Salyut 1 (Soyuz docking).

After losing the race to the Moon, Soviet leaders feared that the Americans would take yet another “first” in the space race by launching Skylab into orbit and claiming the world's first space station. They put their hopes of beating the Americans on a military space platform named Almaz, which was formally approved in 1967. With the goal of evaluating the effectiveness of human spying from space, it was supported by the Soviet military. But the Almaz program had fallen behind schedule. The design bureau of Sergei Korolev offered a solution. It promised that if it were given the hull of an Almaz station-which was built by another organization-it could equip the hull with systems and electronics from the Soyuz ferry spacecraft and have a small station ready for launch long before Skylab. The Soviet government concurred and approved this “new” project in February 1970, which was named the Long-Duration Orbital Station (“DOS” in its Russian language abbreviation). DOS would serve as the source for almost all Soviet space station designs in the following decades.

In April 1971, the Soviets launched the first DOS, named Salyut (or Salyut 1), in “salute” to the first Soviet cosmonaut Yuri Gagarin. The Salyut station was 16 meters long with two major sections, each with different diameters. It weighed about 19 tons and had a single docking port on the front end to receive Soyuz crew delivery spacecraft. Crews would be able to stay in space for about a month in early DOS vehicles and conduct scientific experiments.

The first crew to Salyut was unable to enter the station, but the second crew of Soyuz 11, launched in June 1971, became the first ever to enter a space station and live in it. For 24 days, cosmonauts Dobrovolsky, Volkov, and Patsayev conducted experiments and proved that humans could stay in orbit for relatively long periods. During their return to Earth on June 30, 1971, a valve on the Soyuz ferry failed, letting all the air escape in a matter of seconds. All three cosmonauts were killed, and the Soviet space program was stopped in its tracks.

The next two years brought more bad luck. DOS numbers 2 and 3 failed in 1972 and 1973 respectively and never hosted any crews in space. The tide of misfortunes receded by 1975 when NPO Energia, Korolev's old design bureau, operated DOS number 4. Known publicly as Salyut 4, the station successfully hosted two crews, the second one for more than two months.

 
Salyut 4 successfully hosted two crews, the second one for more than two months.

The Soviets also flew three Almaz stations in 1973-1977. Known as Salyuts 2, 3 and 5, they focused primarily on military experiments. The program was cancelled in 1978 because the Soviet military believed the non-crewed satellites were more efficient and cheaper to use for space-based reconnaissance.

A major turning point for Soviet space station development was the launch of DOS number 5 in September 1977. Known publicly as Salyut 6, the station was an improved version of DOS with two docking ports instead of one and new life support systems that could maintain life for as long as six continuous months. In 1977-1978, cosmonauts Romanenko and Grechko, the first crew to board Salyut 6, spent 96 days in space, breaking the world endurance record set by the American Skylab 4 crew four years earlier. During their mission, they received two “visiting” missions, one of them carrying a “guest cosmonaut” from Czechoslovakia. Additionally, the Soviets introduced an expendable cargo spacecraft known as Progress that was derived from the Soyuz.

Beginning with the 96-day flight of Romanenko and Grechko, subsequent Soviet cosmonauts spent 140, 175, 185, and 75 days on board Salyut 6 between 1978 and 1981. A total of 18 Soyuz and 12 Progress vehicles successfully docked to the station. There were no major failures and no fatalities, and the Soviets gained valuable experience with a variety of complex operations in space such as in-orbit refuelling and docking. The Soviets also gathered important data on the state of the human body in space. Cosmonauts from Communist countries such as Poland, East Germany, Hungary, Vietnam, Cuba, Mongolia, and Rumania also visited Salyut 6 as guest-cosmonauts during weeklong missions.

