Soyuz 7K-LOK

The Soyuz 7K-LOK, usually called the LOK, was the two-person lunar orbiting spacecraft of the Soviet Moon landing program and the largest derivative of the Soyuz ever developed. It was the counterpart of the American Apollo command and service module, designed to carry a crew into lunar orbit, wait while the LK lander went down to the surface and bring the cosmonauts home. It differed sharply from other Soyuz craft. Its orbital module carried the lightweight Kontakt docking system, a forward reaction control module and a cupola that let a cosmonaut dock by sight with the LK. Its descent module was heavier than earlier versions, and its service module had the powerful Block I engine and, for the first time on a Soviet spacecraft, liquid oxygen and liquid hydrogen fuel cells. Never reaching space in its complete form, it remained one of the least known crewed spacecraft to reach flight status, and the LOK and LK were eventually cancelled along with the N1 lunar program.