WASHINGTON — Reducing the amount of time satellites remain in orbit after their missions are over is one of the most cost-effective ways to solve the problem of orbital debris, a NASA report concluded.
The report, released May 20 by NASA’s Office of Technology, Policy and Strategy, follows a March 2023 report that focused on the effectiveness of debris remediation techniques, or ways to remove debris. The new report broadened its scope to include strategies for mitigating or preventing debris, as well as tracking improvement.
The study found that one of the most effective approaches, measured by its benefit-cost ratio, is to reduce the time known as post-mission disposal time. This is the time it takes for a satellite to come out of orbit 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 approved regulations that will go into effect this September that reduce the post-mission disposal period to five years.
A NASA study found that even smaller reductions in post-mission disposal time offer significant benefits. “We estimate that the benefits of moving to the 15-year rule are 20-750 times the costs and could yield up to $6 billion in net benefits” over 30 years, the report said.
Shorter time frames can offer higher net benefits of up to $9 billion in a scenario where spacecraft are de-orbited immediately after their mission ends, albeit at a lower cost-benefit ratio. In all scenarios considered by the NASA study, reducing post-mission disposal time results in a cost-benefit ratio greater than one, meaning the benefits outweigh the costs.
While the study found enhanced post-mission disposal, a debris mitigation measure, to be very effective, it also found benefits for some debris remediation approaches. The most promising is what’s called “just-in-time” collision avoidance, which involves lasers or other technologies that deflect large pieces of debris that are at risk of colliding with each other.
The report concluded that the cost-benefit ratios of these approaches were the same as the most promising mitigation approaches, adding that uncertainties in the models could make remediation even more promising. “We urge the space community to recognize that the effectiveness of remediation can be comparable to—and perhaps superior to—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 the 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 shielding.
The 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 in 30 years, even in the most optimistic scenarios, with the cost of implementing passivation measures outweighing the cost of doing so.
While the study included significant technical analysis, its results were expressed in financial metrics. “By measuring everything in dollars, we can directly compare shielding 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 announced a new space sustainability strategy that emphasizes the need to better characterize the orbital debris problem before developing technologies to solve it. This includes establishing 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 this environment, as outlined in NASA’s recently released Space Sustainability Strategy, by applying an economic lens to this critical issue,” said Charity Weeden, associate administrator for NASA’s Office of Technology, Policy. and strategy, in statement.