
Cancellation in December 1963 came only eight months before drop tests from a B-52 and a first manned flight in 1966.
It evolved from the German Saenger-Bredt Silverbird intercontinental skip-glide rocket bomber. Walter Dornberger, former head of Peenemuende, was at Bell Aircraft in the 1950's and developed the Sanger-Bredt concept through various iterations (Bomi and Robo). In typical Pentagon fashion the final development contract went instead to Boeing. Politics resulted in its primary purpose changing during its life (manned space bomber, high speed test vehicle, reconnaissance platform), with the launch vehicles at various times including Titan I, Titan II, and finally Titan IIIC. Cancellation in December 1963 came only eight months before drop tests from a B-52 and a first manned flight in 1966.
The Dyna-Soar itself would have been developed into Dyna-Soar II, III, X-20X, and Dyna-MOWS (Manned Orbital Weapons System) versions which would have run the gamut of missions - orbital supply, satellite rendezvous and inspection, reconnaissance, research, and orbital bombing.
After its cancellation, the Air Force pursued further development of manned spaceplanes through the Prime, Asset, X-23, and X-24 programs, with suborbital launch of subscale lifting body designs. B-52 drop tests of the X-24A and X-24B lifting body designs continued into the mid-1970's. Reportedly there were also black programs leading to suborbital flight and re-entry of a full-size unmanned lifting body patterned after the NASA HL-10. In the end, the Air Force was pressured by the Nixon Administration to accept participation in the space shuttle program in lieu of separate development of their own designs.
The klaxon sounds in the hardened silo deep beneath the earth. A space-suited astronauts run from the ready room, grabs the bar over the hatch, and hoists his legs into the cockpit. The ground crew attach his suit hoses, check that he is strapped into the ejection seat. The pilot closes the hatch above him. The blast doors open, the rocket is raised to the surface of the earth. Minutes later the Titan roars from the silo, launching the Dyna-Soar space bomber on an intercontinental nuclear strike mission.
This was the original vision of Dyna-Soar, the penultimate manned space bomber project of the 1950's. Following evaluation of the Robo space bomber proposals in the summer of 1957, the decision was made to combine several parallel Air Force and NACA manned spaceplane projects into a single effort. These included the SR 126 Robo; the System 459L Brass Bell hypersonic reconnaissance vehicle; and the System 610A Hywards follow-on to the X-15. The secret form DD-613 was completed on 23 August 1957 for System 464L with the confidential description 'Hypersonic Glide Rocket Weapon System', the confidential nickname 'Dyna-Soar' (for Dynamic Soarer), and the unclassified title 'Hypersonic Strategic Weapon System'.
The proposed project would develop a manned, winged vehicle that would be rocket-boosted to hypersonic speed at an altitude above 30 km. It would then glide from 10,200 to 40,800 km, depending on the mission. The project was to be completed in three phases:
The Dyna-Soar could attack enemy targets from any direction. At its low approach altitude enemy radar systems would only provide three minutes warning of the attack, as opposed to twenty minutes for an ICBM. Unlike a ballistic missile, it could be recalled or retargeted during the mission. On the reconnaissance mission, it could glide over enemy targets between 45 and 90 km altitude, providing better resolution than orbiting satellites at much higher altitudes. The data would be available for analysis within hours of the overflight, compared to having to wait for days for recovery of the capsules from spy satellites. The enemy would also have no warning to conceal its activities, unlike a satellite in its predictable orbit.
