Tupolev OOS

The Tupolev OOS, named for the Russian phrase meaning single-stage orbital plane, was a Soviet concept for a crewed, reusable spaceplane that would reach orbit without dropping any stage. Its designer was the Tupolev design bureau, and it was imagined in the 1980s as an advanced successor to the Buran shuttle. A one-stage craft has to carry a very large load of propellant, so the plan was to lift it to altitude under a giant air-launch carrier, the Antonov AKS, a twin-fuselage aircraft built from two An-225 fuselages and fitted with many turbofan engines. The launch system was proposed in the late 1980s but never developed past the design stage, so no OOS was ever built or flown.