A Comparison Between Tightly Coupled INS/GNSS Strategies for LEO Direct Ascent

he navigation of launch vehicle trajectories typically uses data fusion between an Inertial Navigation System (INS) and independent external measurements given by a Global Navigation Satellite System (GNSS) receiver. This technique is called INS/GNSS Integrated Navigation and is implemented through a Kalman Filter. In particular, the tightly coupled variant of INS/GNSS uses GNSS receiver's raw measurements, which are the code phase, carrier phase and Doppler shift, and associated satellite's data ephemeris. Here, we evaluate different strategies for tightly coupled navigation using numerical simulations and true GNSS measurements taken by a receiver being developed concurrently. We also compare different nonlinear Kalman filters, including the Extended Kalman Filter and the Unscented Kalman Filter. The launch trajectory is a direct ascent to Low Earth Orbit.