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Session A1: Complementary PNT: Navigation by Celestial Objects

Day-to-Night Celestial Positioning Solution Utilizing Multiple Celestial Tracking Methods for Increased Availability
Laura Eshelman, Adam Smith, Jacob Frando, and Katie McCann, Polaris Sensor Technologies
Location: Ballroom A
Alternate Number 1

Military and civilian applications are greatly dependent on the Global Positioning System (GPS) due to its availability and fidelity. Failure of GPS is a critical risk for the warfighter and civilian applications as GPS jammers and other forms of signal denial are increasingly cheap, common, and effective. For the maritime shipping and aviation industries, spotty satellite navigation is a disaster waiting to happen. Inaccurate and incomplete GPS data can be a national security threat, disruptive, and very costly. Novel approaches to navigate and localize in GPS-denied or degraded environments are needed to maintain navigation capability. GPS-denied approaches for vehicles (such as terrain matching, optical flow, or map matching) may fail over environments that have non-distinguishable features like water, forests, and deserts. When this occurs, the vehicle relies solely on inertial navigation. Without GPS aiding, angular drift causes quadratic errors in the navigation solution, quickly rendering the vehicle position estimate ineffective.
Polaris Sensor Technologies, Inc. is developing algorithms to utilize the celestial technology exploited in the Sky Position and Azimuth Sensing System (SkyPASS) to provide an estimate of fixed global position. Inspired by nature, the SkyPASS polarization channel observes Rayleigh scatter of sunlight in the atmosphere to track the sun when the sun is otherwise occluded (clouds, twilight, canopy, etc.). The sun channel tracks the sun when it is visible and can track the moon at night depending on its phase. SkyPASS uses the measured position of the sun to determine global position. For a real-time position solution, the daytime position algorithm needs to know a reliable heading, however, a position fix can be acquired without a known heading if the system has ample time to collect measurements. The star channel (operable at night) can determine position without a known heading.
SkyPASS utilizes multiple celestial technologies combined with novel algorithms to provide position accuracies to within 5-10km on startup. Through averaging multiple measurements over time, position accuracies improve to 100s of meters. These position algorithms do not need a position seed or initial guess. The SkyPASS positioning solution is 24-hour capable, operates in various cloud conditions, provides a driftless position solution, is not affected by magnetic disturbances, cannot be denied or spoofed, is passive (and thus non-detectable), and can operate anywhere on Earth (including at high altitudes and near the North and South poles). Its size, weight, power, and cost (40 cubic inches, under 1.5lbs weight, under 5W power, and less than $10k in production) allows for integration on a variety of platforms, including smaller, low-cost platforms. This novel approach enables GPS-denied navigation over water or other featureless terrain by bounding absolute position.
SkyPASS uses optical sensors, an inertial sensor to provide orientation, a clock for date/time, and an on-board processor to calculate global absolute position without any prior knowledge of starting location; heading can be provided from an external system to improve computation time during the day. This presentation will show test results of the position algorithms implemented on SkyPASS (low SWAP-C hardware) including results when external heading is provided and when it is unavailable.
Polaris’ SkyPASS sensor utilizes the polarization map of the sky to aid its sun, moon, and star tracking capabilities when these traditional celestial tracking methods are not available. SkyPASS is a low SWaP-C system with a visible polarimeter and imagers that utilizes real-time on-board processing to calculate global absolute position, can now operate even when an external heading is not available, and provides a confidence metric to determine projected accuracy including operation during challenging sky conditions, such as twilight, overcast, and fog.

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