Salyut: How We Learned To Make Space Stations
When you think about space stations, which ones come to mind first? You might think Skylab, the International Space Station (ISS), or maybe Russia’s Mir. But before any of those took to the heavens, there was Salyut.
Russia’s Salyut 1 was humankind’s first space station. The ensuing Salyut program lasted fifteen years, from 1971 to 1986, and the lessons learned from this remarkable series of experiments are still in use today in the International Space Station (ISS). The program was so successful at a time when the US manned space program was dormant that one could say that the Russians lost the Moon but won the space race.
Russia’s Own Space Race
The Salyut program’s origins stem from a little know space race within Russia in the 1960s. On the one side was the OKB-52 design bureau which worked on putting up a military space station. On the other side was the OKB-1 which sought to do the same but for civilian science purposes.
The military had an early lead with their Almaz space station cores. In an effort to catch up, the civilians combined the Almaz hull with their own systems from their Soyuz spacecraft and added more solar panels. These were designated DOS (Durable Orbital Station) stations.
The civilian Salyut program was created on February 15, 1970. With the cold war in full swing, the military program was masked from the world by pretending to be a part of Salyut. And by April 19, 1971, the first of the Salyuts and the world’s first space station was launched.
Salyut 1 (DOS-1): Firsts And Tragedy
In contrast to today’s space stations made up of multiple modules, the first Salyuts were monolithic. They were launched as a single unit, filled with all the supplies they’d need as well as all their experiments. The crew arrived separately and when all supplies were exhausted and the experiments done, the space stations were deorbited.
While the Salyut 1 missions held a lot of firsts, they were not without some difficulties. On April 22, 1971, the first crew went up in Soyuz 10 but were unable to enter the station and had to abort the mission.
The second crew in Soyuz 11 successfully entered the station and remained for 23 days, a new record for duration in space at the time. However, tragedy struck during the crew’s return to Earth when a pressure-equalization valve between the Soyuz spacecraft’s orbital and descent modules opened prematurely while still in space. The three cosmonaut’s died of asphyxiation within seconds. To date, they are the only people to have died in space. (For the quibblers, the Columbia disaster occurred around 60 km, and most consider space to start at 100 km.) A redesign of the Soyuz followed with room for only two cosmonauts, but wearing pressure suits.
Setbacks And Military Missions
As is the norm for space travel, the still infant civilian program continued to suffer setbacks.
DOS-2 would have been Salyut 2 before the second stage of its Proton rocket failed causing it to crash into the Pacific. The designation Salyut 2 was instead given to the first military mission using an Almaz space station. DOS-3 was to become the next civilian Salyut, but errors in its flight control system while out of range of ground control led to unnecessary orbital corrections, using up all of its fuel. As a result, the Salyut 3 designation went to the next military mission with another Almaz station. The final military mission was called Salyut 5.
Salyut 4 (DOS-4): Doing Science
The next civilian station, Salyut 4, was essentially a copy of DOS-3. It had three large solar arrays instead of Salyut 1’s two sets of two, generating two kilowatts. Scientific instruments included a solar telescope, shortwave diffraction spectrometer, and two X-ray telescopes. It was also outfitted with equipment for testing and minimizing the effects of zero-gravity on humans.
Two crews spent time on board, the second crew staying for 63 days. A third was planned but experienced a launch abort. An unmanned Soyuz spacecraft also docked to the station for three months to test durability.
Salyut 6 (DOS-5): The Next Generation
Salyut 6 heralded in the next generation of space stations, ones which permitted continuous occupation and could remain in space for long durations, two things which today we think of as normal with the ISS.
Continuous occupation and long durations were made possible mainly by the addition of a second docking port. Previous Salyuts could neither be resupplied nor could their waste be removed, except for that which could be carried in the limited space in the crewed Soyuz spacecraft. A new spacecraft, the unmanned Progress freighter, was created for carrying supplies to the stations. Supplies included air, air regenerators, food, water, clothing, mail, and propellants. Waste was loaded back into the Progress to be burned up on reentry into the atmosphere. Progress vessels are still in use today, making three or four resupply trips to the ISS each year.
You might wonder why you couldn’t use a single docking port for resupply. Why couldn’t you temporarily undock the crew-carrying Soyuz from the station, dock and unload the Progress, and then redock the Soyuz? One reason was made clear a few years later on the Mir space station during terrifying moments when a Progress docking went very wrong. It missed the docking port and instead collided with some solar panels and one of the Mir’s modules, creating an air leak. Luckily they were able to seal off the leaking module but if things had gone a little differently, they would have had to abandon the station. If they had only one docking port, their escape vehicle, the Soyuz, would have been temporarily undocked to make room for the errant Progress freighter. Not good. With two docking ports, the Soyuz was ready and waiting.
The two docking ports also allowed for visitors and for crew handovers, where a new crew would arrive while the previous was still present. The Salyuts never were occupied continuously, but this was the beginnings of such a possibility.
Launched in September 1977, Salyut 6 was deorbited in July 1982 after five years of use. It accommodated five long-duration crews and eleven short-term ones. It could have been used longer, but managing mold in the living compartments had become too difficult.
Salyut 7 (DOS-6): The Final Voyages
In his Diary of a Cosmonaut: 211 Days in Space, Valentin Lebedev talks about how the experience built up from the five years of crews in Salyut 6 led to many changes to the interior of Salyut 7. To start with, the equipment was completely rearranged for more efficient work, service, and repair. They now had a variety of food to choose from as well as improved medical equipment.
The portholes now came with external shutters to keep them clean of fuel from the engines and to protect them from micrometeorites. Similar shutters are used today on the International Space Station to protect the Cupola module’s large windows from micrometeorites.
On Salyut 6, water was brought up in fifteen-kilogram spherical tanks which had to be hand-carried from the Progress supply ship into the Salyut. At least one crew hacked this system by running hoses from the Progress through the docking port to pump water directly into the Rodnik water storage system. This improvement was built into Salyut 7 and later into Mir.
Perhaps most significantly, Salyut 7 started the move from monolithic space stations to modular ones. To help with the design of Mir, testing was performed with docking and making use of “Heavy Cosmos modules”, which were really Russian TKS spacecraft.
Even as Mir began its life in 1986 Salyut 7 was to remain in use, and the station was raised to a higher storage orbit. But with the collapse of the Soviet Union and its ensuing economic difficulties, funding for the station never materialized and the last Salyut’s orbit gradually decayed until 1991 when it underwent an uncontrolled reentry over South America.
We’ve already mentioned a number of things that carried over from the Salyut program, including external window shutters, the Progress resupply ships, and the whole concept of modular space stations. But even modules still in use today are descendants of the Salyuts. Mir’s Code Module was a DOS-7. The Zvezda Service Module on the ISS is a DOS-8. The ISS’s Zarya module is a descendant of the TKS spacecraft tested with Salyut 7.
What other cold war era Russian tech echos into the present day? The powerful RD-180 rocket engine is a modern version of the closed-cycle engine design used for the Russian N-1 moon rocket. Read all about it in [Kristina Panos’s] article Russian Rocket Tech Comes in from the Cold.