# GSAT0104

> decommissioned European navigation validation satellite in the Galileo constellation

**Wikidata**: [Q14083942](https://www.wikidata.org/wiki/Q14083942)  
**Source**: https://4ort.xyz/entity/gsat0104

## FAQs
### Q: Why was GSAT0104 decommissioned?
GSAT0104 was decommissioned on April 16, 2025, following a long period of degraded service. The satellite had experienced a sudden failure in its electric power system on May 27, 2014, which likely limited its operational lifespan and utility for the Galileo constellation.

### Q: What was the "Galileo In-Orbit Validation" phase?
The Galileo In-Orbit Validation (IOV) phase was an early stage of the Galileo program designed to test the system's functionality in space. GSAT0104 (Galileo-IOV FM4) was one of four IOV satellites launched to validate the navigation payload and ground systems before the full operational constellation was deployed.

### Q: What caused the 2014 failure on GSAT0104?
On May 27, 2014, GSAT0104 suffered a failure attributed to its electric power system. The specific cause of the sudden power loss remained a mystery for some time, leaving the satellite in safe mode and affecting its ability to perform its primary navigation role fully.

## Why It Matters
GSAT0104 represents a critical chapter in the development of the European Union's independent satellite navigation capability, Galileo. As the fourth satellite in the In-Orbit Validation (IOV) phase, its primary role was to prove the technical viability of the Galileo system alongside its three counterparts. Its successful launch and initial operation helped validate the European-designed hardware and orbital parameters.

However, its operational history also provided vital, if difficult, lessons for the program. The sudden power system failure in 2014 offered engineers crucial data on satellite reliability and anomaly resolution in the harsh environment of medium Earth orbit. Despite this setback, the satellite was not immediately discarded; it continued to orbit for over a decade before being formally decommissioned in 2025. This extended "tail" of service—even if limited—underscores the resilience of space hardware and the careful management of orbital assets by the European Union Agency for the Space Programme.

## Notable For
*   **IOV Phase Member:** One of the four initial Galileo In-Orbit Validation satellites used to test the system.
*   **Longevity After Failure:** Remained in orbit for over 10 years after a critical power system failure in 2014, surviving until decommissioning in 2025.
*   **Launch Configuration:** Launched on a Soyuz-2.1b with a Fregat-MT upper stage, a key configuration for early Galileo deployments.
*   **Naming:** Carried the alias "Sif," named after the Norse goddess (consistent with the Galileo naming convention for IOV satellites).

## Body

### Development and Specifications
GSAT0104, designated as Galileo In-Orbit Validation Flight Model 4 (Galileo-IOV FM4), was a navigation satellite manufactured by a consortium led by Astrium, with Thales Alenia Space responsible for assembly, integration, and testing. The satellite had a launch mass of 640 kilograms and was powered by two spacecraft solar arrays.

**Technical Specifications:**
*   **Mass:** 640 kg (Launch Weight)
*   **Power Source:** 2 Solar Arrays
*   **Space Tug:** Fregat-MT (used during launch deployment)
*   **Manufacturer:** Astrium (Prime), Thales Alenia Space

### Mission History
The satellite was launched on October 12, 2012, at 18:15:00 UTC from the Ensemble de Lancement Soyouz (Soyuz Launch Complex). It was placed into a Medium Earth Orbit (MEO) specifically designed for the Galileo constellation.

**Orbital Parameters:**
*   **Regime:** Medium Earth Orbit
*   **Semi-major Axis:** 29,599.8 km
*   **Inclination:** 56 degrees
*   **Eccentricity:** 0.0

### Operational Challenges
On May 27, 2014, the satellite experienced a significant anomaly involving its electric power system. This failure caused a sudden power loss, forcing the satellite into safe mode. Despite the severity of the 2014 failure, the satellite was not immediately deorbited. It remained in its orbital slot until it was officially decommissioned on April 16, 2025.

### Identifiers
*   **SCN:** 38858
*   **COSPAR ID:** 2012-055B
*   **NSSDCA ID:** 2012-055B
*   **Aliases:** Sif, Galileo-IOV FM4, Galileo-FM4, GalileoSat-4

## References

1. [Source](https://www.gsc-europa.eu/system-status/orbital-and-technical-parameters)
2. [Source](https://www.esa.int/Applications/Satellite_navigation/Galileo/Galileo_partners)
3. [Source](https://www.esa.int/Newsroom/Press_Releases/Deployment_of_Europe_s_Galileo_constellation_continues)
4. Jonathan's Space Report
5. [Source](https://space.skyrocket.de/doc_sdat/galileo-iov.htm)
6. [Source](https://www.gsc-europa.eu/news/goodbye-galileo-gsat0104)
7. [Source](https://www.esa.int/Applications/Satellite_navigation/Thank_you_for_your_service_Galileo_GSAT0104)
8. [Source](https://spacenews.com/41130sudden-power-loss-leaves-a-galileo-satellite-in-safe-mode/)
9. [Source](https://insidegnss.com/galileo-iov-satellite-failure-mystery-still-unsolved/)