Mercury Magnetospheric Orbiter Research Articles

Pre-flight Calibration and Near-Earth Commissioning Results of the Mercury Plasma Particle Experiment (MPPE) Onboard MMO (Mio)

BepiColombo Mio (previously called MMO: Mercury Magnetospheric Orbiter) was successfully launched by Ariane 5 from Kourou, French Guiana on October 20, 2018. The Mercury Plasma/Particle Experiment (MPPE) is a comprehensive instrument package onboard Mio spacecraft used for plasma, high-energy particle and energetic neutral atom measurements. It consists of seven sensors including two Mercury Electron Analyzers (MEA1 and MEA2), Mercury Ion Analyzer (MIA), Mass Spectrum Analyzer (MSA), High Energy Particle instrument for electron (HEP-ele), High Energy Particle instrument for ion (HEP-ion), and Energetic Neutrals Analyzer (ENA). Significant efforts were made pre-flight to calibrate all of the MPPE sensors at the appropriate facilities on the ground. High voltage commissioning of MPPE analyzers was successfully performed between June and August 2019 and in February 2020 following the completion of the low voltage commissioning in November 2018. Although all of the MPPE analyzers are now ready to begin observation, the full service performance has been delayed until Mio’s arrival at Mercury. Most of the fields of view (FOVs) of the MPPE analyzers are blocked by the thermal shield surrounding the Mio spacecraft during the cruising phase. Together with other instruments on Mio including Magnetic Field Investigation (MGF) and Plasma Wave Investigation (PWI) that measure plasma field parameters, MPPE will contribute to the comprehensive understanding of the plasma environment around Mercury when BepiColombo/Mio begins observation after arriving at the planet Mercury in December 2025.

BepiColombo Ground Segment and Mission Operations

The ESA/JAXA BepiColombo mission to Mercury was launched in October 2018. It includes two scientific Mercury orbiters, flying as a single stack during the seven years interplanetary transfer, and as individual spacecraft operated by their respective space Agencies ESA and JAXA once deployed in their respective scientific orbit around Mercury. Three ground segments are closely collaborating on this mission. The European Space Operations Center of the European Space Agency, in Darmstadt, Germany, responsible for mission operations of the composite stack during the interplanetary transfer and of the Mercury Planetary Orbiter (MPO) once at Mercury, the JAXA Sagamihara Space Operation Center (SSOC) in Sagamihara, Japan, responsible for Mercury Magnetospheric Orbiter (MMO) operations throughout the mission, and the European Space Astronomy Center of the European Space Agency, in Villanueva de la Canada, Spain, responsible for MPO scientific archiving and Mercury science operations. The mission benefits from infrastructure and concepts developed on previous interplanetary missions of ESA and JAXA. However, it also includes specific operational challenges, such as electric propulsion, and a complex Mercury Orbit Insertion sequence, exploiting weak stability boundaries, and interleaving three module separations with 15 chemical propulsion manoeuvers to deliver MPO and MMO in their respective science orbits, requiring specific developments and operational approaches. In view of the nominal mission duration of 8.5 years, the mission also requires the adoption of specific measures for knowledge preservation and long-term maintenance.

Mercury Dust Monitor (MDM) Onboard the Mio Orbiter of the BepiColombo Mission

An in-situ cosmic-dust instrument called the Mercury Dust Monitor (MDM) had been developed as a part of the science payload for the Mio (Mercury Magnetospheric Orbiter, MMO) stage of the joint European Space Agency (ESA)–JAXA Mercury-exploration mission. The BepiColombo spacecraft was successfully launched by an Ariane 5 rocket on October 20, 2018, and commissioning tests of the science payload were successfully completed in near-earth orbit before injection into a long journey to Mercury. MDM has a sensor consisting of four plates of piezoelectric lead zirconate titanate (PZT), which converts the mechanical stress (or strain) induced by dust-particle impacts into electrical signals. After the commencement of scientific operations, MDM will measure the impact momentum at which dust particles in orbit around the Sun collide with the sensor and record the arrival direction. This paper provides basic information concerning the MDM instrument and its predicted scientific operation as a future reference for scientific articles concerning the MDM’s observational data.

