Are LEOs the future for military GNSS requirements?

Global navigation satellite services (GNSS) are critical to modern militaries. Credit: NicoElNino / Shutterstock

Global navigation satellite services (GNSS) are indispensable to any fighting force that needs accurate, real-time positioning services. Whether it’s the location of infantry units in the field, fighter planes in the sky, missiles in flight or frigates out at sea, they can only be fully effective using PNT (position, navigation and timing) data that is sent from satellites.

Users in the UK have tended to access either the European Galileo or legacy American GPS system, which was given over for general use by the US government back in the 1980s. Since then, this infrastructure of approximately 30 satellites (per system) has been allowed to degrade somewhat (in the case of GPS), with the US Space Agency outsourcing its maintenance to third parties.

The fact that the GPS network is ultimately out of the control of most of its users, makes many in defence, aviation, and government nervous about its long-term viability. The ongoing war in Ukraine has also highlighted the susceptibility of GPS to malicious attack, with satellite networks the subject of unwanted attention from those determined to block signals or even disable them completely.

Since 2023 entrepreneurs such as Jeff Bezos and Elon Musk have stepped in to develop their own, flexible, low cost, low-earth orbit communication systems, with the dream of providing connectivity ‘wherever you can see the sky’.

The idea is to move away from fragmented, outdated geo-stationary systems, replacing them with high volumes (with several thousand planned) of smaller, smarter mobile satellites. While Musk’s Starlink has over 5,000 satellites in orbit already, Bezos’ Kuiper network is catching up.

Launched in March 2024, the UK Space Agency's Connectivity in Low-Earth Orbit (C-LEO) programme will provide up to £160m ($203m) of funding over the next four years to UK companies and researchers to develop innovative satellite communications technology. This is a much-welcomed catalyst to the UK space and electronics sector.

However, there are significant challenges facing the use of C-LEO satellites for PNT applications. The first issue concerns the cost of production (primarily the user equipment), which needs to be reduced while not sacrificing quality or reliability. Previously, the design and manufacture of GPS or Galileo orbiting satellites, which were universally reliable, had the luxury of low volumes and significant, government-backed budgets.

Conversely, today’s new generation of satellites need to be manufactured in much higher volumes, with good reliability and obsolescence built in.

The second challenge relates to the technical aspects of sending relatively low volumes of data, without a satellite dish to focus the signal. This is where the next generation of (UK designed and built) mobile antenna could play a crucial role.

Historically, PNT signals have occupied L band – a relatively low frequency with relatively good penetration to the surface. However, it does run into issues when faced with dense urban environments or geographical features such as canyons or mountains.

Whether it is GPS, Galileo or even BeiDou, China’s satellite navigation system, GNSS networks all face the same challenges. Given their relatively small numbers (ie GPS and Galileo each operate approximately 30 satellites) these systems are increasingly exposed to denial-of-service techniques or even ‘satellite killers’, where units are rendered inoperable using laser or kinetic attacks.

As OneWeb/Eutelsat, Starlink and Kuiper are some of the most well-known entrants to the satellite market, these LEO operators are positioning themselves as solution providers to military, defence and aviation professionals. With 1000s of satellites planned for each LEO network, the sheer scale of these new networks makes a denial of service much more difficult. While the signal strength offered by LEO satellites is slightly better than traditional GNSS, essentially, they could provide a like for like PNT service as existing GPS or Galileo satellites.

Crucially, LEO offers much more redundancy and flexibility, so PNT users may have more choice in terms of navigational positioning. From critical infrastructure to defence, this provides a much more reliable GNSS service.  

Traditionally, the cost of production for space proof hardware was extremely high. When we had a limited number of space-based satellites, they commanded high costs to ensure good, long-term reliability. Qualification for low volumes made them very expensive.

In our experience, specialised FPGAs alone could cost up to £50,000 for a space qualified part. This made sense for satellites at the time, that were going to last for 25 years. Now we’re being asked to design units that will be replaced within five years – this is due to orbital decay which his caused by residual atmospheric attrition – the wear and tear of space travel. The game is changing fast.

In today’s high-volume, low-cost market, we need to innovate to square this circle. This mean that OEMs need to manufacture high performance, robust satellites in big numbers, while staying within tight budgetary constraints.

