by T. A. Heppenheimer
- The Collier’s Series
- Background to the Space Station
- Winged Rockets: The Work of Eugen Sänger
- The Navaho and the Main Line of American Liquid Rocketry
- The X-15: An Airplane for Hypersonic Research
- Lifting Bodies: Wingless Winged Rockets
- Solid-Propellant Rockets: Inexpensive Boosters
- Dyna-Soar: A Failure in Evolution
Before anyone could speak seriously of a space shuttle, there had to be widespread awareness that such a craft would be useful and perhaps even worth building. A shuttle would necessarily find its role within an ambitious space program. While science fiction writers had been prophesying such wonders since the days of Jules Verne, it was another matter to present such predictions in ways that smacked of realism. After World War II, however, the time became ripe. Everyone knew of the dramatic progress in aviation, which had advanced from biplanes to jet planes in less than a quarter-century. Everyone also recalled the sudden and stunning advent of the atomic bomb. Rocketry had brought further surprises as, late in the war, the Germans bombarded London with long-range V-2 missiles. Then, in 1952, a group of specialists brought space flight clearly into public view.
The Collier’s Series
One of these specialists, the German expatriate Willy Ley, had worked with some of the builders of the V-2 personally and had described his experiences, and their hopes, in his book Rockets, Missiles, and Space Travel [citation in bibliography]. The first version, titled Rockets, appeared in May 1944, just months before the first
firings of the V-2 as a weapon. Hence, this book proved to be very timely. His publisher, Viking Press, issued new printings repeatedly, while Ley revised it every few years, expanding both the text and the title to keep up with fast-breaking developments [expanded versions appeared in 1945, 1948, and 1952].
One day in the spring of 1951, Ley had lunch with Robert Coles, chairman of the Hayden Planetarium in Manhattan. He remarked that interest in astronautics was burgeoning in Europe. An international conference, held in Paris the previous October, had attracted over a thousand people. None had come from the U.S., however, and this suggested to Ley that Americans should organize a similar congress. Coles replied, “Go ahead, the planetarium is yours.”
Ley proceeded to set up a symposium that took place on Columbus Day. Admission was by invitation only. Some invitations, however, went to members of the press. Among the attendees were a few staffers from Collier’s, a magazine with a readership of ten million. Two weeks later, the managing editor, Gordon Manning, read a brief news item about an upcoming Air Force conference, in San Antonio, on medical aspects of space flight. He sent an associate editor, Cornelius Ryan, to cover this meeting and to see if it could be turned into a story [Ley, Rockets, pp. 330-331; AAS History Series, vol. 15, pp. 235-242].
While no space enthusiast, Ryan was a meticulous reporter, as he would show in such books as The Longest Day and A Bridge Too Far. At the meeting, he fell in with Wernher von Braun, who had been the technical director of the V-2 project. Von Braun, a consummate salesman, had swayed even Hitler [Dornberger, V-2, pp. 103-111]. Over cocktails, dinner, and still more cocktails, Von Braun proceeded to deliver his pitch. It focused on a space station with an onboard crew living and working in space. Von Braun declared that it could be up and operating in orbit by 1967. It would have the shape of a ring, 250 feet in diameter, and would rotate to provide centrifugal force that could substitute for gravity in weightless space. The onboard staff of 80 people would include astronomers operating a major telescope. Meteorologists, looking earthward, would study cloud patterns and predict the weather [AAS History Series, vol. 15, pp. 235-242].
To serve the needs of the Cold War, von Braun emphasized the use a space station could have for military reconnaissance. He also declared that it
could operate as a high-flying bomber, dropping nuclear weapons with great accuracy. To build it, he called for a fleet of immense piloted cargo rockets (space shuttles, though the term had not yet entered use) each weighing 7,000 tons, 500 times the weight of the V-2. Yet the whole program—rockets, station and all—would cost only $4 billion, twice the budget of the wartime Manhattan Project that had built the atomic bomb [Ibid.; Time, December 8, 1952, pp. 67, 71; Collier’s, March 22, 1952, pp. 27-28].
With its completion, the space station could serve as an assembly point for a far-reaching program of exploration. An initial mission would send a crew on a looping flight around the Moon, to photograph its unseen far side. Later, perhaps by 1977, a fleet of three rockets would carry as many as 50 people to the Moon’s Bay of Dew for a six-week period of wide-ranging exploration using mobile vehicles [Collier’s, October 18, 1952, pp. 51-59; October 25, 1952, pp. 38-48]. Eventually, perhaps a century in the future, an even bolder expedition would carry astronauts to Mars [Ibid., April 30, 1954, pp. 22-29].
By the end of that evening, von Braun had converted Ryan, who now believed that piloted space flight was not only possible but imminent. Returning to New York, Ryan persuaded Manning that this topic merited an extensive series of articles that eventually would span eight issues of the magazine [Ibid., March 22, October 18 and October 25, 1952; February 28, March 7, March 14, and June 27, 1953; April 30, 1954; reprinted in part in NASA SP-4407, vol. I, pp. 176-200]. Manning then invited von Braun, together with several other specialists, to Manhattan for a series of interviews and discussions. These specialists included Willy Ley; the astronomer Fred Whipple of Harvard, a moon and Mars specialist; and Heinz Haber, an Air Force expert in the nascent field of space medicine [Collier’s, March 22, 1952, p. 23].
In preparing the articles, Collier’s placed heavy emphasis on getting the best possible color illustrations. Artists included Chesley Bonestell, who had founded the genre of space art by presenting imagined views of planets such as Saturn, as seen closeup from such nearby satellites as its large moon Titan. Von Braun’s engineering drawings and sketches of his rockets and spaceships were used by Bonestell and the other artists to create working drawings for Von Braun’s review. They would execute the finished paintings only after receiving Von Braun’s corrections and comments [AAS History Series, vol. 15, p. 237; vol. 17, pp. 35-39].
The first set of articles appeared in March 1952, with the cover illustration of a space shuttle at the moment of staging, high above the Pacific. “Man Will Conquer Space Soon,” blared the cover. “Top Scientists Tell How in 15 Startling Pages.” Inside, an editorial noted “the inevitability of man’s conquest of space” and presented “an urgent warning that the U.S. must immediately embark on a long-range development program to secure for the West ‘space superiority'” [Collier’s, March 22, 1953, p. 23].
Collier’s, March 22, 1952, spurred a surge of interest in space flight. (Courtsey of Ron Miller)
Cargo rocket of the Collier’s series, with winged upper stage. (Art by Rolf Klep; courtesy of Ron Miller)
The series appeared while Willy Ley was bringing out new and updated editions of his own book. It followed closely The Exploration of Space by Arthur C. Clarke, published in 1951 and offered by the Book-of-the-Month Club [citation in bibliography]. The Collier’s articles, however, set the pace. Late in 1952, Time magazine ran its own cover story on von Braun’s ideas [Time, December 8, 1952]. In Hollywood, producer George Pal was working already with Bonestell, and had brought out such science fiction movies as Destination Moon (1950) and When Worlds Collide (1951). In 1953, they drew on von Braun’s work and filmed The Conquest of Space, in color. Presenting the space station and Mars expedition, the film proposed that the Martian climate and atmosphere would permit seeds to sprout in that planet’s red soil [Miller and Durant, Worlds Beyond, pp. 100-102].
Walt Disney also got into the act, phoning Ley from his office in Burbank, California. He was building Disneyland, his theme park in nearby Anaheim, and expected to advertise it by showing a weekly TV program of that name over the ABC television network. With von Braun’s help, Disney went on to produce an hour-long feature, Man in Space. It ran in October 1954, with subsequent reruns, and emphasized the piloted lunar mission. Audience-rating organizations estimated that 42 million people had watched the program [Ley, Rockets, p. 331].
In its 1952 article, Time referred to von Braun’s cargo rockets as “shuttles” and “shuttle rockets,” and described the reusable third stage as “a winged vehicle rather like an airplane.” His payload weight of 72,000 pounds proved to be very close to the planned capacity of 65,000 pounds for NASA’s space shuttle [Time, December 8, 1952, pp. 67, 68]. He expected to fuel his rockets with the propellants nitric acid and hydrazine, which have less energy than the liquid hydrogen in use during the 1960s. Hence, his rockets would have to be very large. While his loaded weight of 7,000 tons would compare with the 2,900 tons of America’s biggest rocket, the Saturn V [NASA SP-4012, vol. III, p. 27], his program cost of $4 billion was wildly optimistic.
Still, the influence of the Collier’s series echoed powerfully throughout subsequent decades. It was this eight-part series that would define nothing less than NASA’s eventual agenda for piloted space flight. Cargo rockets such as the Saturn V and the space shuttle, astronaut Moon landings, a space station, the eventual flight of people to Mars—all these concepts would dominate NASA’s projects and plans. It was with good reason that, in the original Collier’s series, the space station and cargo rocket stood at the forefront. By 1952, the concept of a space station had been in the literature for nearly 30 years, while large winged rockets were being developed as well.
Background to the Space Station
The concept of a space station took root during the 1920s, in an earlier era of technical change that focused on engines. As recently as 1885, the only important prime mover had been the reciprocating steam engine. The advent of the steam turbine yielded dramatic increases in the speed and power of both warships and ocean liners. Internal-combustion engines, powered by gasoline, led to automobiles, trucks, airships, and airplanes. Submarines powered by diesel engines showed their effectiveness during World War I [Scientific American, May 1972, pp. 102-111; April 1985, pp. 132-139].
After that war, two original thinkers envisioned that another new engine, the liquid-fuel rocket, would permit aviation to advance beyond the Earth’s atmosphere and allow the exploration and use of outer space. These inventors were Robert Goddard, a physicist at Clark University in Worcester, Massachusetts, and Hermann Oberth, a teacher of mathematics in a gymnasium in a German-speaking community in Romania [Ley, Rockets, pp. 107, 116]. Goddard experimented much, wrote little, and was known primarily for his substantial number of patents [Lehman, High Man, pp. 360-363]. Oberth contented himself with mathematical studies and writings. His 1923 book, Die Rakete zu den Planetenraumen (The Rocket into Interplanetary Space), laid much of the foundation for the field of astronautics.
Both Goddard and Oberth were well aware of the ordinary fireworks rocket (a pasteboard tube filled with blackpowder propellant). They realized that modern technology could improve on this centuries-old design in two critical respects. First, a steel combustion chamber and nozzle in a rocket engine could perform much better than pasteboard. Second, the use of propellants such as gasoline and liquid oxygen would produce far more energy than blackpowder. Oberth produced two conceptual designs: the Model B, an instrument-carrying rocket for upper-atmosphere research, and the Model E, a spaceship [Ley, Rockets, pp. 108-112; NASA TT-F-9227, p. 98].
Having demonstrated to his satisfaction that space flight indeed was achievable, Oberth then considered its useful purposes. While he was not imaginative enough to foresee the advent of automated spacecraft (still well in the future), the recent war had shown that, using life support systems, submarines could support sizable crews underwater for hours at a time. Accordingly, he envisioned that similar crews, with oxygen provided through similar means, would live and carry out a variety of tasks in a space station as it orbited the Earth.
