Title of Presentation: C-20A/GIII Precision Autopilot Development in Support of NASA’s UAVSAR Program

Primary (Corresponding) Author: James Lee

Organization of Primary Author: NASA Dryden


Abstract:  The NASA Unmanned Aerial Vehicle Synthetic Aperture Radar (UAVSAR) program is developing a Synthetic Aperture Radar (SAR) for ground measurements.  A key element for the success of this program is a Platform Precision Autopilot (PPA).  An interim vehicle (NASA C-20A/GIII) was selected to carry the radar pod and develop the PPA.  The PPA interfaces with the C-20A/GIII making the aircraft think it is flying an Instrument Landing System (ILS) approach.  This technique retains the safeguards in the aircraft’s autopilot.  The PPA entered initial flight testing in early 2007.

The PPA uses a Kalman filter to generate a real-time position solution with information from the C-20A/GIII and a near real-time differential GPS unit designed by JPL.  The real-time navigation solution is used to compute commands (Guidance and Control modules) which in turn drive two modified ILS testers.  The ILS tester units produce modulated RF signals fed to the onboard navigation receiver.  These correction signals allow the C-20A/GIII autopilot to fly a simulated ILS approach that meets the PPA requirement for UAVSAR applications.  The PPA requirement is to make repeat pass flights within a 10 meter tube for a 200 kilometer course in conditions of light turbulence.

At time of presentation, we expect to have results of flight tests.