The main mission of these first Galileo satellites is intended to secure the Galileo frequency filings, validate new technologies for operational use, characterise the radiation environment of medium earth orbit that the operational satellites will occupy and enable experimentation with live Galileo signals.

To ensure the success of this phase, two satellites have been ordered from industry, currently known as GSTB-V2/A and GSTB-V2/B, and they are being built in parallel. They are the first step towards the 'in-orbit validation' phase, which will require a constellation of four satellites.

Satellite assembly and test

GSTB-V2/A is being developed by Surrey Satellite Technology Ltd (UK). Galileo Industries (GaIn) is developing the GSTB-V2/B satellite. GaIn is a European consortium including Alcatel Space Industries (F), Alenia Spazio (I), Astrium GmbH (D), Astrium Ltd (UK) and Galileo Sistemas y Servicios (E).

Much of the testing of the units and subsystems that will make up the two spacecraft has been completed. Both satellites are now being assembled and prepared for their environmental tests, which ensure that the satellite is able to withstand the stress of launch and that it will operate correctly in space.

GSTB-V2/A will be transported to the European Space Research and Technology Centre (ESTEC) to undergo testing early in the summer. GSTB-V2/B, currently being assembled at Astrium in the UK, will begin its test campaign at Alenia in Rome before moving to ESTEC for final testing in the autumn.

ESA payload procurement
In GSTB-V2, the European Space Agency (ESA) has direct responsibility for the procurement of all of the GTSBV2/B payload units and some of the GSTB-V2/A payload units. The other part of the GSTB-V2/A payload is a parallel signal generation chain developed by SSTL, the satellite prime contractor.

• The units procured by ESA include:
• rubidium frequency standards (both satellites)
• a passive hydrogen maser (GSTB-V2/B)
• clock monitoring and control units (both satellites)
• navigation signal generation units (both satellites)
• frequency generation and upconversion units (both satellites)
• solid state power amplifiers (GSTB-V2/B)
• output filters and diplexer (GSTB-V2/B)
• navigation antennas (both satellites)

The flight versions of all units have been successfully delivered to the satellite prime contractors and production of the spare units is in progress.

Ground facilities

In parallel with the construction of the two spacecraft, the ground facilities required for controlling the satellites and performing the validation experiments are being developed and tested. The primary ground systems for GSTB-V2/A are located at the Chilbolton Observatory and Rutherford-Appleton Laboratory in the UK. The control centre for GSTB-V2/B is at Fucino in Italy.

Launch

Preparations for the launch of both satellites have been initiated. Soyuz vehicles will launch both spacecraft from the Baikonur cosmodrome in Kazakhstan. An inspection of the launch facilities was completed in April. The launch of the first Galileo test satellite is currently scheduled for December this year.

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