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The Cassini Plasma Spectrometer (CAPS) measures the energy and electrical charge of particles such as electrons and protons that the instrument encounters. The instrument is used to study the composition, density, flow, velocity, and temperature of ions and electrons in Saturn's magnetosphere. Shaped much like a teardrop, Saturn's magnetosphere is huge. It spreads out almost a million miles, engulfing the orbits of Titan and most of the ringed planet's icy moons, as well as the famous rings.

The instrument consists of three sensors: an electron spectrometer, an ion beam spectrometer, and an ion mass spectrometer. A motor-driven actuator rotates the sensor package to provide 208-degree scanning in the azimuth of the spacecraft. The electron spectrometer makes measurements of the energy of incoming electrons; its energy range is 0.7 to 30,000 electron volts. The ion beam spectrometer determines the energy to charge ratio of an ion; its energy range is 1 electron volt to 50 kilo-electron volts. The ion mass spectrometer's energy range is 1 electron volt to 50 kilo-electron volts.

For more information, read the engineering technical write-up or visit the science team's Web site:

Cassini Plasma Spectrometer (CAPS)
Cassini Plasma Spectrometer (CAPS) instrument
Cassini Plasma Spectrometer (CAPS) diagram
CAPS on the Cassini Spacecraft

CAPS Instrument

CAPS Diagram

At a Glance

CAPS measures the molecules originating from Saturn's ionosphere and also determines the configuration of Saturn's magnetic field. The instrument also investigates plasma in these areas as well as the solar wind within Saturn's magnetosphere.

  • Mass (current best estimate) = 12.50 kg
  • Average Operating Power (current best estimate) = 14.50 W
  • Average Data Rate (current best estimate) = 8.00 kilobits/s