Limited Air Force Testing Of This Data-Of-Opportunity Navigation System Is A Missed Opportunity

By Eric Tegler, Contributor
Early November flight tests saw AFRL/SDPE’s Complementary-PNT experimentation system paired with a 586th Flight Test Squadron T-38C. U.S. Air Force/2nd Lt. Bowen Lin

The alternative position, navigation and timing (A-PNT) system that the Air Force tested on a T-38 last November could be a vital tool for navigation and targeting in the guaranteed GPS-denied environments of future conflicts. But the apparent lack of urgency to test and develop this data-of-opportunity PNT system misses the chance to patch a serious tactical and strategic vulnerability.

The Air Force Research Laboratory (AFRL) leads what’s called the “Complementary-PNT experimentation campaign” with the USAF’s Strategic Development Planning and Experimentation (SDPE) office, a modest 15-person staff dedicated to advancing new capabilities.

Over the last year, the two have sought to demonstrate fused PNT technologies within an externally carried pod which was first flown on testbed aircraft in Centennial, Colorado last summer. (Interestingly, the Air Force won’t specify what aircraft, possibly a C-12 or RC-26B.) The external carrier is the reconfigurable AFRL-developed Agilepod whose common electro-mechanical connections and open-architecture software have served a variety of sensor development experiments in the last five years.

In this case, Vision Navigation (VisNav), Signals of Opportunity (SoOP) and magnetic anomaly navigation (MAGNAV) sensor systems are combined within the Agilepod to provide a sort of data-of-opportunity PNT capability, using any and all of the above alternatives to determine an aircraft’s position and provide navigation for targeting or guidance.

This catch-all approach to gathering navigational cues theoretically gives manned and unmanned aircraft the flexibility to operate with precision when GPS is down or disrupted.

It’s referred to as “complementary PNT” not simply because it’s an alternative to GPS. The combined approaches compliment each other and a traditional inertial navigation system (INS) which would serve as a baseline anchor for them in an operational environment.

“We’d like to be able to fuse multiple sources regardless of what type of technology they are,” says Major (USAF) Andrew Cottle, of the SPDE office. “We expect we’ll need multiple alternatives to meet the [PNT] need. There won’t be one single silver bullet.”

That seems commonsense but it’s hitched to the reality that, so far, there’s only one silver bullet test platform - an Edwards AFB-based 586th Flight Test Squadron T-38C - that’s made just eight sorties with the potentially in-demand system. When I initially asked Major Cottle if the test team has firm test plans for 2022, he said it did not.

A closeup of the AFRL-developed Agilepod carrying the base complementary PNT system on T-38C. USAF, 2nd Lt. Bowen Lin, 586th Flight Test Squadron

Just to be sure, I queried again and Cottle replied in an emailed response that the experimentation campaign “intends to conduct two additional PNT operational utility demonstrations [flight tests] in CY22. We’re working to finalize those details this month and expect concrete milestones to be in place by February 2022.”

The fact that, as the year begins, there’s no determined energy or clarity on firm plans to develop and potentially field a system that Air Force units and COCOMs would like to have yesterday is disappointing, if all too predictable. When I asked about the apparent lack of urgency and how quickly AFRL/the Air Force could move on this, Major Cottle said, “Good question.”

It’s evident that the SPDE understands the gravity of the PNT problem and the desirability of getting to a fielded system as soon as possible. Nevertheless, Cottle added that the prognosis for moving ahead was changing “week by week”. His office is pushing he says but there are “a lot of stakeholders with different needs and requirements. We can only do it as fast as that allows.”

That probably won’t be too fast. The Air Force’s FY ‘22 Budget included a $204.7 million request for a "Lifecycle Prototyping" line item which includes developing PNT prototypes for use with externally carried pods for manned/unmanned aircraft.

