FREEZING THE DESIGN

Although the decree of 17 February 1976 constituted the formal approval of the Soviet shuttle, it did not stipulate what type of design should be chosen. It merely endorsed the basic requirements for the system laid down earlier by the military (30 tons up, 20 tons down). By the time the decree was passed, the OS-120 and MTKVP concepts had been pretty much abandoned and engineers had settled on the January 1976 OK-92 plan, namely a winged orbiter strapped to the side of a massive launch vehicle consisting of a core stage with three RD-0120 cryogenic engines and four strap-on boosters with one RD-123 LOX/kerosene engine each.

A change made soon afterwards was to increase the number of main engines on the RLA-130 core stage to four and reduce their vacuum thrust from 250 to 190 tons. The additional engine provided extra redundancy in case of a main engine failure during the climb to orbit [59]. At the same time, the sea-level thrust of the LOX/ kerosene engines in the strap-on boosters was increased from 600 to 740 tons, resulting in an improved engine called the RD-170. The RLA-130 had now almost acquired the configuration that would eventually become known as Energiya.