The International Space Station just passed its 25th anniversary, when the first sections were launched, and since late 2000, has been the major facility to conduct space research in orbit.
After 25 years, the space station is starting to show its age. And, like all things, equipment has a finite lifetime and won't last forever.
NASA, Roscosmos, and other partners were previously committed to funding the ISS until 2024. Last year, NASA, JAXA, and ESA extended their involvement and the operation of the space station until 2030. Going to 2030 will allow private companies to build up their role in space.
Multiple companies are planning on building and maintain their own private space stations, that NASA can buy shares or pay for their astronauts and experiments to go on them, just like they pay for rides into space on SpaceX rockets.
What will happen though to the space station, something that weighs around 420 tons and is about the size of a football field? It will have to be decommissioned - and it is going to be difficult and expensive.
There are three main places it can go - stay in orbit around the Earth, up away from the Earth, or come back down to Earth. All of which are not great options.
Leaving it in orbit is the worst option. If left in space, eventually bits will break off or they will lose control over it and it will turn into one large piece of space junk - an already growing problem.
Raising it out of its orbit and pushing it away from Earth into a graveyard orbit would require so much energy and fuel that it would be extremely difficult, if even possible, and likely more expensive than it cost to build it.
The least bad option is a controlled de-orbit - into the Earth's atmosphere and eventually the ocean.
Instead of ending up in the scenario of an uncontrolled re-entry, like the US's Skylab which crashed in Western Australia in 1979, it plans to bring it down controlled, landing in the most remote place on Earth - Point Nemo in the South Pacific Ocean.
Point Nemo is the place on Earth furthest way from any land, and already serves as a spacecraft graveyard with lots of other space objects having crashed there.
The space station wasn't built to detach into sections and be taken down separately so it will have to come down all together. To do so, a spacecraft will be launched to the space station, which over months will have naturally slowly fell back to Earth.
At this point, the spacecraft will guide the space station into the Earth's atmosphere, as directly as possible, to break apart and crash around Point Nemo.
If it happens over a long period, the debris from bits breaking off will be scattered over a large area, so quick and direct is key.
However, a spacecraft that has enough power to do this doesn't really exist. It means building a new one, upgrading an existing one, or using multiple - which has its own coordination issues.
And this is all likely to cost $1 billion US to do so - the least bad option.
- Brad Tucker is an astrophysicist and cosmologist at Mount Stromlo Observatory, and the National Centre for the Public Awareness of Science at ANU.
