SMART Attitude Acquisition and Control

This paper deals with the attitude acquisition and control for the Italian Scientific Microsatellite for Advanced Research and Technology. Since the microsatellite is aimed at remote sensing applications, three-axis fine attitude control (0.1°-0.01°) during station keeping is required. The attitude acquisition technique exploits the magnetic control to despin the microsatellite initial tumbling and uses a small reaction wheel to despin the microsatellite residual rotation around the axis perpendicular to the orbit plane, due to the magnetic control. Three-axis attitude control during station keeping is performed by means of three small reaction wheels, whose reaction torque vector is computed using Proportional Derivative control laws and optimum control theory. Coarse attitude control is first performed in which the microsatellite attitude angles are determined by a technique based on the use of sensors with low mass and power consumption. Fine attitude control is then achieved by using a small star tracker for fine attitude measurement. The proposed techniques for attitude acquisition, determination and control during station keeping are numerically tested with a code that simultaneously integrates the microsatellite attitude dynamics and control. Numerical results show that the attitude acquisition is performed in about 20 orbits, after the separation from the launcher, while coarse attitude determination and control during station keeping are achieved with accuracies 0.7° and ±2°, respectively.