Moving satellites to meet a plane for rare reentry data

“Moving two satellites to meet a plane sounds extreme, but the unique reentry data we’ll collect is worth orchestrating the challenging encounter over a remote stretch of ocean,” says Beatriz Jilete, space debris systems engineer at ESA.

“The remaining Cluster 3 and 4 satellites, nicknamed Samba and Tango, were already set on a trajectory to burn up safely over a remote corner of the South Pacific Ocean in 2024. They’ll reenter one after the other, about 24 hours apart.

The problem is that we’ll need time in between the reentries to fly back to land, refuel, let the pilot and scientists rest, and then fly out again to the second one. To make sure we can make it, we’re very happy that the mission operations team tweaked their trajectory just enough to have them come down a bit closer to each other and reachable by a small plane from the same airport.”

With the Cluster quartet’s ‘targeted reentries’, ESA is setting a precedent for a responsible approach to reducing the ever-increasing problem of space debris and uncontrolled reentries also from less commonly used orbits. It shows that older missions can be disposed of in safer and more sustainable ways than thought possible at the time of design.

“The four Cluster satellites are identical and so by watching them reenter the atmosphere in a predictable location with slightly different trajectories and in different weather conditions, we get a unique opportunity to conduct a valuable reentry experiment to study the break-up of satellites.” says Beatriz.

“The only drawback for us is that the need to safely dispose of the satellites over remote corners of the ocean makes it so much harder to get there and observe the reentries from below.”

The team was not deterred. The very first of the four Clusters to reenter on 8 September 2024, Cluster 2 or Salsa, was observed by scientists aboard a plane. They flew for hours to reach the edge of the no fly safety zone directly around the location of the reentry.

“The reentry was captured by various onboard instruments, even though the predictions were slightly off. It was a tense time until the sighting could be confirmed definitively,” says Stijn.

“To repeat this observational experiment twice more with the lessons learned from Salsa will add an extra dimension to the data, allowing for comparisons and establishing patterns.”

“An interesting opportunity might also be the Cluster satellites themselves reporting until shortly before their demise. Their power is working better than in the first two Clusters to reenter, so we are hopeful that we might be able to stay in contact longer and collect some more data this time around,” says Bruno Sousa, Cluster operations manager at ESA.

“The first two to reenter went into safe mode when passing through their last perigee before the reentry, because their solar panels overheated. The panels of Samba and Tango have not degraded as much. If they remain active throughout their last perigee pass, maybe we can collect valuable data on the satellites’ temperatures as they dip as deep as 110 km.”