Frederick L. Scarf, plasma wave Principal Investigator
Plasma Waves
The plasma wave investigation on Voyager was a late addition to the scientific payload. It was selected to broaden the capability of the mission to study a wide variety of plasma processes. Because of the electrically charged nature of the plasma, it responds to energy inputs in ways that ordinary gas cannot. One of these modes of response yields plasma waves, which are oscillations in density and electric field that generally cover the audio range of frequencies. Measurement of such waves characterizes the density and temperature of the local plasma surrounding the spacecraft, and it also allows remote sensing detection of distant events from the plasma waves they produce.
The plasma wave Principal Investigator is physicist Frederick L. Scarf of the TRW Defense and Space Systems Group of Redondo Beach, California—he is the only Voyager Principal Investigator to come from industry. Scarf has been associated with many particles and fields investigations in the terrestrial magnetosphere, although he is better known as a theorist than as an experimenter. A member of the Space Science Board of the National Academy of Sciences, he is familiar in Washington as an eloquent advocate of space physics—the study of plasma-physical processes in the space environment.
The plasma wave instrument shares with the planetary radio astronomy investigation a pair of 10-meter-long antennas. Whereas the PRA uses these as electric antennas to detect radio radiation, the plasma wave system uses them to detect directly the oscillations in the plasma near the spacecraft. Waves are measured over a broad frequency range, from 10 hertz (a bit deeper than the lowest bass note we can hear) to 56 kilohertz (about three times higher than the highest pitch to which the human ear responds). The instrument electronics have a total mass of only 1.4 kilograms.
Low Energy Charged Particles
Charged particles with energies greater than a few thousand electron volts are not easily measured by a plasma instrument such as that designed by Herb Bridge. Instead, these faster moving particles, with speeds up to a few percent the speed of light, are the subject of a pair of Voyager instruments called collectively the LECP, or low energy charged particle instrument. Like the other particles and fields investigation, the LECP is designed to provide basic data on plasma-physical processes in the Jovian magnetosphere and the solar wind, and on their interactions.
The Principal Investigator for the LECP investigation is Stamatios Mike Krimigis, a Greek-born physicist from Johns Hopkins University. Krimigis has participated in a number of satellite studies of the terrestrial magnetosphere, and he now serves as Head of Space Physics and Instrumentation at the Johns Hopkins Applied Physics Laboratory. He is joined in this investigation by one German and five U.S. Co-Investigators.
The LECP instrument consists of two subsystems. The first, called the low energy magnetospheric particle analyzer, is optimized for measurement of particles within the Jovian magnetosphere, with high sensitivity over a broad dynamic range. Measurements of electrons, protons, and other positive ions can be carried out, determining the energy and composition of individual particles. The total energy ranges covered are 10 kiloelectron volts (keV) to 11 million electron volts (MeV) for electrons and 15 keV to 150 MeV for protons and ions.
