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
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.
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.