Protecting the space debris environment and protecting against it

摘要

Today's particle environment of the Earth is dominated by man-made space objects, except at a small particle size regime below 1 mm, where meteoroids provide a significant contribution, or even prevail in some orbit regimes. The mass of man-made objects in Earth orbits is on the order of 5,800 tons, of which more than 99% is concentrated in trackable objects larger than typically 10 cm. The mass of meteoroids within the regime of Earth orbits is on the order of 3 tons, with most probable sizes around 200 μm. As a consequence of their size spectrum and associated mass man-made space debris represent a considerably higher risk potential to space assets in Earth orbits. The debris related risk is even higher shortly after a break-up event, when a cloud of fragments first spreads along the orbit, and then disperses in the orientation of its orbit planes. These dispersion phases are not yet fully completed for two major collision events in the recent past: an ASAT test that caused the fragmentation of FengYun 1C on Jan. 11, 2007, at an altitude of 862 km, and the first unintentional hypervelocity collision between two intact objects (Iridium 33 and Cosmos 2251) on Feb. 18, 2009, at an altitude of 788 km. The FengYun 1C event increased the size of the US Catalog of ～10,000 unclassified, trackable objects by 2,500 objects (+25%), while the Iridium-Cosmos collision increased it by another 1,500 objects (+12%). The related, combined collision risk increase for ESA's Envisat and ERS-2, both operating near 780 km altitude, was on the order of 60% for Catalog objects. The paper will address the collision risk for manned spacecraft (e.g. ISS) and robotic spacecraft (e.g. Envisat) in low Earth orbits (LEO). Statistical predictions will be compared with actually performed avoidance maneuvers for large-size objects, and with impacts on space hardware for small-size objects. Special attention will be given to periods of elevated particle flux in close spatial and temporal vicinity of large fragmentation events. Apart from protecting space hardware against space debris, aspects will be highlighted of protecting the space debris environment against collisional cascading of remnant space hardware. Long-term debris environment projections indicate that even a complete halt of launch activities cannot prevent the onset of a collisional run-away situation in some LEO altitude regimes. The paper will outline effective methods of space debris environment remediation, with active removal of mass from critical orbit altitudes.