ESA was the first to reach out. SpaceX responded, saying it had no plans to adjust the position of the satellite. The probability of a collision was about one in 50,000 then, and satellite operators usually don’t make moves until the likelihood reaches more than one in 10,000.
The satellites hit that threshold within a day of the email exchange. ESA sent SpaceX another email. Then another. But the agency didn’t hear back.
Had the operator seen the messages, a SpaceX spokesperson later said, “we would have coordinated with ESA to determine best approach with their continuing with their maneuver or our performing a maneuver.” But SpaceX, it turned out, didn’t see those emails, thanks to a computer bug in their on-call paging system.
By the time they did, the ESA satellite had already ignited its thrusters and dodged. SpaceX had stumbled into a painfully relatable circumstance: missing an important email and then scrambling to explain why with a sorry, just seeing this!
The two satellites avoided a crash, which can produce thousands of pieces of debris, increasing the chance of other collisions.
But the scenario raised concerns about how satellite operators manage space traffic as it becomes even more congested. The SpaceX satellite, launched in May, was part of the company’s Starlink project, which is meant to provide internet around the world, especially in isolated spots. Musk says he wants to launch about a thousand satellites each year to eventually build a fleet of 12,000. Jeff Bezos wants to launch thousands of satellites of his own, for a similar effort under Amazon. The internet-satellite company OneWeb plans to deploy hundreds.
Read: Private companies are building an exoskeleton around Earth
As these constellations of satellites grow, so does the risk of collision. And more risk means more emails and phone calls.
“If you have to deal with one or two close approaches a month, picking up the phone might be fine,” says Brian Weeden, a space-policy expert at the Secure World Foundation, a nonprofit group that promotes peaceful uses of space. “But if you now have to deal with dozens or hundreds, it’s not going to scale.”
Collision avoidance is a knotty process from start to finish. ESA, SpaceX, and virtually every satellite operator rely on orbital data collected by a unit of the U.S. military. The Air Force’s 18th Space Control Squadron tracks about 23,000 artificial objects bigger than a softball, a tiny slice of which are functioning satellites. If a collision starts looking possible, the unit issues warnings to the appropriate operators.
But the data are limited, which Weeden attributes to aging computer systems and information-sharing policies, aimed at protecting national-security interests, that can leave operators in the dark. In practice, that means satellite trackers don’t know exactly where something is in space, so they cannot say with certainty whether two objects will collide. When operators prepare for potential maneuvers, they combine the military data with their own knowledge of the satellite’s position, taking into account “uncertainties in orbit information,” as ESA put it.