A Global Strategy to Clear the "Space Protected Zones" from the Spacecrafts, at their End of Operative Life

The increasing number of orbiting spacecrafts is "pushing-up" the problem of controlling the risk of collision with orbital debris. Several European Space Agencies (ASI, BNSC, CNES, DLR and ESA) recently decided to adopt a common "European Code of Conduct for Space Debris Mitigation". This paper focuses on the Code Requirement relevant to clear the space volume around Geosyncronous Earth Orbit (GEO) at the satellite end of life, as well as the one that imposes a maximum residual orbital life of 25 years to defunct Spacecrafts (S/C) orbiting up to 2000 Km of altitude. The optimal technical solution to meet such requirements is significantly different basing on mission and S/C characteristics, namely the orbit altitude, the S/C dimensions and ballistic coefficient, the dry mass, the on board propulsion type. This paper intends to help the S/C designers to identify the most promising technical solutions that guarantee the compliance with the Space Debris Mitigation Code requirements, and minimise the impact on their S/C. After an introduction, where the Code Requirements are recalled and commented, the paper defines the orbit altitude ranges for which an homogeneous debris control strategy can be efficiently developed. Then, the core part of the paper is constituted by the analysis of each orbital ranges above, and to the consequent definition of the most promising approach for clearing the orbit after the End Of Service (EOS). Such approaches include: a)"do nothing" where Code Requirements will be met by any S/C original design, b) utilise aero-brakes to accelerate the natural de-orbiting, c) utilise a propulsion module to de-orbit from Low Earth Orbit (LEO) or, d) to increase orbital altitude above the LEO protected one, e) utilise the S/C own propulsion to perform the graveyard firing of GEO satellites, supported by the use of an accurate, and reliable, residual propellant gauging system that assures the availability of the propellant for the manoeuvre. In addition to a) to e) technical solutions for the future space mitigation systems should be conceived to actively remove the large and intact satellite or upper stage debris. Its design should consist of a spacecraft having on board a proper randez vous and docking system, able to approach the debris, assume an identical tumbling motion, rigidly grab it and manoeuvre to a disposal orbit.