• analisi di missione
• bassa spinta
• detriti spaziali
• propulsione elettrica
• schiume espandibili

For over twenty years man has been sending into orbit thousands of satellites, creating the problem of space junk. As of today, the orbiting satellites still serviceable are only a few hundreds, the remaining being objects, called space debris, of dimensions ranging between a few centimetres and tens of metres, which represent a danger for current and future space activities. The number of such fragments is constantly increasing, due not only to new satellites which are being and will be sent into orbit, but also to the collisions between the orbiting ones which determine the birth of numerous new fragments.

This study analyses debris in low earth orbit, and the proposed removal method is based on the use of polyurethanic foam capable of expanding under vacuum, to create a large sphere of foam around the fragment. Such sphere increases the surface-mass ratio of the fragment, and the effect of atmospheric drag on it. In such a way, the deorbit time due to friction is reduced with respect to the natural one.

The purpose of this study is to investigate a number of low-thrust mission scenarios, in which the foam-carrying satellite is transferred towards the debris to be deorbited using the thrust generated by an electric thruster. Such fragments are appropriately chosen from a database based on real objects: the SL-8, SL-3 and SL-14 stages of Russian launchers.

The dynamic model used to study the motion of satellite and debris is the two-body problem with perturbations (atmospheric drag, J2 effect, thrust). Mission analysis is carried out with an approximate approach, by studying the secular rate of the orbital parameters, calculated by integrating along an orbit the Lagrange planetary equations, written in the Gaussian form.

The results obtained from several mission scenarios highlight the advantages and disadvantages of the assumptions made on satellite and thrusters models. It has been found that using the removal method based on expanding foam, it is possible to remove a total of 50 SL-8 with 4 launches and a total mission duration of about 23 years each, 50 SL-3 and 50 SL-14 with only one single launch and a total mission duration of 8.6 and 21.7 years respectively.