The Space Shuttle, 1972-91

Meanwhile, the Space Shuttle marked a radical departure from the pattern of previous launch vehicles. Not only was it (mostly) reus-

able, unlike its predecessors, but it was also part spacecraft, part airplane. In contradistinction to the Mercury, Gemini, and Apollo launch vehicles, in which astronauts had occupied the payload over the rocket, on the shuttle the astronauts rode in and even piloted from a crew compartment of the orbiter itself. The mission com­mander also landed the occupied portion of the Space Shuttle and did so horizontally on a runway. The orbiter had wings like an air­plane and set down on landing gear, as airplanes did. Indeed, the very concept of the Space Shuttle came from airliners, which were not discarded after each mission the way expendable launch vehi­cles had been but were refurbished, refueled, and used over and over again, greatly reducing the cost of operations.

Because of the complex character of the Space Shuttles, their ante­cedents are much more diverse than those of the expendable launch vehicles and missiles discussed previously. Given the scope and length of this book, it will not be possible to cover all of the various aspects of the orbiters in the same way as other launch vehicles.117

Studies of a reusable launch vehicle like the shuttle—as distin­guished from a winged rocket or orbital reconnaissance aircraft/ bomber—date back to at least 1957 and continued through the 1960s. But it was not until the early 1970s that budgetary realism forced planners to accept a compromise of early schemes. Grim fiscal real­ity led to NASA’s decision in the course of 1971-72 to change from a fully reusable vehicle to an only partly reusable stage-and-a-half shuttle concept. Gradually, NASA and its contractors shifted their focus to designs featuring an orbiter with a nonrecoverable external propellant tank. This permitted a smaller, lighter orbiter, reducing the costs of development but imposing a penalty in the form of ad­ditional costs per launch. McDonnell Douglas and Grumman sepa­rately urged combining the external tank with strap-on solid-rocket boosters that would add their thrust to that of the orbiter’s engines. Despite opposition to the use of solids by Marshall Space Flight Center (responsible for main propulsion elements) and in spite of 92 their higher overall cost, solid-rocket boosters with a 156-inch di­Chapter 2 ameter offered lower developmental costs than other options, hence lower expenditures in the next few years, the critical ones from the budgetary perspective.

On January 5, 1972, Pres. Richard M. Nixon had announced his support for development of a Space Shuttle that would give the country “routine access to space by sharply reducing costs in dol­lars and preparation time." By mid-March 1972, the basic configura­tion had emerged for the shuttle that would actually be developed. It included a delta-winged orbiter attached to an external tank with

two solid-rocket boosters on either side of the tank.118 Meanwhile, in February 1970, Marshall released a request for proposals for the study of the space shuttle main engine. Study contracts went to Rocketdyne, Pratt & Whitney, and Aerojet General. The engine was to burn liquid hydrogen and liquid oxygen at a combustion-chamber pressure well above that of any other production engine, includ­ing the Saturn J-2. In July 1971, NASA announced the selection of Rocketdyne as the winner of the competition.119

The SSME featured “staged combustion." This meant that un­like the Saturn engines, whose turbine exhaust contributed little to thrust, in the shuttle the turbine exhaust—having burned with a small amount of oxygen and thus still being rich in hydrogen— flowed back into the combustion chamber where the remaining hydrogen burned under high pressure and contributed to thrust. This was necessary in the shuttle because the turbines had to burn so much fuel to produce the high chamber pressure critical to performance.120

Timing for such an engine was delicate and difficult. As a result, there were many problems during testing—with turbopumps as well as timing. Disastrous fires and other setbacks delayed develop­ment, requiring much analysis and adjustment to designs. In 1972, the shuttle program had expected to launch a flight to orbit by the beginning of March 1978. By then, the expected first-flight date had slipped to March 1979, but various problems caused even a Septem­ber 1979 launch to be postponed. Not until early 1981 was the space shuttle main engine fully qualified for flight. Finally on April 12, 1981, the first Space Shuttle launched, and the main engines per­formed with only a minor anomaly, a small change in mixture ratio caused by radiant heating in the vacuum of space. Some insulation and a radiation shield fixed the problem on subsequent flights. It had taken much problem solving and redesign, but the main en­gines had finally become operational.121

The sophistication of the SSME explained all its problems. “In assessing the technical difficulties that have been causing delays in the development and flight certification of the SSME at full power, it is important to understand that the engine is the most advanced liquid rocket motor ever attempted," wrote an ad hoc committee of the Aeronautics and Space Engineering Board in 1981. “Chamber pressures of more than 3,000 psi, pump pressures of 7,000-8,000 psi, and an operating life of 7.5 hours have not been approached in previous designs of large liquid rocket motors."122

