Galileo Satellite Recovered, Transmitting Navigation Signals

Galileo satellite’s revised orbit. Photo: Galileo

Report by the European Space Agency

Europe’s fifth Galileo satellite, one of two delivered into a wrong orbit by VS09 Soyuz-Fregat launcher in August, transmitted its first navigation signal in space on Saturday, November 29. It has reached its new target orbit and its navigation payload has been successfully switched on.

A detailed test campaign is under way now the satellite has reached a more suitable orbit for navigation purposes.

Recovery

The fifth and sixth Galileo satellites, launched together on August 22, ended up in an elongated orbit traveling up to 25,900 km above Earth and back down to 13,713 km.

A total of 11 maneuvers were performed across 17 days, gradually nudging the fifth satellite upwards at the lowest point of its orbit. As a result, it has risen more than 3,500 km and its elliptical orbit has become more circular.

“The maneuvers were all normal, with excellent performance both in terms of thrust and direction,” explained Daniel Navarro-Reyes, ESA Galileo mission analyst. “The final orbit is as we targeted and is a tribute to the great professionalism of all the teams involved.”

The Launch and Early Operations Phase (LEOP) for Galileo satellites is overseen by a joint operations team from ESA and the French space agency CNES, alternately working from ESOC in Darmstadt, Germany, and the CNES LEOP Control Centre in Toulouse, France. Photo: ESA

The commands were issued from the Galileo Control Centre by spaceopal, the Galileo operator, at Oberpfaffenhofen in Germany, guided by calculations from a combined flight dynamics team of ESA’s Space Operations Centre, ESOC, in Darmstadt, Germany and France’s CNES space agency. The commands were uploaded to the satellite via an extended network of ground stations, made up of Galileo stations and additional sites coordinated by France’s CNES space agency. Satellite manufacturer OHB also provided expertise throughout the recovery, helping to adapt the flight procedures.

Until the maneuvers started, the combined ESA–CNES team maintained the satellites pointing at the Sun using their gyroscopes and solar sensors. This kept the satellites steady in space but their navigation payloads could not be used reliably.

In the new orbit, the satellite’s radiation exposure has also been greatly reduced, ensuring reliable performance for the long term.

A Galileo Full Operational Capability (FOC) satellite, following on from the first four Galileo satellites already in orbit. A total of 22 FOC satellites are on the way, built by OHB in Germany with navigation payloads from Surrey Satellite Technology Ltd. in the UK. Photo: ESA

A suitable orbit

The revised, more circular orbit means the fifth satellite’s Earth sensor can be used continuously, keeping its main antenna oriented towards Earth and allowing its navigation payload to be switched on.

Significantly, the orbit means that it will now overfly the same location on the ground every 20 days. This compares to a normal Galileo repeat pattern of every 10 days, effectively synchronizing its ground track with the rest of the Galileo constellation.

The navigation test campaign

The satellite’s navigation payload was activated on November 29, to begin the full In-Orbit Test campaign. This is being performed from ESA’s Redu centre in Belgium, where a 20-meter-diameter antenna can study the strength and shape of the navigation signals at high resolution.

“First, the various payload elements, especially the Passive Hydrogen Maser atomic clock, were warmed up, then the payload’s first ‘signal in space’ was transmitted,” said David Sanchez-Cabezudo, managing the test campaign.

“The satellite-broadcast L-band navigation signal is monitored using the large antenna at Redu, with experts from OHB and Surrey Satellite Technology Ltd — the payload manufacturer, based in Guildford, UK — also on hand to analyze how it performs over time.”

The first Galileo FOC navigation signal-in-space transmitting in the three Galileo frequency bands (E5/E6/L1) was tracked  by Galileo Test User Receivers deployed at various locations in Europe, namely at Redu (B), ESTEC (NL), Weilheim (D) and Rome (I). The quality of the signal is good and in line with expectations.

The Search And Rescue (SAR) payload will be switched on in few days in order to complement the in-orbit test campaign.