On Course for a Better, Stronger GPS
BY JASON HENDRIX
The United States Air Force Global Positioning System (GPS), developed to provide precision navigation and timing to the nation’s military, has become equally essential to the rest of society, with applications ranging from transportation and communications to financial transactions. Although illegal, jamming, spoofing, and other forms of general GPS signal interference are not difficult to accomplish for those who want to hide illicit activities or disrupt industries. This, combined with our general reliance on GPS for so many critical functions, has created an urgency to push forward strategies and technology for a more resilient GPS.
IMPROVING SIGNAL STRENGTH AND ACCURACY
Current GPS radio signals are faint, designed to be only around 1.5 dB and coming from satellites 13,000 miles away. (In comparison, home television signals usually range from 25-46 dB.) They are also complex, containing multiple components such as time, ephemeris data, and information about the health of the satellite. The continual production and broadcasting of GPS signals from solar-powered satellites requires a design that successfully balances the allocation of energy, equipment, and other resources. For many years, signal strength was not considered a critical vulnerability. But times have changed.
GPS is now considered an enabler for critical infrastructure, integral to both military operations and the economies of nations around the world. As such, it has become a potential target for those with ill intent. In response, the next generation of GPS satellites is being developed to be more resilient. The navigation payloads Harris is delivering for GPS III space vehicles (SVs) 1-10 have the capability to deliver signals that are three times stronger than those from previous GPS satellites, making jamming more difficult, providing better coverage in “urban canyons” and forests, and improving location accuracy by three times.
GPS’ atomic clock technology, fundamental to the system’s positioning and navigation capability, is already the most accurate in the world. For the next generation of GPS satellites, it will be even more precise, achieving an accuracy of one-tenth of a nanosecond over a day.
FURTHERING GPS RESILIENCE
Shoring up GPS is not just smart, it is essential to world stability. So what will make tomorrow’s GPS more resilient? Looking ahead to GPS III SV 11 and beyond, Harris has developed a fully digital navigation payload that will improve performance for the U.S. Air Force by providing even more powerful signals, making it harder to interfere with GPS signals. The design is fully mature as an engineering development model—not simply a prototype—and is ready to be inserted into the satellite. Modular and fully redundant, the payload uses independent circuit cards for critical algorithms and data processing, command and control, maintenance, and telemetry functions.
Our timekeeping technology will deliver even greater stability as well as provide the clock signal for a new GPS III search and rescue payload. Looking further into the future, on-orbit reprogrammability capability for the navigation payload “brains” could enable more efficient mission updates and the graceful insertion of new technologies. Potential new components like wideband, solid-state gallium nitride transmitters could support new signals and offer better anti-jam support for military operations, as well as make a significant difference in signal efficiency size, weight, and power requirements.
While the mission of GPS is simple—to provide “navigation data to military and civilian users all over the world”—widespread use of, and dependency on, this global utility have elevated GPS accessibility to a level of importance probably never envisioned when the first satellite launched in 1978. Improvements like those identified here will enable GPS to evolve into the more resilient system we need to better address the threats and demands of a changed world.
Jason Hendrix, is program director of Harris’ Positioning, Navigation, and Timing (PNT) business area, Harris PNT solutions are on every U.S. GPS satellite launched and are critical to GPS availability, accuracy, and integrity.