The Development of a Flight Test Real Time GPS Navigation Tool (GNAV)

Abstract

The real time acquisition and monitoring of the aircraft trajectory parameters is essential for the safety of the flight tests campaigns held by most of the tests centers. Nowadays the us age of an airborne GPS receiver as the main sensor for these parameters has become the preferred solution for the Flight Tests Instrumentation (FTI) systems. The main problem arises when it is required a high accuracy for these measurements (e.g. air data calibration) where the solution is achieved through differential GPS techniques. The integration of this solution requires the acquisition and the correlation of the pseudorange and phase measurements for all GPS satellites in view observed by both base and rover GPS receivers. To avoid the usage of an additional uplink for the GPS differential corrections (i.e. from the base receiver to the rover), it was developed a novel solution where the GPS observables acquired by the rover receiver are merged into the FTI PCM data stream and processed in the Telemetry ground station by a Real Time GPS Navigation (GNAV) tool together with the GPS observables acquired by the base receiver. The GNAV development is divided into several phases where the accuracy for the trajectory parameters and the complexity of the solution increases. The prototype system was built and evaluated against the post-mission Ashtech PNAV® tool and the initial tests results show a satisfactory performance for the GNAV. The tests profiles are fully compliant with the Federal Aviation Administration (FAA) Advisory Circular (AC) 25-7A.