Geoscience Reference
In-Depth Information
LOW ENERGY ION OBSERVATION BY MERCURY
MAGNETOSPHERIC ORBITER: MMO
YOSHIFUMI SAITO
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510, Japan
saito@stp.isas.jaxa.jp
DOMINIQUE DELCOURT
CETP-IPSL, 4 avenue de Neptune, 94107, Saint-Maur des Fosses, France
dominique.delcourt@cetp.ipsl.fr
ANDREW COATES
MSSL, University College London, Holmbury
St Mary, Dorking RH5 6NT, UK
ajc@mssl.ucl.ac.uk
According to the previous satellite observation (Mariner10 fly-by), Mercury
has a magnetosphere with its own strong intrinsic magnetic field. In order
to elucidate the detailed plasma structure and dynamics around Mercury, an
orbiter BepiColombo Mercury magnetospheric orbiter (MMO) is planned to be
launched in the timeframe between 2012 and 2013 as a joint mission between
ESA and ISAS/JAXA. For measuring low energy ions, two sensors Mercury
ion analyzer (MIA) and Mercury ion mass spectrum analyzer (MSA) will be
onboard the MMO. MIA measures energy spectrum (5 eV/q-30 keV/q) of ions
around Mercury as well as solar wind ions while MSA measures mass discrim-
inated energy spectrum (5 eV/q-40 keV/q) of ions around Mercury. MIA is
a toroidal top-hat type electrostatic analyzer with dynamic range as wide as
10
6
, while MSA consists of a similar electrostatic analyzer followed by a time-
of-flight section for mass discrimination. In order to realize the wide dynamic
range, electrical sensitivity control and attenuation grid are applied at the same
time. The thermal environment around Mercury is so severe that the thermal
design of the instrument is very important. Each sensor should have its own
thermal shield in order to minimize the thermal input and to maintain the
sensor temperature within an acceptable range.
1. Introduction
Mercury is one of the least explored planets in our solar system. No
spacecraft has visited Mercury since Mariner 10 made three flybys two
in 1974 and one in 1975. Although nearly 30 years have passed since the
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