In the nearly seven decades of space exploration, approximately 10,000 intact satellites and rocket bodies have reentered the atmosphere. However, the details of what occurs during reentry remain largely unknown.

An airborne observation experiment has been planned to witness Salsa's reentry. A team of scientists aboard a small aircraft will attempt to collect rare data on how and when a satellite breaks apart, which could lead to safer and more sustainable satellite reentries in the future.

Gaining Insight from Salsa's Reentry
"To keep Earth's valuable orbits clean, it is important to remove a satellite quickly from orbits after their mission comes to an end, and thereby prevent more space debris," said Holger Krag, Head of Space Safety at ESA.

"Reentry science is an essential element of these efforts. Cluster's reentry can help us understand how to design and operate satellites so that they can be disposed of easily, safely, and sustainably in the future."

The Cluster mission offers a unique opportunity, with its four identical satellites reentering under slightly different conditions, creating a repeatable experiment for scientists.

"Together with our partners at Astros Solutions, we are sending a plane to observe Salsa's reentry live from the sky to observe a satellite class and reentry conditions which have never been accessible before," added Stijn Lemmens, Space Debris Analyst at ESA.

"There's testing we can do on the ground, and we have virtual modeling, but we also need real-life observations right at the scene of a reentry to complete the picture. The observation experiment from a plane is an exciting new possibility for us to collect data and gain confidence in the modeling to support new missions."

Targeting the Pacific for Salsa's Final Moments
In January 2024, operators adjusted Salsa's trajectory to ensure it would target a specific remote location in the South Pacific Ocean for its reentry on September 8, 2024. This region was chosen to minimize the risk to populated areas, as most of the satellite will disintegrate in less than a minute, though some fragments may survive.

The highly eccentric orbit of the Cluster satellites allowed for a "targeted reentry." This orbit causes significant altitude loss at perigee, and operators can predict when Salsa will reenter the atmosphere, burning up around 80 km altitude.

"It's because of this predictability in the reentry time and location that we can outfit a plane with scientific instruments and observe the reentry from as close as safely possible," Lemmens explained.

"There is, however, one unknown: the atmospheric density as we go lower and lower. Therefore, over the next weeks, ground stations will keep listening for Salsa, hoping it can send telemetry right until the end. Telescopes are also tracking the spacecraft, as any minor deviations from its predicted trajectory could be important for the flight plan from Easter Island."

Conducting the In-Flight Observation Experiment
The airborne observation mission, dubbed "ROSIE-Salsa," is a collaborative effort involving academic and industrial partners, including the University of Stuttgart, Comenius University in Bratislava, University of Southern Queensland, Hypersonic Technology Gottingen, and Astros Solutions, in close cooperation with ESA.

"This is a very challenging mission due to the unpredictable nature of reentry events, which makes the reentry break-up prediction as well as the planning of the aircraft positioning for the best observation very demanding," said Jiri Silha, CEO of Astros Solutions. "However, with experts in both science and technical preparation, our team consists of exceptionally capable people who will ensure that once the object is in sight, we will get all the relevant scientific data we need."

The aircraft will be equipped with over 20 scientific instruments, including cameras and spectrographs, to capture the reentry. Despite the challenges posed by daylight reentry, which makes observation more difficult, the team is hopeful for successful data collection.

Looking Ahead in Reentry Science
The opportunity to observe satellite reentries from the air is rare but promises to yield valuable insights. Following Salsa's reentry, the remaining Cluster satellites - Rumba, Samba, and Tango - will undergo similar reentries in remote regions over the South Pacific Ocean by 2026.

"On top of the four Cluster reentries, we are also looking ahead to ESA's exciting DRACO mission," said Tim Flohrer, Head of the Space Debris Office at ESA. "With DRACO, we want to get the telemetry from a satellite recording what is happening from the inside during its own reentry. If all goes well, we're hopeful that we can have similar airborne observation campaigns of these reentries in the future."

Related Links
Space Safety at ESA
Space Technology News - Applications and Research