Not many rockets get to live long to go for 300+ launches! Proton-K, by the time it retired on 30th March 2012, had completed 310 launches! That’s an incredible feat, especially recognizing the fact that the first launch was in 1967.
The Proton-K, also designated Proton 8K82K after its GRAU index, 8K82K, was a Russian, previously Soviet, carrier rocket derived from the earlier Proton. It was built by Khrunichev, and launched from sites 81 and 200 at the Baikonur Cosmodrome in Kazakhstan. The first lander on Mars — Mars 3, was launched by Proton-K, carrying it in an upper stage called Blok D.
From 1969 through 1976, Proton launched a series of Luna missions to the Moon. Luna 15 famously attempted, but failed, to land while the U.S. Apollo 11 astronauts were on the Moon during July, 1969. One year later, Luna 16 performed the first successful robotic lunar sample return and Luna 17 landed with Lunakhood 1, the first robotic rover on another celestial body. Luna spacecraft continued to regularly land on or orbit the Moon until 1976, when Luna 24 performed a final lunar sample return mission. It was the last lunar landing until China repeated the accomplishment in 2013, some 37 years later.
During the 1970s and 1980s, Protons boosted missions to Mars and Venus. In 1971, Mars 2 and 3 became the first spacecraft to orbit the Red Planet and to attempt landings. Mars 2 crash landed, becoming the first man made object on Mars in 1976. Sister ship Mars 3 achieved the first soft landing on Mars a few days later, but ceased transmitting data shortly after landing. In 1975, Venera 9 became the first spacecraft to orbit and land on Venus, and the first to return an image from the surface of another planet. Sister ship Venera 10 duplicated both feats. With Proton and Venera, the USSR achieved its greatest planetary exploration successes. Venera 11 and 12 landed on Venus in 1978, as did Venera 13 and 14 in 1981. Venera 15 and 16 orbited Venus and mapped portions of its surface with radar in 1983.
Proton-K payloads included all of the Soviet Union’s Salyut space stations, almost all Mir modules (with the exception of the Docking Module, which was launched on the United States Space Shuttle), and the Zarya and Zvezda modules of the International Space Station.
Proton-K fueled by hypergolic fuels— unsymmetrical Dimethyl Hydrazine and Nitrogen Tetroxide. These ignite on contact, avoiding the need for an ignition system, and can be stored at ambient temperatures. This avoids the need for components that are tolerant of low temperatures, and allows the rocket to remain on the pad indefinitely. In contrast, cryogenic fuels need periodic replenishment as they boil off.
The fourth stage has multiple variants, depending on the mission. The simplest, Blok D, was used for interplanetary missions.