Salyut 7, which followed in 1982, was equally successful. Between 1982 and 1986, it hosted five long-duration crews that were visited for short periods by Soyuz ships carrying cosmonauts from France and India as well as the second Soviet woman cosmonaut, Svetlyana Savitskaya. During these missions, the Soviet cosmonauts carried out extensive spacewalks, conducted a variety of successful repairs in space, and performed the dramatic rescue mission of Soyuz T-13, which brought the dying Salyut 7 back to full operating condition after a series of catastrophic failures. The longest host crew set a record of 237 days in space.

The successful missions of Salyut 6 and 7 led to the launch of Mir (Russian for “peace” or “community”) in February 1986. Mir, otherwise known as DOS number 7, was a vastly improved DOS that had six docking ports. The goal was to slowly add at least six modules, each about the size of Mir itself, until the whole complex would be a full-scale space station weighing about 100 tons. Each of the add-on modules was derived from Transport-Supply Ship (or “TKS”) vehicles that were originally developed for the abandoned Almaz program.

 
Mir-18 commander Vladimir N. Dezhurov performing in-flight maintenance in the Core module of the Mir space station.

In 1988, a three-person crew set a new endurance record by spending an entire year in space on Mir. The Mir core was briefly uninhabited for a few months in 1989, but beginning in September 1989, the Soviets began what would turn out to be 10 years of continuous crewed presence in space. During this period, in 1991, the Soviet Union fell apart and the Russian Federation took over operations of Mir.

 
Mir space station. Cosmonauts assembled Mir piece-by-piece during a busy ten-year period beginning in 1986. The station's modules include the voluminous Core, Mir's original 20-ton segment that harbours the crew's living quarters; plus Spektr, a 19-ton science laboratory famous for its 1997 collision with a Progress spacecraft; and the 19-ton Priroda Earth observatory.

Modules were added to Mir over a period of a decade. The first was Kvant, an astrophysics research module launched in 1987. Kvant 2, a huge spacewalk airlock, was added in 1989. Kristall, a multipurpose module, linked up in 1990 followed by Spektr, a power module in 1995 and Priroda, a remote sensing platform in 1996. A specialized piece of equipment known as the Docking Module was added later to allow Mir to be visited by NASA's Space Shuttle. In total, with two visiting Soyuz or Progress ships, the station weighed as much as 120 tons in orbit.

During its 15-years in space, the Mir complex was the site of some notable achievements. In 1994-1995, a Russian doctor, Viktor Polyakov, spent a year-and-a-half in space, a duration record that still stands. Another cosmonaut, Anataoly Solovyov, set the world record for the most time spent “spacewalking.” The world's first journalist, a Japanese television reporter, visited Mir in 1990. Guest cosmonauts from Bulgaria, Afghanistan, France, Japan, Kazakhstan, Austria, Great Britain, Germany, and Slovakia also visited the station.

The United States and Russia initiated the Shuttle-Mir program in 1995 to acquire experience in international cooperation before the launch, assembly, and operation of the much larger International Space Station. Over three years, seven American astronauts lived aboard the Mir complex with their Russian counterparts, each for an average of four to six months. During this phase two of the most dramatic events in the history of space exploration occurred. One was a flash fire inside the station in which the crew had to don emergency masks and extinguish the fire as quickly as possible. The second was a near-catastrophic impact between a Progress cargo ship and the Mir complex. In the crash, the Spektr module completely depressurized, and the crew had to rapidly seal the hatch before all the air leaked out. In both cases, the crews could have been killed. As a result, NASA was severely criticized for neglecting safety concerns although later events vindicated NASA's position.

Once Shuttle-Mir ended, in 1998, the Russians tried in vain to keep Mir occupied, but lack of money forced the last host crew, the 28th main expedition, to return to Earth in August 1999, thus ending nearly 10 years of continuous piloted operations.

A private company named MirCorp managed to raise enough money for a single 2-1/2- month mission in 2000, but the Russians finally said goodbye to Mir on February 20, 2001, almost exactly 15 years after launch, when the entire complex was deliberately deorbited over the Pacific Ocean, ending a memorable saga in the history of space exploration.