentary about it, to look Essentially an ablator heat shield was a was detrimental to technological back at the development of its thermal sacrificial outer layer that would burn progress. This led them to state that had protection system and reveal both the up on re-entry. The concept employed NixonÕs Administration allowed NASA difficulties and the socio-technical materials that had almost no ability to to build its original two-stage Shuttle processes that were involved in its cre- transfer heat, but would turn white hot, design, such a catastrophic failure ation. char and then melt away without trans- would not have occurred. Such state- mitting energy into the primary struc- ments, as sociologist Bruno Latour TECHNOLOGY AND CHOICE ture. Although the development of a rightly points out, Òsay nothing.Ó They low-density ablator system for Shuttle are simply tautologies that are Òfeasible The starting point of any history of application would be uncomplicated only at the end of the roadÓ long after technology is with the exposure of and workable, engineers at the Ames history has distinguished success from choice and controversy. In relation to Research Center did not regard it as failure.1 the ShuttleÕs thermal protection system, feasible unless some of the design To understand the dynamics of one Shuttle observer noted in 1970 that: requirements imposed were relaxed. An technological change and in so doing, ÒIf there is any clear cut lack of agree- expensive and complicated refit of the come to know our machines, it is nec- ment among those planning the Space orbiterÕs thermal protection system essary to dispel the myth that the tech- Shuttle, it is in the area of thermal pro- after every flight was not in harmony nological is independent from the tection.Ó The problem of shielding the with the Shuttle discourse on economic social. Although technological practi- orbiterÕs primary structure from the and routine access to space. The Office Q U E S T 10:3 2003 39 of Manned Space FlightÕs requirement that the Shuttle system perform routine- ly over 100 missions with a cost-effec- tive level of refurbishment and maintenance placed a heavy demand on the design of a thermal protection system. The inter-related nature of the thermal protection system went further than its influence on other subsystems. The problems and solutions associated with thermal protection were integral to the overall justification of the programme. Without a reusable thermal protection system, the Shuttle programme was in grave danger of not being able to rationalize itself. Nevertheless, Ames continued its research into ablator techniques in case a backup would be required.4 Repeatedly withstanding the ther- The Space Shuttle Columbia glides down over Rogers Dry Lake as it heads for a landing at Edwards Air Force Base at the conclusion of its first orbital mission. mal environments of re-entry was the Image courtesy of NASA key determinant of a thermal protection backed with micro-quartz insulation, repeatedly exposed to high tempera- system design. Coupled with this were except for the rudder, which was made tures, which could have a detrimental other induced environments within of Inconel-718. Thus, in the early phas- influence on aerodynamic stability. which the system had to perform, such es, design emphasis was on a thermal Overall, metallic concepts were com- as acoustic loads, structural deflections protection system that was an integral plex. Design features to minimize ther- induced by aerodynamic loads, the part of the load bearing structure, pro- mal distortion, intricate panel-to-panel extreme heat and radiation of the Sun, viding commonality between materials joints, as well as the additional insula- the extreme cold of space, and the nat- for airframe structure and thermal pro- tion blanket that would be required to ural environments on Earth, such as tection and with a minimum reliance on protect the primary structure of the salt, fog, wind and rain; and because the exotic materials.6 orbiter, all conspired against a metallic thermal protection system was to cover Nonetheless, a perception pre- thermal protection system.7 the exterior of the vehicle, it also had to vailed at the Office of Manned Space In contrast to the complexity of the provide an acceptable aerodynamic sur- Flight that all the metallic heat shield metallic systems, the non-metallic heat face.5 concepts possessed some significant shield concepts appeared to possess the Due to the inter-related nature of drawbacks. Many of the metallic mate- advantage of design simplicity. the thermal protection system, most rials required coatings, such as Lockheed Missiles and Space Com- contractors involved in Space Shuttle Sylvania R-512E, to provide oxidation panyÕs early Space Shuttle proposal had proposals exhibited a tendency towards protection. Application of the coatings an orbiter constructed from convention- combinations of metallic materials in would have to be so thorough, both al aluminum with a thermal protection their design proposals. McDonnell inside and outside (including fasteners), system comprised of titanium on the Douglas and Martin Marietta proposed that complicated inspection techniques upper surfaces and its proprietary silica a titanium alloy hot-structure for the between each flight would negate the system, called LI-1500, on the lower wings and fuselage, with the lower sur- advantages of commonality. Although surface. The silica system captured faces covered with columbium shin- superalloys that did not require any NASAÕs attention. Composed of tiles gles. The contractors proposed a cobalt coatings, such as nickel chrome fabricated from 99.6 percent pure superalloy for the control surfaces and (TDNiCr), were also on the agenda as amorphous silica fibers derived from the vertical tail was to be made of a they could withstand temperatures up to common sand, the system had the nickel superalloy. North American 2,400 degrees F, the production rate of potential of offering a low density, low Rockwell also adopted a radiant heat TDNiCr (around 10,000 pounds per maintenance, reusable thermal protec- shield configuration constructed of var- year in 1970) was not sufficient to meet tion system that could be installed on a ious metallic superalloys including Shuttle demands. In addition, superal- conventional airframe. While engineers columbium-129Y, Haynes-188 and loys also showed a tendency to produce recognized that a major development Inconel-718. Grumman/BoeingÕs de- a rippling effect over the surface when programme would have to be undertak- sign consisted of metallic panels Q U E S T 10:2 2003 40 en to bring the non-metallic materials strengthen the material to levels com- lower trajectory, but the silica system out of the laboratory to a state of high patible with the predicted thermal demanded that the initial entry angle of production and vehicle application, the stresses of re-entry; thus Lockheed, the attack should be as high as possible significant weight savings and inherent contractor working with silica, won the (around

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