Abstract

Altair is an acquisition, tracking, and pointing (ATP) space experiment sponsored by the Strategic Defense Initiative Organization (SDIO) Directed Energy Program Office. The experiment is configured as a free-flying satellite with an electro-optical payload designed to address target acquisition and pointing issues. The payload was designed by a government-led Phillips Laboratory team. The Altair optical tracking system requires diffraction-limited performance for the IR intermediate tracking camera and the visible fine tracking camera. Size and weight considerations were balanced by the economy of utilizing existing hardware from the Starlab program. A trade study demonstrated that the optical tolerances were equivalent for a Mersenne telescope and a Cassegrain telescope, but that the latter reduced the size of the relay optics considerably. An off-axis parabola used to collimate the light introduces astigmatism and coma, which degrade the images. Diffraction-limited performance was obtained where necessary without introducing additional off-axis elements. In addition, the extent of the point spread function for the visible-intermediate-tracking camera, while not diffraction limited, was less than the pixel size of the focal plane array. An additional consideration was that the pupils remain in registration during beam deflections introduced by the steering mirrors. This requirement was met by placing the steering mirrors close to the pupil locations. The final conceptual optical design for the Altair payload will be presented.

© 1992 Optical Society of America