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 impact up to 1% of GDP, according to estimates by the European Commission.
Global navigation satellite systems (GNSS) are a key tool for applications that require positioning, navigation and time synchronization (PNT) and are crucial for our daily activities – from getting to to our destination, knowing the time 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 transportation, agriculture or emergency services, among many others. The first satellite navigation system developed to know our position, navigate and synchronize times was the American GPS. In use since the 1980s, it dominated satellite communications for several years, a hegemony that later gave way to other satellite navigation systems that coexist and operate on a global scale: GPS in the US, GLONASS in Russia, Galileo in Europe, Beidou in China and regionally: IRNSS in India or QZSS in Japan. In the coming years, other systems currently in the definition period could complete the list.
Global GNSS systems share a common characteristic: all of them are located in MEO constellations, that is, in medium Earth orbit – between 2,000 and 35,786 km altitude – although in recent times the possibility of using low orbit is being considered. , LEO, —between 200 and 2,000 kilometers altitude—, to also provide PNT services, an option that was ruled out in the past among other reasons due to the greater number of satellites that would be necessary to provide the same service coverage: for a LEO constellation to provide an independent navigation service equivalent to that currently offered by Galileo or GPS, it would be necessary to launch around 300 satellites, ten times more than those needed in the MEO constellations.
With the difference being so great, why has the use of LEO orbits to provide PNT services begun to be valued again? While it is true that MEO orbits offer a greater coverage area due to their greater height, it is also true that the greater distance of MEO orbits makes the signals on Earth weaker than those that would be received from satellites located in orbits LEO.
Consequently, in recent years there has been a resurgence of 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 light 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 that fit 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 motion of the LEO satellite with respect to a ground point is much faster than that of a MEO satellite, providing several benefits for precision positioning.
LEOs could offer the ability to transmit signals different from 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 that a bidirectional communication channel could be implemented 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 case of accidents.
GMV, leader of the mission
The European Space Agency (ESA) has launched the LEO-PNT program to respond to the growing needs for more resilient and precise navigation and ensuring that Europe leads global satellite navigation. The first and fundamental step in the development of said 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, leading a consortium of about 50 European entities. Within the framework of the project, a total of five satellites will be developed and put into orbit that will transmit new advanced signals in UHF, L, S and C bands that will complement the signals currently transmitted by navigation satellites such as Galileo and GPS. This new contract marks the beginning of a new era that will open the doors to a new generation of navigation systems. With it, GMV consolidates its position as a leader in the European space sector.
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