ESA’s Salsa (Cluster 2) satellite making controlled reentry over Pacific Ocean on September 8

After 24 years of studying Earth’s magnetosphere, the ESA’s Salsa satellite from the Cluster mission is on course to reenter the atmosphere in a controlled descent. The reentry, scheduled for 18:48 UTC, on September 8, 2024, is part of a broader effort by the ESA to mitigate space debris risks by ensuring the satellite disintegrates safely over the South Pacific.

One of the four satellites from the European Space Agency’s (ESA) Cluster mission, Salsa (Cluster 2), is scheduled to re-enter Earth’s atmosphere over the South Pacific Ocean at 18:48 UTC on September 8. This re-entry is significant being ESA’s first-ever “targeted” satellite reentry from an eccentric orbit.

The Cluster mission, which began in 2000, focused on studying Earth’s magnetosphere, the magnetic field that shields the planet from solar winds. Salsa, weighing 550 kg (1 200 pounds), has contributed to this research for 24 years.

The satellite is expected to mostly disintegrate during reentry, with only 10% of its mass potentially surviving. ESA has planned the satellite’s reentry to occur over an uninhabited stretch of the South Pacific, minimizing any risk to human life or property.

Teams at ESA’s European Space Operations Centre (ESOC) in Germany and Easter Island have been preparing for the re-entry. Scientists involved in an airborne observation experiment are on-site, aiming to capture the event from a plane flying at an altitude of 10 km (6.2 miles).

The final stages of preparation included a series of tests on the plane’s instruments, conducted across multiple stops, including Australia, New Zealand, and Tahiti.

Initial uncertainty about the exact time of reentry, due to variations in atmospheric drag during Salsa’s final low perigee passes has reduced. After a tense moment when Salsa failed to respond following its last close pass to Earth, teams were able to restore communication. A deep power loss in its solar arrays caused the satellite to reboot, but it has since returned to normal for its final orbit.

ESA’s Flight Dynamics team used radiometric data and telescope observations to determine the reentry time and location with high precision.

Currently, there is only a two-minute window of uncertainty for Salsa’s reentry. Further monitoring of the satellite is ongoing, with additional data being collected by the Estrack ground station in Kourou, French Guiana.

Salsa’s unique orbital pattern has made its reentry possible. With an elliptical orbit extending as far as 130 000 km (80 778 miles) from Earth, Salsa has gradually descended closer to the atmosphere.

During its final approach, it will enter the atmosphere at around 80 km (49.7 miles) above the planet’s surface, where it will begin disintegrating due to intense friction with atmospheric particles.

ESA says that this is part of its broader effort to reduce space debris. Space debris has become a growing concern for scientists, as the increasing number of defunct satellites poses a risk to active space missions. ESA signed a “zero-debris” charter in 2023, committing to designing future satellites that fully burn up during atmospheric reentry. Data from Salsa’s reentry, along with the future reentries of the remaining Cluster satellites, will aid in this effort.

The remaining three Cluster satellites, part of the mission’s original quartet, are expected to meet a similar fate in the coming years, with reentries planned for 2025 and 2026. The conclusion of the Cluster mission signals the end of a long period of scientific exploration of Earth’s magnetic environment, though analysis of data collected during the mission will likely continue for years.

Space debris experts have noted that while fragments of dead satellites fall to Earth daily, the risk to human life is extremely low. According to ESA, the chance of injury from reentering debris is less than one in 100 billion. Nevertheless, ESA is taking steps to ensure that future missions are conducted in a way that minimizes this already small risk.

Salsa’s reentry also presents a unique research opportunity for scientists to study atmospheric reentry processes. By observing how different materials survive or disintegrate during reentry, ESA scientists hope to improve satellite designs for future missions, ensuring that spacecraft are built to fully burn up during reentry.

References:

¹ All is ready to observe Salsa’s reentry from the air at 18:48 UTC, Sunday 8 September – ESA – September 7, 2024

² Cluster’s Salsa satellite primed to reenter and break up –ESA – August 30, 2024

³ Old satellite to burn up over Pacific in ‘targeted’ re-entry first – AFP – September 7, 2024

Featured image credit: ESA