Long term effects of the mitigation and remediation measures in view of the changing space activities

The recent huge increment of launches in Low Earth Orbit (LEO) calls for effective Space Traffic Management proce- dures based on efficient space surveillance systems. Collision avoidance for active satellites, mitigation measures (Post- Mission Disposal, PMD, at end-of-life) and remediation measures (Active Debris Removal, ADR) for non operational satellites should all be considered together to reach the final goal of a viable orbital regime in LEO and a stable debris environment. Using the long term evolution model SDM (Space Debris Mitigation) different future scenarios considering a signifi- cantly increased traffic launch, including the currently deployed and the most probable future large constellations, were simulated. The effectiveness of different PMD and ADR measures was tested. The simulations clearly show the need for improved mitigation and remediation measures. In particular, ADR appears almost fundamental to moderate the growth of the debris population in the next decades. A very effective Space Surveil- lance and collision avoidance system must be in place to limit the large number of lethal collisions suffered by the con- stellations satellites observed in our scenarios. In particular, even objects of several cm in size should be tracked and cataloged to allow effective collision avoidance and limit the number of stranded damaged satellites in highly populated orbital shells. Two "black swans" scenarios, to test the bearing capacity of the most crowded region around 800 - 900 km of altitude, before a local collisional cascade is triggered are simulated too. In this cases, one of the highly probable collisions be- tween two very massive objects in the crowded region is artificially introduced in the simulation and a few cascading fragmentations in the same region are simulated in the following years. The simulations performed so far show that the adopted mitigation and remediation measures can somehow moderate the effects of two subsequent forced massive fragmentations. Nonetheless the region remains dangerously "perturbed" above the reference level for decades. The simulation scenarios will serve as reference for a successive economic analysis which will be performed consider- ing the implications of the adopted or non-adopted mitigation and remediation measures.