Although more advanced, the SSMEs (producing 375,000 pounds of thrust at sea level and 470,000 pounds at altitude) were consid-

erably less powerful than the Saturn V’s F-1s (with 1.522 million pounds of thrust). At a length of 13.9 feet and a diameter of 8.75 feet, the SSMEs were also smaller than the F-1s, with a length of 19.67 feet and diameter of 12.25 feet. Nevertheless, they were im­pressively large, standing twice as tall as most centers in the Na­tional Basketball Association.123

Because they ignited before launch, the SSMEs did perform some of the same functions for the shuttle that the F-1s did for the Saturn V, but in most respects the twin solid-rocket boosters served as the principal initial sources of thrust. They provided 71.4 percent of the shuttle’s thrust at liftoff and during the initial stage of ascent until about 75 seconds into the mission, when they separated from the orbiter to be later recovered and reused.124

Even before the decision in March 1972 to use solid-rocket boost­ers, Marshall had provided contracts of $150,000 each to the Lock­heed Propulsion Company, Thiokol, United Technology Center, and Aerojet General to study configurations of such motors. Thiokol emerged as winner of the competition, based on its cost and mana­gerial strengths. NASA announced the selection on November 20, 1973.125 The design for the solid-rocket boosters (SRBs) was inten­tionally conservative, using a steel case of the same type employed on Minuteman and the Titan IIIC. The Ladish Company of Cudahy, Wisconsin, made the cases for each segment without welding. Each booster consisted of four segments plus fore and aft sections. The propellant used the same three principal ingredients employed in the first stage of the Minuteman missile. One place shuttle design­ers departed from the Marshall mantra to avoid too much innova­tion lay in the tang-and-clevis joints linking the segments of the SRBs. Although superficially the shuttle joints resembled those for Titan IIIC, they were different in orientation and the use of two O-rings instead of just one.126

In part because of its simplicity compared with the space shuttle main engine, the solid-rocket booster required far less testing than 94 the liquid-propellant engine. Testing nevertheless occasioned sev – Chapter 2 eral adjustments in the design. The SRBs completed their qualifica­tion testing by late May 1980, well before the first shuttle flight.127 Of course, this was well after the first planned flight, so if the main – engine development had not delayed the flights, presumably the booster development would have done so on its own.

The third part of the main shuttle propulsion system was the ex­ternal tank (ET), the only major nonreusable part of the launch ve­hicle. It was also the largest component at about 154 feet in length and 27.5 feet in diameter. On August 16, 1973, NASA selected Mar-

FIG. 2.11 The static test of Solid Rocket Booster (SRB) Demonstration Model 2 (DM-2) at the Thiokol test site near Brigham City, Utah. (Photo courtesy of NASA)

tin Marietta (Denver Division) to negotiate a contract to design, develop, and test the ET. Larry Mulloy, who was Marshall’s project manager for the solid-rocket booster but also worked on the tank, said that the ET posed no technological challenge, although it did have to face aerodynamic heating and heavy loads on ascent. But it had to do so within a weight limit of about 75,000 pounds. As it turned out, this was in fact a major challenge. It came to be fully ap­preciated only after loss of Space Shuttle Columbia on February 1, 2003, to a “breach in the Thermal Protection System on the leading edge of the left wing" resulting from its being struck by “a piece of insulating foam" from the ET. During reentry into the atmosphere, this breach caused aerodynamic superheating of the wing’s alumi­num structure, its melting, and the subsequent breakup of the or – biter under increasing aerodynamic forces.128

The air force had a great deal of influence on the requirements for the shuttle because its support had been needed to get the program approved and make it viable economically. NASA needed a com­mitment from the military that all of its launch needs would be carried on the shuttle. To satisfy DoD requirements, the shuttle had to handle payloads 60 feet long with weights of 40,000 pounds for polar orbits or 65,000 pounds for orbits at the latitude of Kennedy Space Center. On July 26, 1972, NASA announced that the Space Transportation Systems Division of North American Rockwell had won the contract for the orbiters.129

That firm subcontracted much of the work. The design, called a double-delta planform, derived from a Lockheed proposal. The term referred to a wing in which the forward portion was swept more heavily than the rear part. Throughout the development of the shuttle, wind-tunnel testing at a variety of facilities, including those at NASA Langley and NASA Ames Research Centers plus the air force’s Arnold Engineering Development Center, provided data, showing the continuing role of multiple organizations in launch – vehicle design. Before the first shuttle flight in 1981, there was a total of 46,000 hours of testing in various wind tunnels.130

