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the crew would by partly recycled using a condenser in the air conditioning system. And the scientific payload was increased to about 2 tonnes. The improved DOS had the capacity to support two men for 180 days, and the plan was to send three crews, each of which would spend two months on board. It was fully expected that DOS-3 would significantly upstage the American Skylab.

In the period October 1972 to April 1973 the crews who had trained for the lost DOS-2 switched their attention to DOS-3:

• Aleksey Leonov and Valeriy Kubasov

• Vasiliy Lazaryev and Oleg Makarov

• Aleksey Gubaryev and Georgiy Grechko

• Pyotr Klimuk and Vitaliy Sevastyanov

However, although DOS-3 was successfully launched on 11 May 1973, it became one of the rare spacecraft of the manned space programme over which control was almost immediately lost. This fiasco illustrated all the institutional deficiencies that had accumulated over the years, and it is therefore worth examining in detail.

The first in a series of details that brought about the demise of DOS-3 was related to the altitude of the initial orbit. Although its overall dimensions were the same as those of DOS-1, because DOS-3 carried more scientific equipment it was a little bit heavier. Whereas the Proton had been able to insert the lighter DOS-1 into an orbit of 200 x 222 km, the best that it would be able to achieve with DOS-3 would be 155 x 215 km. The station's first assignment would therefore be a series of manoeuvres designed to achieve its 350-km circular operating orbit. Before each engine firing, it would have to orientate itself appropriately. An ionic sensor was to be used to sense the orientation of the station relative to the ionosphere through which it was passing. DOS-3 was the first station to be provided with this sensor. An analysis showed that the station would have at most four days to escape from its initial orbit, as after this the orbit would have decayed to such an extent that the engine would not be able to achieve the desired operating orbit. It was therefore vital to raise the orbit as soon as possible.

A second factor which contributed to the loss of DOS-3 was the use of the ionic sensor. Because such a sensor detects not only ions but also glowing particles from the attitude control thrusters, it is an unreliable means of finding the orientation of a spacecraft that is manoeuvring. In fact, before the activation of the ionic orientation procedure, the station's thrusters must be fired to orient it to maximise the number of ions entering the sensor's tube. Measuring their angle of entry provides a point of reference for controlling the station. Once the station has rotated to place the ionic flow at the desired angle, the KTDU-66 main propulsion system can be activated to manoeuvre towards a higher orbit. If the orientation is not performed accurately, a spacecraft can end up in the wrong orbit, possibly decreasing its altitude instead of increasing it - in the worst case diving back into the atmosphere! But the problem with the ionic orientation method is that the tube is exposed to particles in the efflux of the thrusters, which can confuse the analysis. A further complication is that the efficiency of ionic orientation varies with the strength of the Earth's magnetic field, and so with the station's geographical latitude. In given conditions, ionic orientation

Left: Kubasov and Leonov training for the first mission to DOS-3. Right: a model of DOS-3 at the TsPK, with the descent module of Soyuz 2 visible in the distance and cosmonaut Shatalov on the left.

The 'first crew' for DOS-3: Kubasov (left) and Leonov by the Soyuz simulator.
The 'second crew' for DOS-3: Lazaryev (left) and Makarov.
The 'third crew' for DOS-3: Grechko (left) and Gubaryev in the station simulator.
The 'fourth crew' for DOS-3: Sevastyanov (left) and Klimuk.

can mislead the attitude control system, and thereby increase the consumption of fuel. The DOS designers were aware of this, and decided to operate the thrusters at their weakest level in order to minimise the efflux. However, the disadvantage in using weak thrusters was that it would take a long time - possibly several hours - to achieve a major change in orientation, and the longer the time the greater the risk of the control system being misled. Unfortunately, because the system was new, it had not been tested in space to measure its susceptibility to thruster efflux. Nevertheless, the flight controllers were told to perform the ionic orientation as soon as the station was released into its initial orbit.

