The UR-700 was
Vladimir Chelomei's heavy-lift entry for the
Soviet moonshot. It was meant to carry
cosmonauts to the
Moon on a
direct ascent mission in the
LK-1 lunar craft.
Sergei Korolev's
N1 booster and
Soyuz 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. 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. A
nuclear variant known as the UR-700A was also designed to have an increased payload capacity of 250 t (500,000 lb) to LEO, capable of launching a lunar landing mission with up to seven crew. There was also another proposed variant named UR-700M with an even larger payload capacity of 750 t (1,500,000 lb) to LEO ==UR-900==