WASHINGTON — Decreasing the time satellites remain in orbit after the end of their missions is one of the most cost-effective ways to address the orbital debris problem, a NASA report concluded.
The report, released by NASA’s Office of Technology, Policy and Strategy 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 for debris mitigation, or preventing the creation of debris, as well as tracking improvements.
The study found one of the most effective approaches, as measured by the ratio of its benefits to its costs, is reducing what is known as the post-mission disposal time. That is 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 with 25 years. The Federal Communications Commission, though, passed regulations that take effect this September that reduce the post-mission disposal period to five years.
The NASA study found that even smaller reductions of post-mission disposal timeframes offer significant benefits. “We estimated that the benefits of moving to a 15-year rule are 20–750 times the costs and may produce up to $6 billion in net benefits” over 30 years, the report states.
Shorter timeframes can offer increased net benefits, up to $9 billion for a scenario where spacecraft are deorbited immediately after the end of their mission, although with lower cost-benefit ratios. In all scenarios considered by the NASA study, reducing post-mission disposal timeframe produces cost-benefit ratios greater than one, meaning that the benefits outweigh the costs.
While the study found improved post-mission disposal, a debris mitigation measure, very effective, it also found benefits for some approaches to debris remediation. The most promising is what it called “just in time” collision avoidance that involves lasers or other technologies to nudge large pieces of debris in danger of colliding with each other.
The cost-benefit ratios of those approaches, the report concluded, are like those for the most promising mitigation approaches, while adding that uncertainties in the models could result in remediation being even more promising. “We encourage the space community to realize that the effectiveness of remediation can be comparable to—and perhaps better than—mitigation and tracking,” 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 for “high-risk” conjunctions to allow satellite operators make more informed decisions about collision avoidance maneuvers. However, there are significant uncertainties in those estimates, particularly regarding shielding.
Other techniques scored surprisingly poorly. Improving spacecraft passivation — removing sources of energy from batteries and propellant tanks that could produce a debris-generating explosion — failed to produce a net positive benefit over 30 years even in the most optimistic scenarios, with the cost of implementing passivation measures outweighing the costs of doing so.
While the study involved significant technical analysis, its results were expressed in financial metrics. “By measuring everything in dollars, we can directly compare shielding spacecraft to tracking smaller debris or removing 50 large pieces of debris to removing 50,000 smaller ones,” said Jericho Locke, lead author of the report, 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 orbital debris problem before developing technologies to address it. That includes developing a framework for assessing space sustainability and determining what uncertainties are the 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 issue,” said Charity Weeden, NASA associate administrator the Office of Technology, Policy and Strategy, in a statement.
