When it comes to timing, navigation, targeting, and weapons systems, GPS has become an integral part of the daily operations of the U.S. Air Force. But what happens when GPS becomes denied, degraded, or unavailable? It’s an important question, and increasingly relevant as dependence on GPS grows.
It’s the question that Capt. David Levene, an F-15E Weapon Systems Officer (WSO) at the U.S. Air Force Test Pilot School, chose to address in his thesis.
His assignment was to create an algorithm that would calculate realistic GPS jamming effects to be injected directly into an aircraft’s navigation system. His research began while he was a student at the Air Force Institute of Technology and continued into his time at TPS.
Now, almost two years later, Levene’s team is testing his project, the Simulated Programmable AirCraft-Embedded JAMmer, or SPACE JAM, as part of their Test Management Project, a six- to eight-month initiative that gives the students hands-on experience and oversight of a real test program. The TPS graduation requirement serves as a thesis project and authorizes students to be awarded a master’s degree.
The hardware for SPACE JAM resides inside a modified AE-4 antenna electronics unit, which already exists in many military aircraft, including the TPS F-16D aircraft that is being used for the test. A normal AE-4 receives the GPS signal from the aircraft’s antenna and simply conditions the signal for the aircraft’s GPS receiver. The AE-4 used in SPACE JAM performs the same function, but it can also inject jamming directly into the aircraft’s GPS system without affecting any other nearby aircraft.
“The jammers are simulated, but the jamming is real,” said Levene. “It’s really jamming your aircraft’s system, based on the effects of a configurable laydown of simulated jammers.”
But, as AFIT engineer Tom Pestak, explained, it’s kind of a Catch-22. “You need to jam your GPS system, but in order to know the effects of your jamming you need to know where you are,” said Pestak. “But, how do you know where you are if your GPS is jammed?”
He went on to explain that to see the effects of the jammers, you need to know where they are relative to the aircraft and the angles at which the aircraft sees them. The solution was to put in a secondary, MEMS-grade inertial navigation system that receives the GPS signal upstream from the jamming and is therefore not affected. This serves as SPACE JAM’s position and attitude source and is small enough to fit inside the modified AE-4.
SPACE JAM uses Control Monitoring and Debugging of SPACE JAM, or CMDoS, a custom software interface that allows the flight test engineer (FTE) or WSO to control the various jamming scenarios from the cockpit. Using the CMDoS software, the FTE or WSO can invoke a jamming scenario using any number of jammer configurations. These scenarios contain not only the locations of the jammers, but also signal parameters such as bandwidth, frequency, and power. Basically, everything on the software is configurable to meet the needs of the training mission. The system was developed jointly with AFIT’s Advanced Navigation Technology Center and the Air Force Research Laboratory’s Sensors Directorate.
Levene and his team have scheduled eight flights on an F-16 to test the system. The first flight took place Sept. 10 and characterized the integrity of the hardware in a high-G environment. Once the components proved durable, the team began a series of tests to profile the effects of GPS jamming on various aircraft systems, including not only the navigation system, but also the targeting pod and GPS-guided munitions.
“The testing we’re doing now has never been done before,” said Levene. “My hope for the future is that every military aircraft will include a navigation system that can be jammed for training purposes.”
For now, SPACE JAM is controlled using CMDoS by the FTE or WSO in the back seat. Eventually, Levene would like to see it fully integrated into the aircraft, giving the pilot control as well.
Prior to SPACE JAM, pilots only had one option to train for GPS jamming – a designated open-air jamming range. But those ranges are sparse, operationally-limited, and very expensive to use. Since real jammers can be large in size, they present physical restrictions as well. If an open-air test is delayed or moved, the jammers cannot be easily moved from one area to another. If the flight is delayed, the equipment and airspace might not become available for months. These limitations do not exist with SPACE JAM. Any jamming simulation can be loaded and flown at any time, anywhere in the world.
“We’ve been trying for over a year to coordinate open-air jamming training for the Edwards and China Lake, Calif., area and for a year we’ve been unable to coordinate a single GPS jammer. It’s too difficult, too much paperwork and too much coordination with the FAA to shut down the civilian airspace,” said Maj. Raven LeClair, another TPS student, and a member of Levene’s team.
Levene added that if you used real jammers at the level you can inject through the simulator, you would affect every aircraft within an unacceptably large radius.
“It’s important for aircrew to train to realistic scenarios. 15 years ago our jets didn’t have integrated GPS systems, but our pilots aren’t trained like that anymore,” said LeClair. “We want to be able to test any GPS-dependent device in a jet and see what happens when you jam it, to develop counter tactics. If all this saves one life, it’s worth it.”
He explained that GPS jamming can present safety concerns for the pilot. For example, if the GPS fails, a pilot may accidently cross an unfriendly political border. Ultimately, the project is intended to “prepare the warfighter for GPS jamming.” SPACE JAM provides a cost-effective, practical way to do just that.
“Being part of this project has been one of the coolest experiences I’ve had in the Air Force,” said Levene. “I engineered one piece of a very big puzzle. I remember when this concept was in pencil on the back of an 8.5 x 11 sheet of paper and now it’s on an F-16. We’ve taken a project from conception to a deployable system. We are flying this system and talking to other organizations about how they can get one. Make no mistake, it says TPS, but this is a real test program.”