An artist's concept of NASA's Galileo spacecraft in orbit around Jupiter. Photo: NASA/JPL

The Fields and Particles instruments continue their extended survey of the Jovian magnetosphere this week as the spacecraft moves outward from the heart of the Jupiter system. Two engineering activities are performed during the week. On Tuesday, the spacecraft performs a small turn to keep its radio antenna pointed to Earth. On Wednesday, the spacecraft performs standard maintenance on its propellant lines and thrusters.

The Fields and Particles instruments are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Wave instrument and Plasma Detector. These instruments are mounted on the spinning section of the spacecraft so they can make measurements while sweeping through a 360-degree view of space.

The Dust Detector is built to determine the velocity, mass, charge and flight direction of dust particles in the Jovian system. The Energetic Particle Detector, on the other hand, measures the energy, composition, intensity and angular distribution of ions and electrons. The Heavy Ion Counter is designed to provide data on particle collisions with ionized sulfur and oxygen atoms trapped in the Jovian magnetic field.

The next two instruments are mounted on an 11-meter (36-foot) boom to minimize interference from other electronics on the spacecraft. The Magnetometer senses magnetic fields in the spacecraft's immediate environment, while the Plasma Wave instrument measures electrostatic and electromagnetic components of waves generated by plasma particles. Finally, the Plasma Detector measures the composition, energy, temperature, and three-dimensional distribution and bulk motions of low-energy plasma ions in the spacecraft's immediate vicinity. Plasma is a highly ionized gas, consisting of almost equal numbers of free electrons and positive ions.

The Fields and Particles survey continues for nearly the next three weeks. This will allow Galileo to extend its typical survey of the inner magnetosphere through the outer magnetosphere and into the solar wind beyond the magnetosphere. This activity is part of Galileo's preparation for joint activities with the Cassini spacecraft. In October of this year, joint observations by the two spacecraft will begin in earnest, with Cassini's closest approach to Jupiter occurring in late December.