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Congress, Office of Technology Assessment, Big Dumb Boosters: A Low-Cost SpaceTransportation Option? (Washington, DC: Office of Technology Assessment, February 1989).34. For example, the Minuteman and Polaris, both of which use solid propellants, had proved highlyreliable.35. Eagle Engineering, Inc., “Technology Influence on the Space Shuttle Development,” Report No.86-125C, NASA Johnson Space Center, Houston, TX, June 8, 1986, pp. 5–20, 21.36. As noted above, NASA had awarded the contract for the SSME to Rocketdyne in 1971.****EU4 Chap 2 (161-192)4/2/0112:45 PMPage 173EXPLORING THE UNKNOWN173Figure 2–4. Ames Research Center scientists tested the aerodynamic properties of a Space Shuttle wind tunnel model in 1973.(NASA photo)Kennedy Space Center was to develop methods for Shuttle assembly, checkout, andlaunch operations.Even after the development contracts were let, determining the best design was still amajor task that required close cooperation among the design teams (Figure 2–4).

Duringliftoff and throughout the short passage through the atmosphere, the shape and placement of each of the major Shuttle components would affect flight success. [II-18] Changesin any one of the elements—wing shape, the diameter and length of the SRBs, and thediameter of the external tank—would alter the performance of the others. Thus, the configuration of the Shuttle system and precise shapes of each component passed throughseveral steps to reach the final overall shape and structure.37North American Rockwell began fabricating Orbiter Vehicle (OV)-101 on June 4, 1974;the company rolled out the orbiter from its Palmdale, California, plant on September 17,1976. The OV-101 lacked many subsystems needed to function in space.

It was thus capableof serving only as a full-scale mockup capable of atmospheric flight; this flying testbedproved invaluable in testing the orbiter’s ability to maneuver in the atmosphere and to glideto a safe landing. Flight-testing began in February 1977 at Edwards Air Force Base.Earlier, NASA had purchased a used Boeing 747-100 to ferry the orbiters from landing sites in California and potentially other parts of the world to Kennedy Space Centerfor refurbishment and launch.38 This airplane was also used to conduct flight tests withEnterprise, as OV-101 came to be called.

A NASA committee typically chose the orbiter, butfans of the Star Trek television series had lobbied NASA and Congress to name OV-101the title of the starship of that series. [II-19]Enterprise underwent three major types of tests: (1) captive flight, in which NASA tested whether it could take off, fly, and land the 747 with the orbiter attached; (2) captiveactive flight, in which an astronaut crew rode in Enterprise during captive flight; and37. See Hallion and Young, “Space Shuttle: Fulfillment of a Dream,” pp. 1125–42, for a summary discussion of these points.38. Once the Shuttle began flying, NASA established backup landing sites in several other countries,should a launch failure allow an abort landing elsewhere or extraordinary conditions at both Edwards Air ForceBase and Kennedy Space Center prevent landing at those two primary locations.****EU4 Chap 2 (161-192)1744/2/0112:45 PMPage 174DEVELOPING THE SPACE SHUTTLE(3) free flight, in which Enterprise was released to glide back to Earth on its own.

By August1977, NASA had successfully completed the first two test phases and was ready to test theorbiter in free flight. On August 12, 1977, the 747 carried Enterprise to 24,100 feet, whereit was released for a five-minute glide to a successful landing at Edwards.39 After four additional test glides, NASA wound up its atmospheric flight testing program and turned tovibration and other ground tests of Enterprise.Two major technical problems kept Shuttle development from proceeding smoothly:(1) a series of test failures and other problems with the SSME and (2) difficulties achieving a safe, lightweight, robust thermal protection system.

SSME development proved challenging on several grounds: NASA needed a reusable, throttleable staged-combustionengine that would achieve much higher combustion chamber pressures than any previousengine. The United States had not yet built a rocket engine that was both reusable andcapable of being throttled. Such an engine required high-pressure turbopumps capableof higher speeds and internal pressures than any developed to date.

Reusability and thefact that the SSME would be used on a vehicle rated to carry people imposed specialdemands on the engine. Despite a nine-month delay in starting SSME development,caused by a Pratt & Whitney challenge to the Rocketdyne contract, as well as difficulty inprocuring the necessary materials for the engine, Rocketdyne completed the first development engine in March 1975, one month ahead of schedule.Engine tests were performed at NASA’s Mississippi National Space TechnologyLaboratories (later named Stennis Space Center) and at the Air Force’s RocketPropulsion Laboratory at Santa Susana, California. Although the first test firing was successful, problems began to surface as the tests became more demanding.

