The European Space Agency Aeolus is conducting its first satellite reentry with the satellite, aiming to lead it to an oceanic reentry. Despite the challenges posed by fluctuating atmospheric conditions due to high solar activity, the ESA team utilizes simulations, advanced maneuvers and continuous adjustments to complete a safe and successful mission.
For the first time in ESA’s main control room in Germany, simulations are taking place as teams prepare not for a launch, but for a satellite’s assisted return through Earth’s atmosphere. Mission successful, fuel depleted, and Aeolus is now making a natural descent.
The flight control team at mission control will soon commandeer the last wind-mapping satellite, aiming to re-enter the ocean to minimize the very small risk of reentry. However, in simulations, things don’t go to plan.
The two missions are not the same, but the launches have many milestones and characteristics in common with each other: A satellite or spacecraft is launched into space on a gravity-defying rocket, and the exact sequences differ after separation, but it needs to wake up, deploy solar arrays, operate and test instruments, and thruster.
Five years ago, Aeolus was doing this. Now, the mission is complete and it’s days away from re-entering Earth’s atmosphere, although it wasn’t designed to, but the teams will try to steer it back into its path.
Aeolus was planned and built before current international regulations came into force, however ESA is doing everything it can to bring Aeolus up-to-date to today’s best standards. ESA’s mission control is attempting such an assisted re-entry for the first time, but simulations are ongoing to make sure there are no surprises.
Simulating an Assisted Reentry: First an ESA
How do you simulate something you’ve never done before? Simulation Officer Philip Metello asked:
“First, we create a realistic simulation of the expected behavior upon return from Aeolus, using the various software we already have available, using tried and tested ‘telecommands’ from past reentry scenarios, controlled and uncontrolled,” explains Philip.
“Then we chose specific scenarios that might and might not happen and played them in the main control room. With a ‘walking’ Aeolus and ground system, it feels like the real thing to our teams.
In general, the actual operations shouldn’t be too different from the simulated events now being rehearsed, but this re-entry comes with greater uncertainty than the launches and maneuvers that usually take place in this historic room.
The current high level of solar activity, for one thing, creates unpredictable fluctuations in the thickness of the atmosphere, speeding up the return of Aeolus. As such, aspects of this campaign are continually adjusted as critical operations near.
Key moments in Aeolus’ return will be a series of never-before-seen maneuvers to guide Aeolus on a return path in the most uninhabited areas possible, namely over the ocean.
If no maneuvers are planned, various ground stations around the world will be able to keep track of Aeolus’ signal, and then ESA’s flight dynamics experts can determine its orbit and generate new commands for the flight control team to send to the satellite.
All five simulations are planned more like rehearsals with minor problems, such as losing contact with Aeolus or parts of the spacecraft reaching unexpected temperatures, rather than the doomsday scenarios thrown at the teams before launch.
What makes this re-entry so special and fresh is that it is taking on a mission with a mission in mind and changing its future from Earth.
“I’ve probably participated in more than 60 simulations in my career, but this one is very different because we work to execute the planned operations as accurately and safely as possible, but with many unknowns outside of our control,” continues Isabelle.
“I want to uplink the final set of commands that Iolus executes and see them behave nominally on a spacecraft. Once that is done, our part will be over and let’s hope for the best. I’m definitely upset to see all this planned and any re-entry fragments end up safely in the ocean.
An unexpected end to an impossible mission
Aeolus mission manager Tomasso Parrinello, normally based at ESA’s Earth observation heartland at ESRIN in Italy, participates in simulations in mission control. Shortly after Aeolus launched, he traveled the two worlds of science and operations to see not only how challenging flying the mission was, but why it was so rewarding:
“Aeolus is a magical machine that amazes even the most seasoned engineers around the world,” Tommaso concludes.
“Every day we face and solve many technical and scientific challenges to ensure we can deliver the best data to the climate science community. But it’s difficult because it’s new: Aeolus was always a demonstrator mission, nothing like it had ever been launched into space.
Just as Aeolus went above and beyond during its mission, revolutionizing wind profiling and forever improving climate models, its demise now proves to be a challenge of great importance.
Marking the end of Aeolus’ remarkable mission, ESA worked with composer Jamie Pereira to create a woodwind piece from data spanning the satellite’s lifetime in orbit around Earth.
“Now you realize that an idea that was proposed a year ago has turned into something real and tangible. We all know this re-entry is not easy and may not be successful. Perhaps, this is the biggest challenge of our professional life, but I could not imagine any other end to this “mission impossible”.
“Hearing the different voice loops and being part of the interconnected operations in the main control room is truly a “wow” moment. Hard to describe. Not only is it real, but it comes fast. We’ve never been more prepared than now! “