The story of the Dyna-Soar
It is July 1966. At Cape Canaveral Air Force Station in Florida, a 41-year-old test pilot named Jim Wood is moments away from becoming Americaâ€™s 17th man in space.
Alone, pressure-suited and tightly strapped into the tiny cockpit of a stubby winged ship called â€˜Dyna-Soarâ€™, he will shortly be boosted by a Titan IIIC rocket onto a suborbital trajectory to evaluate the worldâ€™s first reusable manned spacecraft.
It was a precocious forerunner of the Shuttle and, indeed, had it flown, many observers believe it could have revolutionised â€“ perhaps even routinised â€“ todayâ€™s space travel.
Woodâ€™s mission, sadly, never happened. Nor did Dyna-Soar itself reach fruition, although at the time of its cancellation in December 1963 it was supposedly just eight months away from performing a series of airborne drop-tests from a modified B-52 bomber. Much criticism has been levelled at then-Defence Secretary Robert McNamara, accusing him of poor judgement in killing a project so near to completion and whose contractors had already spent nearly half of its $530 million development budget. To be fair, though, Dyna-Soar faced immense problems of its own: one of the most important of which was its own, ill-defined purpose.
The spacecraft was viewed from two different perspectives during its genesis in the late Fifties: as a research vehicle to explore hypersonic flight regimes or, as the US Air Force preferred, as a fully-functional military glider capable of delivering live warheads with precise, pilot-guided accuracy onto targets anywhere on Earth. Ambitious plans were even afoot for the inspection, and maybe destruction, of enemy satellites in orbit, as well as carriage of reconnaissance cameras, side-looking radar and electronic-intelligence sensors. Assuming a manned flight sometime in 1966, it was hoped that Dyna-Soar would evolve into this operational weapons-delivery system by the mid-Seventies.
This would offer military strategists a route around the problem that conventional ballistic missiles might no longer be able to strike hardened targets with the required accuracy. Moreover, a â€˜boost-glideâ€™ flight profile like that of Dyna-Soar â€“ able to cover velocities between Mach 5 and 25 â€“ was perceived as a better alternative to using complex, air-breathing turbojet or ramjet engines, which were difficult to develop and could only operate at lower speed ranges. Indeed, according to studies conducted by the Rand Corporation, vehicles flying slower than Mach 9 might be rendered vulnerable to Soviet air defences as early as 1965â€¦
In the most paranoid days of the Cold War, Dyna-Soar thus provided the United States with a safe and seemingly-invincible means of attacking and snooping on enemy targets from any direction and, when flying at low altitudes, gave barely a three-minute warning of its arrival. Additionally, it could sweep across Soviet territory at altitudes of between 25-50 miles, providing much better imaging resolution than was possible with the best spy satellites and its data could be in the hands of Pentagon officials within a matter of hours.
Size-wise, this astonishing machine was about a third as large as todayâ€™s Shuttle: some 35 feet long, with a wingspan of 20 feet. Powered by a Martin-built â€˜trans-stageâ€™ engine â€“ capable of 72,000 pounds of thrust â€“ it would have ridden into space atop the Titan IIIC rocket. This choice of launch vehicle changed significantly as Dyna-Soarâ€™s own purpose fluctuated. â€œIt was originally scheduled to be launched on the Titan I,â€ said astronaut Neil Armstrong, one of its original pilots, â€œ[then] when the Titan III was introduced, with additional [solid] rocket engines strapped on the side, it [became] an orbital vehicleâ€.
Armstrong left the project in the summer of 1962 to join NASAâ€™s astronaut corps and, in an interview four decades later, revealed that Dyna-Soarâ€™s main aim was for hypersonic research â€“ hence its acronym: the â€˜dynamic soarerâ€™. Its 72.48-degree delta wings were flat-bottomed and its aft fuselage â€˜rampedâ€™ to give directional stability at transonic speeds. This provided a sufficient hypersonic lift-to-drag ratio to permit a cross-range capability of around 2,000 miles; in other words, a diverted landing from Edwards Air Force Base in California meant it could touchdown anywhere in the continental United States, Japan or even Ecuador.
