‘Last Dance of Salsa’: European Satellite Set for Controlled Re-entry in a Groundbreaking Experiment

On September 8, 2024, the European Space Agency (ESA) will conduct a groundbreaking experiment as the satellite named Salsa re-enters Earth’s atmosphere and burns up. What sets this event apart is the meticulous planning behind it. Operators have carefully guided Salsa down from a staggering altitude of 81,250 miles (130,000 km) to ensure it safely burns up over a pre-selected region of the South Pacific — "if all goes to plan."

A New Era of Satellite Re-Entry

This event marks the second instance of a satellite being deliberately guided to a "planned and maneuvered 'guided re-entry,'" following the reentry of ESA's Aeolus weather satellite last year. Such controlled reentries represent a significant step forward in space safety, offering a method for satellite operators to prevent debris from either floating in orbit indefinitely or falling to Earth unpredictably, potentially endangering populated areas.

Cluster Mission: A Legacy of Science

Salsa is part of a quartet of satellites known as Cluster, all named after dances: Salsa, Rumba, Tango, and Samba. These four identical satellites have been orbiting Earth since 2000, monitoring its magnetic field. Initially, the mission was expected to last just two years, but the satellites have exceeded expectations, providing valuable scientific data for nearly a quarter of a century. However, Cluster's mission is now drawing to a close.

Responsible Satellite Decommissioning

Had ESA decommissioned Cluster as initially planned in 2002, the four satellites might have been left to drift aimlessly. However, with the increasing concern over space debris, ESA has opted for a more responsible approach. "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, in a statement.

Reducing Risks with Controlled Re-Entries

More than just preventing old satellites from polluting low Earth orbit, this controlled re-entry method allows operators to precisely control where defunct spacecraft fall to Earth.

Although the likelihood of falling satellites causing damage or injury is incredibly low — "you're three times more likely to be struck by a meteorite than by a piece of satellite debris," according to ESA — the agency is committed to minimizing even that small risk, hence the adoption of these controlled reentries.

Salsa’s Unique Orbital Challenge

Aeolus was the first satellite to undergo ESA's new controlled reentry procedure. Over several weeks, operators gradually maneuvered Aeolus from an orbit of 200 miles (320 km) down to 75 miles (120 km), low enough for Earth's atmosphere to drag it down to a fiery end over the Atlantic Ocean.

Salsa’s re-entry presents a more complex challenge. The satellite has an eccentric orbit, ranging from just 60 miles (100 km) to over 81,000 miles (130,000 km) above Earth. In January, Salsa executed a maneuver that will bring its closest approach down to just 50 miles (80 km) this month, guiding it to its end over a remote area of the South Pacific.

Future of Cluster Satellites

Following Salsa’s re-entry, its three counterparts — Rumba, Tango, and Samba — are scheduled to follow suit. Rumba is set to re-enter in 2025, followed by Tango and Samba in 2026. ESA plans to observe each re-entry carefully, hoping to gain insights from how identical spacecraft burn up at different angles.

These controlled reentries are part of ESA’s broader strategy to develop safer and more sustainable practices for managing aging satellites, ensuring that future spacecraft pose minimal risk to Earth and its inhabitants.