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Radio and Plasma Wave Science instrument (RPWS) instrument
RPWS Instrument

The Radio and Plasma Wave Science (RPWS) instrument receives and measures the radio signals coming from Saturn, including the radio waves given off by the interaction of the solar wind with Saturn and Titan.

The instrument studies the configuration of Saturn's magnetic field and its relationship to Saturn Kilometric Radiation (SKR), and also monitors and maps Saturn's ionosphere and plasma, and lightning from Saturn's atmosphere.

RPWS is also adept at determining the dust and meteoroid distributions throughout the Saturn system and between the icy satellites, the rings, and Titan.

The instrument measures electrical and magnetic fields in the plasma of the interplanetary medium and Saturn's magnetosphere, as well as electron density and temperature.

Radio and Plasma Wave Science instrument (RPWS) Diagram
RPWS Diagram

Plasma is essentially a soup of free electrons and positively charged ions, the latter being atoms that have lost one or more electrons. Plasma makes up most of the universe and is created by the heating of gases by stars and other bodies in space. Plasma is distributed by the solar wind; it is also "contained" by magnetic fields -- that is, the magnetospheres -- of bodies such as Saturn and Titan.

The major components of the instrument are an electric field sensor, a magnetic search coil assembly and a Langmuir probe. The electric field sensor is made up of three deployable antenna elements mounted on the upper equipment module of the Cassini orbiter. Each element is a collapsible beryllium-copper tube that was rolled up during launch and subsequently unrolled to its approximately 10-meter (33-foot) length by a motor drive. The magnetic search coils are mounted on a small platform attached to a support for Cassini's high-gain antenna. The Langmuir probe, which measures electron density and temperature, is a metallic sphere about 50 millimeters (2 inches) in diameter. The probe is attached to the same platform by an approximately 1-meter (3-foot) deployable boom.

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

At a Glance

Radio and Plasma Wave Science instrument  (RPWS) on the spacecraft.
RPWS on the Cassini Spacecraft

  • Mass (current best estimate) = 6.80 kg
  • Average Operating Power (current best estimate) = 7.00 W
  • Average Data Rate (current best estimate) = 0.90 kilobits/s