Without describing the station in any detail, he wrote that it could develop out of a plan for a large orbiting rocket with a mass of “at least 400,000 kg”:
But if we should let a rocket of this size travel around the earth, it would constitute a sort of miniature moon. It would then no longer need to be designed or equipped for descent and landing. Traffic between this satellite and earth could be carried out with smaller vehicles and these large rockets (let us call them observation stations) could be built to further dimensions for their particular purpose. If ill effects result from experiencing weightlessness over long periods of time (which I doubt), two such rockets could be connected with a cable and caused to rotate about each other.
The station could serve as an astronomical observatory:
In space, telescopes of any size could be used, for the stars would not flicker…. Sufficient for an objective glass would be a large, lightly shaded, concave mirror made of sheet metal. If this were mounted by means of three metal rods at a distance of several kilometers from the rocket, we would have a telescope which, for most purposes, would be one hundred times superior to the best instruments on earth.
The station could also carry out Earth observations, while serving as a communications relay:
With their sharp instruments they could recognize every detail on the earth and could give light signals to earth through the use of appropriate mirrors. They would enable telegraphic connections with places to which neither cables nor electrical waves can reach…. Their value to military operations would be obvious, be it that they are controlled by one of the belligerents or be it that high fees could be charged for the reports they could render. The station could observe every iceberg and could warn shipping, either directly or indirectly. The disaster of the Titanic of 1912, for example, could have been prevented in this way.
Oberth also considered the building of immense orbiting mirrors, with diameters as large as 1,000 kilometers:
For example, routes to Spitzbergen or to the northern Siberian ports could be kept free of ice. If the mirror had a diameter of only 100 km, it could make broad areas in the northern regions of the earth inhabitable through diffused light, and in our latitude it could prevent the fearful spring freezes and protect fruit crops from damage by night frosts in both spring and winter.
He recommended sodium as a lightweight construction material. While it reacts strongly with oxygen, sodium would remain inert in airless space. He also described how the observation station also could serve as a fuel station:
… if the hydrogen and oxygen are shielded from the sun’s rays, they could be stored here for as long as desired in a solid state. A rocket which is filled here and launched from the observation station has no air resistance to overcome…. If we couple a large sphere of sodium sheet which is produced and
filled with fuel on location with a small, stoutly built rocket which pushes its fuel supply ahead of it and is continually supplied by it, then we have a very powerful and long-range vehicle which is easily capable of making the trip to other bodies of the universe. [NASA TT F-9227, pp. 92-97.]
Although Oberth was shy and retiring by nature, the impact of his ideas, during subsequent decades, would rival that of von Braun’s a generation later. Die Rakete spurred the founding of rocket-research groups in Germany, the U.S., and the Soviet Union. As early as 1898, Russia’s Konstantin Tsiolkovsky, a provincial math teacher like Oberth, had developed ideas similar to those of Oberth’s. Officials of the new Bolshevik government then dusted off Tsiolkovsky papers, showing that he had been ahead of the Germans. As his writings won new attention, the Soviet Union emerged as another center of interest in rocketry [Ley, Rockets, pp. 100-104].
Fritz Lang, a leading German film producer, then became interested. More than a filmmaker, Lang was a leader in his country’s art and culture. Later, Willy Ley noted that at one of his premieres, “The audience comprised literally everyone of importance in the realm of arts and letters, with a heavy sprinkling of high government officials” [Ibid., p. 124]. In 1926, Lang released the classic film Metropolis, with a robot in the leading role. Two years later, he set out to do the same for space flight with Frau im Mond (The Girl in the Moon).
Drawing heavily on Oberth’s writings, Lang’s wife, actress Thea von Harbou, wrote the script for Frau im Mond. Fritz Lang hired Oberth as a technical consultant. Oberth then convinced Lang to underwrite the building of a real rocket. After all, it would be great publicity for the movie were such a rocket to fly on the day of the premiere. The project attracted a number of skilled workers who went on to build Germany’s first liquid-fuel rockets. Among them, a youthful Wernher von Braun went on to develop the V-2 with support from the German army [Ibid., pp. 124-130; Neufeld, Rocket and Reich, pp. 11-23].
Even during the 1920s, Oberth’s ideas drew enough attention to encourage other theorists and designers to pursue similar thoughts and to write their own books. Herman Potoĉnik, an engineer and former captain in the Austrian
army, wrote under the pen name of Hermann Noordung. In 1929, he published The Problem of Space Travel, a book that addressed the issue of space station design. It was to be his last publication, however, for later that same year, he died of tuberculosis at the age of 36 [NASA SP-4026, pp. xv-xvi].
Hermann Noordung’s space station concept of 1929. K is the electric cable to an external observatory; S is the airlock; Kondensatorrohre are condenser pipes; Verdamfungsrohr is a boiler pipe; Treppenschacht is a stairwell; Augzugschacht is an elevator shaft. (California Institute of Technology)
Potoĉnik introduced the classic rotating wheel shape, proposing a diameter of 100 feet with an airlock at its hub. The sun would provide electric power,
though not with solar cells; these, too, lay beyond the imagination of that generation. Instead, a large parabolic mirror would focus sunlight onto boiler pipes in a type of steam engine. For more power, a trough of mirrors would run around the station’s periphery concentrating solar energy on another system of pipes. Like a flower, the station would face the sun [Ibid., pp. 101-113].
Except for being two and a half times larger, von Braun’s Collier’s space station closely resembled that of Potoĉnik, and it is tempting to view von Braun as the latter’s apt pupil. He certainly had the opportunity to read Potoĉnik’s book (though published initially in its author’s native language of Slovenian, it appeared quickly in German translation [Ibid., pp. ix, xii]). Moreover, von Braun’s concept included a circumferential trough of solar mirrors for power. This, however, came not from Potoĉnik but rather from a suggestion of Fred Whipple (who had not read Potoĉnik’s book), and thus represented an independent invention [Ley, Rockets, pp. 372-373]. The influence of Potoĉnik on von Braun may have been only indirect.
The historian J.D. Hunley, who has prepared an English translation of Potoĉnik’s book, describes its influence on von Braun as “probable but speculative.” Nevertheless, he states unequivocally that “Potoĉnik’s book was widely known even to people who may have seen only photographs of sections from the book in translation” [NASA SP-4026, pp. xxii-xxiii]. His concept of a large rotating wheel was sufficiently simple to permit von Braun and others to carry it in their heads for decades, developing this concept with fresh details when using it as the point of reference for an original design.
In the popular mind, if not for aerospace professionals, the Collier’s series introduced the shape of a space station in definitive form. It carried over to Disney’s Man in Space, and to George Pal’s Conquest of Space. Fifteen years later, when producer Stanley Kubrick filmed Arthur C. Clarke’s 2001: A Space Odyssey, he too used the rotating-wheel shape, enlarging it anew to a diameter of a thousand feet [Clarke, 2001, photo facing p. 112].
Winged Rockets: The Work of Eugen Sänger
While space stations came quickly to the forefront in public attention, it was another matter to build them, even in versions much smaller than von Braun’s 250-foot wheel. Between 1960 and 1980 the concept flourished only briefly, in the short-lived Skylab program. The second major element of the Collier’s scenario, the winged rocket, enjoyed considerably better prospects. At first merely topics for calculation and speculation, the development of long-range winged rockets during World War II was the departure point for a number of serious postwar projects.
In the 1930s, work on winged rockets foreshadowed the development of a high-speed airplane able to land on a runway for repeated flights. The first important treatment came from Eugen Sänger, a specialist in aeronautics and propulsion who received a doctorate at the Technische Hochschule [a technical institute that does not qualify as a university but that offers advanced academic studies, particularly in engineering] in Vienna and stayed on to pursue research on rocket engines. In 1933, he published Raketenflugtechnik (Rocket Flight Engineering). The first text in this field, it included a discussion of rocket-powered aircraft performance and a set of drawings. Sänger proposed achieving velocities as high as Mach 10, along with altitudes of up to 70 kilometers [AAS History Series, vol. 7, Part 1, pp. 195, 203-206; vol. 10, pp. 228-230; Ley, Rockets, pp. 408-410].
While the turbojet engine was unknown at that time, it was this engine, rather than the rocket, that would offer the true path to routine high performance. Because a turbojet uses air from the atmosphere, a jet plane needs to carry fuel only, while its wings reduce the thrust and fuel consumption. Hence, it can maintain longer flight times. By contrast, a rocket must carry oxygen as well as fuel, and thus, while capable of high speeds, it lacks endurance. After World War II, rocket airplanes as experimental aircraft went on to reach speeds and altitudes far exceeding those of jets. Jet planes, however, took over the military and later the commercial realms.
During World War II, Sänger made a further contribution, showing how the addition of wings could greatly extend a rocket’s range. Initially, a winged rocket would fly to modest range, along an arcing trajectory like that of an artillery shell. Upon reentering the atmosphere, however, the lift generated by
the rocket’s wings would carry it upward, causing it to skip off the atmosphere like a flat stone skipping over water. Sänger calculated that with a launch speed considerably less than orbital velocity, such a craft could circle the globe and return to its launch site [Ley, Rockets, pp. 428-434]. After World War II, this concept drew high-level attention in Moscow, where, for a time, Stalin sought to use it as a basis for a serious weapon project [Zaloga, Target, pp. 121-124].
The A-4b, a winged V-2 of 1945. (Smithsonian Institution Photo No. 76-7772)
The Navaho and the Main Line of American Liquid Rocketry
In haste and desperation, winged rockets entered the realm of hardware late in the war, as an offshoot of the V-2 program. The standard V-2 had a range of 270 kilometers. Following the Normandy invasion in 1944, as the Allies surged into France and the Nazi position collapsed, a group of rocket engineers led by Ludwig Roth sought to stretch this range to 500 kilometers by adding swept wings to allow the missile to execute a supersonic glide.
The venture was ill-starred from the outset. When winds blew on the wings during liftoff, the marginal guidance system could not prevent the vehicle from rolling and going out of control. In this fashion, the first winged V-2 crashed within seconds of its December 1944 launch. A month later, a second attempt was launched successfully and had transitioned to gliding flight at Mach 4. Then a wing broke off, causing the missile to break up high in the air [Neufeld, Rocket and Reich, pp. 248-251, 281].
Nevertheless, this abortive effort provided an early point of departure for America’s first serious long-range missile effort. In the Army Air Forces (AAF), the Air Technical Service Command (ATSC; renamed Air Materiel Command in March 1946) began by defining four categories of missiles: air-to-air, air-to-surface, surface-to-air, and surface-to-surface. The last of these included the V-2 and its potential successors [Neufeld, Ballistic Missiles, p. 26].
The program began with a set of military characteristics, outlined in August 1945, that defined requirements for missiles in these categories. AAF Headquarters published these requirements as a classified document. In November 1946, ATSC invited 17 contractors, most of them aircraft manufacturers, to submit proposals for design studies of specific weapons. One of these firms was North American Aviation (NAA) in Los Angeles [Fahrney, History, p. 1291; Neal, Navaho, pp. 1-2].
Test of a small rocket engine in a parking lot at North American Aviation. (Rocketdyne)
NAA had been a mainstay in wartime aircraft production. At the end of World War II, amid sweeping contract cancellations, the company dropped from 100,000 to 6,500 employees in about two months [AAS History Series, vol. 20, pp. 121-132]. The few remaining contracts were largely in the area of jet-powered bombers and fighters. To NAA’s president, James “Dutch” Kindelberger, these bombers represented the way into the future. He decided to bring in the best scientist he could find and have him build a new research lab, staffed with experts in such fields as jet propulsion, rockets, gyros, electronics, and automatic control. The lab’s purview, which would go well beyond the AAF study, was to work toward bringing in new business by extending the reach of the firm’s technical qualifications.
