The Full-Sky Astrometric Mapping Explorer (FAME) instrument was designed to be an extremely accurate star mapper. To map the entire sky, the earth-orbiting FAME satellite rotates about its spin axis every 40 minutes, and uses solar pressure to precess about the spin axis every 40 days. The instrument had two apertures, separated by 84.3 degrees, allowing a star to be imaged twice in one rotation with about a 10 minute delay. This delay enables the elimination of
most measurement errors.
The light enters an aperture, bounces off of a compound fold flat mirror, (2 ULE fold flats bonded together at an 84.3 degree angle), passes through a Cassegrain telescope, and is imaged by the focal plane. The requirement for the fold flat’s dimensional stability is severe - the variation in the angle between the flats (basic angle) must be held to be held to 10 μarcsec during the 10 minute period between the first and second time a star is imaged. This paper presents a transient opto-thermo-mechanical analysis of the optical system.