The Boeing X-20 Dyna-Soar ("Dynamic Soarer") was a United States Air Force (USAF) program to develop a spaceplane that could be used for a variety of military missions, including aerial reconnaissance, bombing, space rescue, satellite maintenance, and as a space interceptor to sabotage enemy satellites. The program ran from 24 October 1957, to 10 December 1963, cost US$660 million ($6.94 billion in 2024 dollars), and was cancelled just after spacecraft construction had begun.
Other spacecraft under development at the time, such as Mercury or Vostok, were space capsules with ballistic re-entry profiles that ended in a landing under a parachute. Dyna-Soar was more like an aircraft. It could travel to distant targets at the speed of an intercontinental ballistic missile, was designed to glide to Earth like an aircraft under the control of a pilot, and could land at an airfield. Dyna-Soar could also reach Earth orbit, like conventional, crewed space capsules.
These characteristics made Dyna-Soar a far more advanced concept than other human spaceflight missions of the period. Research into a spaceplane was realized much later in other reusable spacecraft such as the 1981–2011 Space Shuttle and the more recent Boeing X-40 and X-37B spacecraft.
The concept underlying the X-20 was developed in Germany during World War II by Eugen Sänger and Irene Bredt as part of the 1941 Silbervogel proposal. This was a design for a rocket-powered bomber able to attack New York City from bases in Germany and then fly on for landing somewhere in the Pacific Ocean held by the Empire of Japan. The idea would be to use the vehicle's wings to generate lift and pull up into a new ballistic trajectory, exiting the atmosphere again and giving the vehicle time to cool off between the skips. After the war, it was demonstrated that the heating load during the skips was much higher than initially calculated and would have melted the spacecraft.
Following the war, many German scientists were taken to the United States by the Office of Strategic Services's Operation Paperclip, bringing with them detailed knowledge of the Silbervogel project. Among them, Walter Dornberger and Krafft Ehricke moved to Bell Aircraft, where, in 1952, they proposed what was essentially a vertical launch version of Silbervogel known as the "Bomber Missile", or "BoMi".
These studies all proposed various rocket-powered vehicles that could travel vast distances by gliding after being boosted to high speed and altitude by a rocket stage. The rocket booster would place the vehicle onto a suborbital, but exoatmospheric, trajectory, resulting in a brief spaceflight followed by re-entry into the atmosphere. Instead of a full re-entry and landing, the vehicle would use the lift from its wings to redirect its glide angle upward, trading horizontal velocity for vertical velocity. In this way, the vehicle would be "bounced" back into space again. This skip-glide method would repeat until the speed was low enough that the pilot of the vehicle would need to pick a landing spot and glide the vehicle to a landing. This use of hypersonic atmospheric lift meant that the vehicle could greatly extend its range over a ballistic trajectory using the same rocket booster.
There was enough interest in BoMi that by 1956 it had evolved into three separate programs:
RoBo (Rocket Bomber), an updated version of BoMi
Brass Bell, a long-range reconnaissance vehicle
Hywards (Hypersonic Weapons Research and Development Supporting system), a smaller prototype system to develop the technologies needed for Robo and Brass Bell
Days after the launch of Sputnik 1 on 4 October 1957, on either 10 October or 24 October, the USAF Air Research and Development Command (ARDC) consolidated Hywards, Brass Bell, and Robo studies into the Dyna-Soar project, or Weapons System 464L, with a three-step abbreviated development plan. The proposal drew together the existing boost-glide proposals into a single vehicle designed to carry out all the bombing and reconnaissance tasks examined by the earlier studies, and would act as successor to the X-15 research program.
The three stages of the Dyna-Soar program were to be a research vehicle (Dyna-Soar I), a reconnaissance vehicle (Dyna-Soar II, previously Brass Bell), and a vehicle that added strategic bombing capability (Dyna-Soar III, previously Robo). The first glide tests for Dyna-Soar I were expected to be carried out in 1963, followed by powered flights, reaching Mach 18, the following year. A robotic glide missile was to be deployed in 1968, with the fully operational weapons system (Dyna-Soar III) expected by 1974.
In March 1958, nine U.S. aerospace companies tendered for the Dyna-Soar contract. Of these, the field was narrowed to proposals from Bell and Boeing. Even though Bell had the advantage of six years' worth of design studies, the contract for the spaceplane was awarded to Boeing in June 1959 (by which time their original design had changed markedly and now closely resembled what Bell had submitted). In late 1961, the Titan III was chosen as the launch vehicle. The Dyna-Soar was to be launched from Cape Canaveral Air Force Station, Florida.
The overall design of the X-20 Dyna-Soar was outlined in March 1960. It had a low-wing delta shape, with winglets for control rather than a more conventional tail. The framework of the craft was to be made from the René 41 super alloy, as were the upper surface panels. The bottom surface was to be made from molybdenum sheets placed over insulated René 41, while the nose-cone was to be made from graphite with zirconia rods.
Due to changing requirements, several versions of the Dyna-Soar were considered, all sharing the same basic shape and layout. A single pilot sat at the front, with an equipment bay situated behind. This bay contained data-collection equipment, weapons, reconnaissance equipment, or a four-person mid-deck in the case of the X-20X shuttle space vehicle. A Martin Marietta Transtage upper stage attached to the aft end of the craft would allow orbital maneuvers and a launch abort capability before being jettisoned before descent into the atmosphere. While falling through the atmosphere an opaque heat shield made from a refractory metal would protect the window at the front of the craft. This heat shield would then be jettisoned after aerobraking so the pilot could see, and safely land.
A drawing in the Space/Aeronautics magazine from before the project's cancellation depicts the craft skimming the atmosphere for an orbital inclination change. It would then fire its rocket to resume orbit. This would be a unique ability for a spacecraft, as the laws of celestial mechanics ordinarily mean a change of plane requires an enormous expenditure of energy. The Dyna-Soar was projected to be able to use this capability to rendezvous with satellites even if the target conducted evasive maneuvers.
Unlike the later Space Shuttle, Dyna-Soar did not have wheels on its tricycle undercarriage, as rubber tires would have caught fire during re-entry. Instead Goodyear developed retractable wire-brush skids made of the same René 41 alloy as the airframe.
In April 1960, seven astronauts were secretly chosen for the Dyna-Soar program: