The orbiter would have a mass of 13 metric tons, and could deliver a payload of 4 metric tons to orbit in a 27 cubic meter payload compartment (dimensions 6.0 m long x 2.8 m x 1.6 m).
The Spiral project was not cancelled with the decision to proceed with the large Buran spaceplane. Instead flight test of the orbiter continued but the launcher design was rethought. The ambitious Mach 4 air-breathing first stage was abandoned in favor of launch from an existing subsonic heavy transport. The first iteration of the new design was undertaken in 1977-1978 as the AKS project at the Scientific Research Institute 'Rosa'. This used the second rocket stage and orbiter stage of Spiral, designated RUOS in this study. This design was the starting point that would evolve through the System 49 and Bizan designs, finally resulting in the MAKS of 1988.
The System 49 design had the same arrangement as Spiral. The rocket stages and the Spiral orbiter were mounted on the back of an An-124 subsonic transport. By the time of the design, the Spiral configuration had been proven in the MiG-105-11 and BOR-4. The combined orbiter and rocket stages, weight 200 metric tons, would be launched at an altitude of 10 km and a speed of Mach 0.7. Effective velocity gain compared to a vertical launch from the ground was 270 m/s.
The first stage would use Lox/Kerosene propellants and 2 NK-43 / 11D112 engines. The second stage was equipped with a single RD-57M / 11D57M engine burning Lox/LH2 propellants. Two rocket stage layouts were studied: a traditional tandem scheme, and a 'piston' / 'wrap around' concept, where the toroidal propellant tanks of the first stage surrounded the second stage.
Orbits from 120 to 1000 km altitude, and 45 to 94 degrees inclination could be achieved thanks to the flexibility of airborne launch. The orbiter was flown by a single pilot, had sufficient consumables for 5 to 12 hours of on-orbit operations, and was designed for 100 reuses. It could achieve up to 1000 km cross-range during re-entry and landed at a speed of 300 to 310 km/hr.
The design was found to be feasible but to have little growth potential. Greater payload could only be achieved by the completely different 49M using a new super-heavy carrier aircraft and orbiter. Therefore it was succeeded in the design studies by the 'Bizan' concept.
Crew Size: 1.
Gross mass: 13,000 kg (28,000 lb).
Payload: 4,000 kg (8,800 lb).