This reentry is the first of its kind, known as a "targeted reentry," and demonstrates ESA's leadership in sustainable space exploration by exceeding international standards for mission conclusion.

Launched in 2000, Cluster was designed to study Earth's magnetosphere, a vital magnetic shield that protects the planet from solar wind particles. This natural defense plays a crucial role in maintaining Earth's habitability, shielding life from harmful solar radiation.

The magnetosphere acts as a barrier, deflecting most of the solar wind's charged particles. However, some of these particles manage to penetrate, leading to phenomena such as the auroras. In rarer instances, these solar particles can disrupt power grids, interfere with radio communications, or damage satellites. The term "space weather" refers to these solar influences on Earth's magnetic environment, and before Cluster, space weather remained largely enigmatic.

"For over two decades, Cluster has shown us time and time again how important the magnetosphere is in shielding us from the solar wind," said Cluster Mission Manager Philippe Escoubet. "It has watched the effects of solar storms to help us better understand and forecast space weather."

A Safe and Controlled Conclusion
Cluster's satellites were initially intended for a two-year mission to study the interaction between the Sun and Earth. However, due to the mission's valuable contributions, ESA extended it far beyond its original scope. Despite its extended life, the mission was not originally designed for such a safe conclusion. With this targeted reentry, ESA is not only bringing an end to Cluster's pioneering space weather research but also advancing the agency's goals of space debris mitigation.

Without this controlled reentry, the satellites would eventually reenter the atmosphere in a less predictable manner, possibly over more densely populated areas. By managing the reentry of these satellites, ESA ensures that Cluster's end does not add to the growing problem of space debris orbiting Earth.

Salsa's Final Orbit
The first satellite to reenter will be Cluster 2, nicknamed "Salsa." It is set to make its descent over a remote area of the South Pacific Ocean, far from populated regions.

"Back in January we tweaked Salsa's orbit to make sure that on 8 September it experiences its final steep drop from an altitude of roughly 110 km to 80 km," explained Cluster Operations Manager Bruno Sousa. "This gives us the greatest possible control over where the spacecraft will be captured by the atmosphere and begin to burn up."

The team is closely monitoring the satellite's final movements, with the reentry designed to be so predictable that no additional maneuvers are necessary. While confidence is high that no debris will reach land, data on how satellites behave during reentry is still limited. Observing Salsa's reentry could provide valuable information for future missions.

ESA is considering observing Salsa's reentry from an aircraft to gather more data, with confirmation expected later in August. Since the four Cluster satellites are identical, observing their different reentry conditions could offer a rare opportunity to study satellite break-up processes.

Setting a New Standard
The controlled reentry of Cluster follows similar efforts by ESA with the Aeolus and ERS-2 missions. These initiatives set a precedent for responsible space operations, emphasizing ESA's commitment to reducing space debris and managing reentries more safely.

"By studying how Salsa burns up, which parts might survive, for how long and in what state, we will learn much about how to build 'zero-debris' satellites," said Tim Flohrer, Head of ESA's Space Debris Office. "The lessons learned from this activity will help turn targeted reentries into a safe and well-understood option for the disposal of other space missions in similar orbits, such as Smile and Proba-3."

Future Steps
After Salsa's reentry, the three remaining Cluster satellites will enter a monitoring phase where they will no longer collect scientific data but will be observed to avoid potential collisions with other satellites or Earth. In August 2024, the orbit of Rumba (Cluster 1) will be adjusted in preparation for its reentry in November 2025, followed by Samba (Cluster 3) and Tango (Cluster 4) in 2026.

ESA's next mission focused on Earth's magnetic environment, the Solar wind Magnetosphere Ionosphere Link Explorer (Smile), is scheduled for launch at the end of 2025. This mission, a collaboration with the Chinese Academy of Sciences, will build upon Cluster's legacy, offering new insights into the planet's magnetic surroundings.

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