Abstract: A scanning infrared sensor has a continuously rotating head to which is mounted an infrared telescope with a two-dimensional detector array. Blurring of the image output by the detector array is avoided by means of a fast steering mirror positioned on the head at the input of the telescope. The fast steering mirror is rotated in an opposite sense to the sensor head so that the array stares at a region of space for a sufficient time to allow the capture of an unblurred image from the detector array. The mirror then flies back to a starting position and then begins to rotate once more in an opposite sense to the sensor head so that the array stares at a further region of space, and so on.