An executive recruiter, working in Washington, D.C., recommended William Bollay to head this lab. Bollay, who held a Ph.D. in aeronautical engineering from Caltech, had been a branch chief in the Navy’s Bureau of Aeronautics, with responsibility for the development of turbojet engines. He came to NAA by November 1946, in time to deal with the AAF request for proposals. Working with the company’s chief engineer, Raymond Rice, Bollay decided to pursue the winged V-2, which the Germans had designated as the A-9. During World War II, the Germans had regarded this missile as the next step beyond the standard V-2, hoping that its wings would offer a simple way to increase its range. The V-2’s overriding priority had prevented serious
work on its winged version. Late in 1945, however, the NAA proposal offered to “essentially add wings to the V-2 and design a missile fundamentally the same as the A-9” [Ibid.; author interview, Jeanne Bollay, Santa Barbara, California, January 24, 1989; Report AL-1347 (North American), pp. 1-4; Neufeld, Rocket and Reich, p. 249].
A letter contract, issued to the firm in April 1946, called for the study and design of a supersonic guided missile designated MX-770, with a range of 175 to 500 miles [Report AL-1347 (North American), pp. 5-6]. Meanwhile, rocket research was under way in an NAA company parking lot, with parked cars only a few yards away. A boxlike steel frame held a rocket motor; a wooden shack housed instruments. The steel blade of a bulldozer’s scraper was used as a shield to protect test engineers in the event of an explosion [Threshold, Summer 1993, pp. 40-47]. A surplus liquid-fueled engine from Aerojet General, with a 1,000 pounds of thrust, served as the first test motor. The rocket researchers also built and tested home-brewed engines, initially with 50 to 300 pounds of thrust [Report AL-1347 (North American), p. 37]. Some of these engines were so small that they seemed to whistle rather than roar. In the words of J. Leland Atwood, who became company president in 1948, “We had rockets whistling day and night for a couple of years”.
In June 1946, the first step toward a coordinated plan came in the form of a new company proposal. In the realm of large rocket-engine development, Bollay and his associates proposed a two-part program:
Phase I: Refurbishment and testing of a complete V-2 propulsion system, to be provided as government-furnished equipment.
Phase II: Redesign of this engine to American engineering standards and methods of manufacture, along with construction and testing.
In the spring of 1947, the company added a further step:
Phase III: Design, construction and testing of a new engine, drawing on V-2 design but incorporating a number of improvements [Report AL-1347 (North American), pp. 9-10, 34].
Bollay and his colleagues also launched an extensive program of consultation with Wernher von Braun and his wartime veterans. These included
Walther Riedel, Hans Huter, Rudi Beichel, and Konrad Dannenberg. In addition, Dieter Huzel, a close associate of von Braun, went on to join NAA as a full-time employee [Threshold, Summer 1991, pp. 52-63, Huzel, Peenemünde, pp. 226-228].
Bollay wanted to test-fire V-2 engines. Because their thrust of 56,000 pounds was far too great for the company’s parking lot test center, Bollay needed a major set of test facilities. Atwood was ready to help. “We scoured the country,” Atwood recalls. “It wasn’t so densely settled then—and we located this land”. It was in the Santa Susana Mountains, at the western end of the San Fernando Valley. The landscape—stark, sere, and full of rounded reddish boulders—offered spectacular views. In March 1947, NAA leased the land and built a rocket test center on it as part of a buildup of facilities costing upwards of $1 million in company money and $1.5 million from the Air Force [Report AL-1347 (North American), pp. 23-26; Neal, Navaho, p. 29].
In 1946, two government-furnished V-2 engines arrived at the site. Detailed designing of the Phase II engine began in June 1947; the end of September brought the first release of drawings and of the first fabricated parts. Early in 1949, the first such engine was completed. Two others followed shortly thereafter [Report AL-1347 (North American), pp. 36-37; Fahrney, History, p. 1292; AAS History Series, vol. 20, pp. 133-144].
Still very much a V-2 engine, it had plenty of room for improvement. Lieutenant Colonel Edward Hall, who was funding the work, declared that “it wasn’t really a very good engine. It didn’t have a proper injector, and that wasn’t all. When we took it apart, we decided that was no way to go”. By fixing the deficiencies during Phase III, NAA expected to lay a solid foundation for future rocket engine development.
A particular point of contention involved this engine’s arrangements for injecting propellants into its combustion chamber. Early in the German rocket program, Walter Riedel, von Braun’s chief engine designer, had built a rocket motor with 3,300 pounds of thrust with a cup-shaped injector at the top of the thrust chamber. For the V-2, a new chief of engine design, Walter Thiel, grouped 18 such cups to yield its 56,000 pounds. Unfortunately, this arrangement did not lend itself to a simple design wherein a single liquid-oxygen line
could supply all the cups. Instead, his “18-pot engine” required a separate oxygen line for each individual cup [Ley, Rockets, pp. 204, 212, 215; Neufeld, Rocket and Reich, pp. 74-79, 84].
Thiel had pursued a simpler approach by constructing an injector plate, resembling a showerhead, pierced with numerous holes to permit the rapid inflow and mixing of the rocket propellants. By the end of World War II, Thiel’s associates had tested a version of the V-2 engine successfully that incorporated this feature, though it never reached production [Neufeld, Rocket and Reich, p. 251]. Bollay’s rocket researchers, still working within the company parking lot, were upping their engines’ thrust to 3000 pounds, and were using them to test various types of injector plates [Report AL-1347 (North American), p. 37; Threshold, Summer 1993, pp. 4047]. The best injector designs would be incorporated into the Phase III engine, bringing a welcome simplification and introducing an important feature that could carry over to larger engines with greater thrust. In September 1947, preliminary design of Phase III began, aiming at the thrust of the V-2 engine but with a weight reduction of 15 percent [Report AL-1347 (North American), p. 36].
Top, liquid-fuel rocket engine showing location of injector. Bottom, representative types of injector. (Cornelisse et al., p. 209; Sutton, p. 208)
Bollay had initially expected to design the 500-mile missile as a V-2 with swept wings and large control surfaces near the tail, closely resembling the A9. Work in a supersonic wind tunnel built by Bollay’s staff showed that this design would encounter severe stability problems at high speed. Thus, by early 1948, a new configuration emerged. With small forward-mounted wings (known as canards) that could readily control such instability, the new design moved the large wings well aft, replacing the V-2’s horizontal fins. In January 1948, four promising configurations were tested in the Ordnance Aerophysics Laboratory wind tunnel in Daingerfield, Texas. By March, a workable preliminary design of the best of these four configurations was largely in hand [Ibid., pp. 30-33, 38-39].
When it won independence from the Army, the U.S. Air Force received authority over programs for missiles with a range of 1,000 miles or more. Shorter-range missiles remained the exclusive domain of the Army. Accordingly, at a conference in February 1948, Air Force officials instructed NAA to stretch the range of their missile to 1000 miles [Fahrney, History, pp. 1293-1294; Neal, Navaho, pp. 6-7].
The 500-mile missile had featured a boost-glide trajectory. It used rocket power to arc high above the atmosphere and then its range was extended with
a supersonic glide. This approach was not well suited when the range was doubled. At the Air Force developmental center of Wright Field, near Dayton, Ohio, Colonel M. S. Roth proposed to increase the missile range anew by adding ramjets [Letter, Colonel M. S. Roth to Power Plant Lab, 11 February 1948 (cited in Fahrney, History, p. 1294)]. Unlike the turbojet engines of the day, the ramjet—which worked by ramming air into the engine at high speed—could
fly supersonically. A turbojet, however, could take off from a standing start whereas a ramjet needed a rocket boost to reach the speed at which this air-ramming effect would come into play.
A Navy effort, Project Bumblebee, had been under way in this area since World War II and NAA had done several relevant aerodynamic studies. In addition, at Wright Field, the Power Plant Laboratory included a Nonrotating Engine Branch that was funding the development of ramjets as well as rocket motors. Its director, Weldon Worth, dealt specifically with ramjets; Lieut. Col. Hall, who dealt with rockets, served as his deputy [Report AL-1347 (North American), p. 6; Jet Propulsion, vol. 25 (1955), pp. 604-614; author interview, Edward Hall, Los Angeles, August 29, 1996].
Though designed for boost-glide flight, the new missile configuration readily accommodated ramjets and their fuel tanks for supersonic cruise. The original boost-glide missile thus evolved into a cruise missile when a modification of the design added two ramjet engines, mounting one at the tip of each of two vertical fins. These engines and their fuel added weight, which necessitated an increase in the planned thrust of the Phase Ill rocket motor. Originally it had been planned to match the 56,000 pound thrust of the V-2. In March 1948, however, the thrust of this design went up to 75,000 pounds. The missile was named the Navaho, reflecting a penchant at NAA for names beginning with “NA” [Report AL-1347 (North American), pp. 39, 42-43].
Navaho concept of 1948. (U.S. Air Force)
By late November of 1949, the first version of this engine was ready for testing at the new Santa Susana facility. Because it lacked turbopumps, propellants were pressure-fed from heavy-walled tanks. Thus, this version of the engine was much simpler than its later operational type, which would rely on turbopumps to force propellants into the engine. Proceeding cautiously, the rocket crew began with an engine-start test at 10 percent of maximum propellant flow for 11 seconds. It was successful and led to somewhat longer starting tests in December. Then, as the engineers grew bolder, they hiked up the thrust. In March 1950, this simplified engine first topped its rated level of 75,000 pounds—for four and a half seconds. During May and June, the full-thrust runs went well, exceeding a minute in duration.
Meanwhile, a separate developmental effort was building the turbo-pumps. Late in March 1950, the first complete engine, turbopumps included, was assembled. In August, this engine fired successfully for a full minute—at 12.3 percent of rated thrust. Late in October, the first full-thrust firing reached 70,000 pounds—for less than five seconds. In seven subsequent tests during 1950, however, only one, in mid-November, topped its rated thrust level. This was due to problems with rough combustion during the buildup to full thrust [Ibid., pp. 75-81].
The pressure-fed tests exhibited surges in combustion-chamber pressure (known as “hard starts”) that were powerful enough to blow up an engine. Walther Riedel, one of the German veterans, played an important role in introducing design modifications that brought this problem under control. The problem of rough combustion was new, however, and went beyond the German experience. It stemmed from combustion instability in the engine’s single large thrust chamber. Ironically, the V-2’s 18-pot motor had avoided this difficulty. Acting as preliminary burners, its numerous injector cups were too small to permit such instabilities [Threshold, Summer 1991, pp. 52-63].
Following the successful full-thrust test of November 1950, it was not until March 1951 that problems of unstable combustion came under control [Ibid., p. 53; Report AL-1347 (North American), p. 81]. However, this marked another milestone. For the first time, the Americans had encountered and solved an important problem that the Germans had not experienced. While combustion instabilities would recur repeatedly during subsequent engine programs, the work of 1950 and 1951 introduced NAA to methods for solving this problem.