Measurements of Magnetic Field Fluctuations for Plasma Wave Investigation by the Search Coil Magnetometers (SCM) Onboard Bepicolombo Mio (Mercury Magnetospheric Orbiter)

This paper describes the design and performance of the search coil magnetometers (SCM), which are part of the Plasma Wave Investigation (PWI) instrument onboard the BepiColombo/Mio spacecraft (Mercury Magnetospheric Orbiter), which will measure the electric field, plasma waves and radio waves for the first time in Mercury’s plasma environment. The SCM consists of two low-frequency orthogonal search coil sensors (LF-SC) measuring two components of the magnetic field (0.1 Hz – 20 kHz) in the spacecraft spin plane, and a dual-band search coil sensor (DB-SC) picking up the third component along the spin axis at both low-frequencies (LF: 0.1 Hz – 20 kHz) and high-frequencies (HF: 10 kHz – 640 kHz). The DB-SC and the two LF-SC sensors form a tri-axial configuration at the tip of a 4.6-m coilable mast (MAST-SC) extending from the spacecraft body, to minimize artificial magnetic field contamination emitted by the spacecraft electronics. After the successful launch of the spacecraft on 20 October 2018, an initial function check for the SCM was conducted. The nominal function and performance of the sensors and preamplifiers were confirmed, even with the MAST-SC being retracted and stowed in the spacecraft body, resulting in the detection of large interference signals likely from spacecraft electronics. The MAST-SC is scheduled for deployment after the Mercury orbit insertion of Mio in 2025, allowing the SCM to make the first higher frequency measurements of magnetic fluctuations in the Hermean magnetosphere and exosphere, and the local solar wind. These measurements will contribute to the investigation of fundamental problems in the Hermean plasma environment, including turbulence, magnetic reconnection, wave-particle interactions and particle acceleration.

Magnetometer in-flight offset accuracy for the BepiColombo spacecraft

Abstract. Recently the two-spacecraft mission BepiColombo launched to explore the plasma and magnetic field environment of Mercury. Both spacecraft, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, also referred to as Mio), are equipped with fluxgate magnetometers, which have proven to be well-suited to measure the magnetic field in space with high precision. Nevertheless, accurate magnetic field measurements require proper in-flight calibration. In particular the magnetometer offset, which relates relative fluxgate readings into an absolute value, needs to be determined with high accuracy. Usually, the offsets are evaluated from observations of Alfvénic fluctuations in the pristine solar wind, if those are available. An alternative offset determination method, which is based on the observation of highly compressional fluctuations instead of incompressible Alfvénic fluctuations, is the so-called mirror mode technique. To evaluate the method performance in the Hermean environment, we analyze four years of MESSENGER (MErcury Surface, Space ENvironment, GEophysics and Ranging) magnetometer data, which are calibrated by the Alfvénic fluctuation method, and compare it with the accuracy and error of the offsets determined by the mirror mode method in different plasma environments around Mercury. We show that the mirror mode method yields the same offset estimates and thereby confirms its applicability. Furthermore, we evaluate the spacecraft observation time within different regions necessary to obtain reliable offset estimates. Although the lowest percentage of strong compressional fluctuations are observed in the solar wind, this region is most suitable for an accurate offset determination with the mirror mode method. 132 h of solar wind data are sufficient to determine the offset to within 0.5 nT, while thousands of hours are necessary to reach this accuracy in the magnetosheath or within the magnetosphere. We conclude that in the solar wind the mirror mode method might be a good complementary approach to the Alfvénic fluctuation method to determine the (spin-axis) offset of the Mio magnetometer.

Plasma Wave Investigation (PWI) Aboard BepiColombo Mio on the Trip to the First Measurement of Electric Fields, Electromagnetic Waves, and Radio Waves Around Mercury

