Imagine you’re driving a car. You’re relying on GPS to traverse an unfamiliar environment. You lose GPS when you drive through a tunnel, but the car’s inertial navigation system tracks your movement in space so it can maintain your position relative to the road. It’s a temporary solution, but without GPS — without the ability to reorient yourself in time and space — you’ve lost yourself in the bigger picture. You don’t know your next turn. Without GPS or a backup system, you’re in the dark.
Naval Information Warfare Center (NIWC) Pacific solves this problem for the fleet through technology that provides resilient and assured positioning, navigation and timing (PNT) data with holdover capability in a GPS-challenged environment.
When it comes to allocating GPS solutions, the U.S. Navy’s surface combatants with high-value platforms take priority over platforms on other vessels which can’t support the cost of current solutions and don’t have room for the large racks of equipment typical on a combatant ship. This creates a capability gap for resource- and space-constrained platforms on smaller vessels.
Before GPS, there was the inertial navigation system (INS). Modern high-end INS uses lasers and fiber optics to compute a platform’s dead-reckoning position. INS sensors that can maintain positioning without GPS are expensive and proprietary, which makes their integration and lifecycle support costs unaffordable for most platforms.
Enter the NIWC Pacific PNT Systems Integration Branch and its mission: create a low-size, weight, and power — and cost (SWaP–C) PNT data solution which can meet the requirements of resource-constrained platforms. The team’s Advanced Scalable Assured PNT (ASAP) system integrates other sensors in addition to GPS and INS to fill the gap and keep vessels with low operating costs out of the dark.
“That’s the big win here — we’re able to perform that internal navigation that’s been used even before GPS, but now we can do it at a much lower SWaP–C,” said Ken Simonsen, division head for NIWC Pacific’s PNT Division. “The ASAP project is an investment in equipping our warfighters with robust, assured PNT capability under any and all operational conditions and physical environments.”
The NIWC Pacific team rapidly developed the ASAP real-time software framework with the goal of demonstrating the system in an operational environment, achieved in less than two years when the team tested the prototype aboard military sealift command ship USNS Spearhead (T-EPF 1) during an Office of Naval Research fleet experiment.
Regardless of vessel size, ASAP is one more tool in the toolkit, insurance for a fleet that relies on the ubiquitous use of GPS. Along with the introduction of the improved military code known as M-Code and jam-resistant antennas, it’s one more way the Navy is innovating to protect fleet assets so operations may continue in GPS-contested environments.
“ASAP focuses on integrating existing GPS-dependent capabilities, GPS-independent solutions, and miniaturized, scalable PNT solutions,” said Simonsen. “The ASAP team’s focus and excitement on executing the ‘art-of-possible’ captures the entrepreneurial spirit of this team.”
Open Architecture Production
Defense Advanced Research Projects Agency sponsored development of an algorithm for the all-source positioning and navigation (ASPN) particle filter ASAP uses to perform INS functionality. The version used by ASAP, called Assured Data Engine for Positioning and Timing (ADEPT), implements a dynamically reconfigurable particle filter for sensor data fusion and navigation equations. The ASAP team integrated the ADEPT source code, provided to the government with unlimited rights, to its real-time software framework to ensure the particle filter would run in deterministic real-time.
The flexible framework built by the ASAP team — using a government-owned solution not contingent on integration with proprietary technology — means lower costs and greater compatibility with existing fleet hardware, such as sensors from various vendors.
While a commercial system only requires one filter solution designed to meet its particular platform requirements, the ASAP system can run four parallel particle filters at once, useful for further research and development. Running multiple filters concurrently enables accurate comparison of test results under one set of scenario-dynamic motions.
Before testing on Spearhead, the NIWC Pacific ASAP team was invited to join an ongoing collaboration effort with Sweden as part of an undersea surveillance and communications project agreement. Sweden’s location across the Baltic Sea, an area prone to GPS disruption, makes it an ideal partner for the U.S. military, but foreign collaboration doesn’t come without challenges.
