Army gets a move on 'pseudolites' and other non-GPS navigation

Aware of the potential for GPS and other signals being disrupted in the electromagnetic spectrum, the military has been researching ways to get location and navigation information when satellite signals are degraded. One possibility? A “pseudolite,” which is what it sounds like—a pseudo satellite that operates low to the ground, sending stronger signals than soldiers get from a satellite in orbit.

Another possibility is using a Chip-Scale Atomic Clock, or CSAC, which can provide precise time to a GPS receiver when GPS signals are being jammed, in order to enable rapid signal reacquisition or to protect receivers from spoofing, according to a release from the Army’s Communications-Electronics Research, Development and Engineering Center’s Command, Power and Integration Directorate, or CERDEC CP&ID.

They’re both part of CERDEC’s efforts to make sure that soldiers in the field have positioning, navigation and timing, or PNT, capabilities even when the usual signals, such as GPS, are being interfered with.

“Our adversaries are getting better at attacking our PNT capabilities,” said John Delcolliano, CP&ID PNT Integrated Systems Branch chief. “Our military must stay one step ahead of them to ensure mission success and the safety of our troops.”

The directorate, which has worked on PNT solutions since the 1960s—when the tools included maps, compasses and gyroscopes—is taking what it calls a systems-of-systems approach to Assured PNT, or A-PNT, CERDEC said, incorporating a variety of sensors that can be mounted on vehicles or worm by soldier in the field. Pseudolites, which can work in groups of four or more to provide time and position information, are one example.

“Instead of a satellite in space, think of it as terrestrial, such as in a tent, vehicle or even in an aircraft flying at just a few thousand feet altitude,” Delcolliano said. “They act similarly to a satellite, but by being close to the ground, the received power and signal strength is stronger and it is harder for the enemy to jam you.”

Likewise, a CSAC could help a GPS receiver reacquire a signal that’s been disrupted as well as protect it against spoofing.

As CERDEC pointed out, the tools aren’t intended to replace GPS but to serve as effective backups when signals aren’t available, something the military has been working on with other projects as well. CERDEC, for example, also has been developing the Warfighter Integrated Navigation System (WINS), a pocket-sized device that uses a variety of inertial sensors to track a soldier’s movement from a last known location. The Defense Advanced Research Projects Agency has been working on a tiny PNT chip that could provide precise location information without GPS. And the Navy, Air Force and DARPA have collaborated on an anti-ship missile that doesn’t need to rely on GPS or other traditional platforms.  

CERDEC, meanwhile, is working with the Air Force Research Laboratory on an international effort to use the Mutli-Global Navigation Satellite systems, or GNSS, combining the navigation systems used by different countries to ensure PNT. "As we have become dependent on GPS for our PNT requirements, we must be vigilant in ensuring that PNT capabilities are there for our warfighter," said Gary Blohm, director of CERDEC CP&ID. "Our collaboration with our partners in this area is a great example of how the team effort is greater than the sum of its parts.”