The CRASH Clock is ticking as satellite congestion in low Earth orbit worsens
Earth's orbit is starting to look like an LA freeway, with more and more satellites being launched each year. If you're worried about collisions and space debris making the area unusable – and you should be – scientists have proposed a new metric to contribute to your anxiety: the CRASH Clock.
The CRASH (Collision Realization And Significant Harm) Clock is a proposed Key Environmental Indicator (KEI) to give an estimate of how long it would take before a catastrophic collision occurs if collision avoidance maneuvers cease or there is a loss of situation awareness.
The clock is currently 2.8 days, which doesn't sound too bad until you consider that in 2018, before the mega-constellation launches got underway (yes, Starlink, we're looking at you), the CRASH Clock was 121 days.
Professor Sam Lawler explained the origin of the acronym in a post on Mastodon: "We needed a metric. I originally wanted to do something like 'Kessler Countdown' or 'Kessler Clock' but this isn't a countdown to Kessler Syndrome, it's just showing how bad things are in orbit, and how quickly they could get worse. So, our name for this metric is... Collision Realization And Significant Harm: the CRASH Clock!"
Kessler Syndrome is a theoretical scenario where collisions in orbit result in an exponentially increasing amount of debris, effectively rendering some orbital regions unusable. As Lawler noted, the CRASH Clock is more about highlighting how crowded orbit is becoming and how quickly it could get worse in the event of something like a major solar storm or a software issue knocking out collision avoidance systems.
While the CRASH Clock is concerning, if collision avoidance systems continue to perform flawlessly (and any software engineer will know all about coding perfection), there should be no immediate problem.
However, the increasing number of satellites in certain orbital regions is ramping up the pressure. In July, SpaceX submitted a report to the US Federal Communications Commission (FCC) detailing how many propulsive maneuvers its Starlink satellites had to make over the course of a year. For Generation 1 satellites, the average was 37 per year. Generation 2 satellites averaged 44 maneuvers per satellite per year.
The authors of the CRASH Clock paper broke this down to one collision avoidance maneuver every 1.8 minutes across the entire constellation.
In its report to the FCC, SpaceX noted that it "now nominally uses an even more conservative maneuver threshold approximately two orders of magnitude more sensitive than the industry standard." According to the company, Starlink satellites will take evasive action when the probability of collision exceeds 3 in 10 million, while the industry standard is 1 in 10,000.
Lawler posted: "One of the scariest parts of this project was learning more about Starlink's orbital operations.
"I had always assumed they had some kind of clever configuration of the satellites in the orbital shell that minimized conjunctions, and we would see the number of conjunctions grow over time in our simulations. But no! It's just random!
"There's no magic here, it's just avoiding collisions by moving a Starlink satellite every 2 minutes. This is bad."
Regardless of how one feels about the proliferation of satellites in orbit, the CRASH Clock is a sobering statistic of how quickly things could go wrong if collision avoidance systems fail. The report concludes with a call to action regarding how humans utilize low Earth orbit:
"In addition to the dangerously high collision risks calculated here, we are already experiencing disruption of astronomy, pollution in the upper atmosphere from increasingly frequent satellite ablation, and increased ground casualty risks.
"By these safety and pollution metrics, it is clear we have already placed substantial stress on LEO, and changes to our approach are required immediately." ®
