According to the European Space Agency (ESA), the fifth and sixth Galileo European positioning satellites were not successfully placed on their prescribed orbits after a faulty launch two years ago in August 2014. Afterwards, their orbits were modified multiple times to reach orbits that would allow for test operation. Now, preparations have been made to start sending test signals, and the European Union (EU) will determine if these two satellites will be involved in the operation of the Galileo system’s services.

Faulty launch

Galileo FOC（Copyright：ESA-P. Carril）

These satellites were launched on August 22, 2014 on a Soyuz rocket at the Guiana Space Centre in French Guiana as the first Full Operational Capability (FOC) satellites with sufficient capabilities required for positioning system operation.

The planned orbits were circular orbits with an altitude of 23,222 kilometers and inclination of 56 degrees. However, the satellites were not placed on their planned orbits due to a malfunction in the rocket’s upper stage. Reentry was avoided, and the satellites were put on elliptical orbits (the red line in the below photograph) with an apogee altitude of 25,900 kilometers and perigee altitude of 13,713 kilometers.

Setting new orbits and making steady altitude adjustments

The satellites physically lacked sufficient propellant (for orbital transfer) to reach their originally envisaged orbits (green line; the long, elliptical green orbit is a separate plane). New orbits were considered and the orbital altitudes were steadily raised to put the satellites on orbits (blue line) that will allow for test operation.

The ESA says all onboard equipment functions are sound and hopes the test signals will assist in receiver verification and development. The atomic clocks on these satellites will be used for accurate experiments to verify Einstein’s general theory of relativity, which says the progress of time changes according to gravity.
* Header and text images provided by: European Space Agency (ESA)