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
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