Magnetometer
The first of the direct sensing instruments to be discussed is the magnetometer, designed to measure the magnetic fields surrounding the spacecraft. Such measurements can be interpreted to yield the intrinsic fields of Jupiter and its satellites and to characterize, in conjunction with data from particle and plasma instruments, the processes taking place in the magnetosphere of the planet. The Principal Investigator for this instrument is Norman F. Ness of the NASA Goddard Space Flight Center. Ness is an intense, competitive scientist with a great deal of previous experience in spacecraft magnetometers, primarily on board Earth satellites. Ness is also the only Voyager Principal Investigator who has previous experience at Jupiter; he was Principal Investigator on one of the two magnetometer instruments flown on Pioneer 11. For the Voyager investigation, Ness is joined by four colleagues from Goddard and one from Germany.
The magnetometer instrument consists of two systems: a high-field magnetometer and a low-field magnetometer. Each system contains two identical three-axis magnetometers that measure the intensity and direction of the magnetic field. The low-field system requires isolation from magnetic fields induced by electric circuits in the spacecraft itself. To achieve this isolation, it is mounted on the largest component of Voyager—a 13-meter boom, about as long as the width of a typical city house lot. This boom was coiled tightly in a canister during launch; later, when the package was opened, it uncurled and extended automatically.
By using two magnetometers, Ness and his colleagues are able to correct for the residual artificial magnetic fields that reach even 13 meters from the main spacecraft. The dynamic range extends from a maximum field of 20 gauss down to 2 × 10⁻⁸ gauss—a factor of one billion. The fields can be measured as frequently as 17 times per second. The total mass, exclusive of the 13-meter boom, is 5.6 kilograms.
Herbert S. Bridge, plasma particle Principal Investigator