Development of a transient thrust stand with sub-millisecond resolution

A transient thrust stand has been developed to offer 0.1 ms time-resolved force measurements up to 22 N. The system uses a predictor-based subspace system identification (PBSID) algorithm to obtain a high order state space model of the thrust stand. The state space model defines high-frequency vibration modes within the thrust stand. The high-frequency vibration modes are necessary to provide the time response of 0.1 ms. Thruster forces are then estimated using an augmented Kalman filter (AKF) to combine sensor traces from four accelerometers, a velocity sensor, and a displacement transducer. Fusing low-frequency displacement data with high-frequency acceleration measurements provides accurate force data from 0 kHz to 10 kHz. Combining the AKF with the PBSID state space model inherently attenuates external noise sources such as pumps. The transient thrust stand uses a torsional configuration to minimize influence from external vibrations and achieve high force resolution independent of thruster weight. Results demonstrated that the system was capable of obtaining dynamic thrust profiles with less than 5% error and a time resolution of 0.1 ms. To date, no thrust stand is capable of measuring up to 22 N forces with a time response of 10 kHz.