Martian Piloted Complex

The Martian Piloted Complex or MPK was a Soviet Union human mission to Mars proposed in 1956-62 by Mikhail Tikhonravov.
It featured a six-cosmonaut crew on a 900-day mission, with a launch in 1975. The craft would have a mass of 1,630 metric tons and employ traditional liquid propellants. It would take 25 N1 rocket launches to assemble the MPK in low earth orbit.
When complete, it would travel from Earth to Mars on a 270 day Hohmann trajectory and maneuver into Martian orbit. Afterwards, a landing craft would descend to the surface for a one-year expedition. Return to Earth would take 270 days and the re-entry vehicle would weight 15 metric tons.