Proton (Russian: Протон, lit. 'proton', formal designation: UR-500, GRAU: 8K82, Sheldon: D-1, DoD: SL-9/-12/-13) is a Soviet and Russian hypergolic expendable heavy-lift launch vehicle family. Developed by the Soviet space program, its first launch was in 1965. The Proton-K flew 310 missions from 1967 to 2012; the modernized Proton-M, operational since 2001, is flown by Roscosmos for commercial and state payloads, scheduled until 2029. Components are manufactured in the Khrunichev State Research and Production Space Center, Moscow, and Chemical Automatics Design Bureau, Voronezh, then transported to the Baikonur Cosmodrome, Kazakhstan, where they are assembled at Site 91 to form the launch vehicle. Following payload integration, the rocket is then brought to the launch pad horizontally by rail and raised into vertical position for launch. As with many Soviet rockets, the names of recurring payloads became associated with the launch vehicle itself. The moniker "Proton" originates from a series of similarly named scientific satellites, which were among the rocket's first payloads. Launch capacity to low Earth orbit is about 22.8 tonnes (50,000 lb). Geostationary transfer capacity is about 6.3 tonnes (14,000 lb). Commercial launches are marketed by International Launch Services (ILS). During the 1970s and 1980s, Proton-K launched every interplanetary probe of the Soviet space program's Venera and Mars missions, using its Blok D fourth stage. In three-stage configuration, it launched the Zond program's circumlunar flights and all seven space stations of the Salyut program. The Soviet program also considered the Proton for launching the TKS crewed spacecraft and LKS spaceplane. From 1986, Protons launched six of the seven modules of Mir, the first modular space station, and from 1998, launched the Zarya, Zvezda, and Nauka modules of the International Space Station's Russian Orbital Segment. Protons launched the first two generations of GLONASS satellites and various commercial satellites; the Proton-M upgrade first flew in 2001 and uses the Briz family for fourth stages. In 2013, the rocket was intended to be retired before 2030. Since 2018, Proton has been approaching retirement; Russia's Angara A5, a replacement in the heavy-lift role, conducted four test flights and one operational flight between 2014 and 2025. No new launch service contracts for Proton are likely to be signed; its latest scheduled launches are the Science Power Module 1 to the ISS and an Ekspress satellite, both in 2029.
History Proton started its life as a "super heavy ICBM". It was designed to launch a 100-megaton (or larger) thermonuclear weapon over a distance of 13,000 km. It was hugely oversized for an ICBM and was never deployed in such a capacity. It was eventually used as a space launch vehicle. It was the brainchild of Vladimir Chelomei's design bureau as a foil to Sergei Korolev's N1 rocket, whose purpose was to send a two-man Zond spacecraft around the Moon; Korolev openly opposed Proton and Chelomei's other designs for their use of toxic propellants. The unusual appearance of the first stage results from the need to transport components by rail. The central oxidizer tank is the maximum width for the loading gauge of the track. The six tanks surrounding it carry fuel and serve as the attachment points for the engines. Despite resembling strap-on boosters, they are not designed to separate from the central oxidizer tank. The first and second stages are connected by a lattice structure. The second stage engine ignites shortly before separation of the first stage and the lattice allows the exhaust to escape. This is called "hot staging" and it eliminates the need for ullage motors on the second stage. A rushed development program led to dozens of failures between 1965 and 1972. Proton did not complete its State Trials until 1977, at which point it was judged to have a higher than 90% reliability. Proton's design was kept secret until 1986, with the public being only shown the upper stages in film clips and photographs, and the first time the complete vehicle was shown to the outside world happened during the televised launch of Mir. Mass-production of the guidance, navigation and control system for Proton began in 1964 by "Communard" Industrial Association (Kharkov, Ukraine). Proton launched the uncrewed Soviet circumlunar flights and was intended to have launched the first crewed Soviet circumlunar spaceflights, before the United States flew the Apollo 8 mission. Proton launched the Salyut space stations, the Mir core segment and expansion modules, and both the Zarya and Zvezda modules of the ISS. Proton also launches commercial satellites, most of them being managed by International Launch Services. The first ILS Proton launch was on 9 April 1996 with the launch of the SES Astra 1F communications satellite. Between 1994 and mid-2010, Proton revenues were $4.3 billion, and were projected to grow to $6 billion by 2011. In January 2017, the Proton was temporarily grounded due to the manufacturer, Voronezh Mechanical Plant, having substituted a heat-resistant alloy in the engines with a cheaper metal. In June 2018, the state corporation Roscosmos announced that the Proton rocket would cease production as the new Angara launch vehicle comes on line and becomes operational. No new launch service contracts for Proton are likely to be signed. Proton flew its last scheduled commercial mission on 9 October 2019, delivering Eutelsat 5 West B and Mission Extension Vehicle-1 to geostationary orbit. A number of Roscosmos and other Russian government missions remain on Proton launch manifest.
Proton K
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