An elaborate thermal protection system (designed primarily for reentry and passage through the atmosphere at very high speeds) and the guidance, navigation, and control system presented many design problems of their own. The launch vehicle that emerged from the involved and cost-constrained development of its many com­ponents was, as the Columbia Accident Investigation Board noted, “one of the most complex machines ever devised." It included “2.5 million parts, 230 miles of wire, 1,060 valves, and 1,440 cir­cuit breakers." Although it weighed 4.5 million pounds at launch, its solid-rocket boosters and main engines accelerated it to 17,500 miles per hour (Mach 25) in slightly more than eight minutes. The three main engines burned propellants fast enough to drain an aver­age swimming pool in some 20 seconds.131

From the first orbital test flight on April 12, 1981, to the end of 1991, there were 44 shuttles launched with 1 failure, an almost 98 percent success rate. On these missions, the shuttles had launched many communications satellites; several tracking and data relay satellites to furnish better tracking of and provision of data to (and from) spacecraft flying in low-Earth orbits; a number of DoD payloads; many scientific and technological experiments; and several key NASA spacecraft.132

Before launching some of these spacecraft, such as Magellan, Ulysses, and the Hubble Space Telescope, however, NASA had en – 96 dured the tragedy of losing the Space Shuttle Challenger and all Chapter 2 of its seven-person crew to an explosion. Since this is not an op­erational history, it is not the place for a detailed analysis, but be­cause the accident reflected upon the technology of the solid-rocket boosters and resulted in a partial redesign, it requires some discus­sion. On the 25th shuttle launch, Challenger lifted off at 11:38 a. m. on January 28, 1986. Even that late in the day, the temperature had risen to only 36°F, 15 ° below the temperature on any previous shuttle launch. Engineers at Morton Thiokol (the name of the firm after 1982 when the Morton Salt Company took over Thiokol Cor-

poration) had voiced reservations about launching in cold tempera­tures, but under pressure to launch in a year scheduled for 15 flights (6 more than ever before), NASA and Morton Thiokol agreed to go ahead. Almost immediately after launch, smoke began escaping from the bottommost field joint of one solid booster, although this was not noticed until postflight analysis. By 64 seconds into the launch, flames from the joint began to encounter leaking hydrogen from the ET, and soon after 73 seconds from launch, the vehicle exploded and broke apart.133

On February 3, 1986, Pres. Ronald Reagan appointed a commission to investigate the accident, headed by former Nixon-administration secretary of state William P. Rogers. The commission determined that the cause of the accident was “the destruction of the seals [O-rings] that are intended to prevent hot gases from leaking through the joint during the propellant burn of the rocket motor." It is pos­sible to argue that the cause of the Challenger accident was faulty assembly of the particular field joint that failed rather than faulty design of the joint. But it seems clear that neither NASA nor Morton Thiokol believed the launch would lead to disaster. The fact that they went ahead with it shows (in one more instance) that rocket engineers still did not have launching such complex vehicles com­pletely “down to a science." Some engineers had concerns, but they were not convinced enough of their validity to insist that the launch be postponed.134

Following the accident there was an extensive redesign of many aspects of the shuttle, notably the field joints. This new design al­legedly ensured that the seals would not leak under twice the an­ticipated structural deflection. Following Challenger, both U. S. policy and law changed, essentially forbidding the shuttle to carry commercial satellites and largely restricting the vehicle to missions both using the shuttle’s unique capabilities and requiring people to be onboard. A concomitant result was the rejuvenation of the air force’s expendable launch-vehicle program. Although the Delta II was the only launcher resulting directly from the 32-month hia­tus in shuttle launches following the accident, the air force also ordered more Titan IVs and later, other expendable launch vehicles. The shuttle became a very expensive launch option because its eco­nomic viability had assumed rapid turnaround and large numbers of launches every year. Yet in 1989 it flew only five missions, in­creased to six in 1990 and 1991.135

As further demonstrated by the Columbia accident, the shuttle clearly was a flawed launch vehicle but not a failed experiment. Its flaws stemmed largely from its nature as an outgrowth of

heterogeneous engineering, involving negotiations of NASA man­agers with the air force, the Office of Management and Budget, and the White House, among other entities. Funding restrictions dur­ing development and other compromises led to higher operational costs. For example, compromises on reusability (the external tank) and employment of solid-rocket motors plus unrealistic projections of many more flights per year than the shuttles ever achieved vir­tually ensured failure in this area from the beginning. Also, as the Columbia Accident Investigation Board pointed out, “Launching rockets is still a very dangerous business, and will continue to be so for the foreseeable future as we gain experience at it. It is unlikely that launching a space vehicle will ever be as routine an undertak­ing as commercial air travel."136

Yet for all its flaws, the shuttle represents a notable engineering achievement. It can perform significant feats that expendable launch vehicles could not. These have ranged from rescue and relaunch of satellites in unsatisfactory orbits to the repair of the Hubble Space Telescope and the construction of the International Space Station. These are remarkable accomplishments that yield a vote for the overall success of the shuttle, despite its flaws and tragedies.