Real-Time Navigation Algorithm for the SHEFEX2 Hybrid Navigation System Experiment

Abstract

The Hybrid Navigation System was developed to achieve the required attitude accuracy and calculate a navigation solution for the SHEFEX2 mission, which launched on June 22, 2012 from And�ya Rocket Range in Norway by the German Aerospace Center (Deutsches- Zentrum f�ur Luft- und Raumfahrt, DLR). The real-time navigation algorithm fuses data from an IMU, GPS receiver, and star tracker using a delayed error state extended Kalman filter. The navigation algorithm uses a two part scheme to spread the work load and to ensure real-time requirements are met. Whole states are propagated at 400Hz as IMU data is available and the filter operations are done at 1Hz. A high-rate task propagates the whole states using a strapdown navigation routine, calculates the state transition matrix, maintains clock calibrations and executes part of the filter reset routine using the delayed error state estimates. A low-rate task propagates and updates the filter when measurement data is available. All measurements are synchronized to the GPS pulse per second signal so the sensor measurements have approximately the same reference time. Hardware-inthe- loop results show the navigation and computational performance of the algorithm in a real-time simulation.