A compact Fast Steering Mirror(FSM) with a rigid support structure was designed for adapting to the great vibrancy, impact and high-low temperature conditions of an airborne platform. The support shafting, actuators, angle measurement elements of the FSM were designed and selected respectively on the basis of design requirements of the FSM. Then, a device to adjust shafting clearance was designed to improve shafting precision and provide additional supporting for mobile parts of the FSM. The special grating displacement sensors with small sizes were designed and four grating sensors were placed on the diagonal symmetrically to measure the position of the mirror by quadratic average of each measuring result, which reduces the volume of the FSM, improves its measuring precision, and removes the influence of clearance in the shaft direction on measuring results. Finally, the control bandwidth and pointing precision of the FSM for the airborne platform were tested, and the results show that the designed FSM offers the control bandwidth about 110 Hz, azimuth pointing error less than 3.4″ and the pitch pointing error less than 3.8″, which satisfies application requirements of vehicle platforms.