Published On: Tue, Sep 3rd, 2019

SpaceX didn’t move its satellite out of the way of a potential collision because of a computer bug


On Monday, a European satellite changed its position in orbit to avoid a potential collision with one of SpaceX’s Starlink satellites — one of 60 probes the company launched in May to beam internet coverage down to Earth. The European Space Agency (ESA), which operates the satellite, performed the maneuver after calculating a higher than usual probability that the two satellites might run into each other. SpaceX did not move its satellite, blaming a computer bug that prevented proper communication with ESA.

Maneuvers like this aren’t uncommon. Every now and then, satellite operators will slightly alter a spacecraft’s position if they calculate an uncomfortable chance that their vehicle might hit someone else’s vehicle. No one wants a collision, since these satellites are moving through space at several thousands of miles per hour. At those speeds, an impact can cause spacecraft to break apart into hundreds of pieces. The resulting high-speed junk could potentially run into other satellites, possibly creating more dangerous debris.

This particular scenario with ESA raises some concerns, since SpaceX’s probes are the first of nearly 12,000 internet-beaming satellites the company intends to put into a low orbit around Earth. The sheer size of the planned Starlink constellation has prompted many space experts to speculate how these vehicles might increase the chances of collisions in space. If satellites are already having to move out of the way of a Starlink satellite now, how often is this going to happen when there are thousands of these vehicles in orbit?

Another worry revolves around SpaceX’s decision not to move the Starlink satellite. ESA officials said that they did not have the best communication with SpaceX leading up to the maneuver, and that the agency ultimately made the decision on its own to move its satellite without SpaceX’s input. Initial reports claimed that SpaceX had “refused” to move the Starlink satellite, but SpaceX says the bad communication was not intentional and that a bug in the company’s “on-call paging system” prevented the Starlink team from getting additional email correspondence from ESA.

“SpaceX is still investigating the issue and will implement corrective actions,” a company spokesperson said in a statement. “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.”

This situation started last week, when ESA realized that its Aeolus satellite — an Earth-observing spacecraft launched in August 2018 — might come close to a Starlink satellite that was in a relatively low orbit, about 198 miles (320 kilometers) up. Most of the Starlink satellites have raised their orbits to around 342 miles (550 kilometers) up, but SpaceX decided to lower a couple of them to test the process of taking these vehicles out of orbit. And one of these two satellites was coming into close proximity with Aeolus.


SpaceX’s first batch of 60 Starlink satellites, just prior to deployment in orbit
Image: SpaceX

Officials at ESA said that they contacted SpaceX about a week ahead of the potential collision to see if the company planned to move the Starlink satellite. “Every now and then, the other object is actually an operational spacecraft,” Klaus Merz, with ESA’s Space Debris Office, tells The Verge. “And then of course, we try to coordinate. The very basic thing is you want to know if the other one has maneuvering plans already.” On August 28th, SpaceX informed ESA via email that the company did not intend to move the Starlink probe, according to Merz. “They said at that point in time they had no plans,” says Merz. SpaceX confirmed that it exchanged the initial email with ESA. At that time, the probability of collision was about 1 in 50,000, according to SpaceX, which is too low to require any preventive action.

As the potential collision date drew closer, Merz says that ESA gathered data from the US Space Surveillance Network, an array of ground-based telescopes that track objects in orbit, and combined it with their internal data about the size and shape of the Aeolus spacecraft. Using that information, the ESA experts calculated even higher probabilities that the two satellites might hit one another — eventually getting to a less than 1 in 1,000 chance of an impact. For the satellite community, that’s high. Typically, satellites make moves when there is a 1 in 10,000 chance of collision.

Merz says ESA contacted SpaceX daily about its evolving calculations, but the agency did not receive any additional replies after the original email response. SpaceX acknowledges that it failed to communicate due to the bug and missed the emails about a higher probability of collision. Finally, on Monday morning in Europe, ESA made the call and used the thrusters on Aeolus to raise the satellite’s orbit by about 984 feet (300 meters), without waiting for SpaceX to take corrective action.

Typically, the United States Air Force, which monitors space traffic, will issue conjunction warnings if there is a high probability of a collision. SpaceX did not say if the company received an alert from the Air Force or if the bug prevented the company from seeing one. The Verge has reached out to both the Air Force and SpaceX and will update this story with their response.

Even if ESA hadn’t moved the Aeolus satellite, it’s possible the Starlink spacecraft may have moved on its own if it detected a potential impact. SpaceX CEO Elon Musk claims that each Starlink satellite is programmed with its own autonomous space debris tracking system, which it will use to move out of the way of potential debris if necessary. SpaceX has not indicated that this system has been used in orbit yet.

Ultimately, the entire situation illustrates a need for better communication, argues Merz, especially as more and more satellites are launched into space by SpaceX and others. Companies like OneWeb and Amazon have also proposed sending hundreds to thousands of satellites into orbit to beam internet connectivity to the Earth below. “I think trying to solve these things via email is not the future,” says Merz. “We should have something that is getting more efficient.”





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