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 2015 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 Baikonur Cosmodrome in Kazakhstan.
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.
Payloads can be fitted with either a Blok D or Briz-M upper stage. 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).