Salsa Probe’s 24-Year Space Journey Ends with Earth Crash

The European Space Agency (ESA) is preparing to say goodbye to one of its longest-running and most successful missions: Cluster. Cluster is a constellation of four identical satellites that have been investigating the interaction between the Sun and Earth’s magnetosphere, our shield against the solar wind, for almost 24 years. The first of the four satellites, named Salsa, will make a controlled reentry into Earth’s atmosphere over the South Pacific Ocean in September 2024, ending its remarkable space journey.

Cluster’s scientific legacy

Launched in 2000, Cluster was designed to last for only two years, but it has exceeded all expectations and become one of ESA’s most productive missions. Cluster has made over 3,200 scientific publications and counting, revealing new insights into the Sun-Earth connection and the processes that take place within Earth’s magnetosphere. Cluster has also improved our understanding of space weather, the variations in the solar wind that can affect satellites, communications, navigation and power grids on Earth.

Some of Cluster’s key discoveries include:

  • Detecting the elusive ‘foxes’ and ‘whale spouts’, structures in Earth’s magnetic field that allow solar wind particles to enter our magnetosphere and create auroras.
  • Observing how magnetic reconnection, a process that releases energy and accelerates particles, occurs in different regions of the magnetosphere and at different scales.
  • Measuring the turbulence and waves in the plasma that fills the space around Earth, and how they affect the transport and heating of particles.
  • Studying how Earth’s bow shock, the boundary where the solar wind meets our magnetosphere, reflects and accelerates some of the incoming particles back to the Sun.
  • Investigating how Earth’s magnetosphere interacts with the Moon, which has no global magnetic field of its own.

Salsa’s last dance

Cluster consists of four satellites: Rumba, Salsa, Samba and Tango. They orbit Earth in a tetrahedral formation, allowing them to make simultaneous measurements from multiple points in space. This gives scientists a three-dimensional view of the phenomena they study.

The orbits of the Cluster satellites are highly eccentric, ranging from about 19,000 km to 119,000 km above Earth’s surface. They are also strongly influenced by the gravitational pull of the Sun and the Moon, which causes them to change over time. Sometimes, their orbits drop by more than 30 km in a single revolution. Other times, they remain stable.

Salsa will be the first of the Cluster satellites to reenter Earth’s atmosphere, followed by Rumba in December 2024, Samba in March 2025 and Tango in June 2025. To ensure a safe reentry, ESA has performed a series of manoeuvres to lower Salsa’s orbit and target a specific region over the South Pacific Ocean, where there is minimal risk of harming people or property on the ground.

The reentry of Salsa will mark the end of an era for ESA and the scientific community, but also an opportunity to learn more about how spacecraft behave when they plunge back to Earth. ESA will monitor Salsa’s reentry using ground-based radars and optical telescopes, and compare its trajectory with predictions from computer models. This will help improve the accuracy of reentry forecasts and inform future mission design and operations.


Salsa is one of four satellites that have made history with their exploration of Earth’s magnetic environment. For 24 years, they have provided us with unprecedented data and discoveries about the Sun-Earth connection and space weather. As Salsa prepares for its final descent into Earth’s atmosphere, we celebrate its achievements and look forward to continuing its legacy with other missions that will further advance our knowledge of our planet and its place in space.

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