The work done so far has chiefly been confirming systems functionality within the Agilepod. The T-38 flight tests were carried out both on the Edwards AFB test range and in coastal airspace near Vandenberg Space Force Base in California. The sensor/navigation systems were strictly onboard capabilities with no data input or transfer from/to offboard PNT sources.

While the test team used the T-38 to capture more relevant navigation profiles over varied altitudes, terrain, and water, it did not focus on any particular tactical sortie scenarios. The T-38 was used more or less to confirm the Agilepod/A-PNT combo will work on a dynamic maneuvering platform.

“The test points were designed as stepping stones to enable us to look at more operational events in the future,” Major Cottle affirms.

The breadth of focus of such operational events would be wide. Questions about what type of platforms complementary PNT can be deployed on, whether it would remain a pod-carried affair or be integrated within new or existing aircraft, and whether it would be widely distributed or available for dedicated pathfinder aircraft have not been determined.

An MQ-9 Reaper flew with an Agilepod in three demonstration sorties sponsored by the Air Force Life Cycle Management Center. Air Force Lifecycle Management Center

The applicability of such a system to unmanned aircraft appears possible but not as straightforward as one might imagine. Agilepods have been in use aboard RQ-4 Global Hawk and MQ-9 Reaper drones so carriage is not an issue but navigating may be.

The GPS PNT that unmanned aircraft (and weapons) presently rely on can be relatively easily expressed in a digital format. Alternatives like visual navigation which compares a database of terrain features or landmarks tracked by onboard sensors in order to calculate vehicle position require degrees of interpretation.

The signals of opportunity portion of the complementary PNT system assess a range of local radio frequency signals (cellular networks, RFID, TV and more), calculating the relative distance between an aircraft and those signals against an initial estimate (INS) of the aircraft’s original position to navigate precisely.

The MAGNAV element employs magnetic field sensors to measure variations in the Earth’s magnetic field as an aircraft travels over the surface of the planet. The readings are compared with existing maps of the Earth’s geomagnetic field to determine one’s location relative to magnetic field anomalies. Air Force researchers have been assessing new techniques and building new magnetic maps/databases to increase precision. The MAGNAV portion of the system was not navigating during the test flights. It was simply “on and collecting data” according to Cottle.

The Major acknowledges the challenge of presenting such alternative navigational data to remotely piloted or autonomous systems.

“The system doesn’t necessarily have to restrict itself to interpretation [solely] by an unmanned system. I think there’s a range of options, whether we integrate it directly into an unmanned system or rely on some TTP [tactics, techniques, procedures] in the UAS realm that we can investigate.”

Simply presenting A-PNT information to pilots (whose interpretive skills still surpass AI and automation) is a problem AFRL has yet to address. The T-38 test vehicle had no complementary PNT user interface. Its aircrew simply flew the desired profiles while test engineers on the ground monitored telemetered data from the Agilepod.

While the complementary PNT system has flown through varied electromagnetic environments in its testbed and T-38 outings, the test team has no assessment or experimentation with its ability to operate in contested scenarios. These would include electromagnetic disruption and any visual, signals or magnetic disruption that an adversary, or Mother Nature, could potentially throw at it.

The U.S. Navy has been a partner in some of the complimentary PNT system research and several of the contractors working on the system have expressed their desire to progress to an operational version but Cottle declined to name them or discuss what sort of timeline they could achieve if pressed. The Army is pursuing its own A-PNT research for ground systems. While that application is different from airborne or maritime PNT, it would seem logical for the services to pursue a common approach.

The complimentary PNT system fits snugly inside the Agilepod but doesn't seem to have fired rapid acquisition enthusiasm. U.S. Air Force

There’s no obvious evidence that that is happening. Nor is there a traceable train of experimentation that could see complementary PNT migrate to weapons or unmanned teaming platforms.

“That’s something we would like to figure out but at this point I don’t really have an answer as to whether we can,” Cottle says.

The building blocks are there but the will to rapidly assemble them isn’t obvious. It continues to be a missed waypoint, an opportunity lost.


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