Second experimental spacecraft to act as back-up for Galileo system components

The UK's Surrey Satellite Technology (SSTL) is to build a second experimental spacecraft for Europe's delayed Galileo satellite navigation system, to ensure there is always a spacecraft in orbit to maintain European rights to the frequencies. The contract is worth €25-30 million ($33-40 million), says the European Space Agency.

Based on SSTL's successful GIOVE-A experimental satellite, launched at the end of 2005 to secure the Galileo frequencies, the new GIOVE-A2 spacecraft will act as a back-up in case of further delays or launch failures involving GIOVE-B and four in-orbit validation (IOV) satellites that will precede the 26 operational Galileo spacecraft.

Delayed by a failure during ground tests, GIOVE-B is now planned for launch at the end of this year, while manufacturing delays have already pushed the launch of the first IOV satellite to the end of 2008. These spacecraft are being built by European Satellite Navigation Industries (formerly Galileo Industries), the consortium that will produce the operational satellites once a contract is awarded (Flight International, 6-12 March).

GIOVE-A began transmitting Galileo navigation signals in January last year, allowing Europe to meet the International Telecommunication Union (ITU) deadline for securing the frequencies. The satellite was designed to operate for 27 months and, in case of a failure of GIOVE-A or GIOVE-B, the A2 satellite will be available for launch by the middle of next year to maintain the frequency rights for another 27 months. If required, GIOVE-A2 will be launched by Soyuz from either Baikonur or Kourou, depending on timing, says ESA, adding: "It could even not be launched."

The agency says: "The reason for GIOVE-A2 is not to replace GIOVE-B. It is a risk-mitigation activity to overcome satellite or launcher failures, which can always occur, with a view to securing the Galileo frequency filing. If GIOVE-A stops working now and we lose GIOVE-B on lift-off, we have a potential gap of two years, and ITU regulation gives us only two years to demonstrate that we use the frequencies."

The A2 satellite will generate additional signals and allow early in-orbit experimentation with the baseline L1 open-service signals, says ESA. These signals will provide free positioning and timing services once Galileo is operational. The A2 will use the same rubidium atomic frequency clock carried by GIOVE-A, ESA says, while GIOVE-B is to test the passive hydrogen maser clock planned for the operational satellites.

Source: Flight International