In the aftermath of the N1 failure, Chelomei was proposing the UR-900 for the Mars expedition. A garbled description of this launch vehicle appears in Chertok's memoirs. This would seem to be a version of the UR-700 using 15 RD-270 modules in the first and second stages in place as opposed to the nine modules of the UR-700. The third and fourth stages were derived from the UR-500. The booster could deliver 240 tonnes to low earth orbit.

Chertok asked Chelomei what would happen if, God forbid, such a booster exploded on the launch pad. Wouldn't the entire launch complex be rendered a dead zone for 18 to 20 years? Chelomei's reply was that it wouldn't explode, since Glushko's engines were reliable and didn't fail. Aside from that, these propellants had been used in hundreds of military rockets, deployed in silos, aboard ships and submarines, with no problem. Fear of these propellants was irrational. Related propellants were used by the Americans on the Apollo manned spacecraft.