Dos An Improved Station

In sounds strange, but between December 1972 and April 1973 two stations were simultaneously in preparation at Baykonur, which was fairly buzzing with activity. One was OPS-1 for the military and the other was DOS-3 for the Soviet Academy of Sciences. The relationship between the TsKBM and the TsKBEM was strained by competition for access to the altitude chamber and other service/test facilities. Mishin's engineers had also to prepare the Soyuz that was to deliver the first Almaz crew. And Chelomey's people were also preparing two Protons: one for OPS-1, the other for DOS-3. All this activity followed the fiasco of the fourth N1 lunar rocket on 22 November 1972, which exploded after 107 seconds, a few seconds before the first stage was to have shut down and been jettisoned. The Kremlin finally accepted what had long been evident to many at the TsKBEM - the N1, and indeed the entire N1-L3 programme, was so complex that to perfect it would take much more money, resources and time than anybody had ever expected. Following the final American manned lunar landing in December 1972 the Kremlin turned its back on the Moon, preferring instead to pursue manned stations in low Earth orbit. Having lost OPS-1 precisely one month before the Americans were due to launch Skylab, the Kremlin demanded that every effort be made to launch DOS-3 ahead of its rival.

Even as DOS-1 and its backup DOS-2 were being built, the TsKBEM's engineers were designing an improved station. Two identical vehicles were built: DOS-3 and DOS-4.7 The testing of DOS-3 was completed at the TsKBEM in the second half of 1972, and it was delivered to Baykonur in December.

One of the limitations of the first two DOS stations was the power supply. DOS-1 had two pairs of solar arrays, one pair at the front and the other pair at the rear, and they were in a fixed alignment. To provide the maximum power output, the station had to maintain an orientation in which its arrays were illuminated by sunlight. But having to manoeuvre in such a way consumed precious fuel. And holding this solar-inertial orientation made it difficult to make astronomical or terrestrial observations. The improved DOS-3 design had three much larger solar arrays, all mounted on the narrower section of the main compartment, and which could rotate to face the Sun while the station was oriented optimally to perform specific observations. The total collection area was 60 square metres and the power was 4 kW, which was double that available to DOS-1. It is interesting that these solar arrays were borrowed from the TKS spacecraft that Chelomey had intended to use to supply his Almaz military station. But to compensate for the mass of these large solar arrays the fuel capacity of DOS-3 had to be reduced, which in turn required that the operating altitude had to be increased to about 350 km - recall that the higher a spacecraft's orbit, the less it is required to fire its engine in order to sustain that altitude. There were also some changes in the propulsion compartment. Other additions were the Delta navigation system and Kaskada (Cascade), which was a new and more economical system for controlling the station's orientation in space. For the first time, the water supply for

The improved DOS-3 space station.

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