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
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