Yikes! SpaceX satellite almost collides with ESA’s Aeolus

*Updated: 03/09/19 18:24UTC with comment from SpaceX*

Yesterday, 2nd September, a European Space Agency (ESA) satellite had a near-miss with one of the satellites of SpaceX’s Starlink constellation. Reportedly, SpaceX refused to move its satellite out of the way, forcing ESA’s Aeolus Earth observation satellite to make evasive maneuvers.

ESA Aeolus
ESA’s Aeolus had to take evasive action. Photo: ESA

The incident has raised questions about how Low Earth Orbit (LEO) satellites will impact on other near-Earth operations, and how safety can be assured in the future.

What happened?

Headed by Tesla entrepreneur Elon Musk, SpaceX launched an extensive Starlink beta test on the 23rd May, 2019. This involved the placement of an unprecedented number of satellites into LEO; 60 in total. According to reporting in Teslarati, 50 of these 60 satellites have arrived at their 340 mile circular orbit, and all but three are in communication and, largely, under the control of SpaceX.

However, at 11:02 yesterday, the ESA were alerted to a potential collision course between its Aeolus satellite and a member of SpaceX’s Starlink constellation, Starlink 44. The US military, who monitor space traffic, raised the alert with both parties.

According to Forbes, Aeolus has occupied this region of space for nine months prior to Starlink 44. Despite this, SpaceX declined to move its satellite, meaning Aeolus had to use its thrusters to avoid a potential collision.

Holger Krag, head of the Space Debris Office at ESA, told Forbes that the risk of a collision was 1:1,000, ten times greater than the threshold requiring avoidance maneuvering.

SpaceX refused to move

Krag said to Forbes that they had repeatedly tried to get in touch with SpaceX since Starlink launched, but to no avail. In light of the collision course of the satellites, Krag said,

“Based on this we informed SpaceX, who replied and said that they do not plan to take action. 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.”

SpaceX Starlink
60 SpaceX Starlink satellites are in orbit right now. Photo: SpaceX

Although the reason for SpaceX’s refusal is unclear, Krag has speculated it could be due to the electric propulsion system on board Starlink. This, he says, potentially has a longer reaction time than the chemical propulsion technology on board Aeolus.

Matt Desch, the CEO of Iridium who operate one of the largest LEO constellations ever flown, has come out in support of SpaceX, stating that his company performs avoidance maneuvers at least once a week.


ESA themselves have noted that no wrongdoing was incurred. Krag confirmed this, saying,

“There are no rules in space. 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.”

Get Connected reached out to SpaceX for their take on the situation. A spokesperson provided us with the following statement,

“Our Starlink team last exchanged an email with the Aeolus operations team on August 28, when the probability of collision was only in the 2.2e-5 range (or 1 in 50k), well below the 1e-4 (or 1 in 10k) industry standard threshold and 75 times lower than the final estimate. At that point, both SpaceX and ESA determined a maneuver was not necessary. Then, the U.S. Air Force’s updates showed the probability increased to 1.69e-3 (or more than 1 in 10k) but a bug in our on-call paging system prevented the Starlink operator from seeing the follow on correspondence on this probability increase – SpaceX is still investigating the issue and will implement corrective actions. However, had the Starlink operator seen the correspondence, we would have coordinated with ESA to determine best approach with their continuing with their maneuver or our performing a maneuver.”

The spokesperson also confirmed to us that the satellite was one of two that are being intentionally deorbited to simulate an end of life disposal. This explains why it was in a lower orbit than the others in the constellation, and therefore at risk of collision with Aeolus. SpaceX also confirmed that the satellite is operating as intended.

Concerns for future safety

SpaceX are reportedly planning to launch a further 300 satellites in the next seven months. Four FCC STA licenses have been applied for, relating to four launches all with ‘no earlier than’ (NET) dates before the end of 2019. Although the STA will last six months, launches typically happen within a few weeks of the permit being granted.

And that’s not the half of it. Once the full constellation is launched, it will number in the region of 11,800 satellites. Add to this the thousands more LEO satellites planed for launch by OneWeb and Kuiper, and it’s clear that, pretty soon, space is going to become pretty crowded.

ESA say that, soon, manual avoidance maneuvers will become impossible to perform. As such, they are preparing to integrate AI for satellite collision avoidance in the future.

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