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Salvaged Galileo Performs Its First Navigation Fix

December 17, 2014  - By
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Scatter plot of the Galileo fix performed in ESA's Navigation Laboratory at its ESTEC technical centre on 9 December 2014. The plot was calculated by the Lab's Septentrio Test User Receiver, with dispersion of less than 2 m.

Scatter plot of the Galileo fix performed in ESA’s Navigation Laboratory at its ESTEC technical centre on 9 December 2014. The plot was calculated by the Lab’s Septentrio Test User Receiver, with dispersion of less than 2 m.

News from the European Space Agency

Galileo’s fifth satellite — recently salvaged from the wrong orbit to begin navigation testing — has been combined with three predecessors to provide its first position fix.

Test receivers at ESA’s technical centre in Noordwijk, the Netherlands, and at the Galileo In-Orbit Test station at Redu in Belgium received the signals at 12:48 GMT on December 9 from the quartet of satellites and fixed their horizontal positions to better than 2 meters.

This achievement is particularly significant because the fifth satellite is the first of a new design of 22 Galileo satellites set to be launched over the next few years.

Further position fixes were then made by France’s CNES space agency in Toulouse, France, as noted by Bernard Bonhoure: “The results are as good as those for the first Galileo fixes in 2013 with the initial four satellites.”

The following day, fixes were performed using Galileo’s Public Regulated Service, the encrypted highest-precision class of signal.

“The very good geometry of the satellites in the sky relative to the receivers helped us to achieve this result, plus the signal strength of the fifth satellite,” explained Gustavo Lopez Risueno, coordinating the receiver team at the Navigation Laboratory in ESA’s ESTEC technical centre.

“This is a significant milestone for the Galileo program because it marks the very first time that a Full Operational Capability satellite has performed a fix together with its In-Orbit Validation predecessors — which were the first four satellites launched into orbit, in 2011 and 2012. This establishes they work together well.

“While it is not yet possible to make routine use of the fifth Galileo, this shows such an outcome is within our reach.

Galileo satellite geometry and received signal strength for the December 9 fix using the first Galileo FOC satellite. The first Galileo FOC satellite corresponds to E19 on the left display; IOV PFM to E11, FM2 to E12 and FM3 to E19.

Galileo satellite geometry and received signal strength for the December 9 fix using the first Galileo FOC satellite. The first Galileo FOC satellite corresponds to E19 on the left display; IOV PFM to E11, FM2 to E12 and FM3 to E19.

“In particular, it opens the door to its immediate use in combination with additional navigation message information provided through ground networks, which is a standard mode of operation for mass market receivers, such as those found in our smartphones.”

The fifth and sixth satellites were delivered into the wrong orbit by their Soyuz–Fregat rocket in August. Their elongated orbit took them out to 25,900 km above Earth and back down to 13,713 km, rather than the planned circular path at 23,222 km. The angle of the orbit to the equator was also wrong.

The satellites’ shifting altitude left them unable to lock onto Earth for part of each orbit, preventing them from being used for navigation purposes.

But, last month, a series of 11 maneuvers took the fifth satellite into a more circular orbit, some 3500 km higher, allowing its navigation payload to be switched on for testing. A similar salvage operation is planned soon for its companion.

The main hurdle in using the fifth (and subsequently sixth) satellite operationally is that mass market receivers in particular might take longer to find it. Their orbits fall outside the almanacs satellite-locating standard broadcast within navigation messages.

Utilizing navigation-assistance information would be a way of shortening acquisition times — and ESTEC’s Navigation Laboratory has already demonstrated it with mass market receivers.

Working in conjunction with the European Commission and Europe’s Global Navigation Satellite Systems Agency, the Lab performed position fixes with both Galileo and GPS satellites using only navigation-assistance information.

Test position fix in the grounds of ESTEC, performed with a mass-market receiver using navigation-assistance information, based on signals from the fifth Galileo satellite plus GPS satellites. This satellite's elliptical orbit means extra data are needed to speedily utilize its signals, which could be provided through ground networks. Navigation-assistance information is already employed by the mass market receivers found within smartphones.

Test position fix in the grounds of ESTEC, performed with a mass-market receiver using navigation-assistance information, based on signals from the fifth Galileo satellite plus GPS satellites. This satellite’s elliptical orbit means extra data are needed to speedily utilize its signals, which could be provided through ground networks. Navigation-assistance information is already employed by the mass market receivers found within smartphones. Source: European Space Agency


EDITOR’S NOTE: Researchers at the German Aerospace Center (DLR) report on their success in producing a pseudorange-based all-Galileo position fix using precisely determined satellite orbits and clocks from Technische Universität München (TUM) in the January issue of GPS World. Richard Langley reports that his team at the University of New Brunswick has managed to produce a Galileo-only carrier-phase-based precise-point-positioning solution with better than decimeter accuracy using TUM’s orbits and clocks.

Also, GMV performed a first Galileo-only PPP with IOV + FOC-1 satellite with data from December 6, obtaining centimetric accuracy. Read about their results on their blog.

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