WASHINGTON – Reducing the time that satellites remain in orbit after the end of their missions is one of the most cost-effective ways to tackle the problem of orbital debris, a NASA report concludes.
The report, released by NASA’s Office of Technology, Policy and Strategy on May 20, follows a March 2023 report that focused on the effectiveness of debris clearance techniques, or ways to remove debris. The new report expanded its scope to include strategies for mitigating debris, preventing debris from building up, and tracking improvements.
The study found that one of the most effective approaches, as measured by benefit-to-cost ratio, is reducing so-called post-mission cleanup time. That’s the time it takes for a satellite to be deorbited after it completes its mission. U.S. government regulations, based on international guidelines, require satellites to be deorbited within 25 years. However, the Federal Communications Commission has adopted regulations, effective in September, that will reduce the post-mission disposal period to five years.
The NASA study found that even smaller reductions in post-mission cleanup deadlines provide significant benefits. “We estimate that the benefits of moving to a 15-year rule would be 20 to 750 times the costs and could yield up to $6 billion in net benefits over 30 years,” the report said.
Shorter time frames could yield greater net benefits, up to $9 billion in a scenario where spacecraft are retired immediately after the end of their mission, albeit with lower cost-benefit ratios. In all scenarios considered by the NASA study, reducing post-mission disposal time yields cost-benefit ratios greater than one, meaning the benefits outweigh the costs.
While the study found that enhanced post-mission disposal, a debris mitigation measure, was highly effective, benefits were also found for some approaches to debris remediation. The most promising is what it calls “just in time” collision avoidance, which uses lasers or other technologies to nudge large pieces of debris that are in danger of colliding with each other.
The cost-benefit ratios of these approaches, the report concluded, are comparable to those of the most promising mitigation approaches, while adding that uncertainties in the models could make restoration even more promising. “We encourage the space community to recognize that the effectiveness of recovery can be comparable to – and perhaps better than – mitigation and tracking,” the report concludes.
Other promising tools, also based on cost-benefit analyses, include adding some degree of shielding to spacecraft to protect them from impacts, and improving tracking of “risky” conjunctions so satellite operators can make more informed decisions about collision avoidance maneuvers. However, there are significant uncertainties in these estimates, especially with regard to foreclosure.
Other techniques scored surprisingly poorly. Improving spacecraft passivation – removing energy sources from batteries and fuel tanks that could cause a debris-generating explosion – has not produced a net positive benefit even under the most optimistic scenarios over 30 years, with the cost of implementing passivation measures being greater than the cost of doing so.
Although the study involved significant technical analysis, its results were expressed in financial measures. “By measuring everything in dollars, we can directly compare shielding spacecraft to detecting 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, which highlights the need to better characterize the orbital debris problem before developing technologies to address it. That includes developing a framework for assessing the sustainability of space and determining which uncertainties are most critical to resolve.
“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 lens to this critical problem,” said Charity Weeden, NASA associate administrator of the Office of Technology, Policy and Strategy, in a statement.