Entitling its release “From Orbit with Love,” the European Space Agency (ESA) proudly announced today, March 12, 2013, that the first four satellites of the future Galileo Satellite Navigation constellation achieved their first-ever autonomous position fix. The positioning was replicated and confirmed by a team at the NavSAS group of Politecnico di Torino, Italy.
The obtained accuracy lies in the 10-meter range, according to ESA. ESA added that considering the infrastructure is only partly deployed, this fulfills expectations. As with GPS or any satellite navigation system, a minimum of four satellites is required to make a position fix in three dimensions.
The position fix was obtained by ESA’s navigation laboratory in the Netherlands, using the four satellites, launched in October 2011 and 2012, and the Galileo programme’s ground infrastructure, consisting of control centers in Italy and Germany and a global network of ground stations.
“This fundamental step confirms the Galileo system works as planned,” read the official statement.
“Once testing of the latest two satellites was complete, in recent weeks our effort focused on the generation of navigation messages and their dissemination to receivers on the ground,” explained Marco Falcone, ESA’s Galileo system manager.
This first position fix of longitude, latitude, and altitude took place at the Navigation Laboratory at ESA’s technical heart ESTEC, in Noordwijk, the Netherlands, early on the morning of March 12, with an accuracy between 10 and 15 meters, which was expected, taking into account the limited infrastructure deployed so far.
“The test of today has a dual significance: historical and technical,” notes Javier Benedicto, ESA’s Galileo project manager. “From the historical perspective, this is the first time ever that Europe has been able to determine a position on the ground using only its own independent navigation system, Galileo. From the technical perspective, generation of the Galileo navigation messages is an essential step for beginning the full validation activities, before starting the full deployment of the system by the end of this year.”
With only four satellites for the time being, the full Galileo constellation is visible at the same time for a maximum two to three hours daily. This frequency will increase as more satellites join the constellation in orbit, along with extra ground stations coming online, for Galileo’s early services to start at the end of 2014.
The European Commission’s program head for Galileo, Paul Flament, granted an interview last week with GPS World, recapping the coming launch activities and expectations for initial and full operational capabilities, the latter with a target constellation of 30 satellites. The interview will appear in the April issue of the magazine, which is specially devoted to Galileo and European navigation initiatives.
With the validation testing activities under way, users might experience breaks in the content of the navigation messages being broadcast, said ESA. In the coming months the messages will be further elaborated to define the offset between Galileo System Time and Coordinated Universal Time (UTC), enabling Galileo to be relied on for precision timing applications, as well as the Galileo to GPS Time Offset, ensuring interoperability with GPS.
Galileo Is Real, and NavSAS Has the Evidence
Almost simultaneously with the ESA announcement, the NavSAS group of Politecnico di Torino and Istituto Superiore Mario Boella in Turin, Italy, also achieved a position fix using the signals of the four In-Orbit Validation Galileo satellites (PFM, FM2, FM3, FM4) that started today to broadcast a valid navigation message. The researchers of the NavSAS team successfully computed the positions by using full software receivers developed by the team.
The positions obtained are depicted in Figure 1, as red squares on the rooftop of the NavSAS Lab in Turin, Italy, where the antenna is positioned (latitude 45°03’54.98767″ N, longitude 7°39’32.28920″ E, height 311.9667 meters). The navigation message was first successfully decoded at 11.28 on March 12.
The configuration of the four Galileo satellites as seen by the NavSAS lab is reported in Figure 2.
The NavSAS team was earlier among the first research teams worldwide able to receive and process the signal of the PFM and FM2 satellites, in December 2011 after the launch of the earliest Galileo IOV satellites, and again at the end of 2012 for the FM3 and FM4.
The milestone in both accounts of Galileo-only positioning is that it is real-time positioning using the Galileo navigation message. Galileo positioning using a post-processing mode had already been demonstrated, and described by Peter Steigenberger, Urs Hugentobler, and Oliver Montenbruck of the Technische Universität München and the German Space Operations Center, in an account in GPS World, February 2012 issue. (scroll down to “First Demonstration of Galileo-Only Positioning”).