So many satellites orbit the earth that evasive maneuvers are the order of the day to avoid collisions. One way out would be international agreements that regulate traffic in orbit. However, these are currently still a long way off.
An employee at the Aerospace Control Center in Beijing observes the routes of various satellites.
At the beginning of December, China turned to the United Nations Office for Space Affairs Unoosa: Two satellites from SpaceX’s Starlink fleet had come dangerously close to the Chinese Tiangong space station, first in July and then again in October of this year the writing. The station had to evade in order not to endanger “the safety and life” of the astronauts on board, according to Beijing. The subliminal accusation against the US, which echoes in the letter, became even clearer on Tuesday of this week. The Chinese Foreign Ministry commented on the incidents at a press conference. The US has repeatedly ignored international treaty obligations on space, a spokesman said on the occasion, which poses a serious threat to the safety of astronauts.
However, China’s accusation of blame is unlikely to have any concrete consequences. Because to date there have been no traffic regulations for near-earth space. It is simply not agreed who has to evade whom and when. According to the current legal situation, anyone stationing any objects in orbit must see to it that collisions are avoided – in their own interest as well as in the interest of the general public. In this respect, SpaceX can at best be made a moral reproach with regard to the rapprochement with Tiangong.
Evasive maneuvers in orbit are part of daily business
On another level, however, China’s complaints point to a deeper and quite serious problem. Evasive maneuvers in orbit are already part of the daily business of space travel. In the near future, however, they are likely to become necessary even more frequently because more and more states and private companies are pushing into space and the orbits of the earth that can be used for space travel are constantly becoming fuller. This applies in particular to the comparatively lower orbits, in which a large part of the communications infrastructure is located – including Elon Musk’s Starlink fleet – and manned spaceflight.
SpaceX has played a major role in the rapid growth of infrastructure in orbit, primarily because of the Starlink program, with which Elon Musk wants to make high-speed Internet connections available even in the remotest corners of the world. The Starlink fleet currently comprises more than 1,600 satellites; in the final stage of expansion it should be over 30,000. Because of the sheer volume of new missiles, the project has been exposed to a never-ending series of accusations from astronomers, environmentalists and other satellite operators for years.
The fact that Starlink’s satellites became dangerous for a manned space station of all places has in turn to do with its modus operandi. SpaceX is deliberately deploying these communications satellites in a very low orbit, between 210 and 390 kilometers above the earth, explains Manuel Metz, an expert on space debris at the German Aerospace Center (DLR). There the devices would first be tested and only then be lifted piece by piece to higher orbits. This approach has the advantage that malfunctioning satellites can quickly crash again and thus be rendered harmless. On the other hand, it takes months in this way for the compact satellites, which only have comparatively weak propulsion systems, to reach their target altitude of around 550 kilometers.
As a rule, satellite operators have very precise information about the trajectories of their own satellites, explains Götz Neuneck, space expert at the Hamburg Institute for Peace Research and Security Policy. That should also be the case with SpaceX. However, such data would not be made public, neither by SpaceX nor by any space agencies or other private companies. In order to avoid collisions in orbit, all those involved use radar measurements, which can be used to determine from the earth where a certain flight object is currently located. Such radar measurements are only partially accessible to the public, for example in the North American Aerospace Defense Command (Norad) database. It is obvious that the Americans and Canadians who maintain this database are exempting objects of military interest from being published.
Open handling of data would solve the problems
Unfortunately, the radar measurements are far from a perfect solution when it comes to avoiding collisions. On the one hand, they are far less accurate than the operator’s orbit data would be. On the other hand, they can only predict the orbit of a satellite or missile a little way into the future, and in particular calculations of possible collisions are complicated (which also has to do with the fact that the data format used dates back to a time when information was transferred to computers in the form of punch cards). Any planned future changes in the orbit of a satellite cannot logically be read from radar observations either.
All of these problems could be resolved if the operators of the satellites and space stations were willing to exchange detailed orbit data. But this willingness is still lacking at the international level, says Manuel Metz, and so it remains with observing and calculating in advance. A European consortium called the European Union Space Surveillance and Tracking (EUSST) has therefore started to set up a joint database. This is intended to standardize and simplify the exchange of information about traffic in orbit. But they are not yet ready there to be able to provide a catalog for the numerous users of near-earth space, according to Metz.
Time is of the essence, but there is no unity in sight
Whether that is enough is questionable in view of the plans of SpaceX and others to launch mega-constellations comprising several thousand satellites into space. In the long term, the space nations would have to work towards establishing a binding regime for regulating air traffic in orbit, similar to the one that already exists for aviation. This is a topic that is currently being discussed on both a political and a technological level, says Metz. However, he does not expect any major breakthroughs. Opinions about what a globally binding regulation should look like were still too far apart.
Holger Krag, Head of the Space Safety Program Office at the European Space Agency (ESA), is far less pessimistic about the situation: The call for legal regulations should be understood, but users of space are not fundamentally dependent on exchanging data with one another. ESA is already doing this pragmatically and successfully with Starlink, which makes it easier to decide when which evasive maneuvers should be carried out.
In Krag’s view, it will be a long time before all those involved agree on international rules. “It makes sense to agree on practical and feasible standards in the meantime,” says Krag. “In the western world, where most space travel takes place, that will certainly be possible – and what works well in practice also has a chance of being reflected in the law.”