Evaluation of a Complementary Navigation Filter Steering a UAS Autopilot in a GNSS Contested Environment

This paper describes the results for a recent small unmanned aerial system (UAS) flight test during a GNSS-denied navigation exercise at White Sands Missile Range, where GNSS-denied state estimates were fed into an open-source autopilot and utilized to direct and operate the vehicle. Two successful hour-long flights were achieved, accomplishing all objectives. The aircraft flew a pre-planned flight pattern utilizing the autopilot capabilities and was largely unaware of the GNSS-contested conditions. The navigation payload onboard the aircraft consisted of an integrated GNSS-inertial unit, a ranging radio (listening to pseudolites) capable of both range and Doppler range rate measurements, a barometer, and an IR vision camera. The aircraft flew two separate flight patterns: a circular loiter and a square pattern with four waypoints, at three different altitudes (height above ground): 400, 500, and 600 m. The filter script was written using the Navigation Toolkit (NTK), a new library that supports pntOS development and is based on the ANT Center Scorpion framework. Overall, this research provides a starting point for future research in the areas of alternative navigation, software in the loop (SITL) control systems, navigation integrity, and navigation beyond the line of sight (BLOS). This research demonstrates that alternative sensors, such as cameras, radios, and barometers, can be used to successfully inform a commercial off-the-shelf (COTS) autopilot controller to successfully accomplish missions in GNSS-contested environments.