When a new round of shuttle design studies got under way, early in 1969, the field had seen no truly new concept since Max Hunter’s partially-reusable Star Clipper of several years earlier. While work went forward at the contractors, Max Faget, at the Manned Spacecraft Center, carried through a parallel effort of his own that indeed came up with a new approach. His configuration not only went on to dominate the alternatives; it changed the terms of the ongoing discussions. These discussions had emphasized such issues as full versus partial reusability, with neither approach finding expression in a generally-accepted design concept. Faget now introduced a specific concept: a two-stage fully-reusable shuttle. As it gained acceptance, it spurred debate over its specific features, notably size, payload capacity, and choice of wing design. By focusing the debate, Faget’s work thus narrowed the topics that subsequent studies would address, and enabled these studies to achieve greater depth.

Maxime Faget. (NASA)

Faget was an aerodynamicist who had built his career at NACA’s Langley Aeronautical Laboratory. He was a member of the Pilotless Aircraft Research Division, an early nucleus of activity in high speed flight. In 1954, he took part in an initial feasibility study that led to the X-15. He then found a point of departure for his subsequent career in the findings of his fellow NACA aerodynamicists, H. Julian Allen and Alfred Eggers. They had shown that for a reentering nose cone, a blunt shape would provide the best protection against the heat of reentry.

Working with a longtime associate, Caldwell Johnson, Faget proceeded to devise a suitable blunt shape for Project Mercury, which put America’s first astronauts in orbit. His Mercury capsule took shape as a cone, with its broad end forward and covered with a thick layer of material to provide thermal protection. (A cutaway view of this concept, elegantly rendered, hangs in Faget’s offices to this day.) He came to Houston as a founding member of the Manned Spacecraft Center (MSC), where he became Director of Research and Engineering. He also adapted his basic shape to provide capsules for Gemini and Apollo. [Author interview, Max Faget, Houston, March 4, 1997; AAS History Series, Vol. 8, p. 299; NASA SP-4307 and NASA SP-4308, index references under “Faget.”]

“My history has always been to take the most conservative approach,” he declares. In this frame of mind, he disliked much of the work done to date on Space Shuttle concepts. Lifting-body configurations were popular; Lockheed’s Max Hunter had used them in his Star Clipper. Faget acknowledged their merits: “You avoid wing-body interference,” which brings problems of aerodynamics. “You have a simple structure. And you avoid the weight of wings.” He saw difficulties, however, that were so great as to rule out lifting bodies for a practical shuttle design.

They had low lift and high drag, which meant a dangerously high landing speed. As he put it, “I don’t think it’s charming to come in at 250 knots.” Engineers at McDonnell Douglas, studying their Tip Tank lifting body, had tried to improve the landing characteristics by adding small wings that would extend from the body during the final approach. This appeared as very makeshift.

Because they required a fuselage that would do the work of a wing, lifting bodies also promised serious difficulties in development. It would not be possible to solve aerodynamic problems in straightforward ways; the attempted solutions would ramify throughout the entire design. In his words, “They’re very difficult to develop, because when you try to solve one more problem, you’re creating another problem somewhere else.” His colleague Milton Silveira, who went on to head the MSC Shuttle Engineering Office, held a similar view:

If we had a problem with the aerodynamics on the vehicle, where the body was so tightly coupled to the aerodynamics, you couldn’t simply go out and change the wing. You had to change the whole damn vehicle, so if you made a mistake, being able to correct it was a very difficult thing to do. [Author interview, Max Faget, Houston, March 4, 1997; Joe Guilmartin and John Mauer interview, Milton Silveira, Washington, November 14, 1984, p. 14.]

Instead, Faget proposed to build each of his shuttle’s two stages as a winged airplane, with thermal protection on the underside. Before it could fly as an airplane, such a shuttle would first have to reenter, which meant it would need the high drag of a blunt body. “With extremely high drag,” he notes, “you throw a big shock wave in front of you, and all the energy goes into that shock.” Even with thermal protection, he did not want to fly his shuttle during reentry, in the manner of an airplane: “It’s a hell of a lot easier to do a no-lift entry than a lifting entry, from the standpoint of heat protection.” With airplane-style reentry, “you are stuck in the atmosphere, going fast for a long time.” Rather than lose energy to a shock wave, the airplane would experience drag through friction with the atmosphere which would transfer heat to its surface.

