How to maintain reliable military navigation capability without GPS

THE MIL & AERO VIDEO BLOG, 26 June 2012. The Global Positioning System (GPS) has been a monumental improvement for safety and commerce, but military leaders need more. The GPS can be jammed or spoofed, so the military needs reliable navigation capability without GPS. This is the promise of the DARPA All Source Positioning and Navigation sensor-fusion program.

The GPS satellite navigation system has been perhaps the most important and influential navigation technology since the invention of the marine chronometer nearly three centuries ago. The importance of GPS to commerce and safety since its constellation of orbiting satellites went online in the 1980s cannot be overstated.

The GPS originally was developed for military use only, but an aviation disaster 30 years ago put it on the fast track to the widespread civil use we see today. On September first, 1983, Korean Airlines flight double-oh-seven, en-route from Anchorage to Seoul, veered far off course and into Soviet airspace. A Soviet jet fighter, believing the commercial flight was a military intruder, shot the 747 jumbo jet down, killing all 269 aboard.

After that, the U.S. government said never again would navigational error put so many lives at risk, and civil use of the fledgling Global Positioning System went to the head of the line.

Yet despite the monumental importance of GPS, this technology still makes some people in the military nervous whose systems absolutely, positively have to navigate accurately no matter the conditions.

The GPS constellation uses triangulation among satellites and receivers to fix position and altitude. Each satellite also has an accurate clock, so the system can measure speed, as well as position. The weak link in the GPS, however, is the radio links among satellites in space and receivers on the ground, at sea, and in the air.

RF links can be jammed by enemies, turned off at a moment's notice during a national security crisis, or even could be knocked off line permanently if an adversary could find a way to destroy orbiting GPS satellites. That vulnerability simply is not acceptable to those who depend on accurate navigation for mission- and life-critical tasks such as munitions guidance.

That's the reason the U.S. Defense Advanced Research Projects Agency is moving forward with a program called ASPN, which is short for All Source Positioning and Navigation. The ASPN program seeks to develop a navigational sensor-fusion system that can easily and seamlessly accept inputs from many different navigational sensors, like the GPS, ground-based radio beacons, and inertial measurement units, so warfighters can maintain navigation capability -- with or without GPS.

The ASPN program is entering its second phase, which will refine algorithm development, build a prototype ASPN system, and demonstrate it with an arbitrary set of sensor inputs. The initial phase of ASPN saw the Charles Stark Draper Laboratory in Cambridge, Massachusetts, and to Argon ST in Fairfax, Virginia, craft sensor-fusion algorithms that suggest an adaptable, plug-and-play capability for navigation systems is achievable.

In the next phase, DARPA contractors will add sensors such as laser rangers, cameras, and magnetometers to a typical navigation sensor array of GPS and inertial sensors.

If they can pull it off, those in the Pentagon who rely on precision navigation no matter what, can rest a lot easier.