TheUniversal Rocket orUR family ofmissiles andcarrier rockets is a Russian, previouslySovietrocket family. Intended to allow the same technology to be used in all Soviet rockets, the UR is produced by theKhrunichev State Research and Production Space Center. Several variants were originally planned, of which only three flew, and only two of which entered service. In addition, the cancelled UR-500 ICBM formed the basis for theProtoncarrier rocket.
The UR-100 and its variants (e.g. UR-100N) were the standard smallICBM of the Soviet Union during the Cold War. Only the UR-100N (NATO reporting designation:SS-19 Stiletto) remains in active duty, with 20–30 missiles operational.[1] TheStrela andRokot carrier rockets are based on the UR-100N. A number of UR-100Ns have been earmarked for use as launch vehicles for theAvangard maneuverable reentry vehicle.[2]
The UR-200 was intended to be a largerICBM that could also be used as a carrier rocket. Nine test flights were made between 4 November 1963, and 20 October 1964, before the program was cancelled in favor ofMikhail Yangel'sR-36 missile andTsyklon carrier rocket derivative.[3]
The UR-500 was designed to be a very largeICBM, with thethrow-weight necessary to deliver the 50-100 megatonTsar Bomba-likewarhead.[4] Under pressure fromKhrushchev, the UR-500 was reworked as a space launcher, and eventually renamed theProton, the latest version of which is still in service as of 2023.[5]
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The UR-700 wasVladimir Chelomei's heavy-lift entry for theSoviet moonshot. It was meant to carrycosmonauts to theMoon on adirect ascent mission in theLK-1 lunar craft.Sergei Korolev'sN1 booster andSoyuz 7K-LOK /LK Lander were chosen instead for the mission, and it never left the drawing board. It would have had a payload capacity to low Earth orbit of 151 metric tons.[6]
Superficially, the UR-700 was of the well-known design of Soviet launchers with a central core stack and lateral strap-on boosters. But one distinguishing feature was that the engines of the first stage were cross-fed with fuel and oxidizer from the tanks of the strap-on boosters during the initial flight phase. This meant that when the boosters were spent and jettisoned, the central stack still flew with full tanks, thus reducing dead weight and increasing a possible payload.[7]
A nuclear variant known as the UR-700A was also designed to have a much larger payload capacity of 750t (1,500,000 lb) to LEO.[8]
The UR-900 was the ultimate Universal Rocket application, asuper heavy-lift launch vehicle for crewed expeditions to other planets, especially Mars. Proposed in 1969, it would have had 15 RD-270 modules in the first and second stages, and the third and fourth stages were based on those of the UR-500. The UR-900 would have stood 90 metres (295 ft) tall, had a liftoff thrust of 94,000 kN (21,132,000 lbf), and be able to place 240 tons into low Earth orbit. Like the UR-700, it remained a paper project only.[9]