Space Matter is a weekly column that delves into space science and the mechanics of spaceflight. From the latest discoveries in the universe around us to the fits and starts of rocket test flights, youll find analysis, discussion, and an eternal optimism about space and launching ourselves into the cosmos.

We all are aware that the International Space Station is out there, in low Earth orbitbut did you know that there are two other space stations up there as well? Or that the first private space station is currently in development? We have a rich history of space stations, from Skylab to Mir and beyond.

Americas first space station was Skylabwhich was never actually intended or built for that use. Skylab was actually the unused upper stage of a Saturn IVB rocket. It launched in 1973 aboard the last Saturn V rocket and hosted three manned missions before falling back to Earth in 1979. The retrofitted rocket stage was never intended to be a long-term space station, but it proved to Americans that humans can live and work in space. It also advanced space science considerably through its onboard workshop and solar observatory.

The Skylab space station. Photo courtesy of NASA

After Skylab, attention turned to the Space Shuttle program, which was launched on April 12, 1981. The orbiter fleet boasted a large payload bay that was perfect for conducting experiments in space. While we were focusing on a reusable space vehicle, the Russians were still using their trusty Soyuz capsules (still in use today) and instead turned their focus to building a space station.

Between 1971 and 1982, the Russians successfully launched six Salyut space stations. (Salyut 2 was unable to achieve a stable orbit, falling back into the atmosphere two weeks after launch). The last of these, Salyut 7 was in orbit from 1982 through 1991, with 10 manned visits over its lifetime. Through their experience with these space stations, the Russians became experts at living and working in space.

In 1986, the Russians launched Mir, the worlds first modular space station. This means that, much like the ISS, the station consisted of a core that was launched first. Over time, a total of six additional modules were launched and assembled in space, expanding the station over the years. It was on Mir that extended spaceflight became normal; expeditions generally lasted around six months (the same as the ISS).

The United States had plans to build a Mir counterpart: the Freedom space station. In the early 1980s, it was envisioned as a space-based destination at which orbiters could dock. Its cancellation (due to budget and design issues) was part of the reason the shuttle program came under such heavy fire: we spent an extraordinary amount of money to build a reusable space vehicle, but in the end, we had nowhere to actually send it.

The United States wasnt the only country with a desire to launch a space station; the European space agency was also interested in such an endeavor. Russia, in addition, was planning on launching Mir 2 to replace its aging space station. However, a space station is an expensive and difficult proposition, which led to the cooperative development of the International Space Station (among the United States, Russia, Japan, Canada, and the European Space Agency) in 1993, using Freedom and Mir 2 concepts as its core modules.

The International Space Station. Photo courtesy of NASA

The ISS has been in orbit since its launch in 1998; it has been continuously occupied since its first long duration crew arrived on Expedition 1 in November 2000. The station is funded through 2024 by both the U.S. and Russia (though that may be extended to 2028). Its unclear what will come next; Roscosmos (Russias space agency counterpart to NASA) made a statement in early 2015 that the U.S. and Russia had agreed to work on a follow-up space station, but NASA hasnt confirmed that statement.

Regardless of what happens with the future of the International Space Station, its clear that space stations are here to stay. China has launched two space stations: Tiangong-1 and Tiangong-2, which are both currently in orbit. Tiangong-1, designed as a prototype to test the rendezvous and docking of Chinese spacecraft, was only in use for two years. Its orbit is decaying, and it will reenter the atmosphere later this year.

Tiangong-2 is another test space station launched in late 2016, as China plans to launch a larger modular space station to rival the ISS in 2022 (in mission, if probably not in sizethe International Space Station is the most expensive object ever constructed). Tiangong-2 has only been visited oncea two-person crew stayed aboard the station for 30 days.

But its not China or Russia or the United States who are making headlines about space stationsits private companies. Could a private company launch a space station by the end of the decade? Its absolutely possible. Axiom Space, a company youve likely never heard of, is aiming to be the first company to build a private space station.

Axiom is planning on launching the Multi-Purpose Module in 2020, designed as an add-on for the International Space Station. Whether it is launched all at once or assembled in orbit remains to be seen; however, when its ready, it will fly to the ISS (yes, it will have its own engines). Their current plan is to dock it to, and therefore expand, the ISS. When the International Space Station eventually deorbits, the Multi-Purpose Module will undock and function as an independent, private space station.

Theres a lot of money in a private space station; the customers wouldnt be private individuals wanting to go to space (though that is an option). There are many countries that aspire to send their astronauts into orbit. The ISSs max capacity is eight astronauts, and because were all currently dependent on Soyuz to get us there, were further constrained. Russian Soyuz capsules can only hold three astronauts each. Once private human spaceflight is off the ground (primarily through SpaceXs Dragon), that will ease the transportation issues, but the destination constraints are still considerable. Thats where Axiom hopes to step in.

Whether public or private, space stations are here to stay. Lets hope that as the ability to get off of our planet and live and work in space becomes easier and more possible, it encourages all of us to set our sights on destinations beyond low Earth orbit.

Top photo courtesy of NASA/ESA

Swapna Krishna is a freelance writer, editor, and giant space/sci-fi geek.

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Space Matter: Public (and Private) Space Stations - Paste Magazine