In fact, thanks to a unique set of wire-brush â€˜skidsâ€™, it could even land on compacted-earth runways little more than a mile long. Typically, it would have been launched from Cape Canaveral by the Titan IIIC, then remained attached to the rocketâ€™s third and final stage. This would have acted as a restartable â€˜trans-stageâ€™, capable not only of inserting Dyna-Soar into a 90-mile-high orbit, but also adjusting its altitude and inclination. The trans-stage could boost its velocity by an additional 3,500 miles, thus frustrating ground-based efforts to predict its overflight path during bombing or spying missions.
Emergency aborts during a Dyna-Soar launch, however, did not fill Neil Armstrong with great confidence. â€œThere was a question [of] what kind of abort technique would be practical to try to use in case there was a problem with the Titan,â€ he said in September 2001. â€œIt was determined [that] rather than a â€˜pullerâ€™ rocket, [we had a] â€˜pusherâ€™ rocket to push the spacecraft up to flying speed from which it could make a landing, but it wasnâ€™t known at that time what might be practical, how much thrust would be needed and how much performance would be needed.
â€œWe had the F5D [Stingray] aircraft, which I determined could be configured to have a similar glide angle â€“ or lift-to-drag ratio â€“ to the Dyna-Soar for similar flight conditions and devise a way of flying the aircraft to the point at which the pusher escape rocket would burn out, so you would start with the identical flight conditions that the Dyna-Soar would find itself [in] after a rocket abort from the launch pad. Thenâ€¦you only had to work out a way to find your way to the runway and make a successful landing.
â€œI worked on that project for a time and found a technique that would allow us to launch from the pad at Cape Canaveral and make a landing on the [old] skid strip. We practiced that and I believe that [NASA test pilots] Bill Dana and Milt Thompson both continued after I transferred from Edwards to Houston. There was a NASA report written about the technique. It was a practical method. I wouldnâ€™t like to have to really do it in a real Dyna-Soar!â€
During its development, the Air Force also hoped to conduct â€˜synergisticâ€™ exercises in which the spacecraft could dip into the upper atmosphere, employ its aerodynamic manoeuverability to change inclination and refire the trans-stage to boost itself back into orbit. This tricky task was provisionally pencilled-in for the fifth manned test, sometime in the spring of 1967, after which pilots would begin evaluating its precision-landing capabilities. In the event of trans-stage problems, a solid-fuelled abort motor, derived from the Minuteman missile, was attached to Dyna-Soar and would have separated the pair, performed an emergency retrofire and initiated re-entry.
On the other hand, assuming that a successful mission had been completed, the trans-stage would be ordinarily jettisoned over the Indian Ocean and the spacecraft would commence its long glide back through the atmosphere to touchdown at Edwards. Later missions, intended to complete two or even three Earth orbits, were expected to fly at still-higher altitudes of around 115 miles. During each re-entry, the pilots would test Dyna-Soarâ€™s controllability at various pitch angles during a range of hypersonic and thermal flight regimes.
It was not, however, completely controllable by its pilot throughout the entire speed range and a fly-by-wire augmentation system was provided to run in four separate automatic modes. A side-arm controller offered him the ability to perform pitch and roll inputs and, through conventional pedals, to execute yaw manoeuvres; he could even manually fly the Titan IIIC during part of its initial boost in orbit! Throughout re-entry, the guidance computer â€“ capable of storing up to ten airfield locations â€“ would have provided continuous updates on Dyna-Soarâ€™s display to advise on issues such as angle-of-attack, banking angles and vehicle structural limitations.
Physically, the spacecraft was based on a Rene 41 steel truss, which compensated for thermal expansion within the heated airframe during the re-entry phase. Dyna-Soar was roughly divided into four parts: a pilotâ€™s cockpit, pressurised central section and two unpressurised equipment bays. Each internal compartment was encased in a â€˜water wallâ€™ to offer passive cooling during re-entry, allowing their pressure shells to be constructed from conventional aluminium. Additional cooling within each compartment brought temperatures down still further to around 46 Celsius.
