WASHINGTON — The European Space Agency is in the ultimate stages of performing an “assisted reentry” of an Earth science spacecraft, an effort that may try to bring the satellite down over the ocean in a little bit greater than per week.
A series of maneuvers will lower the perigee of the Aeolus spacecraft to enable a reentry, projected over the Atlantic Ocean, on July 28. The maneuvers are intended to reduce any probability that debris from the spacecraft that survives reentry would land in populated areas.
The primary set of maneuvers is scheduled for July 24 and can lower the spacecraft’s perigee from 280 to 250 kilometers, said Isabel Rojo, Aeolus operations director, during a July 19 briefing. A second set of maneuvers on July 27 will further lower the perigee to 150 kilometers.
A final maneuver on July 28 will lower the perigee to 120 kilometers. “After the execution of that last maneuver, the satellite is then expected to reenter inside five hours,” she said.
That last maneuver is timed to have reentry happen during a track the spacecraft’s sun-synchronous orbit takes over the Atlantic Ocean. Limitations of the spacecraft, though, mean that ESA can’t goal a selected area for the reentry.
“This spacecraft was designed and developed just before any guidelines got here in place” mandating a controlled reentry, said Holger Krag, head of ESA’s Space Safety Office. That led to what the agency calls an “assisted reentry” approach, which lacks the precision of a controlled reentry but avoids an uncontrolled reentry. “It can further reduce the danger, which is already small, on the bottom that’s posed by the reentry,”
ESA expects as much as 20% of Aeolus, which weigh about 1,100 kilograms excluding propellant, to survive reentry. The agency said that the assisted reentry approach, if successful, would cut back the danger of debris hitting someone, already extremely small, by an element of 42.
Krag said that is the primary time he’s aware of any satellite operator attempting an assisted reentry. The closest comparison he offered is the reentry of NASA’s Skylab space station in 1979, where spaceflight controllers turned off gyros to make the spacecraft tumble in an effort to manage the reentry location.
ESA officials billed the assisted reentry as a part of a broader commitment to space safety by the agency. That included an announcement through the Paris Air Show June 22 that ESA would work with several European satellite manufacturers on a “Zero Debris Charter” where signatories would commit, by 2030, to deorbiting their satellites at the top of their lives or hiring corporations that provide lively debris removal services to deorbit them.
“I feel ESA has at all times been a responsible actor and, with that motion on Aeolus, we’re demonstrating over again that we’re willing to realize anything, even with an area system that was not originally prepared for this,” Krag said.
The reentry will mark the top of Aeolus, launched in 2018 on what was originally planned as a three-year mission to display the power of a lidar to measure wind speeds globally. Science operations of Aeolus formally resulted in April.
“After almost five years, it has exceeded all of the expectations and gone beyond what were the unique objectives,” said Tommaso Parrinello, Aeolus mission manager. That included using Aeolus data in operational weather forecasting and filling in gaps in wind data when industrial airline traffic, also used to gather wind data, dropped significantly through the onset of the pandemic.
At ESA’s November 2022 ministerial meeting, member states approved plans for a two-satellite follow-on mission, Aeolus 2, slated to launch at the top of the last decade in cooperation with Eumetsat. “This decision taken last yr is essentially the most tangible and most solid demonstration of the worth of the success of this mission, which perhaps was not obvious in the beginning,” he said.
Simonetta Cheli, ESA’s director of Earth remark, said on the briefing that Aeolus was often called the “unimaginable mission” due to the various technical challenges it faced in development. “It’s an actual success story.”