Faget’s shuttle concept. (NASA)

Faget expected to turn his airplane into a blunt body by the simple method of having it reenter at a very high angle of attack, with its broad lower surface facing the direction of flight. In effect, he would take an Apollo capsule, with its large circular heat shield, and trim it to the shape of an airplane with wings. This concept drew on the experience of the X-15 that looked like a fighter plane but reduced its reentry heating by coming in nose-high. It also revived a design approach introduced a decade earlier by NASA’s Charles Mathews. He had also proposed to build a winged spacecraft as a glider that would reenter with its bottom side facing forward.

Faget wrote that “the vehicle would remain in this flight attitude throughout the entire descent to approximately 40,000 feet, where the velocity will have dropped to less than 300 feet per second. At this point, the nose gets pushed down, and the vehicle dives until it reaches adequate velocity for level flight.” This dive would cost some 15,000 feet of altitude. The craft then would approach a runway and land at a moderate 130 knots, half the landing speed of a lifting body.

Faget wrote that because its only real flying would take place during this landing approach, a wing design “can be selected solely on the basis of optimization for subsonic cruise and landing.” The wing best suited to this limited purpose would be straight and unswept, like the wings of fighter planes in World War II. A tail would provide directional stability, again as with a conventional airplane. By moving control surfaces on the horizontal stabilizer, a pilot then could raise the nose slightly just before touching down on a runway, in a maneuver called a flare which adds lift and makes the touchdown gentle. [Astronautics & Aeronautics, January 1970, pp. 52-61; author interview, Max Faget, Houston, March 4, 1997; Faget and Silveira, Fundamental Design Considerations, October 1970.]

Faget’s concept had the beauty of simplicity, and, inevitably, knowledgeable specialists would criticize it as being too simple. The Air Force Flight Dynamics Laboratory (FDL), at Wright-Patterson Air Force Base, quickly emerged as a center of such criticism. The FDL had sponsored space shuttle studies in parallel with those of NASA, and had investigated such concepts as Lockheed’s Star Clipper. One of its managers, Charles Cosenza, had been a leader in the development of ASSET. Another FDL scientist, Alfred Draper, was a leader in the field of space systems. Beginning in early 1969, he took the initiative in questioning Faget’s approach. [Jenkins, Space Shuttle, pp. 36, 56; Hallion, ed., Hypersonics, p. 459; Astronautics & Aeronautics, January 1971, p. 28.]

Draper did not accept the idea of building a shuttle as an airplane that would come in nose-high, then dive through 15,000 feet to pick up flying speed. With its nose so high, the plane would be fully stalled, and the Air Force disliked both stalls and dives, regarding them as preludes to an out-of-control crash. Draper preferred to have the Shuttle enter its glide while still supersonic, thus maintaining much better control while continuing to avoid aerodynamic heating.

If the Shuttle was to glide across a broad Mach range, from supersonic to subsonic, then it would encounter an important aerodynamic problem: a shift in the wing’s center of lift. Although a wing generates lift across its entire lower surface, one may regard this lift as concentrated at a point, the center of lift. At supersonic speeds, this center is located midway down the wing’s chord (the distance from leading to trailing edge). At subsonic speeds, this center shifts and moves forward, much closer to the leading edge. Keeping an airplane in proper balance requires the application of an aerodynamic force that can compensate for this shift.

The Air Force had extensive experience with supersonic fighters and bombers that had successfully addressed this problem, maintaining good control and handling characteristics from Mach 3 to touchdown. Particularly for large aircraft—the B-58 and XB-70 bombers, and the SR-71—the preferred solution was a delta wing, triangular in shape. Typically, delta wings ran along much of the length of the fuselage, extending nearly to the tail. Such aircraft dispensed with horizontal stabilizers and relied instead on elevons, control surfaces resembling ailerons set at the wing’s trailing edge. Small deflections of these elevons then compensated for the shift in the center of lift, maintaining proper trim and balance without imposing excessive drag. [Hallion, Hypersonic, p. 1032; author interview, Dale Myers, Leucadia, California, December 6, 1996.]

Straight-wing orbiter, top, and delta-wing orbiter. (Art by Dennis Jenkins)

Draper proposed that both stages of Faget’s shuttle should feature delta wings, rather than straight ones. Faget would have none of this. Though he acknowledged the center-of-lift problem, he expected to avoid it: “The straight wing never flew at those speeds; it fell at those speeds.” A delta wing with elevons promised problems at landing, when executing the flare prior to touchdown. That flare was to add lift, but raising the elevons would increase the drag-with the added lift coming only after the nose had time to come up. This momentary rise in drag would make the landing tricky and possibly dangerous.

