25 September 2014
SWARMS go up and they don't come down. Tiny, cheap CubeSats are becoming an increasing danger in space. The mini-satellites could cause catastrophic collisions with larger craft, threatening to produce orbiting blizzards of space debris like those in the movie Gravity.
CubeSats measure just 10 centimetres on a side and weigh a maximum of 1.3 kilograms. The satellites can easily launch on multiple types of rockets or from the International Space Station (ISS). This gives students and hobbyists the opportunity to do real space science.
But the more hardware there is in space, the greater the chance of collisions. To mitigate these risks, CubeSats are supposed to come down within 25 years. However, there is no enforcement of this rule.
"Some CubeSat operators are knowingly putting their craft into orbits that will last much longer than 25 years, with some as long as a hundred years," says Hugh Lewis at the University of Southampton in the UK, who will spell out the burgeoning risks at the International Astronautical Congress in Toronto, Canada, on 29 September.
CubeSat popularity looks likely to increase. Around 100 of the craft were launched between 2003 and 2012, then another 100 were launched in 2013 alone. Lewis and his colleagues extrapolated those numbers to model what would happen if between 205 and 700 CubeSats were launched every year for the next 30 years.
At the 205-per-year launch rate, CubeSats will come within a dangerously close 17 kilometres of other spacecraft 16 million times over the three decades. At the highest rate, that rises to 165 million times.
Worryingly, the simulation has already proved accurate in one instance. It predicted CubeSat collisions should have started in the 2013 to 2014 period and, sure enough, the first one happened in May 2013. It resulted in the loss of Ecuador's first CubeSat, NEE-01 Pegaso.
Still, other researchers say Lewis's findings may overestimate the problem. "There is always a choice of model inputs and the spin put on interpretation," says Sara Seager at MIT.
Jer Chyi Liou, chief scientist at NASA's orbital debris programme in Houston, Texas, agrees, though he says the CubeSat risk needs careful study. The US Strategic Command's Joint Space Operations Center, which decides when the ISS should be moved to avoid debris, uses more stringent criteria than Lewis, he says.
Jonathan McDowell at the Harvard-Smithsonian Center for Astrophysics foresees a wider problem in the move to ever-smaller satellites, like Sprites. These are the size of a circuit board and may be too small to be picked up by ground-based radar. "If these ever become popular then we have a big tracking problem," he says.
Whatever the actual risk, the report should be a wake-up call to the CubeSat industry to make sure the satellites have built-in ways to de-orbit, Seager says.
"The proliferation of CubeSats is phenomenal," she says. "Pandora's Box has been opened and it won't be closing."
This article appeared in print under the headline "CubeSat craze is recipe for disaster"