Evaluation of low earth orbit post-mission disposal measures

The substantial benefits arising from the widespread adoption of post-mission disposal in low Earth orbit (LEO) are reflected in a reduced orbital debris population and a reduced frequency of collisions. The benefits are generally seen at higher altitudes whereas some drawbacks in the form of enhanced collision risks have been predicted for lower altitudes. These drawbacks are generally expected to reduce as the post-mission disposal lifetime decreases, as less time at lower altitudes reduces collision probability. This is the rationale used by the Federal Communications Commission (FCC) for its new 5-year rule. To investigate the potential benefits and drawbacks, the DAMAGE computational model was used to investigate the effects of a variety of LEO post-mission disposal rules, including the new 5-year rule, within scenarios involving the deployment of large constellations of satellites. The results suggest substantial reductions in conjunction rates overall, as the post-mission residual orbital lifetime decreases, but indicate an increasing frequency of conjunctions and a corresponding need for risk mitigation maneuvers at low altitudes. The results reinforce the recommendation that disposal must be completed as soon as practicable following end of mission. Additionally, the results highlight the need for careful consideration and further research into post-mission disposal where a residual orbital lifetime is permitted.