PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "Jerry W. Manweiler, Ph.D., May 6, 2005;" RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = CO INSTRUMENT_ID = MIMI OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "Magnetospheric Imaging Instrument" INSTRUMENT_TYPE = "ENERGETIC PARTICLE DETECTOR" INSTRUMENT_DESC = " Abstract: ========= The Cassini Magnetospheric Imaging Instrument (MIMI) consists of three separate sensors: the Charge Energy Mass Spectrometer (CHEMS) sensor, the Low Energy Magnetospheric Measurement (LEMMS) sensor, and the Ion Neutral Camera (INCA) . This combination of sensors provides the capability to perform both global imaging and in situ measurements to study the overall configuration and dynamics of Saturn's magnetosphere and its interactions with the solar wind, Saturn's atmosphere, Titan, the icy satellites and the ring particles. The text of this instrument description has been abstracted from the instrument paper [KRIMIGISETAL2004]: Krimigis, S.M., Magnetosphere Imaging Instrument (MIMI) on the Cassini Mission to Saturn/Titan, in Space Science Reviews, Springer Science and Business Media, B.V., formerly Kluwer Academic Publishers B.V., Vol. 114, No. 1-4, pp. 233-329, December 2004. Scientific Objectives: ====================== The MIMI instrument onboard the Cassini Orbiter has the following primary goals at Saturn: 1. Determine the global configuration and dynamics of hot plasma in the magnetosphere of Saturn through imaging and in situ measurements. 2. Study the sources of plasma and energetic ions through in situ measurements of energetic ion composition, spectra, charge state, and angular distributions. 3. Study magnetospheric substorm-like activity at Saturn. 4. Determine through imaging the formation of clouds of neutral hydrogen, nitrogen, and water products. 5. Investigate the modification of satellite surfaces and atmospheres through plasma and radiation bombardment. 6. Study Titan's cometary interaction with Saturn's magnetosphere via high resolution imaging and in situ measurements. 7. Measure the high energy (E_elec > 1 MeV, E_p > 15 MeV) particle component in the inner (L < 5 Rs) magnetosphere to assess CRAND source characteristics. 8. Study magnetosphere-ionosphere coupling through remote sensing of aurora and in situ measurements of precipitating energetic ions and electrons. Calibration: ============ Calibration processes are accomplished via both flight software and ground processing software. Flight software is used primarily to accommodate variations in measurements due to spacecraft motion. Ground based calibration is accomplished through a combination of calibration data values (see COMIMI_0000) coupled with various algorithms to generate particle flux from measured count rates. Operational Modes: =========================== The INCA detector has the capability to be placed in either ion mode or neutral mode. Ion mode indicates that the potential of the deflection plates is set to zero so that ions are also counted along with neutrals. Neutral mode identifies that there is a potential applied to the plates that will cause the ions to deflect away from the entrance aperture and not be counted. The efficiency of this process is strongly dependent upon the applied plate potential. The applied plate potential is a configurable parameter within the system and is based upon the science goals, dust environment, and the expected plasma and high energy particle distributions. There are no other specific operational modes of the detectors. Operational Considerations: =========================== The MIMI power consumption is nomially ~19.0 W. Typical operations include the capability to sense 6-7 orders of magnitude in particle flux over a dynamic energy range for electrons of 30 KeV to 5 MeV and for ions from 3 KeV to 160 MeV. Data quality is affected by direct sun exposure into the instruments and INCA operations are tailored to reduce the possibility of direct dust particle impacts into the sensor apertureduring ring crossings. Sensors: ========== The MIMI experiment consists of three independent sensors: Charge Energy Mass Spectrometer (CHEMS), Ion Neutral Camera (INCA), and Low Energy Magnetospheric Measurements (LEMMS). Each sensor has specific targeted energies and populations to be examined and collectively provide the ability to fully characterize the energetic charged and neutral particle population in the Saturnian Magnetosphere as well as the Solar Wind, the Jovian Magnetosphere, and the Earth Magnetosphere. Each sensor is a