The Spiral seems to be one of the most ambitious and secret projects in the history of Soviet aviation. Therefore, only 40 years later it became possible to disclose the whole truth of this aircraft...
The launch aircraft would accelerate the whole system to a hypersonic speed of M=6 (about 1,800 metres per second), releasing the components at an altitude of 28-30 km. The launch aircraft would return to its launch base after completing the mission, and the booster, burning fluorine+hydrogen fuel, would propel the aerospaceplane to the orbit.
The orbital aircraft would bring a payload of up to 10.3 tonnes to the circumpolar orbit of 130-150 km at the carrier offset of up to 750 km, if boosted by a launch aircraft with liquid hydrogen power plant, or 5 tonnes if the launch aircraft burnt kerosene.
Props to codewolf.com