An optical apparatus and method for measuring the attitude of an object in outer space includes an optical system having an aperture to receive optical radiation and a focal plane to image the optical radiation and an aperture-sharing element attached to the optical element and at least partially surrounding an optical path into the aperture. The aperture-sharing element directs optical radiation from a field of view of the aperture-sharing element to a corresponding first portion of the focal plane to provide multi-axis stellar attitude measurements, and the aperture receives optical radiation along the optical path into the aperture and directs the optical radiation to a second portion of the focal plane.