Design and Simulation of GNSS Phase Based Attitude Determination of Spacecraft: LAMBDA and EKF Combination Technique

Global Navigation Satellite System (GNSS) is the broad name for satellite based navigation system and one of the application areas of this field is addressed in this contribution. This paper is drafted to present the design and simulation of GNSS phase based Attitude Determination System for small satellite. GNSS Phase based solutions are considered more reliable and accurate as compared to the code based solutions but the phase measurements demand some ambiguity resolution algorithm for the required accuracy. GNSS phase based attitude determination algorithm using Extended Kalman Filter (EKF) for attitude determination and LAMBDA method for ambiguity resolution are analyzed and implemented on the small satellite model. Three commercial-off-the-shelf GPS antennas are used for experimentation where one served as the master and two as the slave antennas. The RINEX data is used for the observations and navigation message and processed in the MATLAB functions to get the position of the satellite using the ephemerides and applying the navigation solution to get the position of the master antenna by using the method of single point positioning while incorporating the different errors like Tropospheric, Ionospheric and Clock errors. Base line is calculated by applying the Least Square Solution after resolving the ambiguity and performing the method of differential positioning using double difference measurements to find the slave antenna positions. Finally, extended Kalman filter is applied to get the attitude measurements that report to be accurate within one degree precision.