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The Plasma Wave Instrument on the Polar spacecraft is designed to provide measurements of plasma waves in the Earth's polar regions over the frequency range from 0.1 Hz to 800 kHz. Three orthogonal electric dipole antennas are used to detect electric fields, two in the spin plane and one aligned along the spacecraft spin axis. A magnetic loop antenna and a triaxial magnetic search coil antenna are used to detect magnetic fields. Signals from these antennas are processed by five receiver systems: a wideband receiver, a high-frequency waveform receiver, a low-frequency waveform receiver, two multichannel analyzers; and a pair of sweep frequency receivers. Compared to previous plasma wave instruments, the Polar plasma wave instrument has several new capabilities. These include (1) an expanded frequency range to improve coverage of both low- and high-frequency wave phenomena, (2) the ability to simultaneously capture signals from six orthogonal electric and magnetic field sensors, and (3) a digital wideband receiver with up to 8-bit resolution and sample rates as high as 249k samples s(exp -1).

During November and December 1973 the spacecraft Pioneer 10 provided the first in situ observations of energetic particles in the magnetosphere of Jupiter. Observations made with a University of Iowa instrument are reported. It is found that Jupiter's magnetosphere consists of two quite different parts. The outer magnetosphere has the form of a thin, disk-like, quasi-trapping region extending from about 20 to 100 planetary radii. The inner magnetosphere is characterized by a dipolar magnetic field and very high intensities of durably trapped energetic particles. Particle intensities throughout both regions are discussed, taking into account conditions at the orbits of Io, Europa, and Ganymede.

A comprehensive technical description is presented of the Radiation Monitor which is part of the GSFC cosmic X-ray experiment to be flown on the OSO-1 satellite. The theory of operation, fabrication and assembly, and cone angle determination are reported.