SpaceX Says a 'Bug' Prevented It From Receiving Warning of Possible Satellite Collision

Depiction of Aeolus satellite.
Depiction of Aeolus satellite.
Image: ESA

The European Space Agency was forced to perform a “collision avoidance maneuver” to prevent its Aeolus spacecraft from potentially smashing into one of Elon Musk’s Starlink satellites, in what is quickly becoming an all-too-common occurrence. According to SpaceX, it never received the expected alert that a collision was possible.


ESA pumped out a series of tweets yesterday describing the incident, in which the Aeolus satellite “fired its thrusters, moving it off a collision course with a @SpaceX satellite in their #Starlink constellation” on Monday morning. Launched in August 2018, the Aeolus Earth science satellite monitors the planet’s wind from space, allowing for better weather predictions and climate modeling.

Experts in the ESA’s Space Debris Team “calculated the risk of collision between these two active satellites,” determining that the safest option for Aeolus was to increase its height and have it pass over the SpaceX satellite, according to an ESA tweet. It marked the first time the ESA had to perform “a collision avoidance manoeuvre’ to protect one of its satellites from colliding with a ‘mega constellation,’” noted the space agency.

Referring to SpaceX’s Starlink as a “mega constellation” is a bit of a stretch at the moment, given that the system currently consists of 60 satellites. This initial batch of satellites was delivered to low Earth orbit in May aboard a Falcon 9 rocket, and it’s the first of many planned deployments. SpaceX envisions a constellation consisting of hundreds and possibly thousands of interlinked Starlink satellites, which would collectively provide broadband internet to paying customers regardless of where they are in the world.

But as the ESA tweeted yesterday, 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...”


An ESA graphic identified the culprit as being Starlink 44. The maneuver was done a half-Earth-orbit before Aeolus’ closest approach to the Starlink satellite. Jeff Foust from SpaceNews provides more insight into the incident:

Holger Krag, director of ESA’s Space Safety Programme Office, said in a Sept. 3 email that the agency’s conjunction assessment team noticed the potential close approach about five days in advance, using data provided by the U.S. Air Force’s 18th Space Control Squadron. “We have informed SpaceX and they acknowledged,” he said. “Over the days the collision probability exceeded the decision threshold and we started the maneuver preparation and shared our plans with SpaceX. The decision to maneuver was then made the day before.”


The odds of a collision were calculated at 1 in 1,000, which was high enough to warrant the maneuver. ESA scientists assessed the threat using data gathered by the U.S. Air Force, along with the “operators’ own knowledge of spacecraft positions,” according to SpaceNews.

In a statement emailed to Gizmodo, a SpaceX spokesperson said the Starlink team “last exchanged an email with the Aeolus operations team on August 28, when the probability of collision was only in the [1 in 50,000 range], well below the [1 in 10,000] industry standard threshold and 75 times lower than the final estimate.”


Once the U.S. Air Force’s updates showed that the probability had increased to more than 1 in 10,000, “a bug in our on-call paging system prevented the Starlink operator from seeing the follow on correspondence on this probability increase,” according to the spokesperson, who said “SpaceX is still investigating the issue and will implement corrective actions.... 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.”

Yikes. This incident reveals the flimsy and primitive state of space traffic management, in which a failed communication led to ESA having to act unilaterally on the issue.


As for the Starlink constellation and its potential to create future risks as it grows in size, SpaceX is equipping its satellites with automated and manual collision avoidance capabilities, according to the Elon Musk-led company. SpaceX also shares position and velocity forecasts, among other data, with the U.S. Air Force and other satellite operators. The spokesperson said SpaceX is “among the first to voluntarily share ephemeris tracking data with other satellite operators and the public at”

In 2018, ESA had to perform 28 avoidance maneuvers, reports C|net, so this isn’t hugely out of the ordinary. That said, it is “very rare to perform collision avoidance manoeuvres with active satellites,” according to an ESA tweet, as the “vast majority of ESA avoidance manoeuvres are the result of dead satellites or fragments from previous collisions.”


Responding to the ESA tweets, Matt Desch, the CEO of satellite communications company Iridium, suggested this incident wasn’t a big deal. “Hmmm,” he tweeted. “We move our satellites on average once a week and don’t put out a press release to say who we maneuvered around...”

Indeed, a cynical reading suggests the ESA used this incident—which was very much a real incident—to raise awareness about the burgeoning issue of space traffic management, which it did by piggybacking off of SpaceX hype. It’s worth pointing out that ESA took the opportunity to note that it’s currently preparing to streamline the collision detection process with artificial intelligence. Eventually, AI could be used to automate the system, from detection of a threat through to carrying out the required action. Both ESA and SpaceX are planning to use autonomous systems in the future to mitigate the risk of collisions, reports SpaceNews. Automated systems, the ESA noted, “are becoming necessary to protect our space infrastructure.”


No doubt, it’s currently the Wild West era in terms of how we’re managing space traffic. Aside from preventing weapons of mass destruction from entering into space, no formal laws or treaties exist to manage the stuff that goes up into orbit nor what operators should do to prevent their satellites from smashing into other satellites. That satellites might crash into each other may not seem like a huge deal, but aside from the loss of an important space-based asset, each collision would produce a field of orbiting debris, increasing the chances of even more collisions.

Jessica West, a program officer at Project Ploughshares and the managing editor of its Space Security Index, said it would be a mistake say this latest incident wasn’t a big deal.


“Yes, satellite maneuvers happen on a regular basis,” West told Gizmodo. “But just because something is business as usual doesn’t mean that it’s good business. The problem that we’re facing in outer space is that the number of satellites and different operators in orbit is increasing drastically, but we don’t have rules for managing this traffic. There are no industry-wide standards for who moves, when, and how.”


Even worse, West said there “isn’t even a single map of all of this traffic.” Existing data remains imprecise, she said, and even though we’re “not flying blind,” we don’t have the required tools to operate safely in the long term, she explained.

“So far we have been lucky,” said West. “But it only takes one collision to create a mess in low Earth orbit.”



Brian Burns

I am curious, if two satellites collide, where is the liability. Like is there some version of “right of way” to determine who would be at fault, and thus who owes money to whom?

I suppose the answer right now is that no one would be liable, both parties just eat their loses. I mean, what court would even have jurisdiction?

That being the case, as far as I can tell, there is nothing legally preventing someone from creating a sort of “hunter” satellite that could knock other satellites out of orbit into deep space...