A core second stage consisting of three modules in a cluster was to be surrounded by three clusters of two modules which would have formed the first stage. Each module was foreseen to have had a diameter of 4.1 m (maximum allowed diameter for railway transportation) and equipped with one RD-270 engine. This engine was developed by what is now known as Energomash, burned UDMH and N2O4 and had a thrust of 600 tons.
The third stage installed on top of the second stage used four (in the bottom view of the third stage it looks like three!!) RD-253 engines (like Proton's first stage). The first and second stages burned in parallell from launch, but the second stage burned a little longer - just like the R-7 rocket.
The preliminary development of UR-700 started in parallell with that of Proton (UR-500), but the first official technical proposal was presented by Chelomei only in 1966, when Proton had just began to fly. Because the N-1 vehicle was in development at the time permission and funding was given only for a detailed design phase.
At the end of this phase, which coincided with the N-1 failures, the project was halted. Later, Chelomei proposed a version, UR-700M, for a manned flight to Mars. It would have been equipped with a fourth stage built around the RD-410 nuclear rocket engine then under developement testing by Energomash. In the UR-700M design the RD-270's would each have been replaced by four RD-253's (because of development problems with the RD-270). The UR-700M would have been able to put 240 tons into LEO. Estimated length of the UR-700 with the LK-700 spacecraft is 75 meters.
The information in this space history note has been obtained from IAA paper IAA-96-IAA.2.1.05 presented by Mr Oleg A Sokolov in Bejing in October 1996. The general diagram of the UR-700 is reproduced here with the kind permission of Mr Sokolov.
