Researchers work to prevent collisions with space debris

Information from these systems will ultimately provide a more complete picture of orbital debris, allowing better warning of collisions.

The issue of space debris is now well publicised. There are some 20,000 objects larger than 10cm — including disused satellites, rocket fragments and other wreckages — orbiting the Earth, completely uncontrolled.

There have been a number of ambitious proposals to remove this debris, including a concept earlier this year by the Japanese Space Agency to use a ‘fishing-net’-type device.

However in the short-to-medium term the focus will be on preventing collisions, which requires a better understanding of what is actually present and where. This essentially involves the identification and technical analysis of objects (reconnaissance) and monitoring of orbits (surveillance).

The US has collated and made public orbital data on known objects (under the USSTRATCOM catalogue) but as Dr Martin Hellmann of the DLR told The Engineer, this is rarely sufficient.

‘We know the position of our satellites quite well, based on telemetry, but the ambiguities of other objects can be anything between a few hundred metres and sometimes up to a kilometre. You have an idea where to look for objects but for real manoeuvring, like saying “this thing will hit your satellite”, it’s just not exact enough.’

A number of countries, including the US and now Germany, have set up space surveillance network systems based on the use of radar, optical telescopes and spaced-based sensors to track potentially dangerous objects in real time.

Hellmann and fellow DLR researchers are also developing more innovative methods, such as a laser-coupled telescope. The optical aspect locates objects, while a pulsed laser pinpoints the angular coordinates and distance. Eventually, a second high-powered laser might be able to de-orbit rogue objects.

They have also shown that radar satellites — initially intended to create ‘digital elevation models’ of the Earth — can be tilted and trained at orbit-level space to gather technical ‘images’ of potentially dangerous objects.

Research and data from the DLR team will feed into the newly operational German Space Situational Awareness Centre (GSSAC), which aims to provide warnings and prevent collisions on a day-to-day basis. 

‘We do the research and the GSSAC is more like the operational side,’ Hellmann said. ’Using our own algorithms we can predict collision probabilities and say: “look guys there is something there, but if you move your satellite and something happens we can’t take responsibility, we can’t give you orders, we can just say watch out”.’