In order to withstand the fiery plunge into the atmosphere, Dyna-Soarâ€™s belly and wing leading edges were coated with molybdenum and its nosecap tipped with zirconium. Theoretical predictions expected the wing edges to reach temperatures of 1,550 Celsius, the nosecap around 2,000 Celsius and the belly some 1,340 Celsius during the most extreme re-entry profiles. During all flight phases, the pilot had clear views through two side windows, but the three-piece forward windshield was covered during ascent, orbital operations and most of re-entry. One can almost imagine the pilotâ€™s unusual â€˜sidewaysâ€™ perspective of re-entry during his fiery descent Earthwardâ€¦
Interestingly, the cover â€“ which guarded against thermal extremes â€“ was not scheduled to be blown off until Dyna-Soar reached a speed of Mach 6, just in time for landing. Tests conducted by Neil Armstrong in the modified Stingray fighter, however, showed that, in the dire eventuality that the cover failed to jettison properly, landings could be safely performed using only the two side windows for visibility. Clearly, this was far from ideal and stands testament to the flying skills of the men chosen to fly Dyna-Soar: Wood, Armstrong, William â€˜Peteâ€™ Knight, Milt Thompson, Al Crews, Hank Gordon and Russell Rogers.
The cockpit in which each of these pilots would have sat provided all the instrumentation and life-support equipment needed to fly the vehicle, together with an ejection seat which could only be used at subsonic speeds. Behind the cockpit, the central section â€“ pressurised with 100% nitrogen â€“ would have carried a 990-pound instrumentation package, fitted with data recorders for more than 750 temperature, pressure, loads, systems performance, pilot biometrics and heat flux sensors. Finally, at the rear of Dyna-Soar were the equipment bays, containing liquid hydrogen and nitrogen supplies, hydrogen peroxide propellant tanks and power system controls.
The leading contenders for building the spacecraft in the late Fifties were Bell and Boeing, both of which offered the capability to cover the entire requirement range from low-Mach speeds to orbital velocity using a single vehicle. Ultimately, despite Bellâ€™s expertise in designing winged spacecraft of this type, Boeing was chosen as Dyna-Soarâ€™s prime contractor in June 1959. Original plans called for three â€˜wavesâ€™ of operations: a series of suborbital flight tests, followed by orbital and eventually operational weapons-delivery missions.
By the autumn of 1962, critical design reviews of Dyna-Soarâ€™s subsystems had been completed and significant breakthroughs achieved in high-temperature materials and fabrication of components for the â€˜realâ€™ airframe. Publicly, it seemed worth the wait. When a mockup of the spacecraft rolled-out for display at Las Vegas in September of that year, it quickly grabbed the imagination of America. Writing in Readerâ€™s Digest after the event, John Hubbel described it as looking â€œlike a cross between a porpoise and a manta rayâ€ and enthused that Dyna-Soar was one of the most important aviation triumphs since the Wright Brothersâ€™ first flight.
Many others agreed with him. The Mercury capsules seen thus far were blunt and uninspiring in comparison to this sleek spaceplane of the future. Despite the public adoration of Dyna-Soar, however, the project was in serious trouble during this time and barely a few months away from cancellation.
Robert McNamara had already expressed serious concerns that it lacked direction or specific purpose â€“ the Department of Defense regarded it as a hypersonic research vehicle, the Air Force as a strategic bomber â€“ and very little attention had been paid to precisely what missions it would undertake. He made his opinions clear during a series of reviews of the project during the course of 1963, before ultimately cancelling it before the yearâ€™s end in favour of a space station called the Manned Orbiting Laboratory. Ultimately that, too, wasted millions of dollars and never reached fruition.
More than four decades later, Dyna-Soar is recognised as an ambitious, far-sighted endeavour, literally at the cutting-edge of the technology of its day. Its legacy remains visible in many elements of the Shuttleâ€™s design and capabilities â€“ from the concept of the â€˜rocket-gliderâ€™ to the payload bay, from landing on pre-determined runways to its reusability â€“ and its extensive wind-tunnel testing provided valuable engineering data for later projects. In the words of a recent NASA study of the X-planes, of which Dyna-Soar was one, â€œvery few vehicles have contributed more to the science of high-speed flight â€“ especially vehicles that were never built!â€
NASAspaceflight.com Features writer Ben Evans is the author of the newly released Springer Praxis publication ‘Space Shuttle Columbia – Her Missions and Crews.’
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