The Plasma Wave Investigation (PWI) aboard the BepiColombo Mio (Mercury Magnetospheric Orbiter, MMO) will enable the first observations of electric fields, plasma waves, and radio waves in and around the Hermean magnetosphere and exosphere. The PWI has two sets of receivers (EWO with AM2P, SORBET) connected to two electric field sensors (MEFISTO and WPT) and two magnetic field sensors (SCM: LF-SC and DB-SC). After the launch on October 20, 2018, we began initial operations, confirmed that all receivers were functioning properly, and released the launch locks on the sensors. Those sensors are not deployed during the cruising phase, but the PWI is still capable performing magnetic field observations. After full deployment of all sensors following insertion into Mercury orbit, the PWI will start its measurements of the electric field from DC to 10 MHz using two dipole antennae with a 32-m tip-to-tip length in the spin plane and the magnetic field from 0.3 Hz to 20 kHz using a three-axis sensor and from 2.5 kHz to 640 kHz using a single-axis sensor at the tip of a 4.5-m solid boom extended from the spacecraft’s side panel. Those receivers and sensors will provide (1) in-situ measurements of electron density and temperature that can be used to determine the structure and dynamics of the Hermean plasma environment; (2) in-situ measurements of the electron and ion scale waves that characterize the energetic processes governed by wave–particle interactions and non-MHD interactions; (3) information on radio waves, which can be used to remotely probe solar activity in the heliocentric sector facing Mercury, to study electromagnetic-energy transport to and from Mercury, and to obtain crustal information from reflected electromagnetic waves; and (4) information concerning dust impacts on the spacecraft body detected via potential disturbances. This paper summarizes the characteristics of the overall PWI, including its significance, its objectives, its expected performance specifications, and onboard and ground data processing. This paper also presents the detailed design of the receiver components installed in a unified chassis. The PWI in the cruise phase will observe magnetic-field turbulence during multiple flybys of Earth, Venus, and Mercury. After the Mercury-orbit insertion planned at the end of 2025, we will deploy all sensors and commence full operation while coordinating with all payloads onboard the Mio and MPO spacecraft.

Geodesy and geophysics of Mercury: Prospects in view of the BepiColombo mission

The BepiColombo mission, which is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), was launched successfully on October 20, 2018 from Kourou, French Guyana. The spacecraft is currently on its 7 yr cruise to Mercury. The main science campaign at Mercury will begin, however, no earlier than spring 2026, after two orbiters, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO) have been inserted in their final orbits in late 2025. Mercury is an intriguing planetary object with respect to its dynamical state and evolution. The planet is differentiated and contains a large iron core overlain by a relatively thin silicate mantle and crust. Mercury is locked in a unique 3:2 spin-orbit coupling and its intrinsic magnetic dipole field shows that at least part of Mercury’s iron core is liquid. From libration measurements it has been concluded that Mercury’s outer core is liquid, decoupling the silicate mantle from the deep interior. Phases of global contraction and phases of volcanic activity are evidence for an eventful thermal evolution of the planet. In this paper the current knowledge on the evolution of Mercury, focusing on its dynamical, rotational and orbital state is summarized. Prospects for investigations with BepiColombo will be discussed.

Mission Data Processor Aboard the BepiColombo Mio Spacecraft: Design and Scientific Operation Concept

BepiColombo Mio, also known as the Mercury Magnetospheric Orbiter (MMO), is intended to conduct the first detailed study of the magnetic field and environment of the innermost planet, Mercury, alongside the Mercury Planetary Orbiter (MPO). This orbiter has five payload groups; the MaGnetic Field Investigation (MGF), the Mercury Plasma Particle Experiment (MPPE), the Plasma Wave Investigation (PWI), the Mercury Sodium Atmosphere Spectral Imager (MSASI), and the Mercury Dust Monitor (MDM). These payloads operate through the Mission Data Processor (MDP) that acts as an integrated system for Hermean environmental studies by the in situ observation of charged and energetic neutral particles, magnetic and electric fields, plasma waves, dust, and the remote sensing of radio waves and exospheric emissions. The MDP produces three kinds of coordinated data sets: Survey (L) mode for continuous monitoring, Nominal (M) mode for standard analyses of several hours in length (or more), and Burst (H) mode for analysis based on 4–20-min-interval datasets with the highest cadence. To utilize the limited telemetry bandwidth, nominal- and burst-mode data sets are partially downlinked after selections of data based on L- or L/M-mode data, respectively. Burst-mode data can be taken at preset timings, or by onboard automatic triggering. The MDP functions are implemented and tested on the ground as well as cruising spacecraft; they are responsible for conducting full scientific operations aboard spacecraft.