The last in the sequence of mistakes which led to the loss of DOS-3 was the weak organisation of the terrestrial NIP sites. While Mishin's team focused on testing the station and preparing it for launch, no real thought was given to the unique aspects of controlling it in flight. In fact, the greatest weakness of the Soviet system at that time was flight control - and not just for Salyut, for Soyuz too. On the one hand the designers failed to prepare the documentation in time to enable the flight controllers to appreciate the dynamical operations which DOS-3 would be required to perform. On the other hand the TsUP neglected to liaise with the experts that developed the control systems to draw up an effective plan for providing all the commands which the station would need during its hectic first few days in orbit. In the past, this kind of inadequate planning had been overcome by Pavel Agadzhanov, Boris Chertok, Yakov Tregub and Boris Raushenbakh, all of whom served on the Chief Operative and Control Group (GOGU). But of this group only Tregub was in the TsUP when DOS-3 was launched and, to make matters even worse, he was short of orientation system operators. General Agadzhanov, the head of the GOGU, was absent. He was represented by his assistant, Colonel Mikhail Pasternak. And, of course, the seven control stations across the Soviet Union were operated by the Army. As a result, the experts in telemetry and control who would require to coordinate closely in order to fly DOS-3 through its vital manoeuvres were isolated from each other. The flow of information through the system was slow, owing to the number of checks, protocols and certifications, and when flying a spacecraft through complex manoeuvres time is precious. Furthermore, as it had been accepted that it was impractical to continue to operate stations for months by communicating long lists of information passed by telephones and telegraphs, an automatic system for data processing was being tested at that time. So we see that the TsUP in Yevpatoriya was ill-prepared to swiftly and efficiently provide the commands which DOS-3 would require if it were to reach its operating orbit.

In fact, the leaders of the TsKBEM, Army and the Ministry of General Machine Building were aware of the difficulty of controlling manned spacecraft. Although a great deal had been done since 1966 to improve the system, it still suffered from the fact that the Army ran the ground stations and the technical communication systems and the civilian specialists were responsible for analysing the data and preparing the commands to be issued to the spacecraft. As yet, no one had attempted to unify the system in the manner that NASA had done a decade earlier by establishing Mission Control in Houston, Texas, and directly linking it to the global chain of tracking and communication stations.

Inspecting the DOS-3 simulator. Note the Soyuz docking probe on the right.

The first attempt to launch DOS-3 on 8 May 1973 had to be halted when a vent on one of the six oxidiser tanks of the first stage developed a leak 20 minutes prior to the scheduled time of lift-off. It prompted a major altercation between Mishin, who was the technical director of the DOS programme, and Chelomey, in charge of the rocket. Recalling that a launcher failure had been responsible for the loss of DOS-2, Mishin demanded that the station be transferred to a new rocket. Chelomey insisted that all that was required was to replace the vent. Chelomey prevailed, and the work was done at the pad. But Mishin persisted in demanding that the rocket be changed! Because this would impose a delay of at least a month his TsKBEM colleagues and members of the State Commission urged him to accept the rocket, so he reluctantly acceded. DOS-3 was successfully launched on 11 May 1973, just three days before the Americans launched Skylab.

