The Proton (Прото́н) rocket (formal designation: UR-500, also known as D-1/ D-1e or SL-12/SL-13) is a Russian unmanned space vehicle design, first launched in 1965. It is still in use as of 2007, for both commercial and government launches. This makes it one of the most successful heavy boosters in the history of spaceflight. All Protons launch from the Baikonur facility.
The name "Proton" originates from a series of large scientific satellites, which were among the rocket's first payloads. The enormous capacity of the new rocket allowed the heavy materials used in particle detectors. Thus the Proton satellites were pioneers of high-energy astronomy. Like many Soviet boosters, the name of the recurring payloads became associated with their launchers.
Launch capacity to low Earth orbit is about 22 tonnes (44,000 lbm). Interplanetary transfer capacity is about 5–6 tonnes (11,000–13,000 lbm).
Krikalev was dubbed by many "the last Citizen of the USSR " as in 1991–1992 he spent 311 days, 20 hours and 1 minute aboard the Mir space station while, back on Earth, the Soviet Union collapsed. A fictional account of how Krikalev may have felt about this is described in the song "Casiopea", written by Cuban songwriter Silvio Rodríguez.