To achieve a suitably slow landing speed, Faget argued that the delta wing would need a large wingspan. A straight wing, having narrow chord, would be light and would offer relatively little area demanding thermal protection. A delta of the same span, necessary for a moderate landing speed, would be physically much larger than the straight wing. It would add considerable weight, and would greatly increase the area that would receive thermal protection.

Draper responded with his own viewpoint. For a straight wing to deal with the shift in center of lift, a good engineering solution would call for installation of canards, small wings mounted well forward on the fuselage that would deflect to give the desired control. Canards produce lift, and would tend to push the main wings farther to the back. These wings would be well aft from the beginning, for they would support an airplane that was empty of fuel but that had heavy rocket engines at the tail, placing the airplane’s center of gravity far to the rear. The wings’ center of lift was to coincide closely with this center of gravity. Draper wrote that the addition of canards “will move the wings aft and tend to close the gap between the tail and the wing.” The wing shape that fills this gap is the delta; Draper added that “the swept delta would most likely evolve.”

The delta also had other advantages as well. Being thick where it joins the fuselage, it would readily offer room for landing gear. Its sharply-swept leading edge meant that a delta would produce less drag than a straight wing near Mach 1. In addition to this, when decelerating through the sound barrier, a delta would shift its center of lift more slowly. The combination of a sudden drag rise near Mach 1, combined with a rapid center-of-lift shift, would produce a sudden and potentially disconcerting change in the stability characteristics of a straight-winged shuttle when slowing through the speed of sound. This change in stability would be much less pronounced with a delta, and would give a pilot more time to react. [Author interview, Max Faget, Houston, March 4, 1997; Astronautics & Aeronautics, January 1970, pp. 26-35; AIAA Paper 70-1249.]

The merits of deltas might have remained a matter for specialists for another important feature of the delta: Compared to the straight wing, it produced considerably more lift at hypersonic speeds. Using this lift, a reentering shuttle could achieve a substantial amount of crossrange, flying large distances to the left or right of an initial direction of flight. The Air Force wanted plenty of crossrange, and the reasons involved its activity in strategic reconnaissance. In particular, these reasons drew on recent experience involving the Six-Day War in the Middle East in 1967, and the Soviet invasion of Czechoslovakia in 1968.

The Six-Day War broke out suddenly, pitting Israel against a coalition led by Egypt whose tanks and aircraft came largely from the Soviet Union. Though America’s intelligence community sought to follow the fighting closely, its means proved to be limited. A ship near the Israeli coast, the USS Liberty, monitored the communications of the belligerents—until the Israelis bombed it. Though spy planes, such as the U-2 and SR-71, could look down through clear desert skies, experience had shown that the U-2 was vulnerable to antiaircraft missiles. Satellite reconnaissance relied on Gambit and Corona, which had been designed to follow the slow development and deployment of missiles and other strategic weapons. They were not well-suited to the swift battle maneuvers of the 1967 war, and Defense Secretary McNamara does not recall that these spacecraft played any role in U.S. intelligence-gathering during those six days. By the time Corona photography became available, the war was over already.

Then, in August 1968, the Soviets stormed into Prague. A Gambit spacecraft, launched on August 6, performed poorly and was deorbited before the invasion took place. In addition to this, the CIA had a Corona satellite that entered orbit on August 7. It carried two capsules for film return. The first one appeared reassuring; it showed no indications of Soviet preparations for an attack. The second capsule returned photos that clearly showed such preparations, including massing of troops. By the time that film reached Washington, however, those photos were of historical interest only. The invasion had already taken place. [Richelson, Secret Eyes, pp. 94-96, 97-99.]

Clearly, the CIA needed real-time space reconnaissance, and its pursuit of this goal would represent one more instance wherein a task originally thought to require astronauts would be accomplished using automated electronics. The true solution would lie in doing away with photographic film, which took time to expose and return. This film would give way to a new electronic microchip called a charge-coupled device. With an image focused onto this chip, it would convert the image into a rapid series of bits. The data, transmitted to the ground, would give the desired real-time photography, and with very high resolution. In addition to this, by freeing reconnaissance satellites from the need to carry and return film, this invention would allow such spacecraft to remain in orbit and to operate for years. [Ibid., pp. 124-132, 362; Quest, Summer 1995, pp. 31-32.]

