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Proceedings Paper

Performance of the Far Ultraviolet Spectroscopic Explorer mirror assemblies
Author(s): Raymond G. Ohl IV; Robert H. Barkhouser; Steven J. Conard; Scott D. Friedman; Jeffrey Hampton; Henry W. Moos; Paul Nikulla; Cristina M. Oliveira; Timo T. Saha
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Paper Abstract

The Far Ultraviolet Spectroscopic Explorer is a NASA astrophysics satellite which produces high-resolution spectra in the far-ultraviolet (90.5 - 118.7 nm bandpass) using a high effective area and low background detectors. The observatory was launched on its three-year mission from Cape Canaveral Air Station on 24 June 1999. The instrument contains four co- aligned, normal incidence, off-axis parabolic mirrors which illuminate separate Rowland circle spectrograph channels equipped with holographically ruled diffraction gratings and delay line microchannel plate detectors. The telescope mirrors have a 352 X 387 mm aperture and 2245 mm focal length and are attached to actuator assemblies, which provide on-orbit, tip, tilt, and focus control. Two mirrors are coated with silicon carbide (SiC) and two are coated with lithium fluoride over aluminum (Al:LiF). We describe mirror assembly in-flight optical and mechanical performance. On-orbit measurements of the far-ultraviolet point spread function associated with each mirror are compared to expectations based on pre-flight laboratory measurements and modeling using the Optical Surface Analysis Code and surface metrology data. On-orbit imaging data indicate that the mirrors meet their instrument-level requirement of 50% and 95% slit transmission for the high- and mid-resolution spectrograph entrance slits, respectively. The degradation of mirror reflectivity during satellite integration and test is also discussed. The FUV reflectivity of the SiC- and Al:LiF-coated mirrors decreased about 6% and 3%, respectively, between coating and launch. Each mirror is equipped with three actuators, which consist of a stepper motor driving a ball screw via a two-stage planetary gear train. We also discuss the mechanical performance of the mirror assemblies, including actuator performance and thermal effects.

Paper Details

Date Published: 18 December 2000
PDF: 12 pages
Proc. SPIE 4139, Instrumentation for UV/EUV Astronomy and Solar Missions, (18 December 2000); doi: 10.1117/12.410517
Show Author Affiliations
Raymond G. Ohl IV, NASA Goddard Space Flight Ctr (United States)
Robert H. Barkhouser, Johns Hopkins Univ. (United States)
Steven J. Conard, Johns Hopkins Univ. (United States)
Scott D. Friedman, Johns Hopkins Univ. (United States)
Jeffrey Hampton, Swales Aerospace, Inc. (United States)
Henry W. Moos, Johns Hopkins Univ. (United States)
Paul Nikulla, Swales Aerospace, Inc. (United States)
Cristina M. Oliveira, Johns Hopkins Univ. (United States)
Timo T. Saha, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 4139:
Instrumentation for UV/EUV Astronomy and Solar Missions
Silvano Fineschi; Clarence M. Korendyke; Oswald H. W. Siegmund; Bruce E. Woodgate, Editor(s)

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