Universal Rocket

Nine test flights were made between 4 November 1963, and 20 October 1964, before the program was cancelled in favor of Mikhail Yangel's R-36 missile and Tsyklon carrier rocket derivative.

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.

[8] The UR-900 was the ultimate Universal Rocket application, a super heavy-lift launch vehicle for crewed expeditions to other planets, especially Mars.

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.