Orbital Piloted Assembly and Experiment Complex

The Orbital Piloted Assembly and Experiment Complex, known by its Russian acronym OPSEK, was a proposed third-generation Russian modular space station for low Earth orbit, under discussion from 2009 to 2017. The concept was to use it to assemble components of crewed interplanetary spacecraft bound for the Moon, Mars and possibly Saturn, and returning crews could also recover aboard before landing on Earth. In early plans it would have started from several modules of the Russian Orbital Segment of the International Space Station. After studying that option, the head of Roscosmos said in September 2017 that Russia would keep working on the ISS, and by 2021 the idea had evolved into plans for the Russian Orbital Service Station, to be built without ISS modules.