In-Flight Performance and First Observations at Venus and Earth of Magnetospheric Imaging Instrument (MIMI) on Cassini/Huygens

The MIMI investigation comprises three sensors, the Ion and Neutral Camera (INCA), Charge-Energy-Mass-Spectrometer (CHEMS), and Low Energy Magnetospheric Measurement System (LEMMS) covering the energy ranges 7 keV/nuc 3 Mev/nuc (ions/neutrals), 3230 keV/e (ions), and 0.02 18 Mev (ions)/0.015 1 Mev (electrons), respectively. Also LEMMS measures high-energy electrons (E>3 Mev) and protons (1.6 E 160 Mev) from the back end of the dual field-of-view telescope. Following Casini's launch on October 15, 1997, the first scientific data from MIMI was obtained for a 4-hour period on June 24, 1999 during the second flyby of Benus (V2), followed soon thereafter by Earth Swingby (ESB) on August 18, 1999. The spacecraft is now on its way to Saturn for a July 2004 arrival, through a Jupiter gravity assist on December 30, 2000. Preliminary analysis of the V2 and ESB data show that the instruments are performing as expected, although significant fine tuning of in-flight software will be uploaded next year to optimize performance during Jupiter flyby and Saturn orbital operations. Results were obtained from all three sensors at both encounters. For Venus, these include the presence of locally accelerated energetic C+ and O+ ions in the ionosheath (CHEMS), observation of a previously unknown Energetic Neutral Atom (ENA) population upstream (INCA), and shock-accelerated energetic ions (LEMMS, CHEMS). During ESB, distinctive signatures of BS and MP crossings were seen, an assortment of several singly and multiply-charged ions observed, the first images by an ENA camera of the Earth's ring current were obtained, and detection of magnetotail flows at about 6,00 RE was made. A description of the overall MIMI sensors will be presented and highlights of the results will be discussed.