The charge-coupled device grew out of the work of two specialists at Bell Labs, William Boyle and George Smith. In 1969, such technology still lay in the future. The view in the Air Force was that the CIA would need piloted spacecraft to produce the real-time photos. The late lamented MOL had represented a possible method, for an onboard photointerpreter might take, develop, and analyze photos on short notice. Now, with MOL in its graveyard, attention turned to the Space Shuttle. It might fly into space, execute a single orbit, and return to its base with film exposed less than an hour earlier.

Because much of the Soviet Union lies above the Arctic Circle, the Air Force was accustomed to placing reconnaissance satellites into polar orbits. It could not do this by firing its boosters from Cape Canaveral; geography dictated that these boosters would fly over populated territory. A launch to the north carried the hazard of impact in the Carolinas; a launch to the south would compromise security if the rocket fell on Cuba. Hence, the Air Force maintained its own space center at Vandenberg AFB, on the California coast. It offered a clear shot to the south, across thousands of miles of open ocean. [Time, December 15, 1958, pp. 15, 41-42.]

While a satellite orbit remains fixed in orientation with respect to distant stars, the earth rotates below this orbit. This permitted single reconnaissance missions to photograph much of the Soviet Union. However, it meant that if a shuttle was to execute a one-orbit mission from Vandenberg, it would return to the latitude of that base after 90 minutes in space only to find that, due to the earth’s rotation, this base had moved to the east by 1100 nautical miles. Air Force officials indeed expected to launch the Shuttle from Vandenberg, and they insisted that the Shuttle had to have enough crossrange to cover that distance and return successfully.

The Air Force had other reasons to want once-around missions. Its planners were intrigued by the idea of using the Shuttle to retrieve satellites in orbit. They hoped to snare Soviet spacecraft in such a fashion—and because Moscow might defend such assets by deploying an antisatellite weapon, the Air Force took the view that if the thing was to be done at all, it was best to do it quickly. A once-around mission could snare such a spacecraft and return safely by the time anyone realized it was missing.

In addition to this, NASA and the Air Force shared a concern that a shuttle might have to abort its mission and come down as quickly as possible after launch. This might require “once-around abort,” which again would lead to a flight of a single orbit. A once-around abort on a due-east launch from Cape Canaveral would not be too difficult; the craft might land at any of a number of sites within the United States. In the words of NASA’s Leroy Day, “If you were making a polar-type launch out of Vandenberg, and you had Max’s straight-wing vehicle, there was no place you could go. You’d be in the water when you came back. You’ve got to go crossrange quite a few hundred miles in order to make land.” [Personal discussions with John Pike, Federation of American Scientists, July 1997; John Mauer interview, Leroy Day, October 17, 1983, p. 41; Pace, Engineering, pp. 146-149.]

The Air Force had ample opportunity to emphasize its desire for crossrange by working within the Joint Study Group that Paine and Seamans had set up to seek a mutually-acceptable shuttle design. There were informal discussions as well. George Mueller, who continued to head NASA’s OMSF through the whole of 1969, met repeatedly with Air Force representatives at his home in Georgetown, close to downtown Washington. One of his guests was Michael Yarymovych, an Air Force deputy assistant secretary. Another guest, Grant Hansen, was assistant secretary for research and development. He and Mueller also were co-chairmen of the joint study. [Mueller, Briefing, 5 May 1969, p. 2; Pace, Engineering, p. 103.]

These Air Force leaders knew that they held the upper hand. They were well aware that NASA needed a shuttle program and therefore needed both the Air Force’s payloads and its political support. The payloads represented a tempting prize, for that service was launching over two hundred reconnaissance missions between 1959 and 1970 [Quest, Summer 1995, pp. 22-33; Winter 1995, pp. 40-45]. In addition to this, Air Force support for a shuttle could insulate NASA quite effectively from a charge that the Shuttle was merely a step toward sending astronauts to Mars.

Yet while NASA needed the Air Force, the Air Force did not need NASA. That service was quite content with existing boosters such as the Titan III. “Sure, NASA needs the shuttle for the space station,” Hansen said in the spring of 1970. “But for the next 10 years, expendables can handle the Air Force job. We don’t consider the Shuttle important enough to set money aside for it.”