The turbopumpswere particularly troublesome because their turbine blades tended to crack under thesevere mechanical stresses they experienced. The engines also experienced a variety ofnozzle failures during tests.40 These problems caused significant delays in the testing program. This prompted the Senate Subcommittee on Science, Technology, and Space of theCommittee on Commerce, Science, and Transportation in December 1977 to request anindependent review of SSME development by the National Research Council. The report,presented in a March 31, 1978, Senate Subcommittee hearing, noted that the problemsNASA was experiencing in the test program were typical of such development efforts, butalso recommended a number of possible SSME modifications and a delay in the timetablefor the first Shuttle flight.41 The National Research Council committee, generally calledthe Covert Committee after its chair, Eugene Covert, a professor at the MassachusettsInstitute of Technology, also recommended that NASA relax its goal of launching theShuttle with the SSMEs operating at 109 percent of full power level, to reduce stress onthe turbopump components.Because NASA was then behind schedule, it decided to save SSME development timeby conducting some tests using all three engines in their flight configuration.

They wereattached to an orbiter simulator using identical components to those on the flight article.NASA also used an external tank to supply propellant to the engines and attached it to the39. Astronauts Fred W. Haise and Gordon G. Fullerton were the pilot and co-pilot for the first free flightof Enterprise.40. Hallion and Young, “Space Shuttle: Fulfillment of a Dream,” pp. 1158–59.41. Eugene Covert, “Technical Status of the Space Shuttle Main Engine,” report of the Ad Hoc Committeefor Review of the Space Shuttle Main Engine Development Program, Assembly of Engineering, NationalResearch Council. Printed in U.S. Congress, Senate Committee on Commerce, Science, and Transportation,Subcommittee on Science, Technology and Space, Space Shuttle Main Engine Development Program. Hearing,March 31, 1978, 95th Cong., 2d sess.

(Washington, DC: U.S. Government Printing Office, 1978), pp. 16–57.****EU4 Chap 2 (161-192)4/2/0112:45 PMPage 175EXPLORING THE UNKNOWN175test stand in a manner identical to its connection to the SRBs on the launch pad. NASAbegan its main propulsion testing in April 1978, but continued to experience test delaysand failures. Despite the delays and problems, the basic SSME design was consideredsound. Rocketdyne proceeded with the manufacturing of the three engines needed forColumbia (OV-102). In May 1978, Rocketdyne finally received approval to start manufacturing the nine additional production SSMEs needed for OV-099 (Challenger), OV-103,and OV-104.Nevertheless, development problems continued.

One of the largest setbacks was a firethat destroyed an engine on December 27, 1978. The Covert Committee, which had beenpreparing a second report on the SSME program, reviewed this and an additional fire.[II-20] Once again, the committee report recommended changes in procedures and further tests, noting: “It appears unlikely that the first manned orbital flight will occur beforeApril or May 1980.”42 The test program continued, “and by 1980 the SSME was no longerperceived to be a pacing factor for the first launch .

. . the thermal protection system wasconsidered the pacing item.”43Thermal protection for the Shuttle’s reentry was a major issue from the earliest designconcepts through the first several flights of the Shuttle. NASA engineers had solved thereentry problem for the Mercury, Gemini, and Apollo capsules by using ablative materialsthat heated up and burned off as the capsule encountered the upper atmosphere uponreentry. However, these capsules were not designed to suffer the rigors of multiple flightsand reentries and were thus retired after use.

Each Shuttle orbiter was designed to experience up to 100 launches and returns. Its thermal protection system had to be robustenough to stand repeated heating loads and the structural rigors of reentry. The systemhad to be relatively light to keep the orbiter’s overall weight acceptably low. In addition,it had to be relatively cheap to refurbish between flights.Between 1970 and 1973, NASA studied a wide variety of technologies to protect theorbiters’ bottom and side surfaces. It investigated:••••“Hot structures,” in which the entire structure took the heat loadHeat shields separated from a lightweight orbiter structure by insulationAblative heat shields over a lightweight structureLow-density ceramic heat shields (tiles) bonded to a lightweight structureThe “hot structures” would have required developing exotic and expensive titaniumor other alloys that could dissipate reentry heating and simultaneously withstand themechanical loads from aerodynamic pressure.