Minisatellite Attitude Guidance Using Reaction Wheels

Abstract

In a previous paper [2], the active torques needed for the minisatellite attitude guidance from one fixed attitude posture to another fixed attitude posture were determined using an inverse dynamics method. But when considering reaction/momentum wheels, instead of this active torques computation, the purpose is to compute the angular velocities of the three reaction wheels which ensure the minisatellite to rotate from the initial to the final attitude. This paper presents this computation of reaction wheels angular velocities using a similar inverse dynamics method based on inverting Euler’s equations of motion for a rigid body with one fixed point, written in the framework of the x-y-z sequence of rotations parameterization. For the particular case A=B not equal C of an axisymmetric minisatellite, the two computations are compared: the active torques computation versus the computation of reaction wheels angular velocities 𝜔̇x , 𝜔̇y and 𝜔̇z. An interesting observation comes out from this numerical study: if the three reaction wheels are identical (with Iw the moment of inertia of one reaction wheel with respect to its central axis), then the evolutions in time of the products between Iw and the derivatives of the reaction wheels angular velocities, i.e. 𝐼𝑤𝜔̇𝑥 , 𝐼𝑤𝜔̇𝑦 and 𝐼𝑤𝜔̇𝑧 remain the same and do not depend on the moment of inertia Iw.

Keywords

• minisatellite
• attitude guidance
• reaction/ momentum wheels
• angular velocity
• inverse dynamics