Design of the Spiral reusable system
The 115-ton Spiral system was conceived as a multi-stage aircraft and rocket combo, made of a large carrier aircraft, serving as a mid-air launch pad for a small orbiter, equipped with its own two-stage rocket booster, capable of accelerating it to an orbital speed. (317)
The Spiral project promised an orbital delivery system where payloads would reach as much as nine percent of the total liftoff mass of the vehicle -- an unprecedented feat for a traditional space rocket. Thus, it promised to cut the cost of delivering one kilogram of payload into orbit by as much as 3-3.5 times, comparing to existing launch vehicles.
The Spiral was expected to deliver a 10.3-ton payload into a 130-150-kilometers orbit.
Hypersonic Carrier Aircraft, GSR
The 52-ton hypersonic carrier aircraft, known by Russian abbreviation as GSR, would be equipped with four air-breathing engines. The initial version would burn kerosene fuel, before a planned switch to hydrogen engines.
After a horizontal takeoff from a runway, the GSR could accelerate up to 1.8 kilometers per second, or Mach 6 (six times the speed of sound), lifting the orbital stage and its two-stage rocket booster to an altitude of between 28 and 30 kilometers. The orbital vehicle would then separate from the back of the carrier aircraft and fire the first stage of its rocket booster, which would accelerate the orbital plane to a speed of 4.5 kilometers per second before dropping away. The second stage would then complete the orbital insertion at an altitude of around 130 kilometers.
The orbital stage
The air-launched space plane will have a capability to enter a wide variety of orbits. The takeoff from the Soviet territory would restrict the inclination of reachable orbits from 45 to 135 degrees relative to the Equator. The orbital stage would be capable of achieving an additional 17-degree change in the inclination of its final orbit.
During reentry into the Earth's atmosphere, the orbiter could vary its landing trajectory from 4,000 to 6,000 kilometers and maneuver from side to side up to 1,500 kilometers. Using its own air-breathing jet engine providing thrust during the final atmospheric phase of the descent, the orbiter could land on any Class II runway. (317)
The most unusual feature of the Spiral space plane was its wings, which could rotate around an axis running along the side of the fuselage. When in near-vertical position, the wings would be shielded from exposure to the most severe heat loads during reentry, leaving only the belly of the orbiter in need of being protected with heavy duty thermal shielding.
The heat shield on the underside of the orbiter was connected to the rest of the body on special hinges, which allowed it to shift relative to the rest of the fuselage and isolate the heat generated during reentry from reaching the main body of the orbiter. The heat shield was to be made of ultra-thin silicon-based fiber and amorphous refined quartz reinforced with a layer of silver.
The hollow nose cap and wings were also designed to serve as radiators to facilitate thermal conditioning of the vehicle during the return home.
Once the most heat-intensive phase of the reentry was over during the descent, the Spiral would unfold its wings into a nearly horizontal position, acquiring good gliding properties for its approach to the runway.
The landing gear was designed in such a way that when in folded position it was located inside a heat-protected area of the ship and it could be lowered into landing position, without any doors or openings in the heavy duty heat shield at the bottom of the orbiter.
The orbiter was expected to carry its own liquid propellant engine with a thrust of 1.5 tons. It would be used for orbital correction and braking maneuvers for the return to Earth. Two backup braking engines with a thrust of 16 kilograms each would also be available. Six small engines with a thrust of 16 kilograms and 10 engines with a thrust of one kilogram would be used for attitude control of the ship in orbit and during the reentry in the upper atmosphere.
Spiral technical characteristics:
Scale model of the Spiral system in the takeoff configuration. Click to enlarge. Copyright © 2001 Anatoly Zak