 Artist's impression of the X-20 during re-entry | |
| Country of origin | United States |
|---|---|
| Specifications | |
| Crew capacity | 1 |
| Production | |
| Status | Canceled just after spacecraft construction had begun |
| Maiden launch | January 1, 1966 (proposed) |
| Last launch | March 1, 1968 (proposed) |
TheBoeing X-20 Dyna-Soar ("Dynamic Soarer") was aUnited States Air Force (USAF) program to develop aspaceplane that could be used for a variety of military missions, includingaerial reconnaissance,bombing, space rescue,satellite maintenance, and as a space interceptor tosabotage enemy satellites.[1] The program ran from October 24, 1957, to December 10, 1963, costUS$660 million ($6.78 billion in current dollars[2]), and was cancelled just after spacecraft construction had begun.
Other spacecraft under development at the time, such asMercury orVostok, werespace 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 anintercontinental 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.[3]
These characteristics made Dyna-Soar a far more advanced concept than otherhuman spaceflight missions of the period. Research into a spaceplane was realized much later in other reusable spacecraft such as the 1981–2011Space Shuttle[4][5] and the more recentBoeing X-40 andX-37B spacecraft.
The concept underlying the X-20 was developed in Germany duringWorld War II byEugen Sänger andIrene Bredt as part of the 1941Silbervogel proposal. This was a design for a rocket-poweredbomber able to attackNew York City from bases in Germany and then fly on for landing somewhere in thePacific Ocean held by theEmpire 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.[6] 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.[7]
Following the war, many German scientists were taken to the United States by theOffice of Strategic Services'sOperation Paperclip, bringing with them detailed knowledge of the Silbervogel project.[8] Among them,Walter Dornberger andKrafft Ehricke moved toBell Aircraft, where, in 1952, they proposed what was essentially a vertical launch version ofSilbervogel known as the "Bomber Missile", or "BoMi".[9][10]
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.[11] The rocket booster would place the vehicle onto asuborbital, butexoatmospheric, trajectory, resulting in a brief spaceflight followed by re-entry into theatmosphere. Instead of a full re-entry and landing, the vehicle would use thelift 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. Thisskip-glide[12] 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 ofhypersonic atmospheric lift meant that the vehicle could greatly extend its range over a ballistic trajectory using the same rocket booster.[11]
There was enough interest in BoMi that by 1956 it had evolved into three separate programs:
Days after the launch ofSputnik 1 on 4 October 1957, on either October 10[18] or October 24,[19] theUSAF 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 theX-15 research program.[19]
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, reachingMach 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.[20]
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, theTitan III was chosen as the launch vehicle.[21] The Dyna-Soar was to be launched fromCape 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, withwinglets for control rather than a more conventional tail. The framework of the craft was to be made from theRené 41 super alloy, as were the upper surface panels. The bottom surface was to be made frommolybdenum sheets placed over insulated René 41, while the nose-cone was to be made fromgraphite withzirconia rods.[22]
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. AMartin MariettaTranstageupper 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 opaqueheat shield made from arefractory metal would protect the window at the front of the craft. This heat shield would then be jettisoned afteraerobraking so the pilot could see, and safely land.[23]
A drawing in theSpace/Aeronautics magazine from before the project's cancellation depicts the craft skimming the atmosphere for anorbital inclination change. It would then fire its rocket to resume orbit. This would be a unique ability for a spacecraft, as the laws ofcelestial 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 tricycleundercarriage, as rubber tires would have caught fire during re-entry. InsteadGoodyear developed retractable wire-brush skids made of the same René 41 alloy as the airframe.[24]
In April 1960, seven astronauts were secretly chosen for the Dyna-Soar program:[25]
Neil Armstrong and Bill Dana left the program in mid-1962. On September 19, 1962,Albert Crews was added to the Dyna-Soar program and the names of the six remaining Dyna-Soar astronauts were announced to the public.[26]
By the end of 1962, Dyna-Soar had been designated X-20, the booster (to be used in the Dyna Soar I drop-tests) successfully fired, and the USAF had held an unveiling ceremony for the X-20 inLas Vegas.[27][28]
The Minneapolis-Honeywell Regulator Company (later theHoneywell Corporation) completed flight tests on aninertial guidance sub-system for the X-20 project atEglin Air Force Base, Florida, using anNF-101B Voodoo by August 1963.[29]
Boeing B-52C-40-BO Stratofortress53-0399[30] was assigned to the program for air-dropping the X-20, similar to theX-15 launch profile. When the X-20 was cancelled, it was used for other air-drop tests including that of theB-1A escape capsule.[31]
Besides the funding issues that often accompany research efforts, the Dyna-Soar program suffered from two major problems: uncertainty over the booster to be used to send the craft into orbit, and a lack of a clear goal for the project.
Many different boosters were proposed to launch Dyna-Soar into orbit.
The original USAF proposal suggestedLOX/JP-4, fluorine-ammonia, fluorine-hydrazine, or RMI (X-15) engines, but Boeing, the principal contractor, favored anAtlas-Centaur combination. Eventually, in November 1959, the Air Force stipulated aTitan,[27]: 18 as suggested by failed competitor Martin, but the Titan I was not powerful enough to launch the five-ton X-20 into orbit.
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TheTitan II andTitan III boosters could launch Dyna-Soar into Earth orbit, as could theSaturn C-1 (later renamed theSaturn I), and all were proposed with various upper-stage and booster combinations. In December 1961, the Titan IIIC was chosen,[27]: 19 ) but the vacillations over the launch system delayed the project and complicated planning.
The original intention for Dyna-Soar, outlined in the Weapons System 464L proposal, called for a project combining aeronautical research with weapons system development. Many questioned whether the USAF should have a crewed space program, when that was the primary domain of NASA. It was frequently emphasized by the Air Force that, unlike the NASA programs, Dyna-Soar allowed for controlled re-entry, and this was where the main effort in the X-20 program was placed.
On January 19, 1963, theSecretary of Defense,Robert McNamara, directed the U.S. Air Force to undertake a study to determine whether Gemini or Dyna-Soar was the more feasible approach to a space-based weapon system. In the middle of March 1963, after receiving the study, Secretary McNamara "stated that the Air Force had been placing too much emphasis on controlled re-entry when it did not have any real objectives for orbital flight".[32] This was seen as a reversal of the Secretary's earlier position on the Dyna-Soar program.
Dyna-Soar was also an expensive program that would not launch a crewed mission until the mid-1960s at the earliest. This high cost and questionable utility made it difficult for the U.S. Air Force to justify the program.
Eventually, the X-20 Dyna-Soar program was canceled on December 10, 1963.[4] On the day that X-20 was canceled, the U.S. Air Force announced another program, theManned Orbiting Laboratory, a spin-off of Gemini. This program was also eventually canceled.
Another black program,ISINGLASS, which was to be air-launched from a B-52 bomber, was evaluated and some engine work done, but was eventually cancelled as well.[33]
Despite cancellation of the X-20, the affiliated research on spaceplanes influenced the much largerSpace Shuttle. The final design also useddelta wings for controlled landings. The later, and much smaller SovietBOR-4 was closer in design philosophy to the Dyna-Soar,[34] while NASA'sMartin X-23 PRIME andMartin Marietta X-24A/HL-10 research aircraft also explored aspects of sub-orbital and space flight.[35] TheESA's proposedHermes crewed spacecraft was superficially similar to but not derived from the X-20.
General characteristics
Performance
Related development
Aircraft of comparable role, configuration, and era
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