Summary: Attitude tracking control problem for rigid spacecraft is investigated in this paper. Two controllers based on unit quaternion attitude parameterization are proposed to solve this problem. Both controllers presented here can guarantee finite time reachability of given desired attitude motion of a rigid spacecraft in the presence of model uncertainties and external disturbances. Ambiguity in quaternion representation exists in the first controller, while it is absent in the second one. The convergences of the proposed controllers for the resulting closed loop systems are proven theoretically. Numerical simulations are also provided to demonstrate the performance of the developed controllers.