SALYUT 6—A SECOND GENERATION SPACE STATION
Salyut 6 was the first space station to have two operational docking ports, and was designed to last 1.5 years. Launched on September 29, 1977, by the end of 1980, it had passed the 3-year mark and appeared in good shape for future utilization. (39)
Salyut 6 is depicted in figures 31-37. As noted above, it has two passive docking ports (the active systems are on the Soyuz or Progress ships). The forward docking port is used for Soyuz, while the aft docking port can be used either for Soyuz or Progress. The restriction for Progress is that the fuel lines which permit in-orbit refueling are located only at the aft port. If a Soyuz is located at the aft port and a Progress mission is needed to resupply the station, the crew dons spacesuits, enters the Soyuz and undocks from the aft end, the Salyut station is rotated by the ground crew around one of its transverse axes (40) so that the forward end is facing the Soyuz, and the crew redocks.
Basic station dimensions are the same as for the previous space stations. Including one Soyuz spacecraft, the space station is 21 to 23 meters long, (41) has a maximum diameter of 4.15 meters, an internal volume of 100 cubic meters, and weighs 25,600 kg. Without Soyuz, it is 13.5 meters long, has an internal volume of 90 cubic meters, and weighs 18,900 kg.
The three individually rotatable solar panels have a total area of 60 square meters, and produce 4 kilowatts of direct current. DC-AC inverters convert the electricity to alternating current. Salyut has a "wing span" of 17 meters with the solar panels and is made of aluminum.
A TOUR OF THE SALYUT 6 INTERIOR
The interior detail is also much the same as on previous space stations. Arriving through the transfer compartment, the cosmonaut enters an area with a volume of about 8 cubic meters. Pressure suits and airlock control panels are located there. Next is the working compartment with walls that are removable and covered with soft, bright-colored cloth. On this space station, the internal sound insulation layer was increased by 50 percent to lessen the noise of the equipment onboard in response to complaints from the crews.
Almost immediately in front of the access hatch is the station's central control post. Behind that is a table for working and eating, and nearby, a water tank. Cupboards for storing food are located to the left and right of the working compartment.
Past the table is the scientific equipment area containing, among other things, a cone which protects the BST-lm infrared telescope. The shower is located to the right of the equipment compartment on the "ceiling" and close to that are two airlocks for disposing of garbage. (42) One of these airlocks is also used for materials processing devices (Splav or Isparitel, depending on which one is in use at a given time).
On the "floor" of this section are the MKF-6M and KATE-140 cameras and infrared sensors for determining the local vertical positions of the station for the navigation system.
Behind the scientific equipment compartment is the toilet, with a soft door with a zipper fastener. Past that is the hatch into the intermediate chamber which leads to the aft docking hatch.
There are 20 portholes in Salyut for visual and photographic observations on Earth. Problems have been encountered with the optical quality of the portholes over a period of time as dust collects on them, and in a few cases, they have been scratched by what appear to be meteorites.
Pipes carrying a liquid heat transfer agent are welded along the inside walls of the station (but behind the panels which the crew sees) for thermal regulation. (43) This is especially important not only for the wellbeing of the inhabitants, but because the station, as described by the Soviets themselves, is a "sieve" with openings to allow electrical and hydraulic leads to connect equipment on the outside of the station (such as the solar panels) with the interior. (44) Rubber gaskets are used to seal the holes, and correct temperatures must be maintained in order for them to maintain their elasticity and strength.
Heat generated inside the station (by the crew and equipment) is retained by using a multilayer thermos material made from metallized film. Excess heat is radiated into space with the thermal regulation system. When no crew is onboard, an electric heater is usedto maintain proper temperatures.
Atmospheric regenerators consisting of nonreusable chemical cartridges are used to maintain the proper air composition (atmospheric pressure—700-960 mm Hg; partial oxygen pressure—ISO-240 mm Hg; partial carbon dioxide pressure—no more than 7-9 mm Hg.) The system also has pressure sensors to warn the crew of unplanned drops in pressure. (Some drops in pressure are "planned" in that they occur when the crew opens an airlock for EVA or disposing of garbage. The air is replenished by Progress cargo ships.) Fans are used to circulate the air.
Sitting in front of the control panel at work station 1, a crewmember sees a globe (called "Globus") in the upper corner which indicates the position of the ship relative to Earth. Next to it is a control panel with lights indicating the status of onboard systems (green), that orders are about to arrive from the ground or that the crew itself has given during the process of controlling the station (yellow), and emergency signal indicators (red). Two command signal systems are located to the left and right of the central post. On the left is the control panel for life support systems, and on the right, the refueling control panel.
There are six other work stations in Salyut 6. Station 2 is used for manual control of the station and has a panel, communication gear, astronomical instruments, and a control handle; station 3 is the control panel for the BST—lm telescope and its cooling systems, and also has communication gear, a viewer, and control handles; station 4 is for medical-biological equipment and the exercise equipment is located nearby; stations 5 and 6 are in the transfer compartment; and station 7 is for the water regenerating systems.
