Operation of the dual magnetometer on Cassini: science performance

As part of the science preparation for the Cassini dual-technique magnetometer experiment, the operational behaviour of the instrument has been considered in terms of the investigation achieving its science aims. The experimental performance falls into two categories: passive, accurate determination of the in situ vector field at Saturn, using nominal mode time series measurements, and event capture, using the data snapshot memory capabilities of the instrument electronics. There are specific science planning aspects during the extended tour of the Saturnian System, for both the magnetospheric coverage in general and for the operational schedule of the instrument. The key science aim of mapping global magnetic structure, for instance, has specific implications for operating the dual mode experiment which differ in each magnetospheric region. The optimal, in situ determination of the intrinsic, planetary magnetic field, in particular, can be achieved through operation of the scalar mode of the Vector Helium magnetometer in addition to the vector measurements taken by the Fluxgate magnetometer. This instrument mode is used in combination with close perigee passes in order to provide high field measurements. During Saturn Orbit Insertion, the start of the Saturnian tour, an extremely low perigee pass is achieved, providing a critical opportunity for measurement. Because the scalar measurement has a restricted field of view, there are also orientation implications for the spacecraft if good science performance is to be realised. A vital opportunity to assess the use of data obtained during scalar operation is provided by the Earth flyby, which can provide high field measurements in a known environment. We relate here the study of these operational issues, based on the expected character of the measured field and in the context of the operating modes of the instrument. (C) 1999 Elsevier Science Ltd. All rights reserved.