Design and evaluation of INS/GNSS loose and tight coupling applied to launch vehicle integrated navigation

Abstract

<abstract><p>A satellite launcher requires accurate and reliable navigation to reach orbit safely. This challenging application includes vertical launch, flying through diverse layers of the atmosphere, discontinuous acceleration and stages separation, high terminal velocities and hostile temperature and vibration ranges. The Inertial Navigation System (INS) is typically coupled with a Global Navigation Satellite System (GNSS) receiver to achieve the desired solution quality along the complete ascent trajectory. Here, several INS/GNSS integrated navigation strategies are described and evaluated through numerical simulations. In particular, we evaluate different INS/GNSS integration using: loose coupling, tight coupling and an intermediate Kalman filter on the receiver to enhance the loosely coupled navigation solution. The main contributions are: a compensation model of tropospheric delays on the GNSS observables, a compensation of processing/communication delays on GNSS receiver outputs, covariance adaptations to consider vehicle's high dynamics, and an specific way to integrate the filtered solution and its covariance provided by the GNSS receiver. The tightly coupled integrated navigation proved to be the best choice to handle possible GNSS receiver positioning solution outages, to exploit more degrees of freedom for the compensation of GNSS observables and the possibility to make a cross validation of individual GNSS observables with INS-based information. This is specially important during the periods with a low number of satellites in view when the GNSS positioning solution can not be validated or even computed by the GNSS receiver alone. Finally, a test with hardware in the loop is provided to validate the numerical result for the selected tightly coupled INS/GNSS.</p></abstract>