28/08/2026
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The final two of ESA’s pioneering Cluster spacecraft, Samba and Tango, will end their journeys as they burn up in our atmosphere on 31 August and 1 September respectively. Their targeted reentries mark the end of a mission that has transformed our understanding of Earth’s magnetic environment. The final moments also offer a rare scientific opportunity for reentry observations from a plane.
“When a spacecraft reenters the atmosphere, it experiences extreme forces. Temperatures soar, materials melt and vaporise, and the spacecraft gradually breaks apart. But how exactly?” says Stijn Lemmens, senior space debris mitigation analyst at ESA.
“We need to understand better how they disintegrate to inform the design of spacecraft that can burn up completely, reducing the risk on the ground, while we also aim to prevent pollution of the atmosphere.”
Engineers can simulate aspects of these conditions on the ground, but reproducing the exact environment of a real atmospheric reentry is not possible. That’s why ESA, as part of its space safety activities, is sending a plane to observe the last two Cluster reentries from below for a repetition of the first airborne observation experiment for Cluster’s Salsa in 2024.
Collecting valuable reentry data
The team will be collecting as much reentry data as possible while the satellites are reentering Earth’s atmosphere about 24 hours apart in a remote location over the South Pacific Ocean.
In January, Cluster’s operations team already set the Cluster satellites on their trajectories for ‘targeted reentries’ to ensure a precise location that is both remote, yet just reachable for observations with a small plane coming from Tonga.
The Cluster spacecraft are unusual because they are not reentering due primarily to atmospheric drag like most satellite circling Earth. Instead, as they fly out far on a highly elliptical orbit, their return is driven by long-term gravitational interactions with the Earth, Sun and Moon, making it possible to plan and target their reentries.
Now, the ROSIE airborne observation campaigns, led by Astros Solutions, will take to the skies from Tonga on 31 August and fly over the ocean for hours to get to the reentry location to witness Samba’s demise. Then, they’ll return to Tonga to rest and regroup before doing it once more for Tango the very next day.
“It’s quite the logistical challenge. The plane has to be at exactly the right time and place, facing the right way, safely on the edge of the no-fly zone. Everything has to come together in exactly the right moment. To capture the reentry, the team will be using a set of instruments, 30 in total, improved from the ones we used during Salsa’s reentry,” says Jiří Šilha from Astros Solutions.
“We have done it once before – a large part of the value of the campaign is the repetition for a strong data set – but now it is a double challenge. To do this twice in 24 hours will ask the absolute maximum from all our team members as well as our equipment. The ROSIE-Samba/Tango missions are a joint effort of academic partners from University of Stuttgart (IRS/HEFDiG), Comenius University in Bratislava (CUB) and industrial partners from Hypersonic Technology Göttingen (HTG), Zafiro Systems (Zafiro) and Astros Solutions in close cooperation with the European Space Agency.”
Multiple of the instruments will be capturing spectral data, looking for the tell-tale signatures of materials dissolving that allow to remotely register what materials are melting and when. These sensors are supported by visual and infrared cameras.
Salsa’s lessons learned
“Witnessing the first Cluster-2 satellite Salsa reenter has already produced intriguing results. For instance, we realised there was a mismatch of up to 20% with the expected atmospheric density, highlighting how uncertainties in the upper atmosphere can affect reentry forecasts,” says Stijn Lemmens.
“And for the break-up itself, this seemed to start slightly earlier than models predicted. Was this an anomaly, or an indication that our understanding needs refinement? Observing Samba and Tango under similar conditions will help answer that question.”
“Another surprise came from the spacecraft themselves. During their penultimate perigee passage before reentry, the satellites remained fully intact and healthy even as they descended to an altitude of about 110 km while travelling at more than 10 km/s—making them the lowest-flying active spacecraft ever,” says Bruno Sousa, Cluster Spacecraft Operations Manager at ESA.
“Unfortunately, the higher temperatures experienced by the solar arrays caused a severe power shortage and eventually triggered a reboot. As a result, the recorded data could not be preserved and retrieved, preventing us from reconstructing what the spacecraft experienced at that altitude. Nevertheless, we were able to resume normal control afterwards.”
“Because Samba and Tango are now in a slightly better power state than the first two spacecraft that reentered, they offer a strong opportunity to collect even more complementary data—provided they avoid rebooting this time.”
Supporting a sustainable future in space
The work to collect the unique reentry dataset for the scientific and engineering community directly supports ESA’s Zero Debris approach, which aims to ensure the sustainable use of space for future generations. As more satellites are launched and more missions reach the end of their lives, understanding exactly how spacecraft behave during reentry becomes increasingly important.
That’s why after Samba and Tango’s reentries, there will be Draco’s, ESA’s reentry mission currently being built. Draco will record its own fiery demise from the inside as it is observed by scientists on a plane, eager to continue the journey they started with the Cluster quartet.
Follow along the events in detail on our blog.