Instrument Investigators Description Some Scientific Objectives

Ultraviolet Imaging Spectrograph

An optical remote-sensing instrument

Principal Investigator: Larry Esposito

Laboratory for Atmospheric and Space Physics, University of Colorado

UVIS is a set of telescopes sensitive to wavelengths from 56 to 190 nm comprising:

Extreme ultraviolet channel: off-axis parabolic mirror section 22 x 30 mm aperture, 100 mm focal length, 3.67° by 0.34° FOV. Mechanism positions one of three entrance slits for different spectral resolutions. Occultation mechanism allows solar flux to enter when the sun is 20° off-axis from telescope. Aberration corrected toroidal grating focuses spectra onto imaging microchannel plate detector.

Far ultraviolet channel: similar, except for grating ruling density, optical coatings, and detector details.

High-speed photometer channel: for stellar ring and atmospheric occultation experiments, measures light from a parabolic mirror, with photomultiplier tube detector.

Hydrogen-deuterium absorption cell channel: measures relative abundance of hydrogen and deuterium from Lyman-Alpha emission, using resonance absorption cells. Channel electron multiplier detector records photons not absorbed in cells.

To map the vertical and horizontal composition of Titan's and Saturn's upper atmospheres, to determine their atmospheric chemistry, map the distribution and properties of aerosols, and infer the nature and characteristics of circulation;

Map the distribution of neutral atoms and ions within Saturn's magnetosphere;

Study the radial structure of Saturn's rings by means of stellar occultations;

Study surface ices and tenuous atmospheres associated with the icy satellites.

All of Cassini's optical remote-sensing instruments, including UVIS, are rigidly mounted on the on the plus-X side of the spacecraft, with their apertures (seen with red aperture covers in the photograph) directed toward minus-Y. Detector electronics are cooled by passive radiation from dedicated radiator plates that face in the plus-X direction into deep, cold space. Pointing the optical instruments at their targets requires rotating the entire spacecraft.

More on UVIS

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