Development of Faraday cup onboard MS-T5 for solar wind measurements

A Faraday cup which will be installed in Japan's first interplanetary satellite, MS-T5 is now ready to go. The cup which consists of four grids and ion collector was designed to measure ion density, bulk velocity and ion collector was designed to measure ion density, bulk velocity and ion temperature by utilizing spacecraft spinning. The range of these parameters to be measured are few, approximately several ten ions/cc for ion density, 10000 K for ion temperature and 300 Km approximately 700 km/sec for bulk velocity. Among three parameters to be measured, bulk velocity and ion density can be measured within 10% accuracy. Ion temperature can be obtained within the accuracy of approximately 20%. The following were undertaken: (1) To study the basic physics on the ion response to the rapidly changing potential; (2) To get a theoretical description of ion current versus satellite spin angle; (3) To check the theoretical equation by means of laboratory experiment; and (4) To make the software to process data after the satellite MS-T5 is launched.