Satellite communication has changed the world as we know it. 7% of the European economy currently depends on satellite navigation. In fact, the loss of these services for at least a week could have an impact of up to 1% of GDP, according to European Commission estimates.
Global Navigation Satellite Systems (GNSS) are a key tool for applications that require positioning, navigation and time synchronization (PNT) and are crucial to our daily activities – from arrival at our destination to knowledge of how long it will take for a bus to arrive. to carry out any banking transaction – and determining factors for a large number of activities and economic sectors, such as transport, agriculture or emergency services, among others. The first satellite navigation system developed to know our position, navigate and synchronize times was the American GPS. Used since the 1980s, it dominated satellite communications for several years, a hegemony which then gave way to other satellite navigation systems that coexist and operate on a global scale: GPS in the United States, GLONASS in Russia, Galileo in Europe, Beidou in China. and at the regional level: IRNSS in India or QZSS in Japan. In the years to come, other systems currently in the definition period could complete the list.
The global GNSS systems share a common feature: they are all located in MEO constellations, that is, in a medium Earth orbit – between 2,000 and 35,786 km altitude – although the possibility of using a low orbit, LEO, — has recently been considered. between 200 and 2,000 kilometers of altitude -, to also provide PNT services, an option that has been excluded in the past, among other reasons, due to the greater number of satellites that would be necessary to ensure the same coverage of service: for a LEO constellation to provide an independent navigation service equivalent to that currently offered by Galileo or GPS, around 300 satellites would need to be launched, ten times more than those needed in MEO constellations.
With the difference being so great, why has the use of LEO orbits to provide PNT services started to be valued again? While it is true that MEO orbits provide a greater coverage area due to their greater height, it is also true that the greater distance of MEO orbits makes signals on Earth weaker than those that would be received from satellites located in LEO orbits.
Consequently, in recent years there has been a renewed interest in LEO constellations for navigation. Private companies, such as SpaceX, offer global internet services from space with constellations made up of thousands of LEO satellites. There have also been technological improvements that allow the manufacture of very small and lightweight satellites and, in addition, launch options are now more economical, since the launch sector has experienced a revolution in the last fifteen years with the incorporation of reusable rockets and startups offering small launchers suitable for small LEO satellites.
Main advantages
LEO satellites could be very useful to complement current GNSS navigation systems. In addition to its greater resilience to interference, the relative movement of the LEO satellite relative to a point on the ground is much faster than that of an MEO satellite, providing several advantages for precise positioning.
LEOs could offer the ability to transmit different signals than those transmitted by current MEO constellations, a diversity that could be exploited to improve overall resistance to interference. Additionally, signals could be designed to implement security features that increase their resistance to attacks. Another possible use of LEOs is the implementation of a two-way communication channel with users fully integrated with the navigation service, which can be very useful for Internet of Things (IoT) applications or for search and rescue in the event of an accident.
GMV, head of mission
The European Space Agency (ESA) launched the LEO-PNT program to meet the growing needs for more resilient and precise navigation and ensure that Europe leads global satellite navigation. The first and fundamental step in the development of this strategy is the LEO In-Orbit Demonstrator (IOD), which aims to demonstrate Positioning, Navigation and Timing (PNT) services and develop key technologies. The Spanish company GMV will be in charge of this development with LEO satellites, at the head of a consortium of around fifty European entities. Under the project, a total of five satellites will be developed and put into orbit which will transmit new advanced signals in the UHF, L, S and C bands which will complement the signals currently transmitted by navigation satellites such as Galileo and GPS. This new contract marks the beginning of a new era which will open the doors to a new generation of navigation systems. GMV thus consolidates its position as leader in the European space sector.
