Space stations are human habitats complete with a pressurised enclosure and life support, which are placed in a geostationary orbit, usually at an altitude of more than 300 kilometres (186 miles) above the surface of our planet. This high altitude puts them far above the thousands of commercial satellites that orbit around the 35-kilometre (22-mile) mark and allows for a number of observational experiments not possible on the ground.
These experiments include the study of the Earth, Sun and other astronomical objects from space beyond the barriers of clouds/pollution, for example, as well as tests under the effects of microgravity and investigations into how the human body responds to weightlessness.
Small space stations, like the Russian reconnaissance platform Salyut 5 and the US Skylab, can be fully assembled on terra firma and launch into orbit in their entirety. Bigger models, like the International Space Station (ISS) and its Russian predecessor, Mir, however, are more problematic.
Their huge mass and awkward shape that includes long and relatively fragile solar panels perpendicular to the body make them impossible for any delivery system to take them into orbit whole.
A typical shuttle or expendable rocket might at most be able to carry around 30,000 kilograms (66,000 pounds) into low Earth orbit (LEO) and much less into higher orbits, whereas the completed Mir space station was about 130,000 kilograms (285,000 pounds) and the ISS is over 400,000 kilograms (880,000 pounds) – way beyond the maximum payload of any current launch system.
The answer to this is to launch the space station a piece at a time. As smaller modules – components with a fraction of the completed station’s mass – they are constructed on the ground and sent on the back of a rocket or shuttle up to the required altitude. Assembling a space station is akin to building a boat while it’s out at sea, so you have to be able to navigate and perform vital functions while building. Manning the space station with astronauts only happens at a convenient later stage with full life support. The first component therefore has to be a core module that is not only capable of propelling itself but also assisting in assembly – although this might not necessarily be its main function when the space station is completed. Once in orbit, pre-programmed commands activate vital functions like communication antennas, allowing mission control to remotely manipulate the core module. At this point it can be piloted within orbit to rendezvous and join with other modules via a bespoke docking port.
Attaching a pressurised module and getting a crew on board as soon as possible speeds up the process, as astronauts can facilitate assembly on-site. Both Mir and the ISS each took more than a decade to go from a single module to planned completion, while China’s Tiangong space station is set to be finished in the early-2020s.
The Columbia disaster
The Columbia was a NASA space shuttle that was destroyed in an accident in 2003. The flight was concerned with experiments in microgravity and, having completed its mission in space, it was re-entering Earth’s atmosphere to return home when it broke apart over Texas: all seven crew members were lost. As a result, all remaining shuttles were grounded while NASA investigated the accident, which put the assembly of the partially completed International Space Station on hiatus for over two years. During this period, research was limited and a two-man crew operated a caretaker role on board the ISS.
A look to the past…
Mir wasn’t the first space station to go into orbit around Earth by a long shot, but it was the first modular space station and, before the ISS was built, by far the biggest and most impressive. It was launched in 1986 and, by the time the Iron Curtain came down in 1991, already consisted of four modules. The Russians were pioneering space station technology alongside NASA’s Skylab in the Seventies, but Mir was a huge technological leap. The Russian Space Agency’s experience building Mir proved invaluable in the assembly of the ISS, from its first module in 1998 through to its completion in 2011.
A look to the future…
Tiangong – or ‘Heavenly Palace’ – is a new space station project solely led by the China National Space Administration (CNSA). It’s currently in its early stages of deployment, with space laboratory Tiangong-1 launched in 2011 and a more advanced lab and cargo ship, Tiangong-2, planned to arrive in the next 12 or so months. Tiangong-3 is scheduled to join it in 2015 with a view to eventually turning temporary living quarters into a multi-module space station. By 2022 at the latest, a much larger Tiangong space station will rival the likes of Mir and the ISS, with a long-term habitat for up to three astronauts.