For nearly 25 years, the International Space Station, located about 250 miles above the Earth's surface, has been the home of astronauts.
However, the ISS is scheduled to be destroyed in 2030, and NASA has now determined how to carry out this program.
The agency chose Elon Musk's SpaceX company to build a "space tug" to pull it back to Earth.
When both enter the Earth's atmosphere, they burn up — but NASA expects the risk of debris falling to the ground is very small.
Whatever SpaceX's tugboat ultimately looks like, it must be unmanned to prevent any Hollywood-style heroic astronaut from sacrificing himself.
This would be a sad end for the International Space Station, which has been home to an in-orbit laboratory and astronauts since 2000.
"The selection of the U.S. ISS orbital descent device will help NASA and its international partners ensure a safe and responsible transition in low-Earth orbit at the end of the station's operations," NASA said in a statement. ”
"While the company will develop the orbital descent spacecraft, once the development is complete, NASA will own and operate it for the entire duration of the mission."
SpaceX has received $843 million for the design and construction of the "American Orbital Descent Device," which could be similar to its Dragon series of spacecraft used to transport people and cargo.
The first step in NASA's program is for the orbit of the ISS to begin to "decay" – meaning that it will naturally approach the Earth due to Earth's gravitational pull.
During this time, atmospheric drag will reduce the orbit from about 250 miles above the surface to 200 miles — although this will take a few years.
By 2030, crews on board the ISS will make a final descent and take away any critical equipment.
The ISS will continue to approach the Earth, reaching a "tipping point" of 175 miles above the surface.
At this time, the SpaceX tugboat will manage to connect with the ISS and pull it towards the Earth's atmosphere.
It is hoped that most of the two spacecraft will be burned out by the heat in the atmosphere - but some parts may pass through the atmosphere.
Dr James Blake, a space debris researcher at the University of Warwick, said the mission should ensure that the material falls into the ocean rather than land.
"While it is expected that much of the structure will separate and burn up as it enters the Earth's atmosphere, some dense or heat-resistant components, such as the trusses that form the backbone of the space station, may survive," Dr. Blake told. ”
"However, NASA and partner agencies have opted for controlled reentry, which means that reentry will be targeted to ensure that any surviving debris will fall into uninhabited ocean areas, minimizing the risk to people and property on the ground."
According to the European Space Agency, the annual risk of injury to any single person from space debris alone is less than 1 in a billion.
That's about 1.5 million times lower than the risk of dying in an accident at home and 65,000 times lower than the risk of being struck by lightning.
Due to the accumulation of structural stresses over time and the aging of components, NASA plans to decommission the ISS early in the next decade.
"The modules and main components of the ISS have specific power, data and structural architectures, which may not be compatible with future platforms," the agency said. ”
Over the past few years, the ISS has seen several gas and coolant leaks, including a mysterious hole that was allegedly deliberately created.
After calling for the ISS to be safely brought back to Earth for public display or to repurpose some of the components, NASA called it an "impractical" and "very complex and expensive" process.