The Air Force considered 12 contractors as capable of bidding on the program. Nine vendor teams submitted bids by March 1958. These were broken into two groups: vehicles which would be accelerated to orbital velocity at 120 km altitude and achieve global range by actually being in orbit; and sub-orbital vehicles that would reach near-orbital speed at 90 km altitude and glide around the planet. The proposals may be summarized as follows:
| Bidder | Layout | Glider Mass | Booster | Comments | |||||
| Satelloid Proposals | |||||||||
| Republic | Delta wing | 7,300 kg | Three solid propellant stages | Separate 'space-to-earth' 2930 kg missile. Global range. | |||||
| Lockheed | Delta wing | 2,300 kg | Modified Atlas ICBM | Sub-global range. judged Booster judged to be insufficient to achieve either satelloid velocity or global range. | |||||
| North American | X-15B | 6,800 kg | 1+1/2 stage booster+stage in glider | Two-place X-15B, boosted by a unique one-and-a-half stage booster with expendable drop tanks for the X-15B. Global range. | |||||
| Boost-Glide Proposals | |||||||||
| Douglas | Arrow-wing | 5,900 kg | 3 x Minuteman solid stages | Suborbital velocity in Phase I using three modified Minuteman stages in parallel. Addition of another stage would give the vehicle orbital capability, although the planned life support system was not designed for sustained flight. | |||||
| McDonnell | Arrow-wing | 5,500 kg | Modified Atlas ICBM | Suborbital velocity in Phase I. | |||||
| Convair | Delta wing | 5,100 kg | None recommended | Hypersonic aircraft using air-breathing engines. No booster was proposed. Suborbital velocity in Phase I. | |||||
| Martin+Bell | Delta wing | 6,050 kg | Titan ICBM | Two crew. Capable of orbital velocity in Phase I. Actively cooled airframe. | |||||
| Boeing+Vought | Arrow-wing | 2,950 kg | Minuteman stages | Payload only 230 kg including one crew. Capable of orbital velocity in Phase I. Passively cooled airframe using refractory metals. | |||||
| Northrop | Delta wing | 6,450 kg | Hybrid booster+liquid core | Hybrid booster - solid fuel burned using a liquid oxidizer. Suborbital velocity in Phase I. |
X-20 Configurations proposed
During the study period, something extraordinary happened: Boeing's configuration evolved from its original Buck Rogers concept, festooned with fins, to something nearly identical to Bell's glider. Boeing's March 1958 configuration was essentially a tetrahedron; triangular planform with a diamond cross-section. That shape was driven by the desire to eliminate thermal stresses by using a determinate truss primary structure. But Boeing already recognized that the ventral fins were thermally untenable and would have to go. They were driven to a flat-bottomed configuration with distinct wings to reduce heating and improve landability. By the time of the final proposals in June 1959, the competing glider systems were nearly indistinguishable, except that Bell's glider used a more sophisticated double-delta wing, foreshadowing the space shuttle of 15 years later. In a shock move, Boeing was selected for the glider in June 1959.
This was Bell's swan song. The small but innovative company had invested millions of its own money in the Bomi and Dyna-Soar. But Bell was considered more of a prototype house by the Air Force. In World War II they were relegated to production of fighters to be sent to the Soviet Union on lend-lease. Although they had built the first American jet aircraft and the X-1, the first aircraft to break the sound barrier, they had not won a full-scale development contract for a manned aircraft since 1955. Boeing, on the other hand, was the premier builder of SAC's B-52 bombers and Minuteman ICBM's. To compensate it for the loss of the B-70 competition at the end of 1957, it was perhaps considered logical for it to build the successor.
On the other hand the service greatly preferred Martin's booster proposal (Titan I for the suborbital tests, Titan C for global flights). Boeing's vague proposal was to use Atlas-Centaur for suborbital flights, and a booster 'to be determined' for orbital flights. The contract awards for Dyna-Soar, were announced on November 9, 1959. By then the program was had gone down to two phases, and then back to three phases - a suborbital test Phase 1, an orbital test Phase 2, and an operational weapon system in Phase 3.
The selection of the Titan C for the Phase 2 booster was controversial. This was a Titan II booster stage topped by a new liquid oxygen/hydrogen upper stage. Even though Aerojet already had the engine under test in Sacramento, the Eisenhower administration wasn't interested in developing yet another new orbital launch vehicle. There were also elements in the Air Force pushing their Space Launching System family of modular launch vehicles. And there was an Air Force requirement, beyond Dyna-Soar, for development of a large booster for its SLV-4 requirement. This new vehicle would be needed by the late 1960's for launch of ten-metric ton reconnaissance satellites into low orbit and heavy communications, ELINT, and early warning satellites into high orbits. Production of Titan I boosters for Phase 1 was authorized while a decision on the orbital booster was deferred.
Meanwhile development of the glider was proceeding well. By the end of 1962 critical design reviews of all major subsystems had been completed. Major breakthroughs had been achieved in high temperature materials and fabrication of parts for the airframe was underway. Delivery of the first Dyna-Soar was to be made by October 1964 and first orbital launch by the end of 1965. While the first glider test would be 14 months later than the original July 1957 schedule, the first orbital flight was expected six months earlier.
Dyna-Soar was seemingly doomed from birth over controversy over its mission and the lack of a strong sponsor. The Eisenhower administration wanted to limit it to suborbital missions (so as not to infringe on the new NASA agency's mission of manned orbital flight). Once Eisenhower was replaced by Kennedy, the catastrophic new Secretary of Defense, Robert McNamara, began to work his malignant magic. There was no weapons system immediately resulting from Dyna-Soar. Nor did he believe there was any need for the military to waste so much money on an aeronautical research vehicle. The back-and-forth was extremely tedious and can be traced through the chronology below. Suffice to say after reviews, audits, and special studies ad nauseum the project was killed by McNamara in December 1963.
