Michael Byers, The University of British Columbia; Ewan Wright, The University of British Columbia; Aaron Boley, The University of British Columbia, Cameron Byers, The University of British Columbia
Keywords: Rocket Bodies, Atmospheric Reentries, Casualty Risk
Abstract:
In 2020, over 60% of launches to low Earth orbit resulted in one or more rocket bodies being abandoned in orbit and eventually returning to Earth in an uncontrolled manner. When they do so, between 10 and 40% of their mass survives the heat of atmospheric reentry. Many of the surviving pieces are heavy enough to pose serious risks to people, on land, at sea, and in airplanes.
There is no international consensus on the acceptable level of risk from reentering space objects. This is sometimes a point of contention, such as when a 21 tonne Long March 5B core stage made an uncontrolled reentry in May 2021. Some regulators, including the US, France, and ESA, have implemented a 1 in 10,000 acceptable casualty risk (i.e., statistical threat to human life) threshold from reenterring space objects. We argue that this threshold ignores the cumulative effect of the rapidly increasing number of rocket launches. It also fails to address low risk, high consequence outcomes, such as a rocket stage crashing into a high-density city or a large passenger aircraft. In the latter case, even a small piece could cause hundreds of casualties. Compounding this, the threshold is frequently ignored or waived when the costs of adherence are deemed excessive.
We analyse the rocket bodies that reentered the atmosphere from 1992 – 2021 and model the associated cumulative casualty expectation. We then extrapolate this trend into the near future (2022 – 2032), modelling the potential risk to the global population from uncontrolled rocket body reentries. We also analyse the population of rocket bodies that are currently in orbit and expected to deorbit soon, and find that the risk distribution is significantly weighted to latitudes close to the equator. This represents a disproportionate burden of casualty risk imposed on the countries of the Global South by major spacefaring countries.
Modern rockets have reignitable engines, allowing controlled reentries into remote areas of the oceans. This, combined with updated mission designs, would eliminate the need for most uncontrolled reentries. Some extra costs would fall on launch providers, including additional fuel for the reentry manoeuvre. Government missions should be able to absorb these extra costs, but they could affect the ability of a commercial launch provider to compete.
Countries in the Global South, whose populations are being put at disproportionate risk by uncontrolled rocket bodies, should demand that major spacefaring countries level the playing field by mandating controlled rocket reentries. This solution, which will have to be coordinated multilaterally, must create meaningful consequences for non-compliance while allowing leeway for those who cannot immediately engage in or afford controlled re-entries.
Date of Conference: September 27-20, 2022
Track: SSA/SDA