How does EGNOS work? “Once, when I was sailing along the coast,
my navigational signal (a terrestrial one at the time) told me I
was on the land," recalls Hans Fromm, retired Deputy Head of the
Navigation Department at ESTEC. "Obviously, I knew it was out
and could estimate by how much. But without such an obvious
marker, how would I have known the accuracy of the signal? “Such
knowledge is crucial for many applications. For example, a train
needs to know which rail it’s travelling on. It’s important for
safety, especially where life could be at risk." EGNOS provides
the information needed to use navigational signals from GPS
satellites for such safety critical applications. It improves
the accuracy of position measurements from about five metres to
less than two metres, informs users of the errors in the
position measurements and warns of disruption to a satellite
signal within six seconds. “EGNOS will take responsibility and
guarantee the service,” explains Fromm. Three geostationary
satellites and a comple