By then, the design and mission of the Navaho had changed dramatically. The August 1949 detonation of a Soviet atomic bomb, the fall of China to communism, and the outbreak of the Korean War in mid-1950 combined to signal to the nation that the rivalry with the Soviet Union was serious and that Soviet technical capability was significant. The designers at North American, working with their Air Force counterparts, accordingly sought to increase the range of the Navaho to as much as 5,500 nautical miles, and thereby give it intercontinental capability.
At the Pentagon in August 1950, conferences among Air Force officials brought a redefinition of the program that set this intercontinental range of 5,500 miles as a long-term goal. A letter from Major General Donald L. Putt, director of research and development within the Air Materiel Command, became the directive instructing NAA to pursue this objective [Letter, Maj. Gen. D. L. Putt to Commanding General, Air Materiel Command, 21 August 1950 (cited in Fahrney, History, p. 1297)]. An interim version, Navaho II, with range of 2,500 nautical miles, seemed technically feasible. The full-range version, Navaho III, represented a long-term project that would go forward as a parallel effort [Report AL-1347 (North American), p. 88; Fahrney, History, pp. 1296-1297; Neal, Navaho, pp. 12-14].
The 1,000-mile Navaho of 1948, with its Phase III engine, had amounted to a high-speed pilotless airplane fitted with both rocket and ramjet propulsion. This design, however, had taken approaches based on winged rockets to their limit. The new Navaho designs separated the rocket engines from the ramjets, assigned each to a separate vehicle, and turned Navaho into a two-stage missile. The first stage or booster, powered by liquid-fuel rockets, accelerated the missile to Mach 3 and 58,000 feet. The ramjet-powered second stage rode this booster during initial ascent—similar to the way in which the Space Shuttle rides its external tank today—and then cruised to its target at Mach 2.75 (about 1,800 mph.) [“Standard Missile Characteristics: XSM-64 Navaho” U.S. Air Force, November 1, 1956, Air Force Museum, Wright-Patterson AFB, Ohio].
Lacking the thrust to boost the Navaho, the 75,000-pound rocket motor stood briefly on the brink of abandonment. Its life, however, was only beginning. This engine was handed over to von Braun, who was at Redstone Arsenal
in Huntsville, Alabama, directing development of the Army’s Redstone missile. With a range of 200 miles, this missile needed an engine. In March 1951, the Army awarded a contract to NAA for this rocket motor. Weighing less than
half as much as the V-2’s 18-pot engine (1,475 pounds versus 2,484), this motor delivered 34 percent more thrust than that of the V-2 [Threshold, Summer 1991, p. 63].
V-2 engine, left, and its successor developed for Navaho. (Rocketdyne)
For Navaho II, this basic engine would be replaced by a new one with 120,000 pounds of thrust. A twin-engine installation, totaling 240,000 pounds, provided the initial boost. For Navaho III, NAA upgraded the engine to 135,000 pounds of thrust and designed a three-engine cluster for that missile’s booster [Neal, Navaho, pp. 30-31; AAS History Series, vol. 20, pp. 133-144].
In 1954 and 1955, the Air Force and Army made a major push into long-range missiles—but these were not Navahos. Instead, they were the Air Force’s Atlas, Titan, and Thor, along with the Army’s Jupiter. When these new programs needed engines, however, it was again NAA that produced the rocket motors that would do the job. The Navaho’s 135,000 pounds of thrust was upgraded to 139,000 and then again to 150,000 pounds. In addition to this, a parallel effort at Aerojet General developed very similar engines for the Titan [AAS History Series, vol. 13, pp. 19-35; vol. 20, pp. 133-144].
“We often talked about this basic rocket as a strong workhorse, a rugged engine,” says Paul Castenholz, a test engineer who worked at Santa Susana.
“I think a lot of these programs evolved because we had these engines. We anticipated how people would use them; we weren’t surprised when it happened. We’d hear a name like Atlas with increasing frequency, but when it became real, the main result was that we had to build more engines and test them more stringently”
The Navaho of 1948, designed as a winged rocket with ramjets, stood two steps removed from the missiles that later would go on to deployment and operational status. First, the versions of 1950 and after were designed and built as high-speed aircraft with a separate rocket booster. Subsequently, those versions were replaced by the Atlas and other missiles of that era.
Even though the Air Force cancelled the Navaho program in 1957, its legacy lived on. Bollay’s research center, called the Aerophysics Laboratory, became the nucleus that allowed NAA to take the lead in piloted space flight. In 1955, this laboratory split into four new corporate divisions: Rocketdyne, Autonetics, the Missile Division, and Atomics International. Rocketdyne
became the nation’s premier builder of rocket engines. Autonetics emerged as a major center for guidance and control. The Missile Division, later renamed Space and Information Systems, built the Apollo spacecraft as well as the second stage of the Saturn V Moon rocket [Murray, Lee Atwood, pp. 47, 56, 62-64, 71].
The Navaho also left a legacy in its people. Sam Hoffman, who brought the 75,000-pound engine to success, presided over Rocketdyne as it built the main engines for the Saturn V. Paul Castenholz headed development of the J2, the hydrogen-fueled engine that powered Saturn V’s upper stages. John R. Moore, an expert in guidance, became president of Autonetics. Dale Myers, who served as Navaho project manager, went to NASA as Associate Administrator for Manned Space Flight. [Author interviews: Eugene Bollay, Santa Barbara, California, January 24, 1989; Sam Hoffman, Monterey, California, July 28, 1988; Paul Castenholz, Colorado Springs, August 18, 1988; John R. Moore, Pasadena, California, May 28, 1996; Dale Myers, Leucadia, California, May 24, 1996.]
Navaho’s engines, including those built in the parallel effort at Aerojet General, represented a third legacy. Using such engines, Atlas, Thor, and Titan were all successful as launch vehicles. Upper stages were added to Thor which evolved into the widely-used Delta. Additional upgrades raised the thrust of its engine to 205,000 pounds. A cluster of eight such engines, producing up to 1.6 million pounds of thrust, powered the Saturn I and Saturn I-B boosters, which flew repeatedly in both the Apollo and Skylab programs.’ Between 1946 and 1950, the winged rockets of the Navaho program played a pioneering role, planting seeds that would flourish for decades in aerospace technology.
The X-15: An Airplane for Hypersonic Research
During the 1940s and 50s, the nation’s main centers for aeronautical research operated within a small federal agency, the National Advisory Committee for Aeronautics (NACA; it became the National Aeronautics and Space Administration, NASA, in 1958). After World War II, NACA and the Air Force became increasingly active in supersonic flight. Rocket-powered aircraft such as the Bell X-1 and the Douglas Skyrocket D-558 set the pace. The X-1 broke the sound barrier in 1947; the Skyrocket approached Mach 2 only
four years later. Also, between 1949 and 1951, NAA designed a new fighter, the F-100, planning it to be the first jet plane to go supersonic in level flight [Ley, Rockets, pp. 423-425; Gunston, Fighters. pp. 170-171].
Supersonic aviation brought difficult problems in aerodynamics, propulsion, aircraft design, and stability and control in flight. Still, at least for flight speeds of Mach 2 and somewhat higher, it did not involve the important issue of aerodynamic overheating. Though fitted with rocket engines, the cited aircraft were built of aluminum, which cannot withstand high temperatures. At speeds beyond Mach 4 lay the realm of hypersonic flight, where problems of heating would dominate.
Nevertheless, by the early 1950s, interest in such flight speeds was increasing. This was due in part to the growing attention given to prospects for an intercontinental ballistic missile (ICBM), a rocket able to carry a nuclear weapon to Moscow. In December 1950, the Rand Corp., an influential Air Force think tank, reported that such missiles now stood within reach of technology. The Air Force responded by giving a study contract to the firm of Convair in San Diego, where, a few years earlier, the designer Karel Bossart had nurtured thoughts of such missiles. Bossart’s new design, developed during 1951, called for the use of the Navaho’s 120,000-pound-thrust rocket engine. The design was thoroughly unwieldy; it would stand 160 feet tall and weigh 670,000 pounds. Nevertheless, it represented a milestone. For the first time, the Air Force had an ICBM design concept that it could pursue using rocket engines that were already being developed [Neufeld, Ballistic Missiles, pp. 68-70].
Among the extraordinarily difficult technical issues faced by the ICBM, the problem of reentry was paramount. Because an ICBM’s warhead would reenter the atmosphere at Mach 20 or more, there was excellent reason to believe that it would burn up like a meteor. As early as 1951, however, the NACA aerodynamicist H. Julian Allen offered a solution. Conventional thinking held that hypersonic flight would require the ultimate in slender needle-nose shapes. Allen broke with this approach, showing mathematically that the best design would introduce a nose cone as blunt or flat-faced as possible. Such a shape would set up patterns of airflow that would carry most of the heat of reentry away from the nose cone, rather than delivering this heat to its outer surface [Allen and Eggers, NACA Report 1381; Hansen, Transition, p. 3.]
There was further interest in hypersonics at Bell Aircraft Corp. in Buffalo. Here Walter Dornberger, who had directed Germany’s wartime rocket development, was proposing a concept similar to Eugen Sänger’s skip-gliding rocket plane. The design of the rocket (known as the BomiBomber Missile) required a two-stage vehicle with each stage winged, piloted, and rocket-powered. Dornberger argued that Bomi would have the advantage of being able to fly multiple missions like any piloted aircraft, and it could be recalled once in flight. By contrast, an ICBM could fly only once and would be committed irrevocably to its mission once in flight [Spaceflight, vol. 22 (1980), pp. 270-272].
Bell Aircraft, very active in supersonic flight research, had built the X-1, which was the first through the sound barrier. Also, Bell Aircraft was building the X-1A that would approach Mach 2.5 and the X-2 that would top Mach 3 [Miller, X-Planes, pp. 25-26, 37, 41-42]. Robert Woods, co-founder of the company and a member of NACA’s influential Committee on Aerodynamics, had been a leader in the design of these aircraft. He also took a strong interest in Dornberger’s ideas.
In October 1951, at a meeting of the Committee on Aerodynamics, Woods called for NACA to develop a new research airplane resembling the V-2, to “obtain data at extreme altitudes and speeds, and to explore the problems of reentry into the atmosphere.” In January 1952, Woods wrote a letter to the committee, urging NACA to pursue a piloted research airplane capable of reaching beyond Mach 5. He accompanied this letter with Dornberger’s description of Bomi. That June, at Woods’s urging, the committee passed a resolution proposing that NACA increase its program in research aircraft to examine “problems of unmanned and manned flight in the upper stratosphere at altitudes between 12 and 50 miles” [AAS History Series, vol. 13, p. 296; Hansen, Transition, pp. 5-6].
NACA already had a few people who were active in hypersonics, notably the experimentalists Alfred Eggers and John Becker, who had already built hypersonic wind tunnels [Hallion, ed., Hypersonic, pp. xxxi-xxxv]. At NACA’s Langley Aeronautical Laboratory, Floyd Thompson, the lab’s associate director, responded to the resolution by setting up a three-man study group chaired by Clinton Brown, a colleague of Becker. In Becker’s words, “Very few others at Langley in 1952 had any
knowledge of hypersonics. Thus, the Brown group filled an important educational function badly needed at the time” [Ibid., p. 381].
