ALBERT

Notes: Abstract This paper contains a brief description of the plasma experiment to be flown on the 1977 Voyager Mission, its principal scientific objectives, and the expected results. The instrument consists of two Faraday cup plasma detectors: one pointed along and one at right angles to the Earth-spacecraft line. The Earth-pointing detector uses a novel geometrical arrangement: it consists of three Faraday cups, each of which views a different direction in velocity space. With this detector, accurate values of plasma parameters (velocity, density, and pressure) can be obtained for plasma conditions expected between 1 and 20 AU. The energy range for protons and for electrons is from 10 to 5950 eV. Two sequential energy per charge scans are employed with nominal values of ΔE/E equal to 29%, and 3.6%. The two scans allow the instrument to cover a broad range between subsonic (M 〈 1) and highly supersonic (M-100) flows; thus, significant measurements can be made in a hot planetary magnetosheath as well as in a cold solar wind. In addition, the use of two energy resolutions during the cruise phase of the mission allows simultaneously the measurement of solar wind properties and a search for interstellar ions. The Earth-pointing detector cluster has an approximately conical field of view with a half angle of 90°. The exceptionally large field of view makes this detector especially suited for use on a three-axis stabilized spacecraft. Both the solar wind direction during the cruise phase of the mission, and the deviated magnetosheath flow directions expected at Jupiter and Saturn fall within the field of view of the main detector; thus, no mechanical or electrical scanning is required. An additional sensor with a field of view perpendicular to that of the main cluster, is included to improve the spatial coverage for the drifting or corotating positive ions expected at planetary encounter. This detector is also used to make measurements of electrons in the energy range 10 to 5950 eV. The scientific goals include studies of (a) the properties and radial evolution of the solar wind, (b) the interaction of the solar wind with Jupiter, (c) the sources, properties and morphology of the Jovian magnetospheric plasma, (d) the interaction of magnetospheric plasma with the Galilean satellites with particular emphasis on plasma properties in the vicinity of Io, (e) the interaction of the solar wind with Saturn and the Saturnian satellites with particular emphasis on Titan, and (f) ions of interstellar origin.