Operation of the dual magnetometer on Cassini: science performance

As part of the science preparation for the Cassini dual-technique magnetome ter experiment, the operational behaviour of the instrument has been consid ered in terms of the investigation achieving its science aims. The experime ntal performance falls into two categories: passive, accurate determination of the in situ vector field at Saturn, using nominal mode time series meas urements, and event capture, using the data snapshot memory capabilities of the instrument electronics. There are specific science planning aspects du ring the extended tour of the Saturnian System, for both the magnetospheric coverage in general and for the operational schedule of the instrument. Th e key science aim of mapping global magnetic structure, for instance, has s pecific implications for operating the dual mode experiment which differ in each magnetospheric region. The optimal, in situ determination of the intr insic, planetary magnetic field, in particular, can be achieved through ope ration 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 Sa turnian tour, an extremely low perigee pass is achieved, providing a critic al opportunity for measurement. Because the scalar measurement has a restri cted field of view, there are also orientation implications for the spacecr aft if good science performance is to be realised. A vital opportunity to a ssess the use of data obtained during scalar operation is provided by the E arth flyby, which can provide high field measurements in a known environmen t. We relate here the study of these operational issues, based on the expec ted character of the measured field and in the context of the operating mod es of the instrument. (C) 1999 Elsevier Science Ltd. All rights reserved.