Does Starlink pose a threat to space debris? An expert answers

The Starlink satellites launched by SpaceX two weeks ago have been sharply criticized for their potential sky clutter. Author Jan Hattenbach met Stijn Lemmens, Senior Space Debris Scientist at the European Space Agency (ESA) in Darmstadt, Germany, to explain how Starlink plays a role in the problem of junk food.

Editor's Note: This interview has been slightly modified for reasons of grammar, brevity and the addition of relevant links.

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Jan Hattenbach: The recent launch of first 60 "Starlink" satellites has sparked outrage over social media. Some critics claim that the "mega-constellation" of SpaceX satellites will increase the risk of creating more waste in space, even calling it a threat to space flight itself. What is your opinion – is this criticism justified or exaggerated?

Stijn Lemmens: We are talking about a constellation that – if it materializes fully – would have up to 12,000 members. Several countries have launched nearly 9,000 satellites over the past six decades. Of these, about 5,000 are still in orbit. So we are talking about doubling the amount of traffic in space in a few years, or more than a decade, compared to the last 60 years.

However, the problem of space debris is mainly due to the fact that we leave objects in orbit, which are then the target of collisions with fragments of a previous collision event or with large intact objects. At present, most space debris comes from explosive bursts. in the future, we expect that collisions will drive them. It's like a waterfall: once you have a collision, other satellites may experience further collisions.

Over the past two decades, many efforts have been made to establish guidelines and codes of conduct. For Low Earth Orbits (LEO), there is a well-known directive that allows you to remove your upper level spacecraft, satellite or launcher within 25 years of completing the mission.

To have a reasonable chance of having a stable space environment, the objective is to ensure that at least 90% of the satellites and upper stages of launchers having a life span greater than 25 years come out of orbit or go into orbit with a life span of less than 25 years.

However, we are not really good at doing it yet. We are talking about success rates of 5% to 15% for satellites (the orbital stages of launchers fared much better, with success rates of 40 to 70% in low Earth orbit). Already with the current traffic, we have reasonable concerns to create a real debris problem.

If we are currently planning to install two or three thousand more satellites, with levels of compliance similar to those we have known so far, we are talking about a possible disaster.

Operators of any type of large satellite constellation should behave much better than most current space flight actors. And that's the problem: before you start, operators can of course assert and demonstrate that they will comply with all international standards and guidelines. But it is only after the launch that we know how much their behavior was really responsible.

JH: Do you feel that SpaceX is aware of its responsibilities?

SL: They are certainly aware of the problem. For example, to get a US launch license with a mission like this, where they exchange data between the mainland, Space and other operators, you have to apply for a license, in this case to the Federal Communications Commission (FCC). ). To obtain this license, they must demonstrate what they will do to reduce space debris. They had to demonstrate some adherence to the standards.

But the real question is whether current standards are sufficient for large constellations or whether we are setting the bar too low for future sustainability. We are talking about thousands of new satellites – the risk is that the cumulative effect is not taken into account in the current level of guidelines. So, SpaceX should voluntarily demonstrate higher levels of engagement.

JH: When asked about these questions, SpaceX replied that he thought he had the "most advanced system" for space debris mitigation, for example. that Starlink satellites are "designed to be able to avoid collisions completely autonomously, which means zero human in the loop." Are you confident that such a system will work, especially given the numbers?

SL: I have no technical visibility on how they implement their system, so I can not decide if it will work with their satellites or not. What I can say is that it will require some improvement over the current state of knowledge. On the other hand, if a pair of Starlink satellites collide on the orbit of operation, SpaceX will be the first to be seriously affected by the fragmentation cloud generated by the collision. It is in their interest to make sure their system works.

JH: You mentioned the launch license issued by the FCC, a federal commission of the United States. However, the space is not owned by the United States or any other country. Is there an international body with a say on these issues?

SL: Five space treaties concluded in the 1960s, 1970s and 1980s do not mention space debris. Instead, there is a lot of coordination, first at the agency level. The Inter-Agency Space Debris Coordination Committee coordinates 13 space agencies worldwide, including ESA, NASA, the National Space Administration of China and the Russian Roscosmos, to develop guidelines to reduce debris, share best practices and try to solve the problem. in a way that makes sense to everyone. The United Nations Committee on the Peaceful Uses of Outer Space has adopted these guidelines. This committee includes politicians from many countries, including those who do not currently fly in space. Industries in many countries are also discussing these issues within the International Organization for Standardization.

So there is a lot of coordination at the international level to make sure that we apply the same rules and apply the same set of standards. But for now, there is no way to directly interact with a nation's sovereignty over what it launches. The outer space treaties make the nation-states responsible for the behavior of their individuals or private companies.

JH: What about competitors like OneWeb or Amazon, who want to set up a system similar to Starlink? Who "owns" the orbits – who comes first?

SL: According to the Treaty on Outer Space, there is no appropriation of space. But of course, if you place a large constellation in a given orbit, it means that much coordination is needed with anyone who wants to operate near that constellation or even cross these orbital regions. You can even go further: if an object of a constellation breaks up for any reason, these fragments will not remain limited to the region of the constellation itself. This will affect the operators below and above. Thus, in this perspective, the placing in orbit of a large number of satellites influences the other activities that can take place.

JH: Apart from politics and law, is there a physical limit to the number of constellations of thousands of satellites that can work at the same time? How much space is there in space?

SL: If we do not keep the current guidelines mentioned above, we will come up against the "Kessler syndrome", which is the name of this cascading effect. And at that time, there would indeed be areas that, even without large constellations, would become so full of debris that it would become impractical to place your satellites there. That is why we are actively promoting the idea that space is a shared resource and that it is a limited resource. It is not infinite when one thinks of the number of objects that one can place there. The exact threshold is in some cases computable, but it depends on the behavior of the operators. So you can not say a priori that many thousands of satellites, that is too much. This amount may be achievable, but there should be strict requirements for responsible behavior that have not yet been demonstrated.