ATTITUDE STABILIZATION OF A RIGID SPACECRAFT USING 2 MOMENTUM WHEEL ACTUATORS

It is well known that three momentum wheel actuators can be used to co ntrol the attitude of a rigid spacecraft and that arbitrary reorientat ion maneuvers of the spacecraft can be accomplished using smooth feedb ack. If failure of one of the momentum wheel actuators occurs, we demo nstrate that two momentum wheel actuators can be used to control the a ttitude of a rigid spacecraft and that arbitrary reorientation maneuve rs of the spacecraft can be accomplished. Although the complete spacec raft equations are not controllable, the spacecraft equations are cont rollable under the restriction that the total angular momentum vector of the system is zero. The spacecraft dynamics under such a restrictio n cannot he asymptotically stabilized to any equilibrium attitude usin g a time-invariant continuous feedback control law, but discontinuous feedback control strategies are constructed that stabilize any equilib rium attitude of the spacecraft in finite time. Consequently, reorient ation of the spacecraft can be accomplished using discontinuous feedba ck control.