Partial cutaway of Proton configured for space station launch 클립아트

The three-stage Proton rocket has launched all Soviet space stations and space station modules. Proton first flew as a two-stage vehicle in 1965. The threestage version used to launch stations debuted in 1969 and was declared operational in 1970. All three stages burn UDMH and N2O4 propellants. The three-stage Proton can place 20,000 kg in a circular 185 km orbit at 51.6° of inclination.