A spectrograph is an instrument that records spectral intensity
information in one or more wavelengths of energy and then outputs
the data in the form of a graph. (A spectrometer, in contrast,
outputs spectral information as numerical data.) An imaging spectrograph
converts the points on the graph to digital data that can be output
in the form of a visual image, such as a "false color"
picture.
The Ultraviolet Imaging Spectrograph Subsystem (UVIS) is
a set of detectors designed to mearue ultraviolet light reflected
by or emitted from atmospheres, rings, and surfaces to determine
their compositions, distributions, aerosol contents, and temperatures.
The UVIS will measure the fluctuations of starlight and sunlight
as the sun and stars move behind the rings and the atmospheres
of Titan and Saturn, and it will determine the atmospheric concentrations
of hydrogen and deuterium. These data will be used for studies
of the atmospheres, the magnetosphere, and the rings of the Saturnian
system.
The extreme ultraviolet channel (EUV)
will be used for imaging spectroscopy and spectroscopic measurements
of the structure and composition of the atmospheres of Titan
and Saturn. The EUV consists of a telescope with a three-position
slit changer, a baffle system, and a spectrograph with a CODACON
microchannel plate detector and associated electronics. The telescope
consists of an off-axis parabolic section with a focal length
of 100 mm, a 22 mm by 30 mm aperture, and a baffle with a field
of view of 3.67 degrees by 0.34 degrees. A precision mechanism
positions one of the three entrance slits at the focal plane
of the telescope, each translating to a different spectral resolution.
The spectrograph uses an aberration-corrected
toroidal grating that focuses the spectrum onto an imaging microchannel
plate detector to achieve both high sensitivity and spatial resolution
along the entrance slit. The microchannel plate detector electronics
consists of a low-voltage power supply, a programmable high-voltage
power supply, charge-sensitive amplifiers, and associated logic.
The EUV channel also contains a solar occultation
mechanism to allow solar flux to enter the telescope when the
sun is still 20 degrees off-axis from the primary telescope.
The far ultraviolet channel (FUV)
will be used for imaging spectroscopy and spectroscopic measurements
of the structure and composition of the atmospheres of Titan
and Saturn and of the rings. The FUV is similar to the EUV channel
except for the grating ruling density, optical coatings, and
detector details. The FUV electronics are similar to those for
the EUV except for the addition of a high-voltage power supply
for the ion pump.
The high-speed photometer channel (HSP)
will perform stellar occultation measurements of the structure
and density of material in the rings. The HSP resides in its
own module and measures undispersed (zero-order) light from its
own parabolic mirror with a photomultiplier tube detector. The
electronics consists of a pulse-amplifier-discriminator and a
fixed-level high-voltage power supply.
The hydrogen-deuterium absorption cell
channel (HDAC) will be used to measure hydrogen and deuterium
in the Saturn system using a hydrogen cell, an oxygen cell, a
deuterium cell, and a channel electron multiplier (CEM) detector
to record photons not absorbed in the cells. The hydrogen and
deuterium cells are resonance absorption cells filled with pure
molecular hydrogen and deuterium, respectively. They are located
between an objective lens and a detector. Both cells are made
of stainless steel coated with teflon and are sealed at each
end with MgF2 windows. The electronics consists of
a pulse-amplifier-discriminator, a fixed-level high-voltage power
supply, and two filament current controllers.
The UVIS microprocessor electronics
and control subassembly consists of input-output elements,
power conditioning, science data and housekeeping data collection
electronics, and microprocessor control elements.
The Ultraviolet Imaging Spectrograph Subsystem (UVIS) is
a set of detectors designed to mearue ultraviolet light reflected
by or emitted from atmospheres, rings, and surfaces to determine
their compositions, distributions, aerosol contents, and temperatures.
The UVIS will measure the fluctuations of starlight and sunlight
as the sun and stars move behind the rings and the atmospheres
of Titan and Saturn, and it will determine the atmospheric concentrations
of hydrogen and deuterium. These data will be used for studies
of the atmospheres, the magnetosphere, and the rings of the Saturnian
system.
