update: The word "refused" might be inaccurate:
- CNET: ESA's near collision with SpaceX Starlink satellite blamed on a 'bug'
- Ars Technica: SpaceX satellite was on “collision course” until ESA satellite was re-routed
From the Ars Technica article:
Here's the full statement that SpaceX provided to Ars:
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 US 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 the best approach with their continuing with their maneuver or our performing a maneuver.
The Forbes article SpaceX Refused To Move A Starlink Satellite At Risk Of Collision With A European Satellite uses strong language in the headline.
The article says:
“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.
Question: How quickly can the Starlink spacecraft respond to a potential impending collision? Would it for example take a day or two to raise altitude by a kilometer? I've estimated that the total delta-v available from the Starlink's krypton ion thruster is in the ballpark of 190 m/s, but I have no idea of the magnitude of the thrust or how fast they can change their orbits in response to a detected potential
Just fyi, later in the article it says:
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.”
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.
The risk of collision between the satellites was 1 in 1,000. ESA OPERATIONS/TWITTER