A Kalman-Filter Based Inertial Navigation System Processor for the SCRAMSPACE 1 Hypersonic Flight Experiment

摘要

The design of a navigation processor for the SCRAMSPACE 1 hypersonic flight experiment is detailed. Two cascaded extended Kalman filters provide a fusion of gyroscope, accelerometer, magnetometer, GPS and aerodynamic database sources for vehicle state estimation. Two quantities of great interest for SCRAMSPACE 1 are angle of attack and side-slip angle. The navigation processor performs estimations in two stages. The first stage tracks the vehicle's navigation states with a commercial grade Inertial Measurement Unit (IMU)/GPS combination, starting at the conclusion of a despin manoeuvre. It is initialised by a navigation-grade Inertial Navigation System (INS). A 25-run Monte Carlo sweep shows that without a navigation filter, the first stage cannot hold attitude via raw gyroscope integration over the 468 seconds necessary. The filtered estimate has a 72% chance of holding attitude over this time, with 5.5, 6.3 and 14.9 degrees of standard deviation of roll pitch and yaw error. A prototype proof-of-concept attitude determination system is shown to confirm the performance in reduction of attitude drift, compared with that of integrating the gyroscope measurements directly. In a stationary test over 240 seconds, the integrated gyroscope solution drifts 160 degrees in roll, 12 degrees in pitch and 47 degrees in yaw. The magnetometer-integrated solution drifts 5 degrees in roll, 1 degree in pitch and 10 degrees in yaw. In a dynamic test over 64 seconds, in which pure rotations are induced, the integrated gyroscope solution drifts 40 degrees in roll, 10 degrees in pitch and 20 degrees in yaw. The second stage of the experiment utilises known vehicle dynamics to estimate angle of attack and sideslip on re-entry to the atmosphere. The estimations are shown to be within 0.1 degrees of the truth, even when the INS-computed relative wind angles are an order of magnitude out and the wrong sign.