11K55

The 11K55 was a lighter version of Zenit conceived jointly by KB Yuzhnoye and the Omsk-based PO Polyot in 1976. In its original design it had a modified Zenit first stage with a smaller propellant load and a two-chamber version of the RD-170. The newly developed second stage would be powered by a cluster of three LOX/kerosene 11D58M engines of NPO Energiya’s Blok-DM upper stage. With a launch mass of 210 tons, the rocket had a payload capacity of roughly 5 tons. The 11K55 was seen as an environmentally clean replacement for the Kosmos-3M and Tsiklon launch vehicles, rockets with storable propellants built at Polyot and Yuzhnoye, respectively. Launches were to take place from Plesetsk and Kapustin Yar. Other engines con­sidered for use on the 11K55 in the late 1980s/early 1990s were a cluster of three or four RD-120K engines on the first stage and two different re-ignitable LOX/kerosene engines for the second stage, the RD-133 and RD-134, both with a vacuum thrust of 35 tons. The 11K55 is known to have been the subject of a government decree in 1986 [69].

11K37

In 1976 KB Yuzhnoye also began looking at heavier versions of Zenit. One idea was to build a 5.4m diameter first stage with two RD-171 engines, but this was deemed unrealistic because it required new manufacturing techniques and untested transpor­tation methods by road, water, or air. Instead, planners concentrated on rockets with

two, three, or four Zenit first stages clustered together, capable of putting between about 30 and 60 tons into low orbit. The common designator for these boosters was 11K37.

The most thoroughly studied version was the one with three Zenit first stages. Mounted above that would have been a second stage with a 214-ton thrust single­chamber version of the RD-170 engine known as RD-141 as well as an RD-8 vernier engine. A later idea was to equip the stage with three 90-ton thrust RD-142 engines and several verniers. The RD-142 was apparently an improved version of the RD-120 engine used in the second stage of the 11K77. With the latter second stage, the 11K37 would have been capable of putting 40 tons into low orbit, 35 tons into polar orbit, and about 5 tons into geostationary orbit. Upper stages studied by Yuzhnoye for the 11K37 were an interorbital space tug originally developed for deployment from Buran as well as the Vikhr cryogenic upper stage.

As mentioned earlier, the 11K37 was proposed by KB Yuzhnoye in a com­petition started in 1984 to develop boosters in the 30-60 ton range, with the other candidates being Groza and an upgraded Proton rocket. A major disadvantage of the 11K37 was that it required the construction of a new launch facility. Therefore, the Ministry of General Machine Building recommended in the late 1980s to make the rocket compatible with Energiya’s UKSS launch pad at Baykonur. When a new competition was launched in the early 1990s to develop rockets in the 20-40 ton payload range, the 11K37 was still in the running, but eventually lost out to Energiya – M in 1991 [70].