KEYWORDS: Sensors, Digital signal processing, Control systems, Camera shutters, Electronics, Sun, Spectral resolution, Microchannel plates, Mirrors, Spectrographs
The SPEAR micro-satellite payload consists of dual imaging spectrographs optimized for detection of the faint, diffuse FUV (900-1750 Å) radiation emitted from interstellar gas. The instrument provides spectral resolution, R~750, and long slit imaging of <10' over a large (8°x5') field of view. We enhance the sensitivity by using shutters and filters for removal of background noise. Each spectrograph channel uses identically figured optics: a parabolic-cylinder entrance mirror and a constant-ruled ellipsoidal grating. Two microchannel plate photon-counting detectors share a single delay-line encoding system. A payload electronics system conditions data and controls the instrument. We will describe the design and predicted performance of the SPEAR instrument system and its elements.
We describe the development of optics for the SPEAR space-mission
to map the far ultraviolet (900-1750 Å) sky. The SPEAR
spectrometers contain unusual reflective optics to optimize
sensitivity to diffuse emission. We describe the manufacture, test
and performance of the collecting mirrors: Pyrex parabolic
cylinders with a 90 degree off-axis angle. We also describe the
development of the diffraction gratings: ellipses of rotation that
are holographically-ruled with constant spacing and blazed with
ion-beam ablation.
Far-ultraviolet IMaging Spectrograph (FIMS) is a far ultraviolet diffuse imaging spectrometer which will be launched in 2002 as the main payload of KAISTSAT-4. We have designed the optics for observing diffuse emission sources by employing an off-axis parabolic cylinder mirror in front of a slit which guides lights to a diffraction grating. The reflective diffraction grating is an ellipse of rotation providing angular resolution. We describe our plan to measure the off-axis parabolic mirror and our initial experiments to establish the measurement technique. To assist manufacture of the off-axis parabolic cylinder, a cylindrical wavefront generated using computer generated hologram (CGH) will be used during the polishing to check errors in surface profile using the Fizeau interferometer.
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