From: European Space Agency
Posted: Monday, July 19, 2021
The first Galileo Second Generation hardware has begun testing, with test versions of the satellites' navigation payloads undergoing evaluation by Airbus Defence and Space at their Ottobrunn facility in Germany and by Thales Alenia Space at ESA's ESTEC technical centre in the Netherlands.
These testbed versions of these new navigation payloads designed by the two companies are undergoing testing of their respective navigation antennas to check whether they meet the ambitious performance levels set for the coming generation of Europe's satellite navigation system.
Known as the Galileo Payload Testbeds, or GPLTBs for short, these are development models of the navigation payloads intended for the Galileo Second Generation (G2) satellites.
The main difference is that instead of being assembled from space-ready components like an actual satellite payload, the GPLTBs are built up from 'breadboard' electronic parts placed in test racks, with a proof-of-concept version of a navigation antenna attached.
"The goal with these test campaigns are to prove their design concept early, and anticipate any technical issues that might arise as early as possible," explain Cédric Magueur, ESA's Payload Manager for the Thales G2 satellites.
"These campaigns also allow to develop and validate new performance measurements concepts for these new generation of complex navigation payloads," adds Dirk Hannes, ESA's Payload Manager for the Airbus G2 satellites. "This will allow us to optimize the production efficiency of the Flight Model series."
Cédric adds: "Results from the testing will feed into the up-coming Preliminary Design Review for the new satellites, backing up the analyses by the companies with solid measurements. Such early testing also supports the ambitious timescale for the development and construction of G2 satellites, with the first satellites planned to reach orbit by the middle of this decade."
Galileo is Europe's civil global satellite navigation constellation, currently the world's most precise satnav system, offering metre-scale accuracy to more than 2 billion users around the globe. There are 26 Galileo satellites in orbit, scheduled to be joined by other 12 satellites starting to be deployed by the end of this year.
Next will come the first 12 G2 satellites, featuring enhanced navigation signals and fully digital payloads. This new generation will be made up of two independent families of satellites meeting the same performance requirements, produced by Thales Alenia Space in Italy and Airbus Defence and Space in Germany.
Airbus Defence and Space's GPLTB is currently undergoing radiated testing at the company's Ottobrunn facility, inside a Compact Antenna Test Range (CATR). Meanwhile the Thales Alenia Space GPLTB is about to start testing inside ESTEC's own Hybrid European Radio Frequency and Antenna Test Zone (Hertz) chamber.
These are metal-walled chambers kept isolated from external radio interference, whose inner walls are studded with foam pyramids to minimise radio frequency signal reflections, mimicking the void of space.
"Up until now all GPLTB testing has taken place by plugging them into test boards," adds Cédric. "These test campaigns mark the first time that their performances will be confirmed in terms of radiating signals."
Radio-frequency radiation forming of the navigation signals takes place through a combination of digital processing and interaction with the antenna, so practical radio frequency testing is essential to check the true payload performance.
Cédric explains: "In our first phase we will perform near-field measurements directly around the antenna to measure all the characteristics of the signal shape, to check it matches previous conductance tests. Then via computation we can derive its far-field performance.
"In the second test phase the actual far-field measurements will be performed, using another feature of the chambers. Thanks to a pair of specially-shaped paraboloid reflectors, the signal from the testbed can be reshaped as if it has travelled the very long distance that actual Galileo signals need to stretch, all the way from an altitude of 23 222 km down to Earth's surface."
Dirk comments:"On the Airbus side the methodology is substantially the same, except the far-field measurement are currently being performed, to be followed by the near-field measurements."
The Galileo system is operated by the EU Agency for the Space Programme, EUSPA, based in Prague. ESA and EUSPA are partnering on respectively the development and operations of Galileo.
ESA is in charge of the design, development, procurement and qualification of Galileo satellites and their associated ground infrastructure on behalf of the European Union, the system's owner.
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