Until now, all navigation satellites have flown high up in medium-Earth orbit – up at 23 222 km in the case of Galileo, which delivers metre-level accuracy. At such altitudes the satellites move slowly across the sky, helping ensure global availability of satellite navigation signals, albeit at relatively low power. ESA’s LEO PNT constellation would move to a ‘multilayer system of systems’ approach, with medium-Earth orbit signals supplemented by those from low-Earth orbit (LEO) satellites at altitudes of less than 2000 km – along with additional inputs from terrestrial PNT systems and user-based sensors., made up of approximately a dozen satellites, helping European companies move forward at a time when worldwide commercial interest is high in LEO constellations of all kinds, especially for telecommunications and PNT. The satellites themselves can be stripped down compared to current satellite navigation satellites, because they would essentially be relaying satnav signals from MEO. This is a key point because there will need to be many more satellites to ensure global coverage – because the lower the orbit the faster each individual satellite will pass across the sky. This fact also opens the way to a more agile ‘New Space’ approach to satellite construction for European firms, with smaller payloads and simplified operations from the ground. Their signals will be much stronger (potentially able to penetrate indoors), and transmitted on novel frequencies, which – along with the new geometries made possible by LEO satellites – should enhance overall service resilience. LEO PNT will also deliver faster position fixes and enable rapid two-way authentication checks. And overall signal availability will be boosted enormously, especially in high-latitude and polar regions. Credit: ESA