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Starlink: The SpaceX satellites could lead to disaster
More and more satellites and mega-constellations such as the Starlink project by SpaceX boss Elon Musk are orbiting the earth: Experts believe that this can have devastating consequences. There have long been possible solutions.
More and more satellites are being sent into orbit.
Hundreds of thousands of objects in space race silently towards a potential catastrophe. The idea is scary. Because the number of objects in the orbits around the earth is increasing, sooner or later a fatal chain reaction can occur: satellites collide with other objects and are torn to pieces, which in turn become dangerous projectiles in orbit.
Kessler syndrome is the name of this scenario in the jargon, which is no longer just gray theory. In 2009, the US communications satellite Iridium 33 collided with the Russian reconnaissance satellite Kosmos 2251 at an altitude of 800 kilometers. Both objects were completely destroyed and torn into over 100,000 fragments.
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Even today, the International Space Station (ISS) has to repeatedly fly evasive maneuvers because debris from the two objects is orbiting the earth at high speeds. Even the smallest scrap particles a few millimeters in size can impair the functionality of satellites or space stations in the event of a collision. In the worst case, they would completely destroy parts of about ten centimeters or more in size.
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Megaconstellations such as the Starlink project by the US space company SpaceX increase the likelihood of such a scenario, which experts believe can make space travel more difficult in the long term. The company's own Falcon 9 rocket has already launched several bundles of satellites into space, and more than 300 Starlink satellites are already orbiting the earth. In the long term, SpaceX boss Elon Musk wants to start 12,000 to 40,000, which should provide broadband internet at every point on earth - at least that is the plan, the implementation of which can be a milestone.
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But sometimes there is also a curse in the blessing: if only one satellite fails and is no longer controllable, there is a risk of dangerous collisions. "That is indeed frightening," says Sabine Klinkner from the Institute for Space Systems at the University of Stuttgart. “Operators of such constellations declare that they ensure that only a small percentage of the satellites fail. But when you apply that to thousands of satellites, we are inevitably heading towards the Kessler Effect. " Individual satellites that fail and can no longer be disposed of are an “insanely high risk”, according to Klinkner.
Starlink satellites also at a critical altitude of 1,200 kilometers
Carsten Wiedemann from the Technical University of Braunschweig agrees. At the Institute for Space Systems he works on the subject of space junk. “With thousands or tens of thousands of objects, we have to assume that a certain percentage will fail. That is already part of the idea of such mega-constellations: Instead of flying a few very expensive satellites, it is better to build many cheap, small ones. And if one fails, another takes over. So you can start a cheap series production and then the projects also pay off financially. "
SpaceX was founded in 2002 by Tesla boss Elon Musk, who at the time had made hundreds of millions of dollars in profits with the Internet companies Zip2 and PayPal and invested in the founding of the space company.
One of SpaceX's goals: to develop technologies that will enable Mars to be colonized. In the meantime, SpaceX has become an important supplier of the International Space Station (ISS) with its Falcon 9 rocket and the Dragon spaceship.
There will also be manned flights: SpaceX plans to bring astronauts to the ISS in May 2020, and space tourists should also be able to book spaces from 2021.
With its Starlink project, SpaceX is now also the world's largest private satellite operator.
That is actually sensible, said Wiedemann. But: "The big disadvantage is that a lot of dead satellites are left in space, which we don't want."
Hundreds of thousands of pieces of scrap orbit the earth. For space travel, they can become a problem in the medium term.
Photo: Technical University of Braunschweig.
If parts and particles from a size of one millimeter are added, the earth is hardly recognizable in the model.
Photo: Technical University of Braunschweig
Most of the Starlink satellites are in orbit about 500 kilometers above the earth. There, after the end of their mission, satellites can travel relatively easily towards the atmosphere, where they then burn up. It looks more problematic in orbits from 800 to 1,200 kilometers altitude, where satellite constellations are also circling - in the future several thousand Starlink objects.
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Communication companies also maintain their own satellite constellations, such as the Canadian company Telesat.
The British company Oneweb was last seen as a potential main competitor for SpaceX's Starlink project. Oneweb wanted to bring up to 2000 mini satellites into a near-earth orbit in order to provide an Internet connection even in places without terrestrial broadband access. The project should start in 2020 - but the company is now insolvent, and it is still unclear what will become of the plans. [/ accordionElement]
No rules for disposing of space junk
“In 1,200 kilometers we have very little space debris. In this respect, it makes sense to add satellites there, ”explains Wiedemann. However, there are huge numbers of satellites being released into very long-lived orbits.
