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PLS - Plasma Subsystem

MISSION OBJECTIVES

• Determine the sources of the magnetosperic plasma.

• Investigate the interaction of the ambient plasma with the Jovian satellites.

• Examine the role of plasma as a source of energetic particles in the radiation zones.

• Determine the nature of the Jovian equatorial current sheet.

• Evaluate the roles played, in the Jovian magnetosphere dynamics, of co-rotational forces, field-aligned currents, and magnetic merging.

SUMMARY

Information from PLS helps determine the temperature of the plasma and the manner in which the particles are distributed in space. This information in turn helps scientists understand particle dynamics in the magnetosphere, for example, where particles are being lost and where particles are being energized.

The PLS uses seven fields of view to collect charged particles for energy and mass analysis. These fields of view cover most angles from 0 to 180 degrees, fanning out from the spin axis. The rotation of the spacecraft carries each field of view through a full circle. The PLS will measure particles in the energy range from 9 volts to 52 kilovolts.

The PLS weighs 13.2 kilograms and uses an average of 10.7 watts of power.

PLS DESCRIPTION

• The PLS consists of a concentric set of four spherical-plate electrostatic analyzers and three miniature magnetic mass spectrometers.

• Each analyzer consists of three 70-Deg. spherical-segment plates, with the inner and outer plates grounded. The center plate is supplied with a programmed series of voltages.

• Continuous-channel electron multipliers (Spiraltrons) are positioned at the aperture exit of the analyzers.

• The PLS is divided into two analyzer systems to prevent single-point failures.
• There is multiple cross-strapping capability built into the PLS.

• The aperture cover tailors the fields of view of the internal sensors via shapers when it is deployed.

DESIGN DETAILS

• The PLS has seven detectors for electrons and seven detectors for ions.

• The PLS measures plasma energies in 64 different passbands from 0.9 eV to 52 KeV with an energy resolution of \106E/E~=0.11.

• Each spectrometer has integral and differential sensors. The average mass resolution of the differential sensors is \106M/M=0.24 and the integral sensors is \106M/M=0.5.

• The differential sensors can identify H+, H2+/He++, He+, O++, O+, Na+, S+, and K+.

• The integral sensors can identify H+, H2+/He++, O++, S+, and SO2+.

• Ion species with the same mass to charge ratio cannot be distinguished.

• The PLS is located on the Science Boom and covers nearly the entire unit sphere.

• The PLS has an internal alarm monitor to detect overheating and alert the spacecraft fault protection to turn off its supplemental heater.

INSTRUMENT PARAMETERS

• Instrument Mass: 13.2 Kg
• Power Consumption:
  • Instrument - 5 to 10.5 W
  • Repl. Heater - 4.0 W
  • Suppl. Heater - 4.8 W (max)
  • Inst. + Suppl. Htr. - 11 W (constant)
• Microprocessor: 1802 type
• ROM/RAM: 4 Kb/4 Kb (two redundant sets)
• Fields of View:
  • Total - 4 Pi str. -1%
  • Analyzer plates - 168 degrees (cone) x 12 degrees (clock)
  • Mass spectrometer - 8 degrees (cone) x 2 degrees (clock)
• Size: 20.3 x 38.1 x 44.7 cm
• Thermal Range:
  • Operating (GLL-210)
    • Electronics: -10 to 35 Deg. C
    • Sensors: -20 to 35 Deg. C
  • Non-operating (GLL3-210)
    • Electronics: -15 to 50 Deg. C
    • Sensors: -25 to 40 Deg. C
• Instrument Modes:
  • Off
  • POR
  • On