Mikoyan-Gurevich MiG-105 - Differences Between Dyna-Soar and Spiral

Differences Between Dyna-Soar and Spiral

Although having basically the same mission, Dyna-Soar and Spiral were radically different vehicles. For example:

• While the X-20 Dyna-Soar was designed for launch atop a conventional expendable rocket such as the Titan III-C or Saturn I, Soviet engineers opted for a midair launch scheme for Spiral. Known as "50 / 50", the idea was that the spaceplane and a liquid fuel booster stage would be launched at high altitude from the back of a large, airbreathing mothership travelling at hypersonic speeds. The idea was similar to that used by the United States in launching the D-21 Tagboard reconnaissance drone from the back of the A-12 Oxcart. The mothership was to have been built by the Tupolev Design Bureau (OKB-156) and utilize many of the same technologies developed for the Tu-144 'Charger' supersonic transport (The Soviet equivalent of the Concorde) and the Sukhoi T-4 mach-3 bomber (somewhat similar to the XB-70 Valkyrie). It never made it off the drawing boards. The U.S. purportedly flew a similar design in the 1990s under the secret Blackstar project.
• Dyna-Soar was designed with a fixed, delta-wing planform, while Spiral featured an innovative variable-geometry wing. During launch and reentry, these were folded against the sides of the vehicle at a 60-degree angle, acting as vertical stabilizers. After dropping to subsonic speeds post-reentry, the pilot activated a set of electric actuators which lowered the wings into the horizontal position, giving the spaceplane better flight characteristics.
• Spiral was built to allow for a powered landing and go-around maneuver in case of a missed landing approach. An air intake for a single Koliesov turbojet was mounted beneath the central vertical stabilizer. This was protected during launch and reentry by an electric clamshell door, which would open at subsonic speeds. By comparison, Dyna-Soar was designed primarily for a once-off, unpowered deadstick landing, although some documentation claims that its emergency solid-fuel escape rocket (the third stage engine from an LGM-30 Minuteman ICBM) could be used for a go-around maneuver if necessary.
• Spiral was designed as a lifting body, while Dyna-Soar was designed more like a conventional aircraft.
• High temperature superalloy metals such as niobium, molybdenum, tungsten and rene 41 were to have been used in the heatshield structure of the X-20. Spiral was to have been protected by what Soviet engineers termed "scale-plate armour": individual steel plates hung from articulated ceramic bearings to allow for thermal expansion during reentry. Several BOR (Russian acronym for Unpiloted Orbital Rocketplane) craft were built and launched to test this concept.
• In the event of a booster explosion or in-flight emergency, the insulated crew compartment of Spiral was designed to separate from the rest of the vehicle and parachute to earth like a conventional ballistic capsule; this could occur at any point in the flight. Such an escape crew capsule was also considered for Dyna-Soar, but American engineers eventually opted for a solid-fuel escape rocket that would kick the spaceplane away from an exploding booster, saving both pilot and spacecraft.
• Much like today's Space Shuttle, Dyna-Soar was designed with a small payload bay behind the pressurized crew module. This could be used for lofting small satellites, carrying surveillance equipment, weapons or even an extra crewmember in a pop-in cockpit. Spiral, on the other hand, appears to have been intended to carry only its pilot. Presumably, this was because the extra space which could have held a payload bay was needed for the Koliesov turbojet and its fuel tanks.
• Both Dyna-Soar and Spiral were designed to land on skids. The landing skids on Dyna-Soar were designed to deploy from insulated doors on the underside of the vehicle, like a conventional aircraft. Soviet engineers, most likely concerned about heatshield integrity, designed the landing skids on Spiral to deploy from a set of doors on the sides of the fuselage just above and ahead of the wings. This unusual arrangement resulted in a hard landing on at least one occasion.