According to Thompson, he was looking for fresh unbiased ideas and the three study-group members had shown originality in their work. Their report, in June 1953, went so far as to propose commercial hypersonic flight, suggesting that airliners of the future might evolve from boost-glide concepts such as those of Dornberger. At the more practical level, however, the group warmly endorsed building a hypersonic research aircraft. NACA-Langley already had a Pilotless Aircraft Research Division (PARD), which was using small solid-fuel rockets to conduct supersonic experiments. Brown’s group now recommended that PARD reach for higher speeds, perhaps by launching rockets that could cross the Atlantic and be recovered in the Sahara Desert [Ibid., pp. 381-382; Hansen, Transition, pp. 6-9].
PARD, a NACA in-house effort, went forward rapidly. In November 1953, it launched a research rocket that carried a test nose cone to Mach 5.0. The following October, a four-stage rocket reached Mach 10.4 [Hallion, ed., Hypersonic, p. lxiv]. To proceed with a piloted research airplane, NACA’s limited budget needed support from the Air Force. Here too there was cross-fertilization. Robert Gilruth, head of PARD and an assistant director of NACA-Langley, was also a member of the Aircraft Panel of the Air Force’s Scientific Advisory Board. At a meeting in October 1953, this panel stated that “the time was ripe” for such a research airplane, and recommended that its feasibility “should be looked into” [Astronautics & Aeronautics, February 1964, p. 54].
The next step came at a two-day meeting in Washington of NACA’s Research Airplane Projects Panel. Its chairman, Hartley Soule, had directed NACA’s participation in research aircraft programs since the earliest days of the X-1 project in 1946. The panel considered specifically a proposal from Langley, endorsed by Brown’s group, to modify the X-2 for flight to Mach 4.5. They rejected this concept, asserting that the X-2 was too small for hypersonic work. The panel members concluded instead that “provision of an entirely new research airplane is desirable” [Ibid.; Hansen, Transition, p. 9].
NACA’s studies of such an airplane would have to start anew. In March 1954, John Becker set up a new group that took on the task of defining a
design. Time was of the essence; everyone was aware that the X-2 project, underway since 1945, had yet to make its first powered flight [Astronautics & Aeronautics, February 1964, p. 53]. Becker stipulated that “a period of only about three years be allowed for design and construction.” Hence NACA would move into the unknown frontiers of hypersonics using technology that was already largely in hand [Hallion, ed., Hypersonic, p. 1].
Two technical problems stood out: overheating and instability. Because the plane would fly in the atmosphere at extreme speeds, it was essential that it be kept from tumbling out of control. As on any other airplace, tail surfaces were to provide this stability. Investigations had shown that these would have to be excessively large. A Langley aerodynamicist, Charles McLellan, came to the rescue. While conventional practice called for thin tail surfaces that resembled miniature wings, McLellan now argued that they should take the form of a wedge. His calculations showed that at hypersonic speeds, wedge-shaped vertical fins and horizontal stabilizers should be much more effective than conventional thin shapes. Tests in Becker’s hypersonic wind tunnel verified this approach [Astronautics & Aeronautics, February 1964, pp. 54, 56].
The problem of overheating was more difficult. At the outset, Becker’s designers considered that, during reentry, the airplane should point its nose in the direction of flight. This proved unacceptable because the plane’s streamlined shape would cause it to enter the dense lower atmosphere at excessive speed. This would subject the aircraft to disastrous overheating and to aerodynamic forces that would cause it to break up. These problems, however, appeared far more manageable if the plane were to enter with its nose high, presenting its flat undersurface to the air. It then would lose speed in the upper atmosphere, easing both the overheating and the aerodynamic loads. In Becker’s words, “It became obvious to us that what we were seeing here was a new manifestation of H. J. Allen’s ‘blunt body’ principle. As we increased the angle of attack, our configuration in effect became more ‘blunt'” [Hallion, ed., Hypersonic, p. 386]. While Allen had developed his principle for missile nose cones, it now proved equally useful when applied to hypersonic airplanes.
Even so, the plane would encounter far more heat and higher temperatures than any aircraft to date had received in flight. New approaches in the
structural design of these aircraft were imperative. Fortunately, Dornberger’s group at Bell Aircraft had already taken the lead in the study of “hot structures.” These used temperature-resistant materials such as stainless steel. Wings might be covered with numerous small and very hot metal panels resembling shingles that would radiate the heat away from the aircraft. While overheating would be particularly severe along the leading edges of the wings, these could be water-cooled. Insulation could protect an internal structure that would stand up to the stresses and forces of flight; active cooling could protect a pilot’s cockpit and instrument compartment. Becker described these approaches as “the first hypersonic aircraft hot structures concepts to be developed in realistic meaningful detail” [Ibid., p. 384].
His designers proceeded to study a hot structure built of Inconel X, a
chrome-nickel alloy from International Nickel. This alloy had already demon
strated its potential, when, during the previous November, it was used for the
nose cone in PARD’s rocket flight to Mach 5 [Ibid., p. lxiv]. The hot structure would be of
the “heat sink” type, relying on the high thermal conductivity of this metal to
absorb heat from the hottest areas and spread it through much of the aircraft.
As an initial exercise, they considered a basic design in which the Inconel
X structure would have to withstand only conventional aerodynamic forces and loads, neglecting any extra requirements imposed by absorption of heat. A separate analysis then considered the heat-sink requirements, with the understanding that these might greatly increase the thickness and hence the weight of major portions of the hot structure. When they carried out the exercise, the designers received a welcome surprise. They discovered that the weights and thicknesses of a heat-absorbing structure were nearly the same as for a simple aerodynamic structure [Astronautics & Aeronautics, February 1964, p. 58]. Hence, a hypersonic research airplane, designed largely from aerodynamic considerations, could provide heat-sink thermal protection as a bonus. The conclusion was clear: piloted hypersonic flight was achievable.
The feasibility study of Becker’s group was intended to show that this airplane indeed could be built in the near future. In July 1954, Becker presented the report at a meeting in Washington of representatives from NACA, the Air Force’s Scientific Advisory Board, and the Navy. (The Navy, actively involved
with research aircraft, had built the Douglas Skyrocket.) Participants at the meeting endorsed the idea of a joint development program that would build and fly the new aircraft by drawing on the powerful support of the Pentagon [AAS History Series, vol. 13, p. 299].
Important decisions came during October 1954, as NACA and Air Force panels weighed in with their support. At the request of General Nathan Twining, the Air Force Chief of Staff, the Aircraft Panel of the Scientific Advisory Board presented its views on the next 10 years of aviation. The panel’s report paid close attention to hypersonic flight:
In the aerodynamic field, it seems to us pretty clear that over the next ten years the most important and vital subject for research and development is the field of hypersonic flows…. This is one of the fields in which an ingenious and clever application of the existing laws of mechanics is probably not adequate. It is one in which much of the necessary physical knowledge still remains unknown at present and must be developed before we arrive at a true understanding and competence….
[A] research vehicle which we now feel is ready for a program is one involving manned aircraft to reach something of the order of Mach 5 and altitudes of the order of 200,000 to 500,000 feet. This is very analogous to the research aircraft program which was initiated ten years ago as a joint venture of the Air Force, the Navy, and NACA. It is our belief that a similar cooperative arrangement would be desirable and appropriate now [Hallion, ed., Hypersonic, pp. xxiii-xxix].
In addition to this, NACA’s Committee on Aerodynamics met in executive session to make a formal recommendation concerning the new airplane. The committee included representatives from the Air Force and Navy, from industry, and from universities [Hansen, Transition, pp. 11, 30 (footnote 22)]. Its member from Lockheed, Clarence “Kelly” Johnson, vigorously opposed building this plane, arguing that experience with earlier experimental aircraft had been “generally unsatisfactory.” New fighter designs were advancing so rapidly as to actually outpace the performance of research aircraft. To Johnson, their high-performance flights had served mainly to prove the bravery of the test pilots. While Johnson pressed his views strongly, he was in a minority of one. The other committee members passed a resolution endorsing “immediate initiation of a project to design and construct a research airplane capable of achieving speeds of the order of Mach number 7 and altitudes of several hundred thousand feet” [Ibid., pp. 12-14].
With this resolution, Hugh Dryden, the head of NACA, could approach his Air Force and Navy counterparts to discuss the initiation of procurement. Detailed technical specifications were necessary and would come, by the end of 1954, from a new three-member committee, with Hartley Soule as the NACA representative. The three members used Becker’s study as a guide in deriving the specifications, which called for an aircraft capable of attaining 250,000 feet and a speed of 6600 feet per second while withstanding reentry temperatures of 1200 degrees Fahrenheit [Ibid., p. 14; AAS History Series, vol. 8, p. 299].
In addition to this, as NACA and the military services reached an agreement on procurement procedures, a formal Memorandum of Understanding came from the office of Trevor Gardner, Special Assistant for Research and Development to the Secretary of the Air Force. This document stated that NACA would provide technical direction, that the Air Force would administer design and construction, and that the Air Force and Navy would provide the funding. It concluded, “Accomplishment of this project is a matter of national urgency” [Hallion, ed., Hypersonic, p. 1-6].
Now the project was ready to proceed. Under standard Air Force practices, officials at Wright-Patterson Air Force Base would seek proposals from potential contractors. Early in 1955, the aircraft also received a name: the X15. Competition between proposals brought the award of a contract for the airframe to NAA. The rocket engine was contracted to Reaction Motors, Inc. [Ibid., pp. I-iv, 11-15]. The NAA design went into such detail that it even specified the heat-resistant seals and lubricants that would be used. Nevertheless, in many important respects it was consistent with the major features of the original feasibility study by Becker’s group. The design included wedge-shaped tail surfaces and a heat-sink structure of Inconel X [Astronautics & Aeronautics, February 1964, p. 54].
The X-15 was to become the fastest and highest flying airplane until the space shuttle flew into orbit in 1981. In August 1963, the X-15 set an altitude record of 354,200 feet (67 miles), with NASA’s Joseph Walker in the cockpit.
Four years later, the Air Force’s Captain William Knight flew it to a record speed of 4,520 miles per hour, or Mach 6.72 [Hallion, ed., Hypersonic, pp. I-v, I-viii]. In addition to setting new records, the X-15 accomplished a host of other achievements.
A true instrument of hypersonic research, in 199 flights it spent nearly nine hours above Mach 3, nearly six hours above Mach 4, and 82 minutes above Mach 5. Although the NACA and the Air Force had hypersonic wind tunnels, the X-15 represented the first application of aerodynamic theory and wind tunnel data to an actual hypersonic aircraft. The X-15 thus enhanced the usefulness of these wind tunnels, by providing a base of data with which to validate (and in some instances to correct) their results. This made it possible to rely more closely on results from those tunnels during subsequent programs, including that of the Space Shuttle.
The X-15 used movable control surfaces that substituted for ailerons. It also introduced reaction controls: small rocket thrusters, mounted to the aircraft, that controlled its attitude when beyond the atmosphere. As it flew to the fringes of space and returned, the X-15 repeatedly transitioned from aerodynamic controls to reaction controls and back again. Twenty years later, the Space Shuttle would do the same.
In another important prelude to the shuttle, the X-15 repeatedly flew a trajectory that significantly resembled flight to orbit and return. The X-15 ascended into space under rocket power, flew in weightlessness, then reentered the atmosphere at hypersonic speeds. With its nose high to reduce overheating and aerodynamic stress, the X-15 used thermal protection to guard the craft against the heat of reentry. After reentry, the X-15 then maintained a stable attitude throughout its deceleration, transitioned to gliding flight, and landed at a preselected location. The shuttle would do all these things, albeit at higher speeds.
