mercredi 24 novembre 2021

Galileo prototype GIOVE-A switched off after 16 years in orbit

 







ESA - Galileo GIOVE Mission patch.


Nov. 24, 2021

Europe’s first prototype satellite for Galileo, GIOVE-A, has today been formally decommissioned after 16 years of work in orbit. The 2005-launched mission secured Galileo’s radio frequencies for Europe, demonstrated key hardware and probed the then-unknown radiation environment of medium-Earth orbit.

“If not for GIOVE-A the 26 Galileo satellites in orbit today would not exist,” comments Paul Verhoef, ESA’s Director of Navigation. “Its speedy development and launch opened the way for our working constellation to follow.”

GIOVE-A

ESA had begun designing Galileo at the turn of the century, and radio frequencies had been set aside for the new system by the International Telecommunications Union. But these frequency filings came with a deadline attached: the frequencies had to be used from orbit by mid-2006 or they would lapse.

Galileo In-Orbit validation Element-A, or GIOVE-A was therefore produced at a breakneck pace to meet this deadline. Developed in the second half of 2003, the satellite was designed, built, and tested before the end of 2005 – launched on 28 December of that year.

GIOVE-A launch by Soyuz

“At the time there was a lot of uncertainty: would we make it or not?” recalls Javier Benedicto, Head of the Galileo Project Department in ESA “GIOVE-A transmitted its first Galileo signal-in-space on 12 January 2006, meaning that Europe was formally in the navigation business.”

That March ESA formally confirmed it had brought the Galileo-related frequency filings into use, three months ahead of the official ITU deadline.

The mission also carried a prototype rubidium atomic clock – proving their functionality for the operational Galileo satellites that would follow – as well as a radiation instrument. Medium Earth orbit, circa 23 000 km altitude, was terra incognita at this point for European satellites, but it was known to possess enhanced radiation levels from the impinging of the outer band of Earth’s Van Allen radiation belts.

GIOVE-B

A second Galileo prototype, GIOVE-B, followed its predecessor in 2008, this mission hosting a prototype passive hydrogen maser – the second type of atomic clock that Galileo relies on – along with an enhanced payload able to transmit for the first time the GPS-Galileo common signal. Once the first Galileo satellites were in orbit and working well, ESA ended use of GIOVE-A in 2012. The satellite was placed in a ‘graveyard orbit’ 100 km above the operational satellites’ orbits, as well as GIOVE-B after its own four-year mission.

Side lobe satnav signals available to satellites in higher orbits

Control of GIOVE-A, however, passed to manufacturer Surrey Satellite Technology Ltd (SSTL) in the UK. GIOVE-A was then employed for various in-orbit experiments, including demonstrating the reception of satellite navigation signals from GPS satellites orbiting below it – based on spillover ‘sidelobe’ reception from satellites on the other side of Earth.

This proof that satnav can indeed be relied on further out into space means that satellites in geostationary orbit are making use of satnav for positioning, and, as a next step, ESA is planning to extend satnav coverage all the way to the Moon.

The satellite also continued its radiation survey of medium-Earth orbit, acquiring a unique record extending across more than 10 years, analysed by the Surrey Space Centre with ESA support. Multiple scientific papers have been written on these results, which encompass the “electron desert” of 2008-9 during what was the lowest levels of solar activity during the space era, followed by one of the largest electron storm events on record in April 2010.

Galileo constellation

A new model of the outer Van Allen belt electron fluxes, ‘MOBE-DIC’, has subsequently been produced from this dataset, helping to guide future satellite designs.

“Actually, the satellite itself is still operating well,” explains Sarah Lawrence of SSTL. “The reason for ending the mission is software obsolescence in our control centre. The decommissioning procedure involved transitioning the satellite to Earth pointing mode, turning off the reaction wheels and setting the attitude and orbit control system to standby mode, before finally switching off the on-board computer and transmitter.”

GIOVE-A

Sir Martin Sweeting, SSTL Executive Chairman, adds: “GIOVE-A over-delivered on its original lifetime and mission goals – an inspiring and game-changing mission on so many levels.”

SSTL went on to provide navigation payloads for operational Galileo satellites. Today there are 26 Galileo satellites in orbit and Galileo has become the world’s most precise satnav system, delivering metre-scale accuracy to more than 2.3 billion users around the globe. Two more Galileo satellites are currently being readied for launch.

Galileo: finding our way

About Galileo

Galileo is currently the world’s most precise satellite navigation system, serving more than two billion users around the globe. The Full Operational Capability phase of the Galileo programme is managed and funded by the European Union. The European Commission, ESA and EUSPA (the EU Agency for the Space Programme) have signed an agreement by which ESA acts as design authority and system development prime on behalf of the Commission and EUSPA as the exploitation and operation manager of Galileo/EGNOS. “Galileo” is registered as a trademark in the database of the European Union Intellectual Property Office (n° 002742237).

Related links:

Surrey Satellite Technology Ltd (SSTL): https://www.sstl.co.uk/

Navigation: https://www.esa.int/Applications/Navigation

Images, Video, Text, Credits: ESA/P. Muller/P. Carril.

Best regards, Orbiter.ch

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