Yarymovych has a similar recollection:

NASA needed Air Force support, both for payloads and in Congress. I told Mueller we’d support the Shuttle, but only if he gave us the big payload bay and the crossrange capability, so we could return to Vandenberg after a single orbit. Mueller knew that would mean changing Max Faget’s beloved straight-wing design into a delta wing, but he had no choice. He agreed. [Grey, Enterprise, pp. 67-68.]

It was not that simple, of course; no impromptu discussion in Mueller’s home would settle such an issue. Rather, it was a matter for the formal protocols of Air Force-NASA cooperation. There was strong conflict between these agencies’ wishes, for a NASA baseline document of June 1969, “Desired System Characteristics,” emphasized that NASA needed only 250 to 400 n.mi. of crossrange, enough to assure a return to Cape Canaveral at least once every 24 hours. Faget’s straight-wing shuttle could achieve 230 n.mi.; straightforward modifications would meet NASA’s modest requirements.

To give the Air Force its 1100 n.mi. of crossrange would impose a serious penalty in design, by requiring considerably more thermal protection. The change to a delta wing, even without crossrange, would add considerably to the wing area demanding such protection. Crossrange then would increase this requirement even further. The Shuttle would achieve its crossrange by gliding hypersonically, and hence would compromise the simple nose-high mode of reentry that would turn it into a blunt body. This hypersonic glide would produce more lift and less drag. It also would increase both the rate of heating and the duration of heating. Crossrange thus would call for a double dose of additional thermal protection, resulting in a shuttle that would be heavier-and more costly. [Day, manager, Task Group Report, Vol. II, June 12, 1969, pp. 40-42; Astronautics & Aeronautics, January 1970, pp. 57, 59; Faget and Silveira, Fundamental Design Considerations, October 1970, pp. 5, 17.]

Comparison of types of orbiter. The straight-wing design has low lift, L/D = 0.5. It achieves little crossrange, but its re-entry is brief and limits the heating rate. The delta-wing orbiter has high lift, L/D = 1.7, and achieves large crossrange. But its re-entry is prolonged and imposes both a high heating rate and a high total heat. (NASA)

Even in its simple straight-wing form, Faget’s concept of a two-stage fully-reusable shuttle did not take NASA by storm. It won its pre-eminence only after a process of review and evaluation that extended through 1969 and into 1970. The framework for this process involved the contractors’ studies of shuttle configurations that had begun early in 1969. Those studies ruled out expendable boosters for a reusable shuttle, for such boosters were found to exceed the Saturn V in size. Fully- and partially-reusable shuttle concepts remained in the running, and Faget’s concept counted as a new example of the former. NASA proceeded to examine it alongside several alternatives, beginning in mid-1969.

The initial round of studies, during the first half of 1969, had come to $1.2 million, divided equally among four contractors. NASA now extended these studies by giving $150,000 more to each of three contractors, with McDonnell Douglas receiving $225,000. The participating companies also received new instructions that redirected their work.

North American Rockwell had examined expendable boosters. With this approach now out of favor, this firm was free to direct its attention to something new. This proved to be Faget’s straight-wing concept, largely in the form he recommended.

McDonnell Douglas, which had examined its Tip Tank stage-and-a-half design, now switched to two-stage fully-reusables. These, however, were not Faget’s, but rather continued an earlier line of work. They featured orbiter designs derived from the HL-10 lifting body, with this contractor’s engineers considering 13 possible configurations for the complete two-stage vehicle.

At first, the other two contractors saw little change in their assignments. Lockheed was to continue with studies of Star Clipper and of its own version of the Triamese. General Dynamics, home of the initial Triamese concept, was to study variants of this design, and would also apply its background to design a fully-reusable concept having only two elements rather than the three of Triamese.

The orders for this redirection went out on June 20, 1969. Within weeks, the studies brought a flurry of activity that further narrowed the admissible choices. Expendable boosters had already fallen by the wayside. On August 6, a meeting of shuttle managers brought a decision to drop all partially-reusable systems as well. With this, both Lockheed’s Star Clipper and McDonnell Douglas’s Tip Tank were out. This decision meant that NASA would consider only fully-reusable concepts. [Akridge, Space Shuttle, pp. 53, 71-72, 90; Jenkins, Space Shuttle, pp. 60-64.]

