Everything that goes up must eventually come down, and the International Space Station (ISS) is no exception. NASA has awarded SpaceX the project to build the vehicle that will be used to bring it down in a few years. Perhaps as early as 2030.
Several factors are involved in this decision. The first and most important is that the station has become old. Its first module – of Russian design but paid for by NASA – was launched 26 years ago. That may not seem like such a long time, but the rigour of the space environment takes its toll on materials and much of the equipment has aged. So much so that astronauts now spend a good part of their time in orbit on maintenance and repairs. Another factor is Russia’s decision to abandon its participation in the project in 2028. This is partly due to the tension unleashed with its Western colleagues following the war in Ukraine and subsequent sanctions; but also due to plans to build its own station, probably in collaboration with China.
The ISS is gradually losing altitude due to the friction of the air streams still present at levels of 400 kilometres, the altitude at which it orbits. From time to time it has to fire its engines to rise again. But these engines are installed in the Russian segment of the station. If Russia finally abandons the station, this manoeuvring capacity would disappear.
There have been studies into alternatives, such as launching vehicles equipped with a propulsion system that would attach to the station to return it to its normal flight altitude, but these are expensive projects that require a long development time. Russia had also offered its Progress automatic craft — the same ones it occasionally uses to bring the station back up — although no concrete plan was ever established to bring it down.
Years ago, Russia had promised to collaborate to, if necessary, deorbit the space station using the same Progress cargo ships. But given the current situation, NASA has preferred to develop its own alternative, in case relations with Russia worsen. Thus, in September 2023, it called for a competition for projects, which was attended by several companies in the aerospace sector. The winner was SpaceX, Elon Musk’s company, which once again presented the most economical proposal – around 850 million dollars, closed price -, as happened with the selection of a Starship lander, which will carry the next astronauts to set foot on the Moon.
The station weighs about 420 tons and is the size of a football field. It is by far the largest artificial object orbiting above our heads in Earth’s orbit. To get rid of such a massive object, the only solution is to attach a powerful enough engine to it to slow it down and force it to fall into the ocean – and if possible, in a controlled manner. The station was built piece by piece. More than 40 launches were required. Each module, which usually weighed no more than 20 tons, was sent into space by a rocket (Russian) or in the cargo hold of the shuttle (American). But now the whole thing has to be deorbited at once, and that will require a very powerful engine.
SpaceX’s proposal is, in effect, another monster: an unmanned Dragon capsule, whose luggage carrierThe stern has been expanded to accommodate fuel tanks and around thirty engines with a thrust of 40 kilograms each. It will weigh around 30 tons, roughly the same as a complete Apollo lunar ship.
When will the ISS be destroyed? NASA plans to do so between 2030 and 2031. The last manned expedition will end in 2029. The deorbiter vehicle—which will be built by SpaceX but owned by NASA and controlled from Houston—will remain attached to the station for a whole year, adjusting its orbit under remote control. When the day comes to deorbit the station, the thirty engines will be fired to reduce the speed of the station by about 150 kilometers per hour, which is currently moving at an orbital speed of 27,600 kilometers per hour. This braking will be done gently, so as not to stress the structure that could break. The maneuver will last about an hour, during which the ISS will gradually lose altitude until it hits the densest layers of the atmosphere, about 50 kilometers above the ocean.
An unpredictable process
From there, it is difficult to predict how the disintegration process will take place. It is certain that the first to fall off will be the eight large solar panels. Then the cross beam supporting the radiators and some experiment such as the massive alpha spectrometer, a seven-ton cylinder, will probably give way. And then the connections between the different modules will break and burn up separately, like a pellet of fragments.
There are not many precedents that can serve as a guide. In 1973 the laboratory Skylab It disintegrated somewhat later than expected and some fragments fell in it outback from the Australian outback. NASA was fined $400 for dumping litter on public land. Twenty-eight years later, the Mir station crashed into the Pacific in a spectacular display of fireworks, but without causing any damage.
The ISS will also head towards the South Pacific, specifically towards the so-called Nemo point, the most remote place on the planet, halfway between New Zealand and the southern tip of Patagonia, which puts it more than 2,000 kilometres from the nearest land (generally, uninhabited islets). Since 1971 it has been used as a space graveyard, where useless satellites are brought down. At the bottom, at a depth of about 3,700 metres, lie the battered remains of more than three hundred vehicles that survived the plunge into the atmosphere. The structure of currents makes this area very poor in nutrients and, consequently, in marine life, which mitigates the impact of contamination by possible toxic substances.
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