In an era of increasing global launch rates, heightened by the buckshot approach to tossing mega-satellite constellations into Earth orbit, there’s also escalating anxiety about the ramifications from reentry of defunct space hardware.
What’s lacking in the United States is a single coordinated effort to understand and manage reentry — one that is consistently funded and engages a variety of disciplines — say researchers and experts at The Aerospace Corporation who are studying the impacts and other aspects of reentry. There is also no national agreement, they argue, about who should fund reentry studies; government space interests and roles are spread out over multiple federal agencies.
Most reentries of space hardware are uncontrolled. When and where above Earth they auger in is a happenstance situation, and the inherent challenges of making targeted observations make addressing reentry particularly difficult.
Challenge and opportunity
“It’s definitely a challenging area of research,” said Marlon Sorge, the executive director for The Aerospace Corporation’s Center for Orbital and Reentry Debris Studies (CORDS).
Established in 1997, CORDS has worked on the growing space debris issue by conducting studies of controlled and uncontrolled reentry of rocket bodies, spacecraft and associated human-made clutter, some of which has been recovered on Earth and undergone intensive looks by the group. Similarly, Aerospace specialists are focusing on the impact incoming space junk has upon the Earth’s atmosphere.
Understanding that impact and other key details about reentry such as what happens to hardware as it evaporates during reentry, what survives the plunge and why, “is both a challenge and an opportunity,” Sorge told SpaceNews.
“We’ve got way more things coming back,” Sorge said, “and keeping up with new materials used, new approaches to operating spacecraft and their reentries makes the practical part of this much more challenging.”
The benefit stemming from these changes is that “people are somewhat more aware of what we need to be thinking about,” said Sorge. “As with everything, there’s a plus and minus to all of this that’s going on and, hopefully, we can leverage the pluses to deal with the minuses.”
Observational campaigns
Within the Aerospace Corporation, different teams are tackling each of the main challenges facing reentry mitigation and management, and the consequences of incoming space clutter on Earth.
“My role is to try to model, predict what space debris survives to the ground, from spent upper stages or decommissioned satellites when they reenter, for safety and risk assessment,” said Michael Weaver, director of Aerospace’s fluid mechanics department.
Observational campaigns are fairly rare and difficult to conduct, Weaver said, in part because controlled reentries are not all that common. “When they occur, they are in a very remote part of the world, making them hard to get to, and also logistically and resource intensive,” he said.
For example, the European Space Agency’s spacecraft Salsa made a targeted, destructive nosedive into Earth’s atmosphere on Sept. 8 over a remote area of the South Pacific Ocean. It was the first of four Cluster-series satellites to plow into the atmosphere, with other pre-planned reentries in 2025 and 2026.
In cooperation with ESA, the observational campaign for Salsa’s reentry — part of the Re-entry Observation Setup and International Execution (ROSIE) project — involved the University of Stuttgart, Comenius University in Bratislava, Slovakia and the University of Southern Queensland, along with industrial partners from Hypersonic Technology Göttingen in Germany and Astros Solutions, also in Bratislava.The fiery finale yielded rare ground and airborne looks of the Salsa satellite as it reentered the atmosphere. According to ESA’s space debris team they are hoping to use the collected data to improve current reentry prediction models as well as learn more about how a satellite burns up.
Coordination is key
Weaver said Aerospace was not a participant in the ESA Salsa reentry campaign, although the organization has been involved in some International Space Station supply vehicle reentries in the past.
“It’s rare for these operations to come together,” said Weaver. “But that makes them all the more valuable for validating the reentry models. It’s extremely important to anchor and validate your models against real-world data.”
“Coordination is key,” Weaver added.
Weaver pointed to Aerospace’s recent use of weather radar. “We can see clouds of debris that are settling maybe up to one or two hours after a reentry, giving us some insight into what’s surviving to the ground. Also, what may not be vaporizing at higher altitudes, for example,” he said.
“For whatever reason, it’s a hard sell to pull together a coordinated program here in the U.S.,” said Martin Ross, an Aerospace atmospheric scientist studying how rocket launches and space debris reentry affect Earth’s climate and stratospheric ozone layer. He contrasted it to progress made on the subject in Europe.
“That’s the kind of thing that’s needed now and I don’t see it happening,” Ross told SpaceNews. “It’s a bit of a puzzle. The Europeans are moving out on this, not just observations but models of demise, models of response of the atmosphere, wind tunnel testing. In the U.S. we’re starting to pull this together, but nothing really significant is happening at the moment,” he said.
Next step
Meanwhile, important questions remain unanswered. Ross said that it was only first recognized some four to five years ago that the growth of large constellations of satellites would potentially add significant amounts of material to the stratosphere.
“Last year, we actually saw that,” Ross continued, “all the metallic material embedded in the stratospheric sulfate layer particles. That layer is a key player in climate and ozone. It controls to a large degree the flow of radiation in the atmosphere. It controls ozone chemistry. That layer in the stratosphere we know now is getting polluted.”
Ross’s next step, he suggested, is determining whether space debris pollution matters. That takes laboratory work and chemistry analysis, but nobody is taking the lead on that research at this point, he said.
“Polluting those sulfate particles with metals, does that change anything? I think there’s a very reasonable suspicion that it will,” Ross said. “We need to get to the bottom of this. Every year the amount of material being put into the stratosphere increases. So, every year we delay, the problem is just getting larger.”