The X-15 used a rocket engine of 57,000 pounds of thrust that was throttleable, reusable, and “man-rated” — safe enough for use in a piloted aircraft. The same description would apply to the more powerful Space Shuttle Main Engine.
The demands of the project pushed the development of practical hypersonic technology in a number of areas. Hot structures required industrial shops in which Inconel X could be welded, machined, and heat-treated. The pilot required a pressure suit for use in a vacuum. The X-15 required new instruments and data systems including the “Q-ball,” which determined the true direction of airflow at the nose. Cooled by nitrogen, the “Q-ball” operated at temperatures of up to 3,500 degrees Fahrenheit and advised the pilot of the angle of attack suitable for a safe reentry [Ibid., pp. 157-159; AAS History Series, vol. 8, p. 306; Miller, X-Planes, p. 110].
Like the Navaho, the X-15 also spurred the rise of people and institutions that were to make their mark in subsequent years. At NACA-Langley, the X15 combined with the rocket flights of PARD to put an important focus on hypersonics and hypervelocity flight. Leaders in this work included such veterans as Robert Gilruth, Maxime Faget, and Charles Donlan [NASA SP-4308; see index references]. A few years later, these researchers parlayed their expertise into leadership in the new field of piloted space missions. In addition to this, part of NACA-Langley split off to establish the new Manned Spacecraft Center in Houston as NASA’s principal base for piloted space flight. Gilruth headed that center during the Apollo years, while Faget, who had participated in Becker’s 1954 X-15 feasibility study, became a leading designer of piloted spacecraft [NASA SP-4307; see index references].
The X-15 program brought others to the forefront as well. At NAA the vice president of the program, Harrison “Stormy” Storms, became president of that company’s Space Division in 1960. While Gilruth was running the Manned Spacecraft Center, Storms had full responsibility for his division’s elements of Apollo: the piloted spacecraft and the second stage of the Saturn
V Moon rocket [resume of Harrison A. Storms]. In addition to this, Neil Armstrong, the first man to set foot on the Moon, was among the test pilots of the X-15 [Miller, X-Planes, p. 108].
Lifting Bodies: Wingless Winged Rockets
Although the X-15 emerged as a winged rocket par excellence, an alternate viewpoint held that future rocket craft of this type could have many of the advantages of wings without actually having any of these structures. Such craft would take shape as “lifting bodies,” wingless and bathtub-shaped craft that were able to generate lift with the fuselage. This would allow them to glide to a landing. At the same time, such craft would dispense with the weight of wings, and with their need for thermal protection.
How can a bathtub generate lift, and fly? Lift is force that is generated when the aerodynamic pressure is greater below an aircraft than above it. Wings achieve this through careful attention to their shape; a properly-shaped aircraft body can do this as well. The difference is that wings produce little drag, whereas lifting bodies produce a great deal of drag. Hence the lifting body approach is unsuitable for such uses as commercial aviation, where designers of airliners seek the lowest possible drag. Space flight, however, is another matter.
The lifting body concept can be traced back to the work of H. Julian Allen and Alfred Eggers, at NACA’s Ames Aeronautical Laboratory near San Francisco. Allen developed the blunt-body concept for a missile’s nose cone, shaping it with help from Eggers. They then considered that a reentering body, while remaining blunt to reduce the heat load, might have a form that
would give lift, thus allowing it to maneuver at hypersonic speeds. The 1957 M-1 featured a blunt-nose cone with a flattened top. While it had some capacity for hypersonic maneuverability, it could not glide subsonically or land horizontally. It was hoped that a new shape, the M-2, would do these things as well. Fitted with two large vertical fins for stability, it was a basic configuration suitable for further research [Hallion, ed., Hypersonic, pp. 529, 535, 864-866].
Beginning in 1959, a separate line of development took shape within the Flight Dynamics Laboratory of Wright-Patterson Air Force Base. The program that developed sought to advance beyond the X-15 by building small hypersonic gliders, which would study the performance of advanced hot structures at speeds of up to 13,000 miles per hour, three-fourths of orbital velocity. This program was called ASSET—Aerothermodynamic/elastic Structural Systems Environmental Tests [Ibid., pp. 449-450, 505].
The program went forward rapidly by remaining small. The project’s manager, Charles Cosenza, directed it with a staff of four engineers plus a secretary, with 17 other engineers at Wright-Patterson providing support [Ibid., p. 459]. In April 1961, the Air Force awarded a contract to McDonnell Aircraft Corp. for development of the ASSET vehicle. McDonnell was already building the small piloted capsules of Project Mercury; the ASSET vehicle was also small, with a length of less than six feet. Not a true lifting body, it sported two tiny and highly-swept delta wings. Its bottom, which would receive the most heat, was a flat triangle. For thermal protection, this triangle was covered with panels of columbium and molybdenum. These would radiate away the heat, while withstanding temperatures up to 3,000 degrees Fahrenheit. The nose was made of zirconium oxide that would deal with temperatures of up to 4,000 degrees [Ibid., pp. 451, 452, 464-469].
ASSET’s use of metallic shingle-like panels as thermal protection permitted use of individual panels for specific experiments. (U.S. Air Force)
Beginning in September 1963 and continuing for a year and a half, five of the six ASSET launches were successful. They used Thor and Thor-Delta launch vehicles, the latter being a two-stage rocket that could reach higher velocities. The boosters lofted their ASSETs to altitudes of about 200,000 feet. The spacecraft then would commence long hypersonic glides with ranges as great as 2,300 nautical miles. Onboard instruments
transmitted data on temperature and heat flow. The craft were equipped to float following splashdown; one of them actually did this, permitting direct study of an advanced hot structure that had survived baptism by fire [Ibid., pp. 504-519].
The success of ASSET led to the development of Project PRIME—Precision Recovery Including Maneuvering Entry. Beginning in late 1964, the contract for this Air Force project went to the Martin Co., where interest in lifting bodies had flourished for several years. Unlike ASSET, PRIME featured true lifting bodies, teardrop-shaped and fitted with fins. PRIME was slated to ride the Atlas, which was more powerful than the Thor-Delta and could reach near-orbital speeds [Hallion, Path, pp. 30-31].
Whereas ASSET had executed simple hypersonic glides, PRIME carried out the more complex maneuver of achieving crossrange, namely, flying far to the left or right of its flight path. Indeed, to demonstrate such reentry maneuvering was its reason for being. PRIME did not attempt to produce data on heating, for ASSET had covered this point nicely, nor did it break new ground in its construction. Slightly larger than ASSET, it used a conventional approach for missile nose cones that featured an aluminum structure covered with a thermally-protective “ablative” layer that would carry away heat by vaporizing in a controlled fashion during reentry. The ablative material also served as insulation to protect the underlying aluminum.
With its peak speed topping 17,000 mph, PRIME could bridge the Pacific, flying from Vandenberg Air Force Base in California to Kwajalein, not far from New Guinea. In April 1967, during its best performance, PRIME achieved a crossrange of 710 miles, puting it within five miles of its target. A waiting recovery plane snatched PRIME in mid-air as it descended by parachute [Hallion, ed., Hypersonic, pp. V-ii, V-iv, 702-703].
ASSET and PRIME demonstrated the value of lifting bodies at the hypersonic end of the flight path: gliding, maneuvering, surviving reentry using
advanced hot structures. Both types of craft, however, used parachutes for final descent, making no attempt to land like conventional aircraft. If lifting bodies were to truly have merit, they would have to glide successfully not only at hypersonic speeds but at the slow speed of an aircraft on a final approach to a runway. Under the control of a pilot, lifting bodies would have to maintain stable flight all the way to a horizontal touchdown.
These requirements led to a second round of lifting-body projects focusing on approach and landing. These projects went forward with ASSET and PRIME at the same time. R. Dale Reed, the initiator of this second round of projects, was a sailplane enthusiast, a builder of radio-controlled model air planes, and a NASA engineer at Edwards Air Force Base. He had followed with interest the work at NASA-Ames on the M-2 lifting-body shape, and he resolved to build it as a piloted glider. He drew support from the local community of aircraft homebuilders. Designated as the M2-F1, the aircraft was built of plywood over a tubular steel frame. Completed in early 1963, the aircraft was 20 feet long and 13 feet across.
The homebuilt M2-F1 lifting body, left, and the Northrop M2-F2. (NASA)(E-14339)
The M2-F 1 needed a vehicle that could tow it along the ground to help get it into the air for initial tests. The M2-F1, however, produced a lot of drag and needed a tow car with more power than NASA’s usual vans and trucks. Reed and his friends bought a stripped-down Pontiac with a big engine and a four-barrel carburetor that could reach speeds of 110 mph. The car was turned over to a funny car shop in Long Beach for modification. Like any other flight-line vehicle it was sprayed yellow and “National Aeronautics and Space Administration” was added on its side. Initial piloted tow tests showed reasonable success, allowing the project to use a C-47, called the Gooney Bird, for true aerial tests. During these tests, the Gooney Bird towed the M2-F1 above 10,000 feet, then set it loose to glide to an Edwards AFB lake bed. Beginning in August 1963, the test pilot Milt Thompson did this repeatedly. Through these tests, Reed, working on a shoestring budget, showed that the M2 shape, optimized for hypersonic reentry, could glide down to a safe landing.
During much of this effort, Reed had support from the NASA director at Edwards, Paul Bikle. As early as April 1963, he alerted NASA Headquarters that “the lifting-body concept looks even better to us as we get more into it.” The success of the M2-F1 spurred interest in the Air Force as well, as some of its officials, along with their NASA counterparts, set out to pursue piloted lifting-body programs that would call for more than plywood and funny cars [NASA SP-4303, pp. 148-152].
NASA contracted with the firm of Northrop to build two such aircraft, the M2-F2 and HL-10. The M2-F2 amounted to an M2-Fl built to NASA standards; the HL-10 drew on an alternate lifting-body design by Eugene Love of NASA-Langley. This meant that both NASA-Langley and NASA-Ames would each have a project. In addition to this, Northrop had a penchant for oddly-shaped aircraft. During the 1940s, the company had built flying wings that essentially were aircraft without a fuselage or tail. With these lifting bodies, Northrop would build craft now that were entirely fuselage and lacked wings. The Air Force project, the X-24A, went to Martin Co., which built it as a piloted counterpart of PRIME, maintaining the same shape [Hallion, Path, pp. 29, 31-32].
Martin Marietta’s X-24A. Built for subsonic flight, it duplicated the shape of PRIME, which flew at near-orbital velocity. (NASA)(E-18769)
All three flew initially as gliders, with a B-52 rather than a C-47 as the mother ship. The B-52 could reach 45,000 feet and 500 mph, four times the
altitude and speed of the old Gooney Bird [Miller, X-Planes, p. 153]. It had routinely carried the X15 aloft, acting as a booster for that rocket plane; now it would do the same for the lifting bodies. Their shapes differed, and as with the M2-F1, a major goal was to show that they could maintain stable flight while gliding, land safely, and exhibit acceptable pilot handling qualities [Ibid., p. 151; NASA SP-4303, p. 153].
