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Research highlight of Finnish Centre of Excellence in Inverse Problems Research
Detection of Space Debris
Space debris consists of different sized bits and pieces that are left over from various space missions that have been conducted during the last 50 years. Of the 30000 objects that have been launched into
space, only approximately 1000 remain in use today. A large number of smaller pieces of debris has also been created due to e.g., explosions, reactor coolant releases and even collisions of satellites. There are approximately 1 million objects larger than 1 cm in orbit today  and the number is exponentially increasing. Some models even suggest that a collisional chain reaction (the so called Kessler-syndrome) is already in progress in some orbital regions, which will eventually render these parts unusable for satellite operations.
An artist's impression of the current space debris situation:
The Sodankylä geophysical observatory group together with EISCAT has been active in developing new analysis methods that improve detection sensitivity of high power large aperture space debris measurements. Radar measurements are the only means of obtaining information of the small (0.01 - 0.1 m) space debris population orbiting Earth are therefore important. These objects are too small to be detected optically, but due to their high orbital velocity (7-10 km/s) they still pose a serious threat on impact. Measurements performed by the Sodankylä group together with EISCAT Scientific Association have been used by ESA to estimate the amount of debris produced by the Chinese anti-satellite collision in 2006 and the collision of the Iridium and Cosmos satellites in 2009 [2 and references therein].
Figure 2. EISCAT UHF radar.
A recent measurement produced with the EISCAT UHF radar (Fig 2.) after the Iridium-Cosmos collision is shown in Fig. 3. The analysis methods have been developed and implemented jointly between EISCAT and the Sodankylä geophysical observatory group. Currently the only way for avoiding catastrophic collisions is careful estimation of orbital elements of these objects in space and performing evasive manoeuvres when necessary. Current space surveillance systems cannot cope with the rapidly increasing space debris and new more efficient and sensitive radar measurement methods are needed.
Figure 3. Measurement produced with the EISCAT UHF radar after the Iridium-Cosmos collision.
 Oswald, M., S. Stabroth, C. Wiedemann, P. Wegener and C. Martin:"Upgrade of the MASTER Model", Final Report of ESA Contract No.18014/03/D/HK(SC), Braunschweig, 2006.
 Markkanen J, Vierinen J: "The past present and future of spacedebris measurements at EISCAT", In Proceedings of CEAS 2009.