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Space technology to help the blind 
A new navigation tool to help blind people find their way around city streets is soon to be tested under an ESA project. The hand-held device incorporates ESA's new satellite navigation technologies, EGNOS and SISNET, into the personal navigator for blind people recently developed by GMV Sistemas, Valladolid, Spain and ONCE (Organización Nacional de Ciegos Espaòoles), the Spanish national organisation for the blind. At present, satellite navigation based on GPS and without the use of inertial systems, is not accurate enough to guide pedestrians, especially around cities. When few GPS satellites are in view because of tall buildings, positioning accuracy can be little better than 30 to 40 m. ESA's EGNOS system, however, improves the accuracy of GPS positions to a few metres, making it sensitive enough to locate obstacles in the street. EGNOS does this by broadcasting information from geostationary satellites which enables receivers on the ground to correct for errors in GPS signals. A pedestrian in a city of tall buildings, however, is even less likely to be in direct line of sight of an EGNOS satellite than a GPS satellite. So ESA has also developed a complementary technology, SISNET, which relays the EGNOS signal in real time over the internet.
"We think that the addition of SISNET to TORMES is very interesting," says Alfredo Catalina who is overseeing the project at GMV. "It should allow the blind user to navigate using a map, just as a sighted person can." The addition of an internet connection has the potential to enhance the function of personal navigators in other ways. "When you are connected to the internet you can also send messages back," explains Javier Ventura-Traveset from ESA, Toulouse. "You can ask for directions to a particular place or say that you are lost or have had an accident. By connecting the world of navigation with the internet, we are opening up many new possibilities."
By improving the accuracy of GPS signals, EGNOS is demonstrating new uses for satellite navigation now. However, the possibilities are due to mushroom within a few years when Galileo, Europe's own fully-fledged satellite navigation system comes into operation. Consisting of 30 satellites in medium-Earth orbit plus an associated network of ground stations, Galileo will be guaranteed to deliver an independent, civilian-controlled positioning service worldwide with metre-scale accuracy.
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