"These satellites will remain there for centuries, if not millennia," said Wiedemann.
The air friction at this height is so low that the objects can no longer move away from there by themselves without control. Failed satellites, whose control has failed, remain there as dangerous garbage. "With these constellations at these altitudes, you really have to ensure 100 percent that they don't fail".
Space junk: our legacies in orbit
However, this is difficult to do and extremely expensive. And there are no regulations for this, and the disposal of space debris is nowhere stipulated. “That is one thing that actually gives us stomach ache,” says Sabine Klinkner. “There are no worldwide regulations or globally valid agreements. There are only partial regulations and codes of conduct. Many states state that they want to at least adhere to it. But that also differs from country to country. "
"Someone could screw tuna cans together and send them into space"
There are certainly countries that have laid down the corresponding rules in space law - but many of the rules are only rudimentary. In Germany, for example, the state is responsible for all satellites that are built and launched here and there are regulations for launch and radio frequencies. However, the state does not have any direct influence on the development of the satellites. “We noticed that when we launched our own satellite from the University of Stuttgart. The project is partly funded by the DLR, so there was a certain amount of supervision by the state. But theoretically someone could screw a couple of tuna cans together and send them into space without any conditions - provided you can find someone to start it. "
The team from the University of Stuttgart with its own satellite “Flying Laptop”.
Photo: University of Stuttgart
Another problem: in order to avoid collisions, the satellite operators have to maintain reliable contact with one another. How important this is was shown in September 2019: At that time one of the SpaceX satellites almost collided with the research satellite "Aeolus" of the European space agency Esa. Esa experts calculated the risk of collision and decided to move “Aeolus” a little further away from the earth so that it can fly over the SpaceX satellite.
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Esa had previously contacted SpaceX to ensure that both satellites did not dodge in the same direction and head towards one another. Such arrangements do not always work smoothly.
"There are satellite operators who do not react at all when you write to them," said Holger Krag, head of the Esa office for space residues.
First 3D formation flight of four satellites planned
Experts believe that such evasive maneuvers will become more and more necessary in the future. One possible solution: satellites that communicate independently with each other and move around. This is exactly what a team from the Center for Robotics and Telematics at the Julius Maximilians University of Würzburg is researching. NetSat is the name of the project in which a 3D formation flight of four small satellites in orbit is to be carried out for the first time worldwide. One of the long-term goals of the project: Using computed tomography in space, the researchers want to look inside clouds. “That only works with formation technology, because you need several perspectives,” explains Klaus Schilling, who heads the project. "When satellites fly formations, it is important that they stay close together but not collide."
The satellite fleet is clearly visible in the sky, especially shortly after take-off: Like a chain, they move their orbits across the night sky. Many amateur stargazers are fascinated by the phenomenon these days. The Findstarlink website shows where and when the phenomenon can be observed.
For astronomers, however, Starlink is a problem insofar as the large number of satellites, for example, can falsify long-term exposures and make it difficult to observe space in the long term.
The satellites are equipped with sensors. Using adaptive control, the satellites can recognize changes in the process - and react accordingly. With the help of engines, they can adjust their position and hold the desired position. "We are thus laying the foundations for equipping mega-constellations with more secure technologies in the future," says Schilling. The NetSat satellites are scheduled to start in August.
At the University of Würzburg there were already experiments for the national DEOS program to dock a robot to a space probe - but the project was abandoned.
Photo: Julius Maximilians University of Würzburg
Garbage fees for companies like SpaceX?
The creation of space debris, which is the result of collisions, could thus be avoided in the future. But what about the junk that's already there? Around 6,500 tons of it race around the world. The DEOS robotics mission of the German Aerospace Center (DLR) should show a possible solution: With the help of robots, damaged satellites should be rescued from orbits and brought into a crash orbit, so the idea. A team from the University of Würzburg had already carried out experiments on sensors for reliable docking of a service satellite to a defective space probe that had to be disposed of. But the DEOS project was abandoned in 2018 - also for cost reasons. "Technically that would be possible, but it fails because of the money," says Klaus Schilling. "You should actually collect garbage fees from satellite operators," he says - this is how clean-up projects can be financed.
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A contribution by:
Peter Sieben is content manager and responsible editor for ingenieur.de. After an internship at the Funke media group, he worked as an editor and reporter in various departments. He writes about technology, research and career topics.
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