Partially-reusable designs had represented an effort to meet economic goals by seeking a shuttle that would cost less to develop than a fully-reusable system, even while imposing higher costs per flight. This approach had held promise prior to the spring of 1969, when the Shuttle had been considered largely as a means of providing space station logistics. Now its intended uses were broadening to include launches of automated spacecraft, which meant it might fly far more often. The low cost per flight of a fully-reusable now made it attractive, and encouraged NASA to accept its higher development cost. [Day, manager, Summary Report, December 10, 1969.]

Fully-reusable shuttle concepts of 1969; R indicates the stage is reusable. 1: Triamese of General Dynamics. 2: Two-stage arrangement with both stages thrusting at launch. 3: Two stages, upper stage ignited at high altitude. 4: Faget’s concept. 5: Concept of NASA-Langley, with both stages as lifting bodies. (NASA)

There were at least five ways to build a fully-reusable shuttle, and NASA had appropriate designations and descriptions:

FR-1: the Triamese;

FR-2: a two-stage vehicle with the engines of both stages ignited at launch;

FR-3: a two-stage vehicle with engines in the orbiter ignited only upon staging (Faget’s shuttle was an FR-3; so were the concepts of McDonnell Douglas);

FR-4: a variant of the Triamese with the core stage not of the same length as the twin booster stages;

FR-5: a concept designed to avoid a shift in its center of gravity as its propellant tanks would empty, thus easing problems of stability and control.

On September 4, another meeting eliminated the Triamese configurations. The initial concept, the FR-1, had called for three elements of common length and structural design. It had proven difficult, however, to have one shape serve both as booster and orbiter; to Silveira, “it gets all screwed up, so you get a lousy orbiter and a lousy booster, but you don’t get one that does well.” Advocates of the Triamese had turned to the FR-4, with its unequal-length design. This, however, proved heavier than the FR-3, while requiring two booster elements rather than one. It also lost much of the potential cost saving from design commonality between the three elements.

The FR-3 and FR-5 remained. The latter had few advocates; the problem of center-of-gravity shift was not so severe as to call for the design innovations of this class of concepts. The manager Max Akridge writes, “It was felt at this time that clearly, the FR-3 configuration was the forerunner.” [Akridge, Space Shuttle, p. 93; Jenkins, Space Shuttle, pp. 66-70; Joe Guilmartin and John Mauer interview, Milton Silveira, Washington, November 14, 1984, pp. 12-13.]

These decisions brought a further redirection in the studies, for while North American Rockwell had gotten an early start on Faget’s concept, the other three contractors had to change course. McDonnell Douglas, having found no advantage in its lifting-body orbiters, turned to winged orbiters resembling those of Faget.

While Lockheed also turned to the FR-3, it did not embrace Faget’s concept wholeheartedly. This company had spent several years studying Star Clipper, which featured a lifting-body orbiter, triangular in shape. This now looked like a good way to meet Air Force crossrange requirements, and Lockheed’s new design retained this lifting body, with a broad underside in the shape of a delta.

General Dynamics showed its own individuality. That firm had designed its Triamese with retractable wings, which would fold into the body during flight but swing outward for landing. This eased the problem of providing these wings with thermal protection, because the fuselage would shield them. This feature now reappeared in the company’s new FR-3. It drew on more than Triamese; it also reflected company experience with swinging wings. These were part of the F-111 fighter-bomber, which swung its wings to achieve good performance in both subsonic and supersonic flight. [Reports MDC E0056 (McDonnell Douglas); GDC-DCB69-046 (General Dynamics); SD 69-573-1 (North American Rockwell); LMSC-A959837 (Lockheed); Jenkins, Space Shuttle, pp. 63-70.]

Hence, by the end of 1969 NASA had settled on the FR-3 as its choice, with Faget’s specific concept in the forefront. This raised important questions concerning thermal protection. The booster was to be as large as a Boeing 747, yet was to outperform the X-15, reaching considerably higher speeds. The orbiter would be longer than a Boeing 707. For both, the thermal protection had to be reusable.

Within the industry, a standard engineering solution called for the use of hot structures. This approach had a background that included the X-15, Dyna-Soar, ASSET, as well as the Lockheed SR-71 that was flying routinely above Mach 3. Hot structures typically called for titanium as the basic material, covered with high temperature insulation and an outer skin formed of metallic shingles. The metal was molybdenum or columbium, to withstand extreme temperatures while radiating away the heat. Like the shingles on a roof, those on the surface of a hot structure were loosely attached, to expand and contract freely with temperature change.

