THE SPACE DEBRIS PROJECT

A huge quantity of space debris (inoperative spacecrafts, spent rocket stages as well as fragments of satellites) currently orbits the Earth. The amount of these objects is steadily growing and represents an increasing hazard to the whole space based activities. For this reason the discovery of new space debris and the characterization of the orbital debris environment represent one of the most important research activities carried out by worldwide space agencies (NASA, ESA, etc.). In the framework of the ASI space debris monitoring program, the IRA has been involved, together with other scientific partners, in the ''Progetto detriti spaziali'' funded by ASI-CISAS (Agenzia Spaziale Italiana - Centro Interdipartimentale di Studi e Attivita' Spaziali).

The first test of space debris detection performed using the innovative bistatic radar system, consisting of the 32m VLBI antenna at Medicina as receiver and the 70m antenna at Evpatoria (Ukraine) as transmitter, was successfully carried out. These measurements, mainly performed to validate a new hardware (the high speed back-end BEE2 FPGAs cluster) and to test the detection methods in both frequency and time domain as well as the ''piggy-back'' and ''beam parking'' observational techniques, resulted in the clear detection of extremely small size debris. Centimetric debris, among the smallest catalogued by NASA/NORAD (North American Aerospace Defense Command), were observed with an extremely high signal to noise ratio showing the high sensitivity and the capability of the system in pointing and detecting fast and small targets. The first size estimate, based on the geometry of the events and on the measured S/N ratios, gives diameters of the order of 5 mm. Such results demonstrate that the Medicina-Evpatoria bistatic radar system can play a fundamental role in the detection of small-size space debris and can represent one of the few worldwide systems that are able to detect sub-centimetric debris at LEO orbit.

The use of the Northern Cross antenna, as a receiver end of a bistatic radar configuration, is planned to exploit both its high sensitivity and spatial resolution. Due to the availability of a large number of receivers installed on the Best-2 SKADS array prototype, a multipixel (multibeaming) system has been successfully tested, obtaining a description of the debris trajectory inside the Field of View (FoV). In the fortunate case of available dedicated funds, the plan is to extend such a refurbishment to the whole antenna thousands receivers, obtaining a dramatic increase of both sensitivity and spatial resolution. At present, in order to better define the debris parameters, a way to define the altitude of debris is under investigation.