combination of geometric components, silicon detectors, micrpchannel plates, and electronics/software components that give them the ability to fully answer the missions scientific objectives. When the spacecraft is spinning the MIMI sensors obtain measurements over a full four pi steradians. The different MIMI sensors share common electronics and provide complimentary measurements of energetic plasma distributions, composition, and energy spectrum, and the interaction of that plasma with the extended atmosphere and moons of Saturn. The CHEMS sensor is mounted on the particles and fields instrument pallet with a field of view of approximately 160 degrees in latitude (bisected by the spacecraft x-y plane) by 4 degrees in azimuth centered on the spacecraft -x axis. CHEMS measures ions from approximately 3 to 220 KeV/e. The INCA sensor is separately mounted and nearly co-aligned with the remote sensing instruments, with a field of view of 120 degrees in latitude and 90 degrees in azimuth, centered on a vector rotated 9.5 degrees toward the spacecraft +x axis from the -y axis. INCA makes two different types of measurements. It obtains the directional distribution, energy spectra, and crude composition of magnetospheric ions between 7 keV/nuc and 500 keV/nuc and it makes remote images of the global distribution of the energetic neutral emission of hot plasmas in the Saturnian magnetosphere, measuring the composition and energy spectra of those energetic neutrals for each image pixel. The LEMMS sensor is double ended, with oppositely directed 15 degree and 30 degree (full angle) conical fields of view (FOV). LEMMS is mounted on a rotation platform, with the spin axis parallel with the spacecraft y axis, such that when rotating, the LEMMS telescopes sweep through 360 degrees in the spacecraft x-z plane. The LEMMS spin mechanism failed on February 1, 2005. Frames diagram -------------- All MIMI telescope directions are described in terms of the spacecraft fixed frame. LEMMS telescopes rotate around the -y axis (in the x-z plane) with the 15 degree (low energy) telescope at zero degrees when it is pointing in the -z direction and hence the 30 degree telescope (high energy) telescope is pointing along the +z axis. CHEMS latitudinal field of view of 160 degrees is bisected by the spacecraft x-y plane and its azimuthal field of view of 4 degrees is centered on the spacecraft -x axis. INCA is separately mounted and nearly co-aligned with the remote sensing instruments with a latitudinal field of view of 120 degrees and an azimuthal field of view of 90 degrees centered on a vector rotated 9.5 degrees toward the spacecraft +x axis from the -y axis. There are no otherwise specifically defined Cassini MIMI frames. Electronics: ============ Signals from the sensors are first processed by the analog electronics and then by the digital processing unit (DPU). Analog data are placed into the digital system and with respect to CHEMS and LEMMS minimal processing is done. With respect to INCA the data is shifted into appropriate bins based upon the current spacecraft orientation and spin rates. All channel definitions are predefined by the electronics for the LEMMS sensors and the CHEMS sensor has a variable high voltage potential to determine selection of particle based upon energy and to then subsequently place particles into energy, mass, and/or mass/charge bins. The INCA instrument has the ability through the use of high voltage potentials applied to the aperture plates to deflect ions away from the entrance slit and instead image neutral particles. When the high voltage supply is turned off then the instrument see both neutrals and ions. The DPU unit's primary function is to catalog incoming particle measurements based upon underlying logic and to count events in accumulation bins. The DPU also packages the data along with the instrument housekeeping data (instrument states) and then integrated into telemetry for broadcast to ground station. Parameters that control the high voltage supplies, the selection of priority counters etc, are expected to be updated periodically under normal operating conditions. Data compression and sampling techniques are used to maximize data return within the bandwidth allocated to the experiment." END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KRIMIGISETAL2004" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "MANWEILERETAL2005" END_OBJECT = DATA_SET_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KUSTERER&BURKE2003" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END