Development of a simulator of the SIMBIOSYS suite onboard the BepiColombo mission

ABSTRACT BepiColombo is the fifth cornerstone mission of the European Space Agency (ESA) dedicated to study the Mercury planet. The BepiColombo spacecraft comprises two science modules: the Mercury Planetary Orbiter (MPO) realized by ESA and the Mercury Magnetospheric Orbiter provided by the Japan Aerospace Exploration Agency. The MPO is composed by 11 instruments, including the ‘Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System’ (SIMBIOSYS). The SIMBIOSYS suite includes three optical channels: a Stereoscopic Imaging Channel, a High Resolution Imaging Channel, and a Visible and near Infrared Hyperspectral Imager. SIMBIOSYS will characterize the hermean surface in terms of surface morphology, volcanism, global tectonics, and chemical composition. The aim of this work is to describe a tool for the radiometric response prediction of the three SIMBIOSYS channels. Given the spectral properties of the surface, the instrument characteristics, and the geometrical conditions of the observation, the realized SIMBIOSYS simulator is capable of estimating the expected signal and integration times for the entire mission lifetime. In the simulator the spectral radiance entering the instrument optical apertures has been modelled using a Hapke reflectance model implementing the parameters expected for the hermean surface. The instrument performances are simulated by means of calibrated optical and detectors responses. The simulator employs the SPICE (Spacecraft, Planet, Instrument, C-matrix, Environment) toolkit software, which allows us to know for each epoch the exact position of the MPO with respect to the planet surface and the Sun.

Mutual Impedance Probe in Collisionless Unmagnetized Plasmas With Suprathermal Electrons—Application to BepiColombo

Mutual impedance experiments are active electric probes providing in-situ space plasma measurements. Such active experiments consist of a set of electric antennas used as transmitter(s) and receivers(s) through which various dielectric properties of the plasma can be probed, giving therefore access to key plasma parameters such as, for instance, the electron density or the electron temperature. Since the beginning of the space exploration, such active probes have been launched and operated in Earth ionospheric and magnetospheric plasmas. More recently and in the coming years, mutual impedance probes have been and will be operated onboard exploratory planetary missions, such as Rosetta, BepiColombo and JUICE, to probe the cometary plasma of 67P/Churyumov-Gerasimenko, the Hermean and the Jovian magnetospheres, respectively. Some analytic modeling is necessary to calibrate and analyse mutual impedance observations in order to access to macroscopic bulk plasma quantities. In situ particle observations from various space missions have confirmed that space plasmas are out of local thermodynamic equilibrium. This means that particle velocity distributions can be far from a Maxwellian distribution, exhibiting for instance temperature anisotropies, beams or a suprathermal population. The goal of this paper is to characterize the effect of suprathermal electrons on the instrumental response in order to assess the robustness of plasma diagnostics based on mutual impedance measurements in plasmas characterized by a significant amount of suprathermal particles. The instrumental response directly depends on the electron velocity distribution function (evdf). In this work, we choose to model suprathermal electrons by considering different approaches using: (i) a kappa evdf, (ii) a double-Maxwellian evdf or (iii) a mix of a Maxwellian evdf and a kappa evdf. For each case, we compute the spatial distribution of the electrostatic potential induced by the transmitters, discretized and modeled here as an ensemble of pulsating point charges. We apply our modeling by building synthetic mutual impedance spectra of the PWI/AM2P probe, lauched in October 2018 onboard the Mercury Magnetospheric Orbiter (MIO/MMO) spacecraft of the BepiColombo exploratory space mission, in order to calibrate and analyse the future electron observations in the plasma environment of Mercury.

Wire Probe Antenna (WPT) and Electric Field Detector (EFD) of Plasma Wave Experiment (PWE) aboard the Arase satellite: specifications and initial evaluation results

