In today’s contested battlespace, positioning, navigation and timing (PNT) solutions must withstand jamming, spoofing and degraded visual conditions. For Loitering Munitions and unmanned aerial vehicles (UAVs), precision absolute PNT is mission-critical—not just ideal.
BAE Systems’ recent white paper proposes a Common APNT Package (CAP) to meet these threats head-on.
To gain deeper insight into the thinking behind the paper, Inside GNSS spoke with Mike Shepherd, Director of APNT Strategy at BAE’s Navigation and Sensor System’s Business of BAE Systems. What emerged from that conversation is a layered, modular and verifiable system for achieving assured PNT in the most demanding operational environments.
REDEFINING MISSION SUCCESS WITH CPSM AND QUADRANT D
“Quadrant D—precision absolute PNT—is not a luxury; it’s essential,” Shepherd said. Defined by <10m positional error and <1ms timing error, Quadrant D supports full mission capability across all UAV operations.
Arriving at this framework was no small task. “We weren’t just trying to document requirements. We asked, ‘What’s the real problem here?’ And the answer was simple: Successful mission completion. Not partial. Not degraded—successful.”
This internal reset led to a shift in evaluation metrics. Cost Per Successful Mission (CPSM) became the standard by which effectiveness would be judged. “Every program has a unit cost target,” Shepherd noted, “but if you’re flying a $30k drone and it fails because it lost PNT five minutes in, your CPSM just skyrocketed. That failure costs more than the airframe.”
MERGED MODALITIES: A UNIFIED APNT THREAT RESPONSE
From that mission-first mindset, BAE turned to the question of how to maintain PNT under diverse, overlapping threats. Rather than investing in one dominant sensor type, they are developing a hybrid strategy that leverages the complementary failure modes of GPS/SATNAV and vision-based navigation.
“We realized that vision-based systems degrade for totally different reasons than GPS,” Shepherd explained. “So, if you build an architecture that leans on both, they rarely fail simultaneously. That’s the sweet spot.”
Shepherd reinforced this point by describing real-world use cases. “During a GPS outage—say from jamming, canyoning or terrain masking—vision can carry the load if it has a reliable clock and initialization. It can’t start cold in fog or total darkness. That’s where GPS or even Alternate Navigation systems come in.”
Importantly, this approach is sensor-agnostic but rigorously integrity-driven. “If a sensor can prove itself in the Integrity Ring,” Shepherd said, “then it’s a candidate. It’s not about preference—it’s about credibility.”
ASSURED SENSOR FUSION AND THE INTEGRITY RING
This focus on credibility led to one of the white paper’s core concepts: the Integrity Ring. Rather than simply fusing data from multiple sensors, BAE’s system actively validates each sensor’s input before including it in the final PNT solution.
“We don’t just fuse—we verify,” Shepherd said. “This isn’t a statistical mean. It’s a vetted synthesis. If a sensor starts to diverge from the consensus, we identify and exclude it.”
Shepherd elaborated on the metaphor: “It’s like a courtroom. Each sensor provides testimony, but the Integrity Ring is the judge. It asks: ‘Does this align with the rest of the evidence?’ If not, that sensor’s out.”
This adjudication mechanism enables change to…“multi-sensor PNT integrity, which allows us to use all available signals (even open service GNSS for example) while maintaining high trust in the PNT solution.
“You know where you are, you know what time it is, and you’re ready to reacquire when the environment allows,” Shepherd explained. “That’s a powerful place to be when GPS is denied.”
MODULARITY AND SCALE: COMMON APNT ACROSS ALL CLASSES
The Integrity Ring and its surrounding architecture are not limited to large platforms. In fact, the CAP concept was developed with scalability in mind. Rather than embedding PNT logic in each payload, BAE advocates for a platform-level architecture shared across all mission variants.
“We’re not pushing a $50K box for a $5K drone,” Shepherd said. “We’re scaling the same architectural logic across all classes, from expendables to Group 5 UAVs, using modular components and common interfaces.”
This modularity aligns tightly with the Department of Defense (DoD)’s push for a Modular Open Systems Architecture (MOSA). Shepherd noted the added benefit of continuity in an acquisition environment marked by rapid leadership turnover.
“Program leads change every 12 to 18 months. Without a standard, you’re reinventing the wheel with every rotation. CAP creates that consistency.”
Shepherd pointed to existing prototypes as proof of concept. “We’ve got “MILGPS” based systems flying today in many precision weapons. They’re meeting, or exceeding jamming and spoofing requirements.”
SURVIVABILITY IN A JAMMED AND SPOOFED BATTLESPACE
All of these architectural choices converge on a single battlefield reality: the need to operate in the presence of adversarial interference. In the white paper, BAE modeled identified benefits of M-Code and AJ/AS techniques. The results are dramatic.
GPS receivers can be rendered inoperable while still a significant distance from the interference source. In contrast, modern CAP-equipped UAVs with antijam (AJ) antennas and M-Code capability can retain full Quadrant D precisionfor operation closer to the interference.
Real world scenarios are even more urgent. “We’ve seen in Ukraine that fiber-optic cable is being laid across contested terrain—not because of bandwidth demand, but because RF is being jammed,” Shepherd said. “If that doesn’t underscore the need for assured PNT, I don’t know what does.”
To counter spoofing, the CAP system includes multiple defense layers: M-Code authentication, radio frequency (RF) anomaly detection, cold-start checks, and cross-sensor validation. “We’re not betting on any single trick,” Shepherd emphasized. “We’re building a robust web of trust.”
ARCHITECTING FOR THE FIGHT WE KNOW IS COMING
The Common APNT Package isn’t simply a technical response to a sensor problem—it’s a system-level rethink of how PNT is delivered and trusted in the most hostile environments imaginable.
“Don’t wait for the threat to teach you the lesson,” Shepherd warned. “Assured PNT isn’t about redundancy—it’s about integrity. And that has to be built in from the start.”
Shepherd, with a final call to action: “We’re saying: Start with the threat, build for survivability, and make integrity the default. The white paper is a blueprint. Adapt it. Build on it. But don’t ignore it.”
