Thousands of satellites are tightly packed into low Earth orbit, and the overcrowding is only growing.
Scientists have created a simple warning system called the CRASH Clock that answers a basic question: if satellites suddenly couldn’t steer around each other, how much time would elapse before there was a crash in orbit? Their current answer: 5.5 days.
The CRASH Clock metric was introduced in a paper orginally published on the Arxiv physics preprint server in December, and is currently under consideration for publication. The team’s research measures how quickly a catastrophic collision could occur if satellite operators lost the ability to maneuver—whether due to a solar storm, a software failure, or some other catastrophic failure.
To be clear, say the CRASH Clock scientists, low Earth orbit is not about to become a new realm of collisions that’s about to become unusable. But what they have shown, consistent with recent research and public outcry, is that low Earth orbit’s current stability demands perfect decisions on the part of a range of satellite operators around the globe every day. A few mistakes at the wrong time and place in orbit could set a lot of chaos in motion.
But the biggest hidden threat isn’t always debris that can be seen from the ground or via radar imaging systems. Rather, thousands of pieces of junk too small to track but big enough to disrupt a satellite’s operations are the stuff of satellite operators’ nightmares these days. Making matters worse is SpaceX essentially locking up one the most valuable altitudes with their Starlink satellite megaconstellation, forcing Chinese competitors to fly higher through clouds of old collision debris left over from earlier accidents.
IEEE Spectrum spoke with astrophysicists Sarah Thiele (graduate student at Princeton University), Aaron Boley (professor of physics and astronomy at the University of British Columbia in Vancouver, Canada), and Samantha Lawler (associate professor of astronomy at the University of Regina in Saskatchewan, Canada) about their new paper, and about how close satellites actually are to each other, why you can’t see most space junk, and what happens to the power grid when everything in orbit fails at once.
Does the CRASH Clock measure Kessler syndrome, or something different?
Sarah Thiele: A lot of people are claiming we’re saying Kessler syndrome is days away, and that’s not what our work is saying. We’re not making any claim about this being a runaway collisional cascade. We only look at the time scale to the first collision—we don’t simulate secondary or tertiary collisions. The CRASH Clock reflects how reliant we are on errorless operations and is an indicator for stress on the orbital environment.
Aaron Boley: A lot of people’s mental vision of Kessler syndrome is this very rapid runaway, and in reality this is something that can take decades to truly build.
Thiele: Recent papers found that altitudes between 520 to 1,000 kilometers have already reached this potential runaway threshold. Even in that case, the time scales for how slowly this happens is very long. It’s more about whether you have a significant number of objects at a given altitude such that controlling the proliferation of debris becomes difficult.
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