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UVS - Ultraviolet Spectrometer

MISSION OBJECTIVES

• Study the composition and structure of the upper Jovian atmosphere.

• Determine the loss rates of volatile gases from the Galilean satellites.

• Examine the physical processes occurring in the Io plasma torus.

SUMMARY

Volcanic eruptions on Io are believed to be the source of the Io torus. Temperatures of the sulfur and oxygen ions in this plasma torus can be more than 10 times the temperatures at the surface of the Sun. These ultraviolet observations will help provide a picture of Io's evolution and its relationship with Jupiter's magnetic field.

The Cassegrain telescope of the UVS has a 250-millimeter aperture and collects light from the observation target. Both the UVS and EUV instruments use a ruled grating to disperse this light for spectral analysis. This light then passes through an exit slit into photomultiplier tubes that produce pulses or "sprays" of electrons. These electron pulses are counted, and these count numbers are the data that are sent to Earth.

The UVS is mounted on the scan platform and can be pointed to an object in inertial space. The EUV is mounted on the spun section of the spacecraft. As Galileo spins, the EUV observes a narrow ribbon of space perpendicular to the spin axis.

The two instruments combined weigh about 9.7 kilograms and use 5.9 watts of power.

UVS DESCRIPTION

• The UVS is a Cassegrainian Dall-Kirkham telescope with a 5.03 x 5.28-cm aperture and a 25.0-cm focal length.

• The telescope is the front end to a standard 12.5 cm focal length Ebert-Fastie scanning spectrometer.

• The telescope has a sunshade on the front and the telescope/spectrometer has the control logic box mounted on top.

• Three photo multiplier detectors are situated in the focal plan of the spectrometer.

DESIGN DETAILS

• Three photo multiplier detectors cover the entire ultraviolet and near-visible spectrum between 113 to 432 nm.

• The spectrometer uses a single spherical mirror and a plane diffraction grating.

• The UVS field of view is limited by the spectrometer entrance slit to 1 x 0.1 Deg for two of the detectors (113 to 192 nm and 282 to 432 nm) and by one of the spectrometer exit slits to 0.4 x 0.1 Deg for the other detector (162 to 323 nm).

• The wavelengh resolution of the UVS is 0.7 nm below 190 nm and 1.3 nm above 190 nm.

INSTRUMENT PARAMETERS

• Instrument Mass: 5.2 Kg
• Power Consumption:
  • Instrument - 2.4 W
  • Suppl. Heater - 4.0 W
• Microprocessor: 1802 type
• ROM/RAM: 0 b/0.5 Kb
• Size: 41.7 x 16.3 x 13.5 cm
• Thermal Range:
  • Operating (GLL 3-210)
    • Electronics -10 to 30 Deg. C
  • Non-operating (GLL 3-210)
    • Electronics -20 to 30 Deg. C
• Instrument Modes:
  • Scan
  • Mini-scan
  • Fixed Wavelength
  • Cold start
  • Off
  • POR
  • On