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The problem of fault tolerant attitude stabilization with finite-time convergence is investigated for spacecraft with redundant actuators. On the basis of the sliding mode control technique, a robust controller is derived with uncertain inertia parameters, actuator faults, and external disturbances explicitly addressed. It is shown that finite-time reachability into the small neighborhood of sliding surface, and faster time convergence of attitude orientation are achieved. To address actuator input constraints, an adaptive fault tolerant controller is further proposed. One feature of the proposed strategy is that the design of the fault tolerant control does not require any fault detection and isolation mechanism to detect, separate, and identify actuator faults. The attitude stabilization performance using the controller is evaluated through a numerical example. Copyright a number of researchers have resorted to fault tolerant control (FTC) [8][9][10]. A wide class of FTC controllers have been developed by using absolute stability theory framework [11], control allocation [12], and adaptive control [13]. As for the application of FTC to spacecraft attitude control, to the best knowledge of the authors, there exist minor investigations. In [14], the problem of automated attitude recovery for rigid and flexible spacecraft application was discussed. Another fault tolerant attitude control design was reported in [15] to compensate for effectiveness loss of reaction wheels. The controller was developed in the absence of external disturbances and uncertain inertia parameters. In [16], passive and active sliding mode control laws were developed to solve the attitude stabilization problem with actuator outage fault accommodated. In the work in [17], thruster failures were accommodated by proposing a reliable control scheme. In a more recent work [18], the authors derived a fault tolerant control strategy to follow the desired attitude for flexible spacecraft represented by quaternion. Among various schemes of FTC design, the insensitivity and robustness properties of sliding mode control make it attractive for fault tolerant control. The adaptive sliding mode control design technique was thoroughly examined in [19] to perform attitude tracking maneuver for flexible spacecraft. In [20], the problem of sensor fault estimation and compensation for microsatellite was investigated by using a descriptor system approach. In [21], the authors focused on the problem of rapid reorienting of a rigid spacecraft with no control available on either roll or yaw axis.Sliding mode control has several advantages such as rapid response, insensitive to parameter variations, and low computational costs. However, it usually requires large control power for its use of large bounds on the uncertainties/disturbances. In practical aerospace engineering, because of physical limitations, the outputs of momentum exchange devices and/or thrusters are constrained. A common example of such a constraint is actuator saturation. If an unknown fault occur...

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