Whereas established GPS satellites use MEO satellite that orbit at an altitude of between 2,000 – 3,600km, LEOs are much closer to the planet located anywhere between 160 and 2,000km above the Earth. On the face of it, this change in distance from the Earth to the satellite is a mere detail, however, in practice, this shift in position requires a new type of satellite with a different engineering focus including network communications and manufacturing at much reduced cost.

The current stable of GPS satellites are relied upon to send out communications that may not be rich in terms of data but need to be extremely accurate. Each satellite sends a continuous stream of pseudorandom bits (zeros and ones) which repeats each millisecond. Each satellite has its own individual pattern of bits.

This provides the recipient device with a very precise time from each satellite. Fundamentally thanks to triangulation and clever maths, those using timing signals can get either 2D (land-based) or 3D (air-based) positioning depending on the number of satellites. 

LEO satellites provide various technical challenges. Lower orbits reduce transmission path loss; however, this is normally offset by LEOs operating in higher frequency bands (typically AU, E or V). Given that these are significantly higher than L band, this results in a potential overall increase in path loss.

This means that normally a GPS antenna will be polarised (but non directional) and will achieve the required signal gain to enable reception. However, at these higher bands, antenna gain, and directionality become more challenging. Also, managing timing and position of satellites in a crowded environment of satellites becomes more complex.

At the same time, triangulation normally requires multiple simultaneous connections to achieve accurate positioning. At the satellite end, management of the PNT signals is also more complex. Thousands of devices, all in slowly decaying orbits require highly sophisticated software to maintain the precision.   

PNT needs less complex modulation as the data rates are very low compared to satellite broadband. In practice, this means lower signal to noise ratios can be tolerated and still achieve good reception of the PNT signal.

The simplest solution here would be an antenna with some directionality. Hence, operators could segment the sky into for example four quarters. In this scenario the antenna would not be steerable, but they would be monitoring a specific section of sky.

The big advantage of this solution is that it’s relatively cheap, but with limited performance compared to broadband antennas. The introduction of active steerable antennas with narrower beam widths would drastically improve signal to noise ratios and be more impervious to denial-of-service techniques. This would result in higher costs, but still be relatively commercial as has been experienced in the steerable antennas for 5G mmWave technology.

This higher performance type of antenna is based on work undertaken for consumer products – an area in which we have substantial experience. These more sophisticated antenna are resistant to unwanted attack and provide better interference tolerance compared to older technology. We have been running an R&D programme looking at the development of a new generation of array solutions that meet the challenge of improved security, while achieving commercial viability.

As part of our research in this area, we are developing a solution that provides good operational delivery, while achieving good SWAP (size, weight & power) benefits. These complex technical challenges are now becoming a significant potential gateway to the new world of multi-use LEO orbiting satellites.

A number of technologies, creating hybrid arrays and the novel application of materials, are already showing huge potential in this emerging area of antenna development. Smaller, lighter, and lower power arrays are definitely a key part of the future of satellites providing PNT services – at a cost.

Granted, the defence and aviation sectors may well be prepared to pay for the added security and higher performance delivered by the new LEO satellites, but what about ownership and security issues? There are alternatives to this ‘rental’ model.

Earlier in 2024, the European Defence Agency (EDA) brought together two EU Member States to develop a satellite demonstrator that can manoeuvre from Low Earth Orbit (LEO) to Very Low Earth Orbit (VLEO) – and back again. The €10m ($10.5m) project – called LEO2VLEO: Military Crisis-Response Satellite Constellation – with the Netherlands and Austria, will design, develop, launch and operate a constellation of between two and four satellites. It aims for a space launch within two years. In this innovative approach to space, the project will, once operational, have the capability to support military operations.

While the EDA approach provides perhaps improved security and functionality, it is unlikely to be operationally available for some years to come. To their great benefit, the likes of Kuiper, Starlink and OneWeb are already up there.

Australia could be one of the main beneficiaries of this dramatic increase in demand, where private companies and local governments alike are eager to expand the country’s nascent rare earths production. In 2021, Australia produced the fourth-most rare earths in the world. It’s total annual production of 19,958 tonnes remains significantly less than the mammoth 152,407 tonnes produced by China, but a dramatic improvement over the 1,995 tonnes produced domestically in 2011.

The dominance of China in the rare earths space has also encouraged other countries, notably the US, to look further afield for rare earth deposits to diversify their supply of the increasingly vital minerals. With the US eager to ringfence rare earth production within its allies as part of the Inflation Reduction Act, including potentially allowing the Department of Defense to invest in Australian rare earths, there could be an unexpected windfall for Australian rare earths producers.