Such structures were complex, and the shingles posed difficulties of their own. Columbium and molybdenum oxidize readily when hot, and required coatings to resist this. The Dyna-Soar had been designed to use such thermal protection, and Faget declared that “the least little scratch in the coating, the shingle would be destroyed during re-entry.” In turn, lost shingles could bring the loss of a vehicle.

NASA and Lockheed now were developing a new surface material: an insulation made of interlaced fibers of silica that could be applied to the outside of a vehicle. These could withstand temperatures of 2500 degrees Fahrenheit, making them suitable for all but the hottest areas on a reentering shuttle. The outer surface would radiate away the heat, in the fashion of the shingles. The thickness of the silica then would prevent most of the heat from reaching the vehicle’s skin. This material would not oxidize. It also was light, weighing as little as 15 pounds per cubic foot, or one-fourth the density of water.

This material would form the well-known “tiles” of the Shuttle program, being attached to the skin in the form of numerous small shapes somewhat resembling bricks. In 1969, their immediate prospect lay in simplifying the design of hot structures. These might now dispense with their shingles; engineers instead would use titanium to craft an aircraft structure, with skin covering an internal framework, then provide thermal protection by covering the skin with the tiles. [Author interview, Max Faget, Houston, March 4, 1997; proceedings, NASA Space Shuttle Symposium, October 16-17, 1969, pp. 581-591; Report MDC E0056 (McDonnell Douglas), pp. 10-11; Jenkins, Space Shuttle, p. 64.]

The design studies of 1969 raised another tantalizing prospect: that these tiles might offer enough heat resistance to build the basic structure of aluminum rather than titanium. Titanium was hard to work with; few machine shops had the necessary expertise. Moreover, its principal uses in aerospace had occurred within classified programs such as the SR-71, which meant that much of the pertinent shop-floor experience itself was classified. This metal could withstand higher temperatures than aluminum. Yet, if tiles could protect aluminum, the use of that metal would open the shuttle to the entire aerospace industry. In Silveira’s words, building aluminum airplanes was something that “the industry knew how to do. The industry had, on the floor, standards—things like, ‘What are the proper cutting speeds?’ They knew how to rivet or machine aluminum.” [Heppenheimer, Turbulent Skies, p. 209; Joe Guilmartin and John Mauer interview, Milton Silveira, Washington, November 14, 1984, p. 16.]

Hot structures, built of titanium, would continue to represent an important approach in shuttle design. As early as 1969, however, Lockheed took the initiative in designing a shuttle orbiter built of aluminum and protected with tiles. General Dynamics added its own concept, featuring aluminum protected by shingled hot structures that could keep internal temperatures below 200 °F.

At the end of 1969, the contractors’ orbiter concepts were as follows, with the boosters being similar [reports MDC E0056 (McDonnell Douglas); GDC-DCB69-046 (General Dynamics); SD 69-573-1 (North American Rockwell); LMSC-A959837 (Lockheed); Jenkins, Space Shuttle, pp. 63-71]:

These represented variants of Faget’s two-stage concept, which showed that shuttle design had come a long way during that year. Twelve months earlier, the candidate configurations included expendable boosters as well as partially- and fully-reusable concepts. The range of alternatives included the Titan III-M with an enlarged Dyna-Soar, the Star Clipper, and the Triamese. These were as mutually dissimilar as a fighter, a bomber, and a commercial airliner.

People still debated such issues as delta wings vs. straight, aluminum vs. titanium, and hot structures vs. tiles. By year’s end, however, everyone agreed that the shuttle would look much like Faget’s. This meant that the most basic issues of configuration had been settled, allowing engineers to advance to deeper levels of detail. The studies of 1970 would pursue such levels, and would lay important groundwork for the eventual evolution of complete engineering designs, explicit in all particulars.

The work of 1969 had given the space station more support than the Shuttle. The studies of that year initially had allocated $5.8 million for the station and only $1.2 million for the Shuttle; the additional funds granted for the latter at midyear, totalling less than $0.7 million, did little to redress this imbalance. In 1970, however, NASA would bring the shuttle to the forefront. In this year, the centerpiece of effort would involve two $8-million contracts for further work on the shuttle. There would be no significant amount of new funding for the station. These internal NASA decisions would point toward abandonment of the station, at least for a number of years, and elevation of the Shuttle into the sole focus for NASA’s future. [Logsdon, Apollo, p. III-26; Aviation Week, February 10, 1969, p. 17; Akridge, Space Shuttle, p. 71.]