WASHINGTON — Reducing the time satellites stay in orbit after their mission ends is one of the most cost-effective ways to solve the problem of space debris, according to a NASA report.
The report, released by NASA’s Office of Technology, Policy and Strategy on May 20, is a follow-up to a March 2023 report that focused on the effectiveness of debris remediation techniques, or ways to remove debris. The new report expanded its scope to include strategies to reduce debris, or prevent it from being created, and track improvements.
The study found that one of the most effective approaches, measured in terms of benefit-to-cost ratio, is to shorten the so-called post-deployment disposal time, which is the time it takes for a satellite to deorbit after completing its mission. U.S. government regulations, based on international guidelines, require satellites to be deorbited within 25 years. However, the Federal Communications Commission has issued regulations that will take effect in September this year that will shorten the post-mission disposal period to five years.
The NASA study concluded that even small reductions in post-mission disposal periods provide significant benefits. “We estimated that the benefits of moving to a 15-year rule are 20 to 750 times the costs and could provide a net benefit of up to $6 billion over 30 years,” the report said.
Shorter periods can provide higher net benefits, up to $9 billion for a scenario in which spacecraft are deorbited immediately after the end of their mission, but with a lower cost-benefit ratio. In all scenarios considered by NASA’s study, shortening the post-mission disposal period results in a cost-benefit ratio above one, meaning the benefits outweigh the costs.
While the study concluded that enhanced post-mission disposal, a debris mitigation measure, is very effective, it also found benefits for some approaches to debris remediation. The most promising is so-called “just-in-time” collision avoidance, which uses lasers or other technologies to nudge large pieces of debris that are at risk of colliding with each other.
The cost-benefit ratios of these approaches, the report says, are similar to those of the most promising mitigation approaches, but adds that uncertainties in the models could make remediation even more promising. “We encourage the space community to recognize that the effectiveness of remediation can be comparable to – and perhaps even better than – that of mitigation and tracking,” the report concludes.
Other promising tools, also based on cost-benefit analyses, include adding additional shielding to spacecraft to protect them from impacts, and improving tracking of “high-risk” conjunctions to allow satellite operators to make more informed decisions about collision avoidance maneuvers. However, these estimates have significant uncertainties, particularly regarding shielding.
Other techniques performed surprisingly poorly. Improving spacecraft passivation—removing energy sources from batteries and fuel tanks that could trigger a debris-generating explosion—produced no net benefit over 30 years, even in the most optimistic scenarios, because the cost of implementing passivation measures outweighed the cost of actually implementing them exceeded.
While the study included extensive technical analysis, its results were expressed in financial metrics. “By measuring everything in dollars, we can directly compare spacecraft shielding to tracking smaller debris, or removing 50 large pieces of debris to removing 50,000 smaller ones,” Jericho Locke, lead author of the report, said in a statement.
The new study comes a month after NASA announced a new space sustainability strategy that emphasizes the need to better characterize the problem of orbital debris before developing technologies to solve it. This includes developing a framework for assessing space sustainability and determining which uncertainties are most critical to resolve.
“This study is part of NASA’s work to rapidly improve our understanding of this environment, as outlined in NASA’s recently released Space Sustainability Strategy, by applying an economic perspective to this critical issue,” said Charity Weeden, deputy administrator of the Office of Technology, NASA Policy and Strategy, in a statement.