Galileosatellite

The European Space Agency’s (ESA) second pair of Galileo navigation satellites, Galileo Flight Model 3 (FM3) and Galileo Flight Model 4 (FM4), are ready for launch aboard a Soyuz ST-B vehicle from the European spaceport in French Guiana on 12 October.

Following launch, both the ‘in-orbit validation’ (IOV) satellites will join the first two Galileo satellites that were sent into space in 2011.

The latest launch will be a significant milestone for ESA’s Galileo programme as four satellites are required to fix navigational errors in order to enable full system testing.

ESA said that two satellites’ tanks have been filled up with hydrazine fuel to maintain their behaviour and orbital position during the 12-year stay in space.

The Fregat fourth stage of the Soyuz ST-B rocket will place the satellites into the orbit, preventing them from carrying extra fuel to position themselves into planned orbits.

"The latest launch will be a significant milestone for ESA’s Galileo programme."

In addition, the twin satellites are temporarily equipped with aluminium plates on each side to protect their solar panels and are attached to a dispenser that will hold them safely during launch until pyrotechnic mechanisms release them sideways in opposite directions at an altitude of 14,429 miles above the Earth.

The satellites, dispenser and Fregat upper stage will undergo testing ahead of the fitting of protective launch fairing on 4 October.

In order to achieve full operational capability (FOC), the validation phase will be followed by deployment of further satellites and ground segment components.

The first four Galileo satellites were developed by a consortium led by Germany-based EADS Astrium, with the company producing the platforms and Astrium UK responsible for payloads. They were assembled and verified in Rome by Thales Alenia Space.

Galileo is a programme initiative of the European Commission and the European Space Agency (ESA), and each Galileo spacecraft features an atomic clock for navigation and a powerful transmitter to allow precise broadcast of navigation data globally.

Image: An artistic impression of the four Galileo ‘in-orbit validation’ satellites. Photo: courtesy of ESA – P Carril.