Real time precision attitude determination system /RETPAD/ for highly maneuverable spacecrafts

In this paper an attitude determination system, RETPAD, is developed which provides precision on-board real time attitude informations for highly maneuvering spacecrafts. The system employing a set of two-degree-of-freedom strapdown gyro IMU as the primary attitude determination sensors with periodic attitude update by a set of star trackers when the spacecraft is in slow slew mode. Algorithms were developed and a digital computer simulator was built for error sensitivity analysis, performance study, and assist in the overall system design. An in-flight calibration method was also developed to periodically calibrate the important error sources such as gyro scale factor, gyro-to-gyro misalignment, bias, and star tracker boresight axis misalignment. Simulation results indicated that the developed system satisfies the pointing requirements under highly dynamic environment. Although the system is developed for three-axis maneuvering spacecrafts, it can also be applied to the earth pointing spacecrafts requiring precision on-board attitude determination.