Sharing the top of Mount Stromlo with ANU is a company called EOS. This technology-based venture is scouring the heavens for space junk in order to make the expensive business of satellite operations a safer bet. Collaborations with ANU scientists look set to supercharge the company’s capacity.
Over 50 years of space flight have left the Earth’s near orbital zones littered with space junk ranging from dead satellites to nuts and bolts. This junk is travelling at up to 10 kilometres per second and in multiple directions. Such huge velocities mean even a small bolt will strike another object in space with the same energy as a stick of dynamite. A large communications satellite may cost in excess of $500 million to launch into orbit so a chance collision with a piece of space debris is bad news – and a multi-million dollar insurance claim. In the last three years two major communications satellites have been lost due to such collisions and the problem looks like getting worse.
Space debris is difficult to track. It’s small, fast and can orbit for centuries. 20,000 pieces down to 15cm size are currently radar tracked but radar has an inherent limitation on its accuracy due to the long wavelengths it uses. Moreover, studies show that still dangerous to space travel.
This may be about to change thanks to the work of EOS. The company created a major stir in 2000 by demonstrating that they could track space junk using a laser – a feat thought to be close to impossible at the time.
“Radar tracking is important in that it enables us to stay up to date with the larger pieces of space debris,” says Ian Ritchie, the Operations Manager at EOS. “But using radar wavelengths the best orbital position accuracy you can achieve is of the order of 10-100 metres. This just isn’t good enough to be able to say with certainty where an object will be in a couple of days.”
The EOS system uses an extremely powerful laser coupled to a large and very precise tracking telescope equipped with state of the art auto guiding and laser tracking equipment. In a given pass they may have only 60 seconds to acquire the target at one horizon, then a further 60 to track it before it’s approaching the opposite horizon.
The smallest piece of debris that EOS have been able to track to date is about 8cm across, as estimated by radar. The range accuracy achievable is of the order of a centimetre using laser tracking. For objects smaller than this, the distortion of the beam profile by turbulence in the Earth’s atmosphere spreads the focus too much to get a good return signal.
“Our existing tracking system fires an eye-safe pre-pulse laser and if any reflection comes back from something like an aircraft the main tracking laser pulse is disabled,” Ian explains.
By using adaptive optics to eliminate the distortions generated by the atmosphere it’s possible to improve the beam focus even further. This is where the collaboration with ANU comes in. Researchers are currently developing an advanced adaptive optics suite for the Giant Magellan Telescope and the technology works just as well for sending a laser beam up as it does for starlight coming down.
“When this technology reaches maturity, we should be able to track space debris with unprecedented accuracy,” says Ian. “That means we can tell you that in x days, y hours your satellite is going to be in danger.”
That should give ample warning to manoeuvre it slightly out of harm’s way. And at half a billion dollars saving each time, that’s the sort of information that satellite operators will doubtless be very happy to pay for.