15 January 2007 – One year ago, GIOVE-A began transmitting Galileo navigation signals. This satellite is the first flight element in ESA’s in-orbit validation programme for Galileo. Carried into space from the Baikonur Cosmodrome in Kazakhstan by a Soyuz launch vehicle on 28 December 2005, GIOVE-A then successfully completed the initial tasks in its mission – orbit injection, deployment of its solar arrays and the commissioning and check-out of its various payload systems – before commencing the transmission of navigation signals.
This signal transmission has secured the use of the frequencies allocated to the Galileo system by the International Telecommunication Unit ( ITU ), achieving the primary mission for which the satellite was constructed.
The receivers that have been developed for Galileo were able to receive the first signals at ESA sites at Redu ( Belgium ) and Noordwijk ( Netherlands ), at the Chilbolton Observatory ( UK ) and at the Guildford ( UK ) mission control centre of Surrey Satellite Technology Ltd, the prime contractor for GIOVE-A. The navigation signal has been broadcast continuously to fulfil the other important objectives of the GIOVE mission:
– Verification of the critical technologies for the Galileo satellites, including the on-board Rubidium Atomic Frequency Standard ( RAFS ) clocks, the navigation signal generator and the chain of equipment that comprises the navigation payload
– Characterisation of the novel features of the Galileo signal design, including the verification of user receivers and their resistance to interference and multi-path reception in realistic static and dynamic conditions, aiming to better estimate the effect on navigation services and future applications
– Characterisation of the radiation environment of the Medium Earth Orbit ( 23 260 km altitude ) planned for the Galileo constellation, to better understand this particular environment – particularly the radiation doses and electro-magnetic fields that could affect the design of the operational system
To complete the in-orbit validation mission, ESA has deployed the GIOVE Mission Segment, composed of a network of 13 monitoring stations located around the world and a GIOVE Processing Centre located at ESA’s European Space Research and Technology Centre ( ESTEC ), in Noordwijk, the Netherlands. The processing centre is currently receiving measurements for GIOVE-A, and will also receive data for the GIOVE-B satellite which will be launched by the end of 2007.
The GIOVE Processing Centre computes precise orbits and clock timings for the GIOVE satellites, based on the measurements made by the global network of Galileo Experimental Sensor Stations that collect Galileo and GPS observables once per second. In the future, navigation messages will be generated and up-linked to the satellites through their control centres.
The GIOVE Processing Centre is already started to provide fascinating, first-ever experimental results that will allow risk mitigation for the operational system development in the in-orbit validation phase.
In satellite navigation, the achievable positional accuracy is driven by, among other factors, the performance of the navigation message broadcast by the satellites, the satellite clock stability, and the user’s receiver and environment. The GIOVE mission is confirming the correctness of assumptions made at the early stages of the Galileo system design using actual measurements performed in orbit. This confirmation shows that the service performance requirements can be met and the overall Galileo system design is on track.
– New website
Information on the GIOVE mission is now accessible at www.giove.esa.int. This new website provides general information to the public and measurement data and core products to registered external users who are collaborating with ESA on the mission experiments.
Galileo is a joint initiative of the European Commission ( EC ) and ESA. The EC is responsible for the political dimension and the high-level mission definition. ESA’s responsibility covers the technology development as well as design, development and in-orbit validation of the space and ground elements.