It was replaced by the Manned Orbiting Laboratory (MOL), equipped with a Gemini capsule, also launched by a Titan 3 booster. McNamara killed a project in being, with drawing release nearly 100% complete, and the first spacecraft one month away from final assembly. Expenditures were under control and Boeing had already spent $ 253.5 million of its $ 530 million development budget. Captive-carry flights would have begun within the year. In its place was a vague concept not even studied in any detail yet. After six years of development, it would in turn be cancelled in 1969 after wasting $ 1.5 billion. It was a typical example of McNamara's criminally poor judgment.
If Dyna-Soar and the Space Launching System had been completed, the United States would have had by 1965 a modern modular launch vehicle launching a reusable manned spaceplane -- something it now hopes to accomplish with the Delta IV / OSP by 2010. The nation could have been spared the false premise of the shuttle program and had a space station ferry in being by the beginning of the 1970's. It might even have been flying well into the 21st Century, while the Gemini, Apollo, and Shuttle were consigned to the trash heaps of history.
The glider had a 72.48 deg straight delta wing with a flat bottom. The aft fuselage was ramped, found desirable to provide directional stability at transonic speeds. It was 10.78 m long, with a wingspan of 6.34 m and a wing area of 32 sq m. The design provided a hypersonic lift-to-drag ratio of from 0.8 to 1.9 at hypersonic speeds. This was sufficient to give it a maximum cross-range of 3150 km. This meant if it had to divert from a planned landing at Edwards Air Force base, California, it could land anywhere from Juneau, Alaska, to Talaro, Ecuador, including any airfield in the continental United States. The Dyna-Soar's unique wire-brush skids allowed it to land even on compacted earth runways as short as 2400 m.
The glider had a design mass of 5,055 kg with a 450 kg return payload for the 3150 km cross-range. This design mass was based on the original expected performance of the heat shield materials. Tests prior to cancellation of the project indicated higher-than-expected emissivity of the heat shield. This meant the flight vehicle could have a mass of 6,400 kg with a return payload of 1800 kg at the 3150 km cross range. This capability was to be exploited in planned follow-on versions.
In orbit the glider remained attached to the third stage of the Titan 3. This transtage was a restartable rocket capable of enormous maneuvers. Before ignition it had a gross mass of 12,250 kg, of which 10,300 kg was storable nitrogen tetroxide/Aerozine-50 propellants. The transtage would fire initially to place the Dyna-Soar in orbit. Available remaining propulsion would depend on the mission initial orbit and glider mass. On a typical mission it was expected the total mass (glider+transtage) orbited would be 12,700 kg, leaving the transtage with 5700 kg of propellants, enough for a single maneuver of over 2 km/sec. Such huge maneuvers would greatly complicate the enemy's ability to predict the overflight path and time of the Dyna-Soar on a reconnaissance, bombing, or satellite interception mission.
The Air Force was especially interested in exploring the possibilities of 'synergistic' orbital maneuver. This would involve the X-20 entering the upper atmosphere, and using its aerodynamic maneuverability to change the orbital plane. The transtage would then boost the spacecraft back into orbit. This would change the maximum plane change from 15.8 deg for the pure propulsive engine burn to 20.3 deg for the 'synergistic' turn.
In the fairing between the glider and the transtage was a solid-propellant abort rocket adapted from the Minuteman third stage. This would be used for aborts during launch to blast the glider away from the booster. On orbit, it could be used for emergency retro-fire in case of a transtage propulsion failure.
Structure
The internal structure of the X-20A was a truss structure of Rene 41 steel. This was designed to compensate for thermal expansion of the hot structure during re-entry. Within the body truss were four bays - forward pilot's compartment, a central equipment compartment, aft equipment bay, and secondary equipment bay.
The upper wing, body, and inside fin surfaces were also of Rene 41. Coated molybdenum was used for the leading edge panels and the lower wing surface. The nose cap was of zirconium. Maximum re-entry temperatures during a maximum lateral range re-entry would 2010 deg C at the nose-cap, 1550 deg C on the wing leading edge, and 1340 deg C on the wing lower surface. The internal structure would stabilize at 980 deg C.
Systems
Avionics
The X-20 would not be controllable throughout its speed range with purely manual controls. Therefore a control augmentation system was provided, which could operate in four control modes, all of them fly-by-wire. A side-arm controller provided pitch and roll inputs while yaw commands were via conventional aircraft rudder pedals. The pilot was able to use these controls for manual flight of the Titan 3C launch vehicle during the boost to orbit, if needed. In space, these controls commanded one of two redundant hydrogen peroxide thruster systems for orientation. During re-entry, the control system operated a mix of thruster and aerodynamic controls until the glider reached a dynamic pressure of 0.68 bar. From that point purely aerodynamic controls were used. The thrusters were shut down and the remaining hydrogen peroxide propellant was pumped overboard. Over 8,000 pilot-hours were spent in X-20 simulators before the program was cancelled. These showed the glider's longitudinal and lateral handling characteristics were rated between good and satisfactory in the speed range Mach 1 to Mach 27.