Salyut 6 has two main engines (300 kg thrust each) and 32 orientation engines (14 kg thrust each) positioned in four clusters 90 degrees apart. These are located around the outside of the aft docking port. Fuel is brought up by Progress cargo ships. Additional aspects of the fuel system are described in the next section on the Progess refueling operation.
Salyut has a water regeneration system which removes water vapor from the air produced by breathing and perspiring and recyles it for consumption. Additional water is brought to the station on Progress cargo ships. Despite popular reports to the contrary, the Soviets have specifically stated that there are no provisions for water regeneration from urine on Salyut 6. (45)
Salyut 6 has an orientation and motion control system which the Soviets refer to as SOUD. It automatically orients the station for scientific observations and experiments, and docking manuevers, performs trajectory corrections, and allows for orienting the station via manual controls from the crew. The Kaskad system tested on Salyut 4 is part of SOUD and is used for "economical orientation" and consists of gyroscopes, a mathematical electronic memory, and two sets of sensors: One measuring infrared radiation from the Earth to determine position relative to the planet; the other measuring the flow of the ionic wind to determine orientation with respect to the station's velocity vector.
The Delta autonomous navigation system uses an onboard computer which receives data from a radio altimeter, radial velocity meter, and sunrise/sunset sensors. It can forecast the station's position 24 hours in advance, and compute the times when the station will be within range of tracking sites and automatically turns the communications equipment on and off as appropriate.
There is some question as to how well the navigation systems worked on Salyut 6. There were frequent references to the crews conducting navigation tests, and several Progress missions brought up replacement components. Some of the repairs would be expected considering the length of time the space station was in use, and some of the navigation exercises were probably related to gaining experience with how to best orient the station for certain tasks. Still, the repeated references raise questions about the system's reliability.
SALYUT 6 DESIGN CHANGES
Despite the similarity between Salyut 6 and its predecessors, there were significant changes to this second generation space station. The main difference is the addition of the second docking port, which required redesign of the main engine assembly. Originally the main engines were located in the center of the aft end, with orientation engines around the outside. On Salyut 6, the engine compartment was widened from 2.2 meters in diameter to the 4.15 meter maximum diameter of the station, (46) and the main engines as well as the orientation engines were mounted on the rim, with the docking port in the center.
The engines themselves were redesigned to be pressure fed, instead of turbine driven as on previous Salyuts, and hydrazine was used to fuel all the engines. Previously, on Salyut and Soyuz spacecraft, hydrogen peroxide was used for attitude control engines and to power the turbines for pumping oxidizer and fuel to the main engines; while hydrazine was used for the main engines. The change to a unified fuel system simplified the number of propulsion lines and tanks needed. (Soyuz also switched to a common fuel system with Soyuz T, and Progress uses the same system.) Nitrogen is used to pressurize the fuel system. Salyut 6 has three oxidizers and three fuel tanks; one of each type is a reserve.
A. SOVIET SPACE PROGRAMS: 1976-80, (WITH SUPPLEMENTARY DATA THROUGH 1983) MANNED SPACE PROGRAMS AND SPACE LIFE SCIENCES PREPARED AT THE REQUEST OF HON. BOB PACKWOOD, Chairman, COMMITTEE ON COMMERCE, SCIENCE, AND TRANSPORTATION UNITED STATES SENATE, Part 2, OCTOBER 1984, Printed for the use of the Committee on Commerce, Science, and Transportation, U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON, D. C., 1984
39. In fact, it was used for manned crews through part of 1981, and was deorbited in the summer of 1982 after a year of operations with the unmanned Kosmos 1267 spacecraft, a test of a modular space station design.
40. In different accounts, it has been reported as a pitch or yaw maneuver. It may be that either can be used depending on what orientation the station already is in at the time of the undocking-re-docking activity.
41. As noted in previous sections, the length of Salyut depends on whether external fixtures such as radio antennas are included. Konstantin Feoktistov has stated that Salyut 6 was 13.5 meters long by itself (Moscow, Novoye v Zhizni, Nauke, Teknike, Seriya 'Kosmonavtika, Astronomiya. No. 3, 1980), and since Soyuz is 7.5 meters long, the docked combination, should be 21 meters. The Soviets usually list the length as 23 meters, however, so it is assumed that antennas are included in the latter length.
42. All types of refuse are placed in the garbage containers, including body waste from the toilet. The garbage containers decay naturally from orbit after about 1 month, burning up completely as they enter the dense layers of the atmosphere. They do not present a significant "space pollution" problem.
43. "It is this system which the Soyuz T-3 crew had to repair at the end of 1980 by replacing.
44. "Semenov, Yu. and L. Gorshkov. "Salyut 6" Orbital Station: Home, Laboratory, Vehicle Nauka i Zhizn, Apr. 1981. pp. 44-53, 125.
45. Semenov and Gorshkov, op. cit.
46. Kidger, Neville. The Salyut 6 Space Station. Spaceflight, April 1979, p. 178.