On September 8, 2024, a satellite named Salsa will re-enter the atmosphere and burn up. What makes this re-entry different from other satellites is that, if all goes as planned, operators will carefully guide the satellite from an altitude of 81,250 miles (130,000 kilometers) to burn up safely in a carefully selected area in the South Pacific Ocean.
SALSA will be the second satellite to perform a planned, piloted “guided re-entry,” following last year's re-entry of the European Space Agency's Aeolus weather satellite. Such re-entries could help satellite operators prevent debris from floating in orbit or falling to Earth in an unexpected inhabited area.
Salsa is one of the members of a four-piece group called Cluster, whose three companions are also named after dances: rumba, tango, and samba. Since 2000, four identical satellites have been monitoring the Earth's magnetic field. When Cluster was first launched, its mission was scheduled for just two years. But nearly 25 years later, the satellites are still intact and continue to transmit valuable scientific data. Sadly, Cluster's days are coming to an end.
If ESA had retired the Cluster as scheduled in 2002, the four satellites might have been left adrift. But concerns about rapidly accumulating space debris mean the agency wants to take a more cautious approach to the old spacecraft. “By studying how SALSA burns up, and which parts survive, for how long and in what conditions, we could learn a lot about how to build 'zero-waste' satellites,” Tim Froehler, head of ESA's Space Debris Management Office, said in a statement.
Guiding re-entry not only keeps old satellites from polluting low Earth orbit, it also gives operators more precise control over where defunct spacecraft fall to Earth.
The chances of a falling satellite actually causing damage or injury are extremely low — you're three times more likely to be hit by a meteorite than by a piece of satellite, according to the space agency — but ESA wants to minimize even that risk, which is why it's attempting this new controlled re-entry.
Aeolus was the first test of ESA's new controlled re-entry method. Over the course of several weeks, Aeolus operators carefully lowered the satellite from its old orbit at an altitude of 200 miles (320 km) to an altitude of 75 miles (120 km), low enough that it would be pulled into Earth's atmosphere and burn up. The exercise was carefully planned to have Aeolus burn up over the Atlantic Ocean.
SALSA differs from Aeolus in that its orbit is much more eccentric, varying in altitude from just 60 miles (100 km) to more than 81,000 miles (130,000 km). In January, SALSA performed a maneuver to bring its closest approach this month to just 50 miles (80 km), which will bring SALSA to a halt in a remote location in the South Pacific.
Following Salsa's re-entry, three other spacecraft are scheduled to burn up in similar flames: Rumba will re-enter in 2025, followed by Tango and Samba in 2026. All four deaths are part of a grand experiment in which ESA hopes to observe the same spacecraft burning up at different angles.
