A recent article in Scientific American looked at the likelihood of collisions between satellites and other devices in orbit today and in the foreseeable future. This is becoming an increasingly important question because of the increasing number of satellites. There are currently 18,000 satellites in orbit, and 29,000 total objects, including spent rocket bodies, dead satellites, and large pieces of space debris. Goldman Sachs research says there could be as many as 305,000 satellites in orbit by 2031 and 1.7 million by 2036. Even if the actual numbers are half that, it means a huge number of orbiting objects in space.
As we put more satellites in space, the chance of collisions increases. This matters because major collisions can be disastrous, as colliding satellites break up into smaller debris that can act as orbital bullets to smash other satellites. Scientists have postulated many scenarios where some parts of space become unusable. Space debris generated at the lowest orbits can fall out of space after a few years. However, the article cites a scientist who says that debris at higher altitudes stays in orbit a lot longer. He said that at 1,200 miles above Earth, debris can persist for 100,000 years.
One prediction in the article is that there is already a 29% chance of collisions per year at altitudes between 520 and 605 kilometers since there are numerous discarded rocket stages the size of school buses at those altitudes that can’t be maneuvered to avoid a collision. The danger of collisions at those higher orbits is that the debris will rain down and endanger all other satellites below. This might not create dead orbital zones, but it would greatly increase the risk of operating a constellation and would compel satellite operators to send excess satellites into orbit in anticipation of losing some of them.
Perhaps the biggest concern of all is the process of monitoring satellites to avoid collisions. Until recently, this process was done manually, but this now requires automated tracking of satellites to predict collisions. In the last year, Starlink says it performed 300,000 adjustments to avoid collisions, which works out to 40 maneuvers per satellite per year. Scientists worry that this will become impossible at some point as the number of satellites grows. It’s particularly worrisome since many of the counties and companies that plan to put satellites in orbit may not interface well with rival companies and countries. There’s nothing that compels them to do so.
A really scary scenario is the aftermath of a major solar storm that knocks out the electronics of many satellites. We’ve had several such solar storms just in the century we’ve been tracking solar events. A satellite that is disabled by a solar storm would become a dead object that would not be able to maneuver to avoid collisions. The article cites an expert who predicts that a killer solar storm would lead to major satellite collisions within days.
The biggest concern of all for me is that nobody is governing satellite traffic safety. The International Telecommunications Union (ITU) in Switzerland, which is part of the United Nations, approves worldwide spectrum for satellites and loosely coordinates assigned orbital slots. However, the ITU doesn’t consider the capacity of a given orbit to handle satellites as part of its review process. With dozens of countries planning to launch satellites, space is becoming the Wild West. It might take a major event to get the world interested in doing the hard work needed to make this work.