The Proton delivered DOS-3 into the planned 155 x 215 km orbit without incident. The NIP-3 tracking facility at Sarishagan in Kazakhstan was the first to hear from the station and confirmed that the antennas and solar panels had deployed correctly. Twelve minutes into the flight, NIP-15 at Ussuriysk on Kamchatka, at the eastern end of the Soviet ground network, sent a command to activate the ionic orientation system. But despite the fact that the NIP-15 documentation specified that the thrusters were to be fired at minimum power, they were commanded to operate at their maximum! An investigation found that the order stating that the orientation engines must fire at full power was issued to NIP-15 by the TsUP in Yevpatoriya. A TsKBEM theorist who had modelled the performance of the thrusters in both regimes prior to going to the TsUP had discovered that if they were to be operated at their minimum power the slow pace of the orientation meant that there was a chance of the process halting during the station's second orbit. He therefore recommended that the orientation be conducted as rapidly as possible. This was forwarded to Tregub, who was the flight director. He accepted the reasoning, and ordered that a telegram be sent to NIP-15 to act accordingly. NIP-15 was in communication with the station for ten minutes, which was sufficient time to establish that the station had begun the orientation. But the only person present who was capable of doing so was isolated by the fact that all transmissions from the station had first to be registered by the Army's telemetric experts, who, after recording the data in their diaries, passed it to their superiors for further processing. When the TsKBEM's expert at NIP-15 received the data on the orientation he was shocked to see that the rate of rotation was ten times faster than the planned speed! Chertok later drew an analogy to convey what was happening to the station - it was like when a dog swings around suddenly to try to bite its tail. The thrusters were firing continuously at maximum power in an effort to stabilise a ship weighing 19 tonnes. The TsUP in Yevpatoriya should obviously have been notified immediately, but rather than just picking up the telephone, the operating procedure obliged that a telegram be written, signed by the appropriate senior officer and then entered into the NIP-15 log before being sent. Once the telegram reached the TsUP, it had to be printed out, logged and sealed before it could be delivered. In fact, the procedure was so time-consuming that meanwhile the station had completed its first orbit and entered the communication zone of NIP-16 in Yevpatoriya!

Because the TsUP controllers had expected that by this time the station would be correctly oriented to perform the first of the manoeuvres required to raise its orbit, they had everything ready to command this. But to their astonishment the data from the experimental automated data processing system indicated that it was not in the desired orientation, and that it had used a vast amount of fuel. The first thought was that the data processing system must not be working correctly; it was experimental, after all. But two young engineers, one an expert in the ionic orientation system and the other an expert in flight control, suspected that the data were correct. They ran to the room where the data was received, in order to examine the original tape, and confirmed that the orientation system had used so much fuel that if it continued to operate as it was doing then the tanks would soon run dry. Because the telephone in that room was not working they ran to the main control room and urged Tregub to command that the orientation system be switched off immediately - the station was still in communication with NIP-16, so this was feasible. But Tregub, who had rejected the plan to perform the orientation slowly and had directed that it be done rapidly, was reluctant to turn off the orientation system. He faced a dilemma. What would happen if he were to take the advice of the young engineers and it transpired that they had been wrong? Would it be possible to resume the orientation process in time to make the manoeuvre to increase the orbit? Unfortunately, he was unable to contact the TsKBEM leadership, as they were driving from Baykonur to the airport in order to fly to Yevpatoriya; they would not reach the TsUP for at least six hours. While Tregub pondered what he should do, the station flew out of range of NIP-16. It would not be able to be contacted again until it reached NIP-15 at Ussuriysk. All this time it continued to spin around 'hunting ions', consuming further fuel. Finally, Tregub decided that the best option would be to halt the orientation. He grabbed the telephone and ordered the NIP-15 operator to do this, but unfortunately the station had passed out of range two minutes earlier!

In the 40 minutes before DOS-3 flew back into range of Yevpatoriya, the experts at the TsUP analysed the available data and decided that the young engineers were right to have recommended immediately switching off the ionic orientation system. This was verified when contact was established and it was ascertained that the fuel was totally exhausted. If the orientation had been halted by NIP-16 at the end of the first orbit, it may have been possible to complete the task on the second orbit by firing the thrusters at their minimum level and then raise the orbit. But now it was lost! When the TsKBEM, Air Force, State Commission and MOM representatives reached Yevpatoriya they could not believe that the third space station in a row had been lost - all in a period of only ten months.

To disguise its identity, DOS-3 was announced by TASS as Cosmos 557; and for some reason its orbit was misquoted as 218 x 226 km. It re-entered the atmosphere on 22 May. Meanwhile, the Americans launched Skylab on 14 May. Although that station was damaged during its ascent through the atmosphere, its first crew of three took up residence on 25 May. They returned to Earth after 28 days, having beaten the record of the ill-fated Soyuz 11 cosmonauts. The second and third Skylab crews spent 59 and 84 days in space respectively, leaving the station 'mothballed'.

Flight director Yakov Tregub (left), cosmonaut Grechko (centre) and flight controller Vadim Kravets at the TsUP in Yevpatoriya.

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