These goals were not always met. Under the best of circumstances, a lifting body flew like a brick at low speed. Lowering the landing gear made the problem worse by adding drag. In May 1967, the test pilot Bruce Peterson, flying the M2-F2, failed to get his gear down in time. The aircraft hit the lake bed at more than 250 mph, rolled over six times, and then came to rest on its back, minus its cockpit canopy, main landing gear, and right vertical fin. Peterson, who might have died in the crash, got away with a skull fracture, a mangled face, and the loss of an eye. While surgeons reconstructed his face and returned him to active duty, the M2-F2 needed surgery of its own. In addition to an extensive reconstruction back at the factory, Northrop engineers added a third vertical fin that improved its handling qualities and made it safer to fly. Similarly, while the rival HL-10 had its own problems of stability, it flew and landed well after receiving modifications [NASA SP-4303, pp. 159, 161-162; Spaceflight, vol. 21, (1979), pp. 487-489].
These aircraft were mounted with small rocket engines that allowed acceleration to supersonic speeds. This made it possible to test stability and handling qualities when flying close to the speed of sound. The HL-10 set records for lifting bodies by making safe approaches and landings from speeds up to Mach 1.86 and altitudes of 90,000 feet [NASA SP-4303, p. 162]. The Air Force continued this work through 1975, having the Martin Co. rebuild the X-24A with a long pointed nose, a design well-suited for supersonic flight. The resulting craft, the X-24B, looked like a wingless fighter-plane fuselage. It also flew well [Miller, X-Planes, pp. 156-160].
The X-24B, a lifting body capable of supersonic flight. (NASA)(E-25283)
In contrast to the Navaho and X-15 efforts, work with lifting bodies did not create major new institutions or lead existing ones in important new directions. This work, however, did extend that of the X-15 with the hot-structure flights of ASSET and the maneuvering reentries of PRIME. The piloted lifting bodies then demonstrated that, with the appropriate arrangements of fins,
they could remain stable and well-controlled when decelerating through the sound barrier and gliding to a landing. They thus broadened the range of acceptable hypersonic shapes.
Solid-Propellant Rockets: Inexpensive Boosters
The X-15 and lifting-body programs demonstrated many elements of a reusable launch vehicle in such critical areas as propulsion, flight dynamics, structures, thermal protection, configurations, instruments, and aircraft stability and control. However, the reason for reusability would be to save money, and an airplane-like orbiter would need a low-cost booster as a first stage. During the 1950s and 1960s, the Navy, Air Force, and NASA laid groundwork for such boosters by sponsoring pathbreaking work with solid propellants.
The path to such propellants can be traced back to a struggling firm called Thiokol Chemical Corp. Its initial stock-in-trade was a liquid polysulfide polymer that took its name (Thiokol) from the Greek for “sulfur glue” and could be cured into a solvent-resistant synthetic rubber. During World War II,
it found limited use in sealing aircraft fuel tanks—a market that disappeared after 1945. Indeed, business was so slow that even small orders would draw the attention of the company president, Joseph Crosby.
When Crosby learned that California Institute of Technology (CIT) was buying five- and ten-gallon lots in a steady stream, he flew to California to investigate the reason behind the purchases. He found a group of rocket researchers, loosely affiliated with CIT, working at a place they called the Jet Propulsion Laboratory. They were mixing Crosby’s polymer with an oxidizer and adding powdered aluminum for extra energy. They were using this new propellant in ways that would make it possible to build solid-fuel rockets of particularly large size [Fortune, June 1958, p. 109].
Crosby soon realized that he too could get into the rocket business, with help from the Army. While Army officials could spare only $250,000 per year to help him get started, to Crosby this was big money. In 1950, Army Ordnance gave him a contract to build a rocket with 5,000 pounds of propellant. A year and a half later it was ready, with a sign on the side, “The Thing.” Fourteen feet long, it burned for over forty seconds and delivered a thrust of 17,000 pounds [Ibid., p. 190; Thiokol’s Aerospace Facts, July-September 1973, p. 10; Saturday Evening Post, October 1, 1960, p. 87].
The best solid propellants of the day were of the “double base” type, derived from the explosives nitroglycerine and nitrocellulose. Some versions could be cast in large sizes. These propellants, however, burned in a sudden rush, and could not deliver the strong, steady push needed for a rocket booster. The new Thiokol-based fuel emerged as the first of a type that performed well and burned at a reasonable rate. These fuels drew on polymer chemistry to form as thick mixtures resembling ketchup. Poured into a casing, they then polymerized into resilient rubbery solids [Huggett et al., Solid, pp. 125-128; Ley, Rockets, pp. 171-173, 193, 436-438; Comelisse et al., Propulsion, pp. 170-174].
The Navy also took an interest in solid propellants, initially for use in antiaircraft missiles. In 1954, a contractor in suburban Virginia, Atlantic Research, set out to achieve further performance improvements. Two company scientists, Keith Rumbel and Charles Henderson, focused their attention on the use of powdered aluminum. Other researchers had shown that propellants gave the
best performance with an aluminum mix of five percent; higher levels caused a falloff. Undiscouraged, Rumbel and Henderson decided to try mixing in really large amounts. The exhaust velocity, which determines the performance of a rocket, took a sharp leap upward. By early 1956, they confirmed this discovery with test firings. Their exhaust velocities, 7,400 feet per second and greater, compared well with those of liquid fuels such as kerosene and liquid oxygen [Baar and Howard, Polaris!, pp. 31-32].
By then the Navy was preparing to proceed with Polaris, a program that sought to send strategic missiles to sea aboard submarines. Initial design concepts were unpleasantly large; a submarine would be able to carry only four such missiles, and the submarine itself would be excessive in size. The breakthrough in propellants coincided with an important advance that markedly reduced the weight of thermonuclear weapons. Lighter warheads meant smaller missiles. These developments combined to yield a solid-fueled Polaris missile that was very compact. Sixteen of them would fit into a conventional-sized submarine [Journal of Spacecraft and Rockets, vol. 15 (1978), pp. 265-278].
The new propellants, and the lightweight warheads, also drew interest within the Air Force, though its needs contrasted sharply with those of the Navy. Skippers could take time in firing undersea missiles, for a submarine could hide in the depths until it was ready for launch. Admirals, however, preferred solid fuels over liquids because they presented less of a fire hazard. While the Air Force was prepared to use liquid propellants in its ICBMs, these would take time to fuel and prepare for launch—and during that time they would lie open to enemy attack. With solid propellants, a missile could be fueled in advance and ready for instant launch. Moreover, such a missile would be robust enough to fire from an underground chamber. Prior to launch, that chamber would protect the missile against anything short of a direct nuclear hit.
Lieutenant Colonel Edward Hall, who had midwifed the birth of the Navaho during the 1940s, now played a leading role in this newest project. He was the propulsion officer on the staff of Major General Bernard Schriever who was responsible for the development of the Atlas, Titan, and Thor. Hall developed a passionate conviction that an Air Force counterpart of Polaris would offer considerable advantage in facing the Soviet ICBM capability. At the outset of the new project, he addressed the problem of constructing very large solid-fuel charges, called grains. He could not draw on the grains of the Polaris for that missile had grains of limited size.
Hall gave contracts to all of the several solid-fuel companies that were in business at that time. Thiokol’s Crosby, who had lost the Polaris contract to Aerojet General, now saw a chance to recoup. He bought a large tract of land near Brigham City, Utah, a remote area where the shattering roar of rockets would have plenty of room to die away. In November 1957, his researchers successfully fired a solid-fuel unit with 25,000 pounds of propellant, the largest to date.
Meanwhile, Hall had taken charge of a working group that developed a preliminary design for a three-stage solid-fuel ICBM. Low cost was to be its strong suit, for Hall hoped to deploy it in very large numbers. Early in 1958, with the test results from Thiokol in hand, Hall and Schriever went to the Pentagon and pitched the concept to senior officials, including the Secretary of Defense. But while that missile, named the Minuteman, might be launched on a minute’s notice, it would take most of 1958 to win high-level approval for a fast pace of development.
Barely two years later, in early 1961, the Minuteman was ready for its first flight from Cape Canaveral. It scored a brilliant success as all three stages fired and the missile flew to full range. The Air Force proceeded to raise the Minuteman to the status of a crash program. The first missiles were operational in October 1962, in time for the Cuban Missile Crisis. Because its low cost made it the first strategic weapon capable of true mass production, the Air Force went on to deploy 1,000 of the Minuteman rockets [Emme, ed., History, pp. 155-159; Neufeld, Ballistic Missiles, pp. 227-230, 237, 239; Fortune, June 1958, pp. 190-192].
Military uses of solid propellants. Left, Minuteman ICBM. Right, three generations of the Navy’s Polaris submarine-launched missile, with range up to 2500 nautical miles. Human figure indicates scale. (Art by Dan Gauthier)
The Air Force and NASA also prepared to build solid-fuel boosters of truly enormous size for use with launch vehicles. In contrast to liquid rockets that were sensitive and delicate, the big solids featured casings that a shipyard—specifically, the Sun Shipbuilding and Dry Dock Company, near Philadelphia—would manufacture successfully.
The Minuteman’s first stage had a 60-inch diameter. In August 1961, United Technology Corp. fired a 96-inch solid rocket that developed 250,000 pounds of thrust. The following year saw the first 120-inch tests—twice the diameter of the Minuteman—that reached 700,000 pounds of thrust. The next milestone was reached when the diameter was increased to 156 inches, the largest size compatible with rail transport. During 1964, both Thiokol and Lockheed Propulsion Co. fired test units that topped the million-poundthrust mark.
Large rocket stages can be moved by barges over water as well as by land.
Aerojet was building versions with 260-inch diameters. It took some doing just
to ignite such a behemoth. The answer called for a solid rocket that itself developed a quarter-million pounds of thrust, producing an eighty-foot flame that
would ignite the inner surface of the big one all at once. This igniter rocket
needed its own igniter, a solid motor that weighed a hundred pounds and generated 4,500 pounds of thrust. The 260-inch motor was kept in a test pit with its
nozzle pointing upward. In February 1966, a night firing near Miami shot flame
and smoke a mile and a half into the air that was seen nearly a 100 miles away.
In June 1967, another firing set a new record with 5.7 million pounds of thrust [Quest, Spring 1993, p. 26; Astronautics, December 1961, p. 125; November 1962, p. 81; Astronautics and Aerospace Engineering, November 1963, p. 52; Astronautics & Aeronautics, February 1965, pp. 42-43].
At NASA’s Marshall Space Flight Center, a 1965 study projected that
production costs for a 260-inch motor would run to $1.50 per pound of
weight, or roughly a dollar per pound of thrust. This contrasted sharply with the liquid-fueled Saturn V, which, with 7.5 million pounds of thrust versus 6 million for the big solid, was in the same class. Even without its Apollo moon-ship, however, the Saturn V cost $185 million to purchase, over thirty times more than the 260-inch motor. By 1966, NASA officials were looking ahead already to sizes as large as 600 inches, noting that “there is no fundamental reason to expect that motors 50 feet in diameter could not be made” [Astronautics & Aeronautics, January 1966, p. 33; NASA budget data, February 1970].
Meanwhile, the Air Force not only was testing big solids but it was preparing to use them operationally as part of the Titan program which, in a decade, had evolved from building ICBMs to assembling a launch vehicle of great power. At the outset, Titan I was a two-stage ICBM project that ran in parallel with Atlas and used similar engines in the first stage. While it was deployed as a weapon, it was never used to launch a spacecraft or satellite [Emme, ed., History, pp. 145, 147].
