Aeolus was launched on August 22, 2018.
ESA/ATG medialab
The European Space Agency (ESA) says one of its satellites was forced to avoid a satellite from SpaceX’s Starlink constellation, raising concerns about the impact of Starlink on low Earth orbit operations, after SpaceX refused to move their satellite out of the way.
At 11.02 A.M. today, Monday, September 2, ESA’s Aeolus Earth observation satellite had to use its thrusters to move itself out of a potential collision with a Starlink space internet satellite dubbed “Starlink 44”. The incident took place 320 kilometers above Earth as the two orbital paths of the two vehicles intercepted each other.
According to Holger Krag, head of the Space Debris Office at ESA, the risk of collision between the two satellites was 1 in 1,000 – ten times higher than the threshold that requires a collision avoidance maneuver. However, despite Aeolus occupying this region of space nine months before Starlink 44, SpaceX declined to move their satellite after the two were alerted to the impact risk by the U.S. military, who monitor space traffic.
“Based on this we informed SpaceX, who replied and said that they do not plan to take action,” says Krag, who said SpaceX informed them via email – the first contact that had been made with SpaceX, despite repeated attempts by Krag and his team to get in touch since Starlink launched. “It was at least clear who had to react. So we decided to react because the collision was close to 1 in 1,000, which was ten times higher than our threshold.”
As to why SpaceX refused to move their satellite, that is not entirely clear (the company did not respond to a request for comment). Krag suspected it could be something to do with SpaceX’s electric propulsion system, which “maybe is not reacting so fast” as the chemical propulsion on board Aeolus.
The Aeolus satellite, weighing in at more than 1,300 kilograms, was launched on August 22, 2018, whereas SpaceX launched its first batch of 60 Starlink satellites on May 23 this year. While most of those had their orbits raised from 440 kilometers to 550 kilometers (except at least three that failed), Starlink 44 was lowered to near 320 kilometers to practice deorbit techniques.
Thus Starlink 44 entered a region of space that Aeolus had occupied first. However, there are no rules in space that require one or another operator to move their satellite when there is a risk of collision. This, says Krag, is something that ESA hopes will be addressed in the near future.
“There are no rules in space,” he says. “Nobody did anything wrong. Space is there for everybody to use. There’s no rule that somebody was first here. Basically on every orbit you can encounter other objects. Space is not organized. And so we believe we need technology to manage this traffic.”
The risk of collision between the satellites was 1 in 1,000.
ESA Operations/Twitter
SpaceX has touted the automated collision avoidance systems onboard its Starlink satellites, which are designed to beam high-speed internet around the world. It says that the satellites, each weighing 227 kilograms, are “capable of tracking on-orbit debris and autonomously avoiding collision.” But for this incident, this system does not seem to have been used for some reason.
ESA noted that it performed 28 collision avoidance maneuvers in 2018, but it was mostly to avoid dead satellites or bits of space debris. Maneuvers to avoid active satellites were “very rare”, they said, but the arrival of mega constellations like Starlink raises concerns that many more such maneuvers will be needed in future.
“We see it as part of our changing environment,” says Stijn Lemmens, a space debris analyst at ESA. “We want to raise awareness in this sense, that there’s quite a bit of work that needs to be done on how to make sure that these type of operations will run smoothly in the future.”
Collisions between satellites are not unheard of; perhaps the most famous incident was between the US Iridium 33 satellite and the defunct Russian Kosmos-2251 satellite in 2009, which resulted in thousands of pieces of debris. And many have noted that our systems in place today are simply not adequate to cope with upcoming mega constellations like Starlink, which will far exceed the number of 2,000 active satellites currently in orbit.
“The February 2009 collision between Iridium 33 and Kosmos-2251 was actually predicted, with a miss distance of 584 meters, but that was less than the prediction formal error, and so evasive action was not taken,” says Marshall Eubanks from Space Initiatives. “The existing satellite tracking system is not intended to handle the mega constellations being planned and deployed, and new thinking is going to be required to allow the industry to continue to grow.”
SpaceX alone plans to launch a total of 12,000 Starlink satellites into orbit in the coming years, with considerable concerns about how busy Earth orbit will become. “As the number of satellites in orbit increases, due to mega constellations such as Starlink comprising hundreds or even thousands of satellites, today's 'manual' collision avoidance process will become impossible...” ESA noted in a tweet, adding that artificial intelligence might be needed to handle the high volume of maneuvers in the future.
SpaceX plans to launch 12,000 satellites in the coming years.
SpaceX
And those satellites could come thick and fast. Licenses filed by SpaceX suggest they are planning four more Starlink launches by the end of 2019, which could total at least an additional 240 satellites if they continue to launch 60 on each Falcon 9 rocket. The first launch is expected no earlier than October 10, with subsequent launches in October, November, and December. Other companies like OneWeb, Amazon, and Kepler communications also have plans for thousands of more space internet satellites.
SpaceX has so far remained tight-lipped on how it will handle the growing concerns around its Starlink constellation, including collision avoidance maneuvers and concerns from the astronomy community. As for this most recent incident, Krag and his team just hope that SpaceX will be more responsive in the future, so that situations can be avoided when more Starlink satellites are launched, and more stringent rules are put in place.
“We are not upset by them saying [they wouldn’t move],” says Krag. “My concern is how often will we have such events in the future? These are just two satellites. Now they will add several thousand, and they will also be disposed and end up at various altitudes. And there’s no rule or law on how to react, it’s all goodwill.
“What I want is an organized way of doing space traffic. It must be clear when you have such a situation who has to react. And of course automating the system. It cannot be when we have 10,000 satellites in space that there are operators writing the email what to do. This is not how I imagine modern spaceflight.”
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