WASHINGTON – Shortening the time satellites remain in orbit after their missions are completed is one of the most cost-effective ways to address the problem of orbital debris, a NASA report concludes.
The report, released May 20 by NASA’s Office of Technology, Policy and Strategy, follows up on a March 2023 report that focused on the effectiveness of debris remediation techniques, or debris removal methods. The new report expanded its scope to include strategies to mitigate debris or prevent debris from forming, as well as monitoring improvements.
The study found that one of the most effective approaches, as measured by the benefit-cost ratio, is to reduce what is known as post-mission delay time. This is the time it takes for the satellite to deorbit after completing its mission. US government regulations, based on international guidelines, require satellites to be deorbited after 25 years. However, the Federal Communications Commission has passed regulations that take effect this September that reduce the post-mission grace period to five years.
A NASA study found that even small reductions in post-mission disposal timelines offer significant benefits. “We estimated that the benefits of moving to the 15-year rule are 20-750 times the costs and could produce up to $6 billion in net benefits” over 30 years, the report said.
Shorter timelines can offer increased net benefits, up to $9 billion for a scenario where spacecraft are deorbited immediately after their mission, albeit with lower cost-benefit ratios. In all scenarios considered in the NASA study, reducing the post-mission disposal timeframe produces cost-benefit ratios greater than one, meaning the benefits outweigh the costs.
While the study found improved post-mission disposal, a debris mitigation measure, to be highly effective, it also found advantages for some approaches to debris remediation. The most promising is what has been called “just-in-time” collision avoidance, which involves lasers or other technologies to push large pieces of debris into danger of colliding with each other.
The cost-benefit ratios of those approaches, the report concludes, are similar to those of the most promising mitigation approaches, adding that uncertainties in the models could result in even more promising remediation. “We encourage the space community to realize that the effectiveness of remediation can be comparable to—and perhaps better than—mitigation and monitoring,” the report concluded.
Other promising tools, also based on cost-benefit analyses, include adding some degree of shielding to spacecraft to protect them from impacts as well as improving tracking of “high-risk” conjunctions to allow satellite operators to make more informed decisions about collision avoidance maneuvers. However, there are significant uncertainties in these estimates, particularly with respect to protection.
Other techniques scored surprisingly poorly. Improving spacecraft passivation — removing energy sources from batteries and fuel tanks that could produce a debris-generating explosion — has failed to produce a net positive benefit over 30 years even in the most optimistic scenarios, with the costs of implementing passivation measures exceeding the costs of doing so.
Although the study included significant technical analysis, its results were expressed in financial indicators. “By measuring everything in dollars, we can directly compare protecting spacecraft with tracking smaller debris, or removing 50 large pieces of debris with removing 50,000 smaller ones,” Jericho Locke, lead author of the report, said in a statement.
The new study comes a month after NASA released a new Space Sustainability Strategy that emphasizes the need to better characterize the orbital debris problem before developing technologies to solve it. This includes developing a framework for assessing the sustainability of space and determining which uncertainties are most critical to address.
“This study is part of NASA’s work to rapidly improve our understanding of that environment as outlined in NASA’s recently released Space Sustainability Strategy by applying an economic perspective to this critical issue,” said Charity Weeden, NASA’s Associate Administrator for the Office for Technology, Policy and Strategy, in a press release.