Australasian Science: Australia's authority on science since 1938

Radio Stations Track Space Junk

By Stephen Luntz

Signals from radio stations are being used to locate space debris that threatens satellites.

The demonstration of the viability of the project is the first success from the Murchison Widefield Array (MWA), a precursor project to the Square Kilometre Array (SKA).

The inspiration for the project came when Australian National University PhD student Ben McKinley measured signals from FM radio stations reflected by the Moon. He used these observations to calculate the signal strength at nearby stars, and therefore the size of telescope needed to detect equivalent sources on extra-solar planets.

“It turns out the SKA in its final form would be able to assuming similar frequencies and technologies to ours were used, but the MWA is not in the ballpark,” says Dr Stephen Tingay, Director of the MWA at Curtin University.

The idea inspired further thinking, including the realisation that the same signals are bouncing off much smaller objects. “The MWA was designed to be the most powerful low frequency radio telescope in the Southern Hemisphere, and this was our chance to test its capabilities,” Tingay says. Having detected ten pieces of space junk simultaneously, the MWA also proved its value covering huge areas of the sky at once.

Commercial and ABC radio transmitters are more powerful than anything astronomers could afford to create themselves. “In terms of what is being broadcast it doesn’t matter if it’s talk or music,” Tingay says. More important is the frequency at which the station is transmitting and the source’s location.

“There will be particularly favourable geometries that maximise the signal, but these are unpredictable ahead of time because they depend on the orientation of the space junk,” says Tingay. Consequently a diversity of stations is useful, and the team chose the Perth JJJ and ABC FM signals and two regional stations. Tingay says that these stations are powerful enough to detect objects 1 metre in diameter at heights of 1000 km above the Earth, which is slightly above the thickest space junk fields.

Although the MWA will not be able to find the smallest objects that can pose a risk to satellites, Tingay believes its widefield capacity will make it for useful collaborations with Electro Optic Systems’ laser tracking station at Mt Stromlo (AS, May 2011, pp.28–30) and a US Air Force radar project that is coming to Australia specifically to find space junk and prevent disasters like the 2009 collision between a defunct Russian satellite and the Iridium constellation.