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Galileo satellite GSAT0104 retires after 12 years of navigation service

On 12 March 2013, Galileo satellite GSAT0104, alongside its fellow In-Orbit Validation (IOV) satellites, made history by enabling the first position fix by Europe's independent satellite navigation system Galileo. Now, after 12 years of service mostly in the area of Search and Rescue, GSAT0104 makes history again by becoming the first satellite in the Galileo constellation to be decommissioned.

For a large and long-lasting constellation like Galileo, which serves as a critical public infrastructure and aims to deliver uninterrupted services over decades, decommissioning activities are as essential as launches. To run smoothly, the fleet needs continuous replenishment, and therefore disposing of satellites is not only about making space safer, but about making space for new satellites.

In October 2023, a board chaired by the EU Agency for the Space Program (EUSPA) with the European Space Agency (ESA) and the European Commission (EC) concluded for the first time to retire a Galileo satellite. Decommissioning activities for GSAT0104 began in March 2024 and were completed in April 2025.

GSAT0104 is one of the 38 Galileo First Generation satellites designed, developed and tested by ESA, together with manufacturers EADS Astrium (4 In-Orbit Validation satellites) and OHB (34 Full Operational Capability satellites). After this decommissioning, the constellation provides same level performance services with active satellites in all its prime slots, plus three active spare satellites. Additionally, new satellites will continue to join the fleet, with six First Generation satellites ready to launch and 12 Second Generation ones in development.

Protecting space environment

Sustainability in and from space is a core priority for ESA, that promotes a responsible use of space to benefit both society and the environment. Central to this commitment is reducing space debris, a serious global hazard threatening current and future missions, and the essential services they provide.

To address the growing space debris issue, ESA has set an ambitious goal of net zero space pollution for new missions by 2030. This target is backed by sustainable design practices, rigorous debris mitigation policies and end-of-life satellite disposal protocols.

ESA, as system development prime and design authority for Galileo, has aligned Galileo's space segment management with the agency's Space Debris Mitigation Policy and Requirements, showing dedication to sustainable space activities and setting an example as a key European flagship program. Galileo satellite decommissioning operations are coordinated by EUSPA.

When a Galileo satellite reaches end of service, it is to be moved to a higher and safe orbit and passivated by depleting all its sources of energy. Galileo's graveyard orbits are located at least 300 km above the active constellation and are designed to remain stable for a very long time. This is a vast region that does not interfere with Galileo, geostationary satellites or any other constellation for hundreds of years.

Thanks to the propellant reserves in GSAT0104, it was possible to place it 700 km above the Galileo operational constellation on a very stable disposal orbit. Then, the satellite tank was depleted and the satellite passivated by removing all internal energy, such as battery charge. Future decommissioned Galileo satellites will be disposed at slightly different altitudes to maintain a safe distance between them.

Graveyard orbits are the standard disposal strategy for satellites in medium Earth and geostationary orbits, where Earth re-entry is generally not feasible.

Tidying up the constellation

Protecting space environment is only one of the reasons to properly dispose of satellites that no longer serve the constellation or are at risk of failure. "In Galileo we need to keep our orbits clear and safe to support the continuous renewal of the fleet. A healthy constellation is required to ensure optimal performance and reliable service provision for billions of users worldwide," explains Riccardo Di Corato, Head of the Galileo Constellation Analysis Unit.

All satellites have a design lifetime after which their systems are expected to be less reliable or effective (12 years in the case of Galileo First Generation and 15 years for Second Generation satellites). Galileo partners assess the condition and contribution of older Galileo satellites annually and determine either to extend service by one year or to decommission.

"It is crucial to ensure that the removal of a satellite from the constellation can take place while key components like attitude control, thrusters and telecommunication systems are still available. If we are confident that the disposal of the satellite can be performed successfully later in the future, we extend its use for as long as possible," adds Di Corato.

A last service by historic GSAT0104

GSAT0104 was launched from Europe's Spaceport in French Guiana on 12 October 2012. It was the fourth and last Galileo In-Orbit Validation satellite, enabling the first determination of a ground location using only Galileo satellites.

This satellite provided navigation services for years before shifting to serve Search and Rescue after a malfunction in the L-band antenna. In 2021, it was relocated from a prime to a spare slot to make room for one of the new satellites launched in April 2024. It continued providing service from this position until decommissioning activities started.

GSAT0104 is again involved in a Galileo "first." Its decommissioning has served as a model of responsibility in space activities for constellations to follow. Moreover, it has provided program partners essential experience that will prove crucial as decommissioning efforts become more frequent in the years to come.

The 2024 satellite end-of-life review board for the remaining three Galileo IOV satellites resolved to extend their lifetime by at least one year, until October 2025. Two Galileo IOV satellites have already exceeded their design lifetime by one year and the third has just reached it. All of them are still providing excellent navigation performance.

The service performance of Galileo satellites is independently monitored by the Galileo Reference Center (GRC) and can be consulted at GNSS Service Center (GSC).