The enormous potential benefits of satellite navigation brought the EC together with ESA in collaboration. In the 1990s the two organisations agreed to develop a civilian equivalent of GPS so that Europe could be autonomous in this crucial strategic and commercial sector.
ESA began research and development in cooperation with the EC and civil aviation community. The development strategy was conceived with two major pillars:
EGNOS (European Geostationary Navigation Overlay Service) – a pan-European augmentation system, complementing GPS to deliver sharpened reliability and integrity information to users.
- Galileo – a fully autonomous and interoperable worldwide satellite navigation system, broadcasting global navigation signals for high-performance services, possessing the service integrity guarantees that GPS lacks for commercial and safety-critical services.
EGNOS a reality
Today EGNOS is already operational: its Open Service, for applications where human life is not at stake, such as personal navigation, goods tracking and precision farming, has been available since October 2009.
EGNOS’ Safety-of-Life Service, where safe air transportation depends on the accuracy and integrity of its signals, became available for its primary purpose of aircraft navigation (beginning with vertical guidance for landing approaches) in March 2011. The system is based on a network of ground stations and three geostationary satellites. The ground stations gather data on the current accuracy of GPS signals and embed it in the EGNOS signal, which is uplinked to the satellites to be transmitted to users.
Galileo’s proof of concept
ESA and the EC followed a staggered approach in developing Galileo. ESA began with its Galileo System Test Bed Version 1 in 2002.
This facility performed tests of Galileo orbit determination, integrity and time synchronization algorithms using GPS satellites and an experimental ground segment consisting of a worldwide network of sensor stations.
An Experimental Precision Timing Station, located at the Istituto Elettronico Nazionale (IEN) Time Laboratory in Turin, Italy, provided the reference time scale needed, synchronised to universal time and international atomic time (UTC/TAI), and a Processing Centre located at ESA’s ESTEC technical centre in Noordwijk in the Netherlands. This latter site was used for the generation of navigation and integrity core products based on Galileo-like algorithms.
Tests conducted with GSTB-V1 proved Galileo’s underlying design concepts: that it was indeed possible to ' broadcast' orbit determination and time synchronisation data to a high-precision sub-metre accuracy with a low update rate of under two hours, as envisaged for the Galileo system.
Stepping into orbit
The next stage was to flight-test Galileo elements for real. Two Galileo In-Orbit Validation Element (GIOVE) satellites were built in parallel with complementary capabilities to provide redundancy.
GIOVE-A launched on a Soyuz rocket from Baikonur Cosmodrome in Kazakhstan on 28 December 2005. Constructed for ESA by Surrey Satellite Technology Ltd of the UK, the satellite was equipped with a phased-array antenna of individual L-band microwave elements to illuminate the entire visible Earth beneath it, its signal – the first European navigation signal-in-space - being guided by two very stable rubidium atomic clocks.
The satellite also carried two types of radiation detectors to survey the harsh environment of medium-Earth orbit, which passes through the outer van Allen radiation belt. GIOVE-A possessed a streamlined version of the Galileo ground segment, which served to demonstrate its basic design assumptions were sound. The satellite’s signals were also used for tests with GPS to demonstrate GPS-Galileo interoperability was feasible.
GIOVE-B was launched on a Soyuz rocket from Baikonur Cosmodrome on 27 April 2008.
Built by a consortium headed by Astrium and Thales Alenia Space, GIOVE-B featured an improved phased-array antenna of individual L-band elements, a signal-generation unit able to produce new types of signals, a new radiation sensor and an exceptionally stable passive hydrogen maser atomic clock – the most advanced clock ever flown for navigation purposes – as well as a back-up rubidium clock.
With the first Galileo In-Orbit Validation satellites working well in orbit following their launch on 21 October 2011, there was no longer any need for these experimental GIOVE satellites. GIOVE-A and GIOVE-B were both turned off the following year.
Last update: 13 October 2012