The efficacy of managing space environmental risk by regulating probability of collision with large objects

Abstract

Long-term space sustainability demands effective management and limitation of the growing orbital debris population. Achieving this requires first an improved quantification of environmental risk before proper mitigation can be formulated. A significant contributor to this risk is the creation of debris that is large enough to cause damage to another spacecraft upon impact, small enough to be difficult to track, and prohibitively expensive to remove due to quantity and orbital distribution. Currently, the most effective way to reduce the long-term risk of orbital debris is to prevent its generation in the first place. In line with this, the United States Federal Communications Commission (FCC) requires, as part of their license application processes, compliance with regulations designed to limit the likelihood of events which would generate debris, such as the limitation of the probability of collision with large objects [1]. In this instance, a “large object” is any object exceeding 10 cm in diameter, and the legacy maximum allowable probability of collision is 1.0e-3 per satellite, assessed over its lifetime. To show compliance with this regulation, satellite operators commonly use NASA's Debris Assessment Software (DAS) tool. Historically, DAS has provided adequate means for assessing lifetime collision risk for single-satellite missions operating in low earth orbit (LEO). However, given the rapid increase in the number of spacecraft and large constellations that are being launched into orbit, it is prudent to re-evaluate both the regulation requirement itself, as well as the method by which compliance is determined. This paper explores the origin and intent of the requirement and assesses its efficacy through multiple case studies representing different spacecraft in various orbits. In each case study, the likelihood and impact dimensions of catastrophic fragmentation risk are computed for each spacecraft and then compared to corresponding DAS outputs. Analysis results show that not only does the likelihood of catastrophic fragmentation consistently exceed predictions by DAS, but the environmental impact may also be greatly underestimated for spacecraft more massive than 50 kg.