Cluster’s final mission: A fiery return to Earth

Cluster, a trailblazing mission by the European Space Agency (ESA), is nearing its end with a historic “targeted re-entry” into Earth’s atmosphere.

For over 24 years, the four satellites of Cluster have provided valuable insights into Earth’s magnetic environment and its interactions with solar wind.

As the mission concludes, it marks not only the end of a significant era in space exploration but also the beginning of new standards in sustainable space practices.

Observations of Earth’s magnetic shield

Launched in 2000, the Cluster mission comprised four satellites that tirelessly observed Earth’s magnetosphere, the powerful magnetic shield that protects our planet from solar wind.

In the years since their launch in 2000, these satellites – Rumba, Salsa, Samba, and Tango – have studied how solar wind particles interact with Earth’s magnetic environment, a phenomenon known as space weather.

“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 Philippe Escoubet, Cluster Mission Manager. “It has watched the effects of solar storms to help us better understand and forecast space weather.”

The return of Salsa

Even a mission as important as Cluster must eventually conclude. ESA has taken the initiative to use the mission’s termination to demonstrate responsibility in mitigating space debris, an issue that has gained international attention.

On September 8, 2024, Salsa, the first of the four satellites, will re-enter Earth’s atmosphere over the remote South Pacific Ocean Uninhabited Area. The targeted region is as far from populated regions as possible.

Bruno Sousa, Cluster Operations Manager, emphasized ESA’s commitment to space safety. He noted that back in January, Salsa’s orbit was tweaked to make sure that it experiences its final steep drop on September 8th from an altitude of roughly 110 kilometers to 80 kilometers.

“This gives us the greatest possible control over where the spacecraft will be captured by the atmosphere and begin to burn up,” said Sousa.

Despite the predictability of this re-entry, ESA acknowledges that there is still much to learn about how spacecraft behave in the lower atmosphere. To gather valuable data, ESA is considering observing Salsa’s re-entry from an aircraft, which would offer insights to enhance the safety of future returns.

Cluster’s legacy: Sustainable space practices

Cluster’s targeted re-entry is not just about concluding a mission; it sets a standard for sustainable space practices.

Tim Flohrer, head of ESA’s Space Debris Office, noted: “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.”

The knowledge gained will help ESA develop safer, more predictable re-entry strategies for future missions, such as Smile and Proba-3.

Conclusion of the Cluster mission

Following Salsa’s re-entry, the remaining satellites – Rumba, Samba, and Tango – will enter “caretaker” mode to avoid collisions. They are scheduled for similar controlled re-entries, with the last goodbye set for August 2026.

This farewell, however, is more of a passing of the baton to the next generation of ESA missions, ensuring that the pioneering work of Cluster continues to inform and inspire.

Smile, a collaboration with the Chinese Academy of Sciences, is slated to launch in late 2025 and will continue to explore the complex magnetic environment surrounding Earth, building upon the pioneering work of Cluster.

Cluster’s impact on space weather prediction

The Cluster mission has played a pivotal role in advancing our understanding of space weather, a field critical to protecting both space assets and technological systems on Earth.

By capturing detailed measurements of the magnetosphere’s response to solar wind, Cluster has helped scientists develop better models to predict the impact of solar storms.

These models are crucial for forecasting space weather events that can disrupt satellite communications, affect GPS signals, and even pose risks to astronauts aboard the International Space Station.

In the end, the lessons learned from the Cluster mission will have implications far beyond its current lifecycle, serving as a reminder that responsible stewardship of space is essential as we continue to explore the cosmos.

Image Credit: European Space Agency

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