Though almost unknown today, the X-20A Dyna-Soar can rightly be considered the "grandfather" of the space shuttle. The story begins in 1957, shortly after the success of Sputnik, when the U.S. Air Force set out to build a vehicle capable of repairing satellites, spying on enemy territory, destroying missiles in flight, and — naturally — carrying out surprise nuclear attacks on the then-dismantled USSR. This is the story of the Dyna-Soar, the first spaceplane designed to be reused like a conventional aircraft.
The Birth of an Idea
At the dawn of the Cold War, almost at the same time the Russians launched the first satellite into space, Americans gathered at a conference on hypersonic flight held at the Ames Center in October 1957. They pondered building a very special aircraft: a reusable one that could go into space, perform various tasks related to the nascent aerospace and defense industry, and return to Earth ready for another mission. The future vehicle was named X-20A Dyna-Soar (for Dynamic Soaring), which in English sounds almost like "dinosaur." Its design drew on several earlier projects, such as the Silbervogel intercontinental bomber conceived by Austrian Eugen Sänger in 1934.
A Multitude of Missions
The new craft had to be able to carry out photographic reconnaissance over enemy territory from a height that kept it safe from hostile missiles. The possibility of repairing one's own satellites (or destroying the enemy's) in orbit, along with the advantage of a vehicle that could drop nuclear bombs on the USSR with only three minutes' notice (compared to more than 20 minutes' "advantage" provided by ICBMs), created dreams among the generals of the time. Oddly enough, this great versatility—ultimately seen as a complete lack of a clear objective—was what ended up canceling the Dyna-Soar project years later.
Official Development
Engineers began work on the design, and on December 21, 1957, the USAF issued Directive N464L, detailing the steps needed to develop the X-20A. According to this document, several tests with scaled prototypes performing unmanned suborbital flights would be needed before reaching space. Only when these trials were complete would they attempt the first manned orbital launches. The lack of precedents misled engineers, who initially believed it was a relatively simple challenge and that within a few years the huge budget of the U.S. Air Force would allow them to field a fleet of Dyna-Soars. Time would prove just how wrong they were.
Engineering Obstacles
One of the first problems was designing an aerodynamic shape able to withstand a plunge into the atmosphere at more than 28,000 kilometers per hour. Apart from ICBMs, they had never considered anything like it. The design also had to allow the X-20A to maneuver at that speed in the upper atmosphere and withstand the extremely high temperatures from atmospheric friction. When the project was officially approved in early 1958, the companies that normally built such toys for the government (North American, Convair, General Electric, Lockheed, Martin Marietta, Boeing, Northrop, etc.) began working on proposals, hoping to land a contract promising billions.
Although they all designed very similar aircraft, the finalists in the race to win the responsibility of building prototypes were Bell-Martin and Boeing-Vought. Interestingly, Bell's design closely resembled the space shuttle that would be built some 25 years later, but in November 1959, after analyzing the two proposals, the government chose Boeing's design. On December 11, contracts were signed, and Dyna-Soar officially became USAF Program 620A. Among other things, it was agreed that the newly created National Aeronautics and Space Administration (NASA) would participate, since the X-20A would be capable of orbital missions.
The Dyna-Soar in Detail
The Dyna-Soar's characteristics, compared with the space shuttle's, were very modest. It would be a single-seat craft, just over 10 meters long and weighing 5,000 kilograms. Its wings, with a span of just over 6 meters, would be delta-shaped with an angle of about 72 degrees. It would fly at more than 28,000 kilometers per hour and be able to land on any U.S. military runway. A set of "skis" on the landing gear would even allow emergency landings on any flat terrain. Its payload capacity did not reach 500 kilograms and was placed in a compartment behind the pilot's cabin. Launch would be on a Titan IIIC rocket, whose third stage, loaded with about 5,700 kilograms of fuel usable during orbital maneuvers, would remain attached to the X-20A while in space. Small hydrogen peroxide thrusters, similar to those used to orient satellites, would permit maneuvering during reentry. Everything was ready to begin work.
Testing and Cancellation
Initial tests showed that building the Dyna-Soar would not be easy. The extremely streamlined designs that worked well at high speeds were inefficient at reducing heat generation during reentry. The "thermal shield" required for the aircraft proved a real challenge, and ultimately the X-20A took on relatively rounded shapes, able to withstand about 2,400°C, far more than the 1,650°C the shuttle can resist. Alloys of steel and molybdenum ensured vibrations would not destroy the craft, and the pilot and payload would never experience temperatures above 45°C. During reentry, the graphite and zirconium shield covering part of the forward windows would detach when the craft reached a speed of 7,000 kilometers per hour, to facilitate landing. In early 1960, quite behind schedule, testing of the materials for the thermal shield began.
Test flights were conducted by dropping prototypes from a B-52, verifying the craft's subsonic aerodynamic characteristics. However, just as they were about to begin tests with manned prototypes and after spending about $550 million on the project, Secretary of Defense Robert McNamara officially canceled the Dyna-Soar development. It was December 1963, and only some components of the X-20A survived the cancellation, such as parts of the X-15 rocket plane.
A Controversial End
Was it a mistake to cancel the program? Opinions are sharply divided. While it's true the Dyna-Soar could have given NASA a reusable orbital vehicle 15 years before the "birth" of the space shuttle, the constant delays and rising estimated costs would very likely have forced a cancellation anyway. Certainly, history would not have been much different.
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