ARLINGTON, Va. — A long-standing guideline for deorbiting satellites within 25 years, criticized by many in the space industry for being too long, is still effective for reducing the growth of orbital debris so long as satellite operators abide by it, according to an orbital debris expert.
Guidelines for mitigating orbital debris, including one at the international level published in 2007 by the Inter-Agency Space Debris Coordination Committee, recommend that satellites in low Earth orbit be deorbited no more than 25 years after the end of operations to minimize the risk of collisions that would create debris. That 25-year guideline was maintained in an update to U.S. government orbital debris standard practices released in December.
Even before that recent update, though, many in the space industry argued that the 25-year timeframe was too long, given the growing population of objects in low Earth orbit and projections for future growth in the number of satellites. They called for reducing the period in which satellites should be deorbited to as little as 5 to 10 years, although, there’s little consensus about what that revised timeframe should be.
That extends to the leaders of major space agencies. “I personally believe this is too long,” Jan Woerner, director general of the European Space Agency, said of the 25-year guideline during a Jan. 15 press briefing at the agency’s Paris headquarters. “We have to work on a shorter period,” he said, because of the emergence of satellite megaconstellations.
However, one top orbital debris expert says shortening that time period for deorbiting satellites will not provide much benefit. “The 25-year rule is still a good cost-benefit way for reducing debris,” said J.-C. Liou, chief scientist for NASA’s Orbital Debris Program Office, in a Jan. 14 speech at the Second International Academy of Astronautics Conference on Space Situational Awareness here.
Liou presented the results of simulations that projected the growth of orbital debris over the next two centuries using a number of scenarios. A baseline scenario, where no satellites comply with the 25-year rule, results in a 330% increase in debris over 200 years. However, if 90% of satellites comply with the rule, that increase declines to 110% over the same period.
A similar scenario, but with 90% of satellites complying with a five-year deorbiting rule, reduces the growth in objects only slightly, to 100% over 200 years. “It’s not a very statistically meaningful benefit,” he said. Moreover, he said complying with a five-year rule would incur additional costs for satellite operators, leading him to conclude that the 25-year rule remained useful.
The problem, he said, was not with the guideline itself but with adherence to it. “What’s missing is the compliance level with respect to the 25-year rule,” he said. He estimated that global adherence to the guideline was below 50%.
Exactly what fraction of satellites do attempt to comply with the guideline is “complicated,” he said later, in part because it’s often not clear when a satellite ends operations and thus starts that 25-year clock. ESA, in a “Space Environment Report” published last July, estimated that only 15–25% of satellites in orbits high enough that they will not deorbit naturally because of atmospheric drag within 25 years attempt to comply with the guideline.
“We do have good policies and practices in place,” Liou said, “but we are just not doing a very good job globally to implement those policies, practices and requirements to limit the generation of orbital debris.”