28 August 1998 Assembly and test-induced distortions of the FUSE mirrors: lessons learned
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Abstract
The Far UV Spectroscopic Explorer (FUSE), currently undergoing integration and scheduled for a 1998 launch, is an astrophysics satellite designed to provide high spectral resolving power over the interval 905-1187 angstrom. It consists of four normal incidence primary mirrors which illuminate separate Rowland circle spectrograph channels equipped with holographic gratings and delay line microchannel plate detectors. The mirrors are fabricated from Zerodur blanks, which were 70 percent lightweight and then figured to off-axis parabolas with (lambda) /40 RMS surface figure errors. Each mirror is mounted to its own composite sandwich plate, which serves as a bed for heaters and also isolates the mirror from forces and moments induced by the tip/tilt/focus actuators. A flight-like qualification unit is built up in order to verify that the mirror maintains an acceptable optical figure after assembly and environmental testing. Unexpected optical distortions during assembly and environmental testing of the qualification unit resulted in substantial modifications to the assembly procedure, as well as alteration of component and satellite thermal test limits. Known or suspected sources of distortion which warranted investigation included: assembly- induced thermal test limits. Known or suspected sources of distortion which warranted investigation induced: assembly- induced strain, thermal relaxation of the mirror flexure adhesive, changes in the moisture content of the composite plate facesheets, and warpage of the composite plate with initial thermal cycling. This paper describes how these problems were diagnosed and addressed in order to provide mirrors meting the optical performance requirements of the FUSE program.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Raymond G. Ohl, Robert H. Barkhouser, Michael Joseph Kennedy, Scott D. Friedman, "Assembly and test-induced distortions of the FUSE mirrors: lessons learned", Proc. SPIE 3356, Space Telescopes and Instruments V, (28 August 1998); doi: 10.1117/12.324441; https://doi.org/10.1117/12.324441
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