Scott D. Friedman, Robert H. Barkhouser
Center for Astrophysical Sciences, Department of Physics and Astronomy,
The Johns Hopkins University, Baltimore, MD 21218
Jeff Hampton, Paul Nikulla
Swales and Associates, Inc.,
5050 Powder Mill Road, Beltsville, MD 20705
The Far Ultraviolet Spectroscopic Explorer (FUSE), currently being fabricated and scheduled for a 1998 launch, is an astrophysics satellite designed to provide high spectral resolving power (lambda / delta lambda = 30,000) over the interval 910-1180 Å. It consists of four co-aligned, normal incidence mirrors which illuminate separate Rowland circle spectrograph channels equipped with holographic gratings and delay line microchannel plate detectors.
The FUSE mirrors are rectangular, off-axis paraboloids with stringent reflectivity, imaging, lightweighting, and mechanical requirements. Two mirrors have Al+SiC coatings on Zerodur substrates, and the other two have Al+LiF coatings, also on Zerodur substrates. Important aspects of the optical and mechanical design are discussed, including the surface accuracy specifications at different spatial scales, and the micro-positioning actuators, which provide sub-micron focus and sub-arcsecond tip and tilt adjustment of the mirrors. Also discussed is the proposed design validation, including the predicted surface deformations induced in the mirrors when subject to various gravitational and metrology mount conditions.
Keywords: actuator, FUSE, lightweighting, mirror, ultraviolet