A half-tonne satellite will be watched as it falls to Earth by scientists on a private jet, to understand more about how debris breaks up in our atmosphere.
The satellite is one of four in a constellation called Cluster run by the European Space Agency (ESA) to monitor how Earth’s magnetic field interacts with the sun’s solar wind. Nicknamed Rumba, Salsa, Samba and Tango because of the way they spin like dancers, the satellites were launched in 2000 initially on a two-year mission, but they have carried on working until now. “They remained healthy and fully operational,” says , ESA’s operations manager for Cluster in Germany.
Due to slight fluctuations in their highly elliptical orbits, and the fact they have just 4 kilograms of their initial 600 kilograms of fuel left, the satellites are now on paths that will bring them back into our atmosphere. The first of the four, Salsa, is set to fall into a remote patch of the South Pacific Ocean at midday local time on 8 September.
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The satellite will re-enter at an unusually high speed, up to 11 kilometres per second compared to 7 kilometres per second for lower-orbiting satellites. This, coupled with precise knowledge of its re-entry time, down to seconds, gives scientists a unique opportunity to observe the re-entry.
As Salsa falls to Earth, nine researchers will watch the event from more than 100 kilometres away on a jet flown from Easter Island. “We’re super excited,” says at the University of Stuttgart in Germany, the group’s leader.
Salsa is expected to break apart at an altitude of 75 to 85 kilometres, with the re-entry lasting just a minute. The researchers plan to use 26 cameras with different filters looking out of the windows of the plane to record the re-entry and the satellite’s destruction.
“The main question is, does it disappear during this re-entry?” says Löhle. “Is everything evaporating, or are there pieces that eventually impact on the ground?”
He expects some parts, such as the satellite’s fuel tanks, to survive. “You could learn from the re-entry that if you build a fuel tank differently, it can break up,” he says.
Less than a dozen satellite re-entries have been observed, says Löhle, but Salsa will be one of the fastest. He estimates the total cost of the observation campaign is up to €400,000 (£335,000), about half of which covers the cost of hiring the plane.
at the Secure World Foundation in the US says the event is a useful way to understand more about how debris re-enters the atmosphere. “Space sustainability is a pretty hot topic,” she says, especially with the rise of very large constellations of satellites, such as SpaceX’s Starlink, which comprises thousands of satellites providing internet services.
The next Cluster satellite to re-enter will be Rumba in November 2025, followed by the twin re-entry of Samba and Tango in August 2026, which Löhle also hopes to observe. “We could learn what is the difference if the same object flies under different conditions into Earth’s atmosphere,” he says.
