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Galileo satellite recovered and transmitting navigation signals

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Posted December 5, 2014

Europe’s fifth Galileo satellite, one of two delivered into a wrong orbit by VS09 Soyuz-Fregat launcher in August, has transmitted its first navigation signal in space on Saturday 29 November 2014. 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.

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.. Copyright ESA-P. Carril

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.. Copyright ESA-P. Carril

Recovery

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

A total of 11 manoeuvres 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 3500 km and its elliptical orbit has become more circular.

“The manoeuvres 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 commands were issued from the Galileo Control Centre by Space Opal, 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.

ESA’s fifth Galileo satellite, one of two stranded in an incorrect orbit after a launch anomaly, went a series of orbital modification manoeuvres during November 2014, as a prelude to confirming its operational health. Over the month of November A total of 11 manoeuvres were performed across 17 days, gradually nudging the fifth satellite upwards at the lowest point of its orbit. The aim was to raise the lowest point of its orbit – known as its ‘perigee’ – to reduce its radiation exposure from the Van Allen radiation belts surrounding Earth as well as put it into a more compatible orbit for navigation purposes. The heightened orbit allowed the satellite's Earth Sensor used to point its main antenna back towards Earth to remain switched on throughout its orbit. Previously, at the lowest point of the orbit, the terrestrial disc grew too large so the Earth Sensor could no longer function. The satellite’s navigation payload was activated on 29 November, to begin the full ‘In-Orbit Test’ campaign. Copyright ESA

ESA’s fifth Galileo satellite, one of two stranded in an incorrect orbit after a launch anomaly, went a series of orbital modification manoeuvres during November 2014, as a prelude to confirming its operational health. Over the month of November A total of 11 manoeuvres were performed across 17 days, gradually nudging the fifth satellite upwards at the lowest point of its orbit. The aim was to raise the lowest point of its orbit – known as its ‘perigee’ – to reduce its radiation exposure from the Van Allen radiation belts surrounding Earth as well as put it into a more compatible orbit for navigation purposes. The heightened orbit allowed the satellite’s Earth Sensor used to point its main antenna back towards Earth to remain switched on throughout its orbit. Previously, at the lowest point of the orbit, the terrestrial disc grew too large so the Earth Sensor could no longer function. The satellite’s navigation payload was activated on 29 November, to begin the full ‘In-Orbit Test’ campaign. Copyright ESA

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 manoeuvres 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 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 synchronising its ground track with the rest of the Galileo constellation.

The navigation test campaign

The satellite’s navigation payload was activated on 29 November, to begin the full ‘In-Orbit Test’ campaign. This is being performed from ESA’s Redu centre in Belgium, where a 20 m-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.

Galileo IOT L-band antenna at ESA's Redu ground station. Copyright ESA

Galileo IOT L-band antenna at ESA’s Redu ground station. Copyright ESA

“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 analyse 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.

The way forward

The same recovery manoeuvres are planned for the sixth satellite, taking it into the same orbital plane but on the opposite side of Earth.

The decision whether to use the two satellites for Navigation and SAR purposes as part of the Galileo constellation will be taken by the European Commission based on the test results.

About Galileo

Galileo is Europe’s own global satellite navigation system. It will consist of 30 satellites and their ground infrastructure.

The definition phase and the development and In-Orbit Validation phase of the Galileo programme were carried out by the European Space Agency (ESA) and co-funded by ESA and the European Union. This phase has created a mini-constellation of four satellites and a reduced ground segment dedicated to validating the overall concept.

The four satellites launched during the IOV phase form the core of the constellation that is being extended to reach Full Operational Capability (FOC).

Source: ESA

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