The inertial navigation system was developed by Honeywell at their Saint Petersburg, Florida facility. It used an adaptation of the inertial measurement unit developed for the Bomarc-B missile and later adapted for the Centaur upper stage. The guidance computer was the same used in the Hound Dog missile. The system was tested in-flight in an F-101B fighter and on a high-speed sled at Holloman AFB. After the X-20 cancellation, the system was tested at extreme speed and altitude in the X-15.
For the re-entry the pilot was provided with a unique 'energy management display' which consisted of a series of transparent overlays on a cathode-ray tube. The system was driven by the guidance computer, which changed the overlays every 300 m/s as the re-entry progressed. Two dots were projected on the cathode-ray tube. One showed the current angle of attack and bank angle of the glider; the other the angles the pilot would have to fly to reach the selected airfield. The overlay included a line indicating air vehicle structural limits to ensure the pilot did not over-maneuver the aircraft. The guidance system could store a maximum of ten airfield locations.
Systems
The internal compartments of the Dyna-Soar were encased in 'water walls' which provided passive cooling. These reduced the 980 deg C re-entry equilibrium temperature of the airframe truss structure to 90 deg C and allowed the pressure shells of the compartments to be of conventional aluminum. Cooling systems in the compartments further reduced the maximum internal temperature to 46 deg C. The pilot compartment was pressurized to 0.5 atmosphere, equivalent to an altitude of 5500 m, but with a mixture of 43.5% oxygen and 56.5% nitrogen. The payload compartment was pressurized at 0.7 atmosphere with 100% nitrogen. The other two bays were not pressurized, but had nitrogen purging systems in the case of fires.
The pilot's compartment housed the inertial guidance system, the flight control system electronics, pilot displays, controls, ejection seat, and gas supplies for windshield cover jettison and landing gear extension. The pilot had a view at all times through two side windows. The three-piece forward windshield was covered by a heat shield during ascent, orbital operations, and re-entry. It was only blown off when the glider had slowed below Mach 6, for use on landing. However tests by Neil Armstrong with a modified F5D Stingray fighter showed landing could be safely made using only the side windows if this failed to jettison. The ejection seat could only be used at subsonic speeds between 1,000 and 130 kph.
The equipment compartment provided just over two cubic meters of volume, to be occupied during flight tests with the 450 kg of the Test Instrumentation Subsystem. This processed and recorded data from 750 sensors that captured glider temperature, pressure, loads, subsystems performance, pilot biometrics, and heat flux.
The aft equipment bay was a narrow compartment containing the liquid nitrogen supply, the hydrogen peroxide propellant tanks, and some power system controls.
The large secondary power bay was dominated by the huge liquid hydrogen tank. This worked with two redundant liquid oxygen tanks to provide propellant for the unique Auxiliary Power Unit that provided 12 kVA 400 cycle AC power for the Dyna-Soar. It also housed the glycol secondary cooling system.
Mission Profile
For the 'single-orbit' test flights, Dyna-Soar would be boosted from Cape Canaveral by the Titan 3C and transtage to 7.53 km/s at 98 km altitude. It would then coast to an apogee of 146 km over South Africa. The transtage would be jettisoned over the Indian Ocean, and the long re-entry glide would continue from there until landing at Edwards Air Force Base, California. For multi-orbit flights, booster cut-off would be only 20 m/s faster and 600 m higher. But then the glider would coast to 183 km altitude, where the transtage would fire to circularize the orbit. After three circuits of the earth, the transtage would fire again over Angola to brake out of orbit, with the return demonstrating the spacecraft's cross range capability and the landing again at Edwards.
Growth Versions
Heavier and more capable versions of the Dyna-Soar were planned to follow on the basic ten-flight program. These could use both refurbished gliders from the basic program and new-build spacecraft. The basic vehicle had the capability for a 450 kg return payload and 300 m/s delta-v capability. Expected improvements were as follows:
The X-20 was pushed as an alternate to the Gemini as a space station ferry vehicle in the twilight days of the program. If only it had been accepted, the US would have had a space station and winged ferry vehicle flying before the end of the 1960's.
Characteristics
Crew Size: 1. Habitable Volume: 3.50 m3. Spacecraft delta v: 900 m/s (2,950 ft/sec).
AKA: X-20A.
Gross mass: 10,125 kg (22,321 lb).
Unfuelled mass: 7,435 kg (16,391 lb).
Payload: 450 kg (990 lb).
Height: 14.50 m (47.50 ft).
Span: 6.34 m (20.80 ft).
Thrust: 71.19 kN (16,004 lbf).
Number: 1 .



