First of those challenges for the ASAP team was working within limitations set by U.S. regulatory oversight, which restricts exports of DoD-related technologies. In order to comply with U.S. and Sweden data exchange agreements, the NIWC Pacific team sent the ASAP system to Sweden without its typical antenna and GPS receiver. But the ASAP system was built with flexibility in mind, so its modular open systems architecture configuration allowed for easy integration with Swedish antennas and receivers. The low-SWaP–C system proved easy to transport without complicated logistical planning or high shipping costs by fitting into a carry-on suitcase.
The teams pre-tested the ASAP prototype at the Swedish Defence Research Agency Lab in Linköping, Sweden, then continued testing aboard a Swedish combat vessel (CB90) during sea trials in November 2019. Results aboard CB90 were promising, as was the Swedish team’s commitment to collaboration — in the words of Carl Ahlden of Sweden’s 1st Marine Regiment, who made it clear the purpose of the platform was to serve testing: “If you need to drill a hole, I’ll drill a hole.”
Subsequent technical exchange meetings and water cooler chats pushed the partnering teams to innovate further: Could the system run on a low-resource computer using system-on-a-chip (SoC) technology? Could one of the Swedish engineers install ASAP on a jet ski?
Thanks to ASAP’s adherence to open programming standards, porting the system to run on the SoC’s operating system was straightforward, though it did require validation. Once validated, a new Micro ASAP system with dramatically reduced SWaP–C was baselined, a major achievement that could invite even smaller platforms, such as unmanned underwater vehicles, into the fold after more testing.
Then came the coronavirus, a global pandemic that threw a wrench in collaboration for teams such as NIWC Pacific and their Swedish partners. Before COVID-19, the teams managed to overcome barriers to collaboration, such as differences in time zone and language. When the Centers for Disease Control and Prevention mandated social distance in March, and the Swedish government banned all in-bound travel from most countries the same month, it was just one more opportunity to adapt.
The ASAP system was shipped to Sweden on a loan for continued testing. The ASAP team in San Diego continues to provide remote technical support, which compounds language and cultural challenges more easily handled in person. Data exchange in the form of large log files proved to be a challenge. Still, recent results from testing on CB90 continue to show promise. These latest performance improvements were thanks to use of a higher-performance fiber optic gyro inertial measurement unit (IMU) sensor.
Now the teams are preparing for upcoming sea trials on CB90, during which the boat’s speed log will be integrated into the ASAP system, along with an additional mid-range attitude and heading reference system (AHRS). Another contender for AHRS integration is a lower-cost AHRS based on micro-electromechanical systems (MEMS) technology, which is performing well in current vehicle testing at NIWC Pacific.
That’s the draw of the ASPN particle filter’s flexibility: its ability to integrate with the right mix of sensors for any given platform means the ASAP system can be fine-tuned to a vessel’s existing hardware and meet low-SWaP–C requirements.
A two-year extension to the project agreement allows for continued collaboration, including work on characterizing sensors for dynamic operational performance. Also of interest is the expansion of 3D sensor processing that does not use GPS, which will expand the range of applications ASAP can support. Recent test results that involved using a MEMS-based IMU sensor borrowed from Sweden for the Micro ASAP system show even more promise for lowering SWaP–C capability.
As the NIWC Pacific ASAP team’s innovations continue, it’s possible their Swedish partner could run ASAP on a jet ski after all. That would mean having the capability to navigate without GPS — even on a jet ski. It would be like driving through a tunnel and losing GPS but knowing that even then, you’re never really in the dark. You’re grounded, no matter what. With the ASAP system, that translates into better and cheaper positioning capability for vessels of all sizes, GPS or not. It means navigating foreign waters with confidence. For the fleet at large, it means increased readiness, no matter the mission.
As a part of Naval Information Warfare Systems Command, NIWC Pacific’s mission is to conduct research, development, engineering, and support of integrated command, control, communications, computers, intelligence, surveillance and reconnaissance, cyber, and space systems across all warfighting domains, and to rapidly prototype, conduct test and evaluation, and provide acquisition, installation, and in-service engineering support.