A tiny particle has smashed into a European satellite, causing visible damage on its solar array.
Engineers at the European Space Agency (ESA) realised something was up when they noticed a drop in power supply at the same time as a change in the orbit and attitude (orientation) of Sentinel-1A, a radar satellite that is part of the Copernicus Earth observation programme.
They figured an impact could be the cause, and used the available data to compute the size of the colliding object.
"We came up with a particle of a few millimetres, impacting at orbital velocity—so that's [an impact velocity of] more than 40,000 kilometres an hour," Holger Krag, head of ESA's Space Debris Office, told Motherboard in a phone call. A scar it left on the satellite has a 40 cm diameter.
It's impossible to say for sure yet if the particle is a piece of manmade space debris or a natural micrometeoroid, but Krag said he suspected it to be the former, because space junk is more common in Earth's orbit than meteoroids, which also travel faster than orbiting debris.
It's not unexpected for a satellite to accrue damage in this way—there are hundreds of thousands of chunks of space debris out there, but scientists can only track those that are 5 cm or larger. Krag said the chances of a satellite being hit in its lifetime by a particle of a few millimetres size were between one in 30 and one in 130.
What's unique about this incident, however, is that we know a collision (whether space debris or meteoroid) occurred, and even have images to show it: The team turned on one of the satellite's onboard cameras and caught a clear glimpse of damage on the solar array.
"That's quite unique, we've never had that before," he said.
What you can see in the image is not the hole caused by the impact—that will be much smaller—but "some sort of effect caused by a shockwave." Krag said the loss of power from the solar array also indicates some damage to connectors and cables.
The tiny object managed to cause a lot of damage because it was travelling at high speeds.
Luckily, the satellite produces much more power than it needs and its other functions don't seem to be affected, so it can continue to operate as usual.
There's no real way to protect against impact with such small objects, other than shielding against them and building in redundancies. But we can help prevent them from occurring too often in future by generating less space debris—by venting fuel that's not needed so it doesn't cause an explosion, for instance, and manoeuvring bigger pieces of space shrapnel so they don't collide and make smaller pieces (see Gravity).
"These kind of measures we have to do—everybody has to do it in space—so that we keep space fit for spaceflight in future," said Krag.