Modelling the evolution of the space debris population

The current space activities are already disturbed and jeopardized by the g rowing number of orbiting debris. Those planned for the near future, such a s the launch of large satellite constellations and the construction of the international space station, are even more sensitive to the evolution of th e space environment. Therefore, a clear picture of the present situation in Earth orbit and its future evolution is needed. In this paper we describe in some details the work we have carried out on this problem in the last se veral years. Starting from the current population and simulating a reasonab le scenario for the space activities in the next decades, we have obtained plausible quantitative models of the possible future space environment. We summarize some results concerning the effectiveness of possible mitigation measures and assess the robustness of these results, by checking how sensit ively they depend upon the initial conditions and the choice of some model parameters. We also analyze the effect of the launch of a number of satelli te constellations, showing the importance of the adoption of some debris pr evention measures in their launch policies. Finally, we study the possible problems arising from the recent discovery of a new family of debris compos ed by drops of NaK coolant, that leaked outside the nuclear reactors of the Soviet RORSAT-class satellites. Our preliminary results indicate that thes e drops are going to cause an increasing number of small-scale, possible sa tellite-damaging impacts but, due to their small size, no additional catast rophic collisions; therefore their influence on the long-term evolution of the overall debris population is limited. (C) 1998 Elsevier Science Ltd. Al l rights reserved.