Call it Junk FM. Rogue signals from your radio may help warn about space debris on a dangerous collision course with Earth.
Stray FM signals from radios, bouncing back off space junk, could allow astronomers to track the whole population of space debris, suggest preliminary tests conducted this week at the Murchison Widefield Array (MWA) radio telescope in Western Australia.
More than 21,000 pieces of debris larger than 10 centimetres are currently zipping around Earth at speeds of around 7 kilometres per second, according to NASA. Friction created by brushes with Earth's upper atmosphere can sometimes cause pieces of space junk to drop from orbit, creating a small but real risk for humans.
Meanwhile, millions of smaller pieces in orbit present a serious risk to satellites. This space junk is spotted and tracked using traditional radar or lasers, but the system has its limits.
"The best techniques at the moment can track a max of about 200 bits of debris a day," says Steven Tingay, director of the MWA from Curtin University in Western Australia. "If we can get thousands simultaneously, we could almost get the whole population of space debris in a night."
ISS test
The MWA is a set of some 2000 radio antennas spread out over 3 kilometres. Because of its extraordinarily wide field of view, the MWA can continuously track objects rather than just calculate their orbits from snapshots, Tingay says. That will improve our understanding of how much space junk exists and how much more is being created. "We can quickly characterise it after a launch or a collision," he says.
Continuous tracking would also improve orbital modelling in general and allow better protection of space assets, Tingay says.
To test the radio-tracking concept, the team used the MWA to pick up FM signals rebounding off the International Space Station, which is more than 100 metres wide. The team could clearly track the orbiting lab as it moved about 8 kilometres.
"This first observation gives us some great data to work on," says Tingay. Now that they know it works, the technique should be easy to scale down to objects as small as 10 centimetres, he says.
So far, the telescope has been using only a quarter of its antennas at a time, Tingay adds. Next year it will begin operating at full capacity. "The main thing the final instrument will give is four times more sensitivity, which broadly translates to four times smaller space debris," he says.
"It's a great idea," says Fred Watson, head of the Anglo-Australian Observatory at Coonabarabran. "If you're looking at the whole sky you really have the potential to map the space debris. But it's not the total panacea." There would be some lower limit to the size of debris FM signals could track, he says, and bits only a few millimetres wide can still do damage.
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