The subsequent Titan II represented a major upgrade as the engine contractor, Aerojet General, developed new engines that markedly increased the thrust in both stages. It too reached deployment, carrying a heavy thermonuclear warhead with a yield of nine megatons. By lightening this load somewhat, the Titan II was able to thrust a payload into orbit repeatedly. In particular, during 1965 and 1966, the Titan II carried 10 piloted Gemini spacecraft, each with two astronauts. Their weight ran above 8,300 pounds [NASA SP-4012, vol. II, pp. 83-85; Quest, Winter 1994, p. 42; Thompson, ed., Space Log, vol. 27, 1991; p. 87].
The Air Force’s Titan III-A added, to the Titan II, a third stage (the “transtage”) which enhanced its ability to carry large payloads. It never served as an ICBM, but worked as a launch vehicle from the start. In particular, it served as the core for the Titan III-C, which flanked that core with a pair of 120-inch solid boosters. The rocket that resulted had more than a casual resemblance to the eventual Space Shuttle, which would use two somewhat larger solid boosters in similar fashion. After lifting the Titan III-C with 2.36 million pounds of thrust, its boosters then fell away after burnout, leaving the core to ignite its first stage, high in the air.
Titan I ICBM; Titan II ICBM; Titan III launch vehicle. Human figure indicates scale. (Art by Dan Gauthier)
Solid rocket motor for the Titan III-C. (AIAA)
The Titan III-C had a rated payload of 23,000 pounds. NASA replaced the transtage with the more capable Centaur upper stage, which used liquid hydrogen as a high-energy fuel. This version, the Titan III-E Centaur, increased the payload to 33,000 pounds. Martin Marietta, the Titan III contractor, also proposed to delete the third stage while increasing the thrust of both the solid boosters and the core. This version, the Titan III-M, was never built, but it would have lifted a payload of 38,000 pounds [NASA SP-4012, vol. III, pp. 38-42; Quest, Fall 1995, p. 18; AAS History Series, vol. 13, pp. 19-35].
Hence during the 1960s, the X-15, ASSET, PRIME, lifting body and solid-booster efforts all combined to provide a strong basis for the Space Shuttle program. Such a program might build an orbiter in the shape of a lifting body with a hot structure for thermal protection. Piloted and crewed, it could maneuver during atmosphere entry, ride through the heat of reentry with its nose up, then transition to gliding flight and fly to a landing, perhaps at Edwards Air Force Base. Moreover, long before those early projects had reached completion (and even before some of them were underway), the Air Force set out to build a mini-shuttle that would ride a Titan III-C to orbit and then return. This project was called Dyna-Soar and, later, the X-20.
Dyna-Soar: A Failure in Evolution
During the mid-1950s, with the Bomi studies of Bell Aircraft in the background and the X-15 as an ongoing program, a number of people eagerly carried out further studies that sought to define the next project beyond the
X-15. The ideas studied included Hywards (a piloted hypersonic boost-glide research aircraft), the Robo (Robot Bomber), and two reconnaissance vehicles, the System 118-P and the Brass Bell. With so many cooks in the kitchen, the Air Force needed a coordinated program in order to produce something as specific as the X-15. Its officials were in the process of defining this program when, in October and November 1957, the Soviet Union launched the world’s first satellites. Very quickly, hypersonic flight became one of the means by which the U.S. might turn back the challenge from Moscow.
Having read the work of Sänger, hypersonic specialists knew of his ideas for skipping entry as a way to extend the range of a suborbital aircraft. The Air Force described this maneuver as “dynamic soaring.” The craft that would do this acquired the name Dyna-Soar. By early 1958, this idea was being studied seriously by a number of aeronautical contractors with the clear understanding that the Air Force intended to request proposals and build a flying prototype. In June 1958, the Air Force narrowed the competition to two contenders: Boeing and a joint Bell Aircraft and Martin Co. team [AAS History Series, vol. 17, pp. 255-259].
By then, Dyna-Soar was caught up in the first round of a controversy as to whether this craft should be the prototype of a bomber. While the powerful Air Research and Development Command (ARDC) firmly believed that Dyna-Soar should be the prototype of a piloted military spaceplane, it found it difficult to point to specific military missions that such a craft could carry out. For nuclear weapons delivery, the Air Force was already building the Atlas, Titan, and Thor. For strategic reconnaissance, the Central Intelligence Agency had launched, in 1958, a program that aimed to build automated camera-carrying satellites and put the first ones into orbit in as little as one year [Ibid., p. 260; Ruffner, ed., Corona, pp. 3-14].
Air Force Headquarters, however, with support from the Office of the Secretary of Defense, refused to consider weapon-system objectives unless ARDC could define suitable military missions. Early in 1959, Deputy Secretary of Defense Donald Quarles wrote that his approval was only “for a research and development project and did not constitute recognition of DynaSoar as a weapon system.”
In April, the Defense Director of Research and Engineering, Herbert York, made a clear statement of the program’s objectives. Its primary goal
would involve hypersonic flight up to a speed of 15,000 miles per hour, which would fall short of orbital velocity. The vehicle would be piloted, maneuverable, and capable of landing at a preselected base. York also threw a bone to ARDC, stating that it could pursue its own goal of testing military systems—provided that such tests did not detract from the primary goal. ARDC officials hastened to affirm that there would be no conflict. They promptly issued System Requirement 201, stating that Dyna-Soar would “determine the military potential of a boost-glide weapon system” [AAS History Series, vol. 17, p. 260].
In November 1959, the contract award went to Boeing. Two weeks later, the Air Force’s Assistant Secretary for Research and Development, Joseph Charyk, said “not so fast.” He was well aware that the project already faced strong criticism because of its cost, as well as from Eisenhower Administration officials who opposed space-based weapon systems. In addition to this, a number of technical specialists doubted that the concept could be made to work. Charyk therefore ordered a searching reexamination of the project that virtually re-opened the earlier competition. In April 1960, the Aerospace Vehicles Panel of the Air Force Scientific Advisory Board gave Dyna-Soar a go-ahead by approving Boeing’s design concept, with minor changes.
During the next three and a half years, the program went forward as its managers reached for higher performance. The 1960 plan called for the use of a Titan
I as the launch vehicle. Because the Titan I lacked the power to put it in orbit, the Dyna-Soar would fly suborbital missions only. Over the next year and a half, however, the choice of booster changed to the Titan II and then the powerful Titan III-C. A new plan, approved in December 1961, dropped suborbital flights and called for “the early attainment of orbital flight, with the Titan III booster.”
This plan called initially for single-orbit missions that would not require the craft to carry an onboard retro-rocket for descent from orbit Instead the booster, launched from Cape Canaveral, would place the craft on a trajectory that would re-enter the atmosphere over Australia. It then would cross the Pacific in a hypersonic glide, to land at Edwards Air Force Base. In May 1962, the plan broadened anew to include multi-orbit flights. Dyna-Soar now would ride atop the Titan III transtage that would inject it into orbit and remain attached to serve as a retro-rocket at mission’s end [Ibid., pp. 261-269].
The piloted Dyna-Soar spacecraft also emerged with highly-swept delta wings and two upturned fins at the wingtips. With a length of 35 feet, it lacked an onboard rocket engine and provided room for a single pilot only. Like ASSET, it relied on advanced hot structures, with a heat shield of columbium, well insulated, atop a main structure built from a nickel alloy that had been developed for use in jet engines [Ibid., pp. 277-279]. In September 1962, a full-scale mockup was the hit of the show at an Air Force Association convention in Las Vegas. In addition to this, the Air Force named six test pilots who would fly DynaSoar as its astronauts [Ibid., p. 269].
Mockup of Dyna-Soar displayed in 1962. (Boeing) (P-30793)
The question of military missions raised its head again when in mid-1961 the new Defense Secretary, Robert McNamara, directed the Air Force to justify Dyna-Soar on military grounds. Air Force officials discussed orbital reconnaissance, rescue, inspection of Soviet spacecraft, orbital bombardment, and use of the craft as a ferry vehicle. While McNamara found these reasons unconvincing, he nevertheless remained willing to let the program proceed as a research effort, dropping all consideration of a possible use of the craft as a weapon system. In an October 1961 memo to President Kennedy, McNamara proposed to “re-orient the program to solve the difficult technical problem involved in boosting a body of high lift into orbit, sustaining man in it and recovering the vehicle at a designated place” [Spaceflight, vol. 21 (1979), pp. 436-438].
This reorientation gave the project another two years of life. With its new role as an experimental craft, it was designated by Air Force Headquarters as the X-20. In this new role, however, the program could not rely on a military justification; it would have to stand on its value as research. By 1963, this value was increasingly in question. ASSET, with its unpiloted craft, was promising to demonstrate hypersonic gliding entry and hot-structure technology at far lower cost. In the realm of piloted flight, NASA now was charging ahead with its Gemini program. Air Force officials were expecting to participate in this program as well.
These officials still believed that their service in time would build piloted spacecraft for military purposes. In March 1963, McNamara ordered a study that would seek to determine whether Gemini or the X-20 could better serve the role of a testbed for military missions. The results of the study gave no clear reason to prefer the latter.
In October, Air Force officials, briefing the President’s Scientific Advisory Committee, encountered skepticism in this quarter as well. Two weeks later, McNamara and other senior officials received their own briefing. McNamara asked what the Air Force intended to do with the X-20 after using it to demonstrate maneuvering reentry. He insisted he could not justify continuing the project if it was a dead-end program with no ultimate purpose.
He canceled the program in December, stating that the purpose of the program had been to demonstrate maneuvering reentry and precision landing. The X-20 was not to serve as a cargo rocket, could not carry substantial pay
loads, and could not stay in orbit for long-duration missions. He could not justify continuing with the program because it was costly and would serve “a very narrow objective” [AAS History Series, vol. 17, pp. 271-275].
At that moment, the program, well past the stage of paper studies, called for the production of 10 X-20 vehicles. Boeing had completed nearly 42 percent of the necessary tasks. While McNamara’s decision drew hot criticism, he had support where it counted; the X-20 did not. Eugene Zuckert, the Air Force Secretary, continued to endorse the program to the end, but the project had little additional support among the Pentagon’s civilian secretaries. In the Air Force, the Space Systems Division (SSD) was to conduct pilot training and carry out the flights. Support for the X-20, however, was lukewarm both at the SSD and at Aerospace Corp., its source of technical advice. General Bernard Schriever, commander of the ARDC [redesignated Air Force Systems Command in 1961], was also lukewarm. So was his deputy commander for aerospace systems, Lieutenant General Howell Estes [Ibid., p. 275; Hallion, ed., Hypersonic, p. II-xvii].
This was the life and death of the Dyna-Soar. From its demise one can draw several conclusions. By 1963, the program’s technical feasibility was no longer in question; it was just a matter of putting the pieces together. Although aerospace vehicles were continuing to evolve at a rapid pace, no technical imperative existed that could call the X-20 into existence. The program needed a mission, a justification sufficiently compelling to win political support from high-level officials. Dyna-Soar demonstrated that even though the means were in hand to pursue the development of a vehicle resembling the Space Shuttle, such a project would stand or fall on its merits. To be built, it would require a reason capable of attracting and winning endorsement from presidential appointees and other leaders at the highest levels.