Space Force Boosting an Ecosystem of GPS Alternatives in Low-Earth Orbit

The Space Force is playing midwife to a new ecosystem of commercial satellite constellations providing alternatives to the service’s own Global Positioning Service from much closer to the Earth, making their signals more accurate and harder to jam.

A half-dozen companies, including two with research contracts from Space Force or Air Force tech incubators, are currently planning low-Earth orbit (LEO) constellations of hundreds of small satellites that will offer position, navigation, and timing services to augment or back up GPS.


The military has long been concerned about its reliance on GPS, but over the past few years civilian users have experienced increasingly severe GPS interference around conflict zones in Eastern Europe and the Middle East.

In particular, civil aviation has been hard hit, said Lisa Dyer of the GPS Innovation Alliance, a trade association that represents GPS receiver manufacturers, satellite operators, and user groups like boaters, surveyors, and autonomous vehicle developers.

GPS jamming, used to stop drone attacks and smart bomb targeting, creates “unnecessary extra burdens on our air traffic controllers and flight crews, and it’s increasing risks to the safety of the flight crews and the passengers,” Dyer told Air & Space Forces Magazine.

PNT signals from low-Earth orbit are harder to jam, experts say, because they are broadcast from much closer to the earth’s surface. New cryptographic techniques make the signals hard to impersonate with bogus data, a problem known as spoofing. And two of the new constellations also plan to use a completely different frequency band for their signals, which will also make jamming more difficult and more complicated.

LEO satellites orbit between 100 and 1,200 miles above the surface of the Earth. GPS and its other major PNT constellations like China’s BeiDu, Russia’s GLONASS, and Europe’s Galileo are all in medium-Earth orbit, 11,000-15,000 miles above the surface.


“There are some advantages to medium-Earth orbit and some advantages to low-Earth orbit,” said Dyer.

The main advantage of MEO, she explained, is the smaller number of satellites required. From a higher orbit, a satellite is visible over a greater proportion of the earth’s surface. In MEO, 24 satellites is enough to offer near-global coverage. The current GPS constellation has 31 satellites in orbit, which means there’s some redundancy, Dyer said.

The main advantage of LEO is the signal can be orders of magnitude stronger when it arrives at the receiver, making it easier to receive and harder to jam, said Patrick Shannon, co-founder and chief executive officer of TrustPoint, a LEO PNT startup that launched its third satellite last month.

With several hundred satellites in a large LEO constellation, users can also see more satellites in the sky at one time, and therefore receive more triangulating signals, making LEO PNT potentially more accurate than MEO-based systems...