SOLUTION OF SPACECRAFT ATTITUDE VIA ANGULAR MOMENTUM IN BODY AND INERTIAL FRAMES

Attitude solutions for spin-stabilized rigid spacecraft are presented that are direct functions of the torque and angular momentum vectors in the body and in the inertial frame. Two solutions are found: an approximate solution and an exact algebraic solution. Unfortunately, in applications, the algebraic method is not practical because the torque and angular momentum vectors usually are not precisely known in the inertial frame. The approximate method, which tolerates approximate values for the angular momentum vector in inertial space, is verified numerically for a spin-stabilized rigid spacecraft in the following three maneuver cases: 1) the spinning, thrusting problem, 2) the thrust ramp-up problem, and 3) the spin-up problem. The numerical results for the approximate method are accurate for small excursions of the inertial angular momentum vector from its initial orientation in space. However, for the same conditions the numerical investigations show that the results of the exact method are poor due to the error in the axial component of the torque in the inertial frame.