A team of researchers from the Royal Institute and Observatory of the Navy (ROA) in Cádiz (Spain) has developed a method to track the movement of geostationary（与地球旋转同步的） objects using the position of the stars, which could help to monitor space debris. The technique can be used with small telescopes and in places that are not very dark. Objects or satellites in geostationary orbit (GEO) can always be found above the same point on the Equator, meaning that they appear immobile when observed from Earth. By night, the stars appear to move around them, a feature that scientists have taken advantage of for decades in order to work out the orbit of these objects, using images captured by telescopes, as long as these images contain stars to act as a reference point.

This method was abandoned when satellites started to incorporate transponders（变换器） (devices that made it possible to locate them using the data from emitted and reflected signals). However, the classic astrometric techniques are now combing back into vogue due to the growing problem of space waste, which is partly made up of the remains of satellites engines without active transponders.

"Against this backdrop, we developed optical techniques to precisely observe and position GEO satellites using small and cheap telescopes, and which could be used in places that are not particularly dark, such as cities", Francisco Javier Montojo, a member of the ROA and lead author of a study published in the journal Advances in Space Research, tells SINC.

The method can be used for directly detecting and monitoring passive objects, such as the space junk in the geostationary ring, where nearly all communications satellites are located. At low orbits (up to around 10,000 km) these remains can be tracked by radar, but above this level the optical technique is more suitable.

Montojo explains that the technique could be of use for satellite monitoring agencies "to back up and calibrate（校正） their measurements, to check their manoeuvres, and even to improve the positioning of satellites or prevent them from colliding into other objects".

"The probability of collisions or interferences occurring between objects is no longer considered unappreciable since the first collision between two satellites on 10 February 2009 between America's Iridium33 and the Russians' Cosmos 2251", the researcher points out.