This paper summarizes the specifications and initial evaluation results of Wire Probe Antenna (WPT) and Electric Field Detector (EFD), the key components for the electric field measurement of the Plasma Wave Experiment (PWE) aboard the Arase (ERG) satellite. WPT consists of two pairs of dipole antennas with ~ 31-m tip-to-tip length. Each antenna element has a spherical probe (60 mm diameter) at each end of the wire (15 m length). They are extended orthogonally in the spin plane of the spacecraft, which is roughly perpendicular to the Sun and enables to measure the electric field in the frequency range of DC to 10 MHz. This system is almost identical to the WPT of Plasma Wave Investigation aboard the BepiColombo Mercury Magnetospheric Orbiter, except for the material of the spherical probe (ERG: Al alloy, MMO: Ti alloy). EFD is a part of the EWO (EFD/WFC/OFA) receiver and measures the 2-ch electric field at a sampling rate of 512 Hz (dynamic range: ± 200 mV/m) and the 4-ch spacecraft potential at a sampling rate of 128 Hz (dynamic range: ± 100 V and ± 3 V/m), with the bias control capability of WPT. The electric field waveform provides (1) fundamental information about the plasma dynamics and accelerations and (2) the characteristics of MHD and ion waves in various magnetospheric statuses with the magnetic field measured by MGF and PWE–MSC. The spacecraft potential provides information on thermal electron plasma variations and structure combined with the electron density obtained from the upper hybrid resonance frequency provided by PWE–HFA. EFD has two data modes. The continuous (medium-mode) data are provided as (1) 2-ch waveforms at 64 Hz (in apoapsis mode, L > 4) or 256 Hz (in periapsis mode, L < 4), (2) 1-ch spectrum within 1–232 Hz with 1-s resolution, and (3) 4-ch spacecraft potential at 8 Hz. The burst (high-mode) data are intermittently obtained as (4) 2-ch waveforms at 512 Hz and (5) 4-ch spacecraft potential at 128 Hz and downloaded with the WFC-E/B datasets after the selection. This paper also shows the initial evaluation results in the initial observation phase.

Telecommunication system specific to high temperature environment for JAXA Mercury exploration program

BepiColombo is the joint Mercury exploration program between JAXA (Japan Aerospace Exploration Agency) and ESA (European Space Agency). MMO (Mercury Magnetospheric Orbiter) is JAXA's satellite in this program. She requires a telecommunication system that survives a harsh heat environment surrounding Mercury. She will stay in a polar orbit circulating Mercury for a year for continuous observations of Mercury magnetosphere. MMO has an X-band telecommunication system. We newly developed a high gain antenna for the use of her daily operations and wider field of view antennas for critical events. They are ones directly exposed to a high temperature environment of Mercury. The remains of the telecommunication system such as a transponder and a power amplifier were selected from the heritage of our past deep space missions. These instruments are placed inside MMO where a milder environment is expected than the outside. The total telecommunication system has been designed so that it should work through the MMO mission lifetime from the launch in 2016 to the end of the mission in 2025 including an extra year of extension. The system has experienced thermal environmental tests and proved its excellent resistivity to predicted environments. We will discuss these technologies incorporated in MMO and her telecommunication system design.

The Mercury Electron Analyzers for the Bepi Colombo mission

Bepi Colombo is a joint mission between ESA and JAXA that is scheduled for launch in 2014 and arrival at Mercury in 2020. A comprehensive set of particle sensors will be flown onboard the two probes that form Bepi Colombo. These sensors will allow a detailed investigation of the structure and dynamics of the charged particle environment at Mercury. Onboard the Mercury Magnetospheric Orbiter (MMO) the Mercury Electron Analyzers (MEA) sensors constitute the experiment dedicated to fast electron measurements between 3 and 25,500 eV. They consist of two top-hat electrostatic analyzers for angle-energy analysis followed by microchannel plate multipliers and collecting anodes. A notable and new feature of MEA is that the transmission factor of each analyzer can be varied in-flight electronically by a factor reaching up to 100, thus allowing to largely increasing the dynamical range of the experiment. This capability is of importance at Mercury where large changes of electron fluxes are expected from the solar wind to the various regions of the Mercury magnetosphere. While the first models are being delivered to JAXA, an engineering model has been tested and proven to fulfill the expectations about geometrical factor reduction and energy-angular transmission characteristics. Taking advantage of the spacecraft rotation with a 4 s period, MEA will provide fast three-dimensional distribution functions of magnetospheric electrons, from energies of the solar wind and exospheric populations (a few eVs) up to the plasma sheet energy range (some tens of keV). The use of two sensors viewing perpendicular planes allows reaching a ¼ spin period time resolution, i.e., 1 s, to obtain a full 3D distribution.

Principle and Performance of a Dual-Band Search Coil Magnetometer: A New Instrument to Investigate Fluctuating Magnetic Fields in Space

Search-coil magnetometers are of common use in space physics thanks to their simplicity, robustness and ability to measure weak magnetic fields: their sensitivity can reach a few tens of fT/¿Hz in the range 10-100 kHz. The frequency band is grossly determined by the resonance of the coil. Simply adding a second coil does not efficiently extend the frequency band beyond the first resonance due to the mutual impedance of the two coils. We present a solution, called ¿mutual reducer,¿ which allows us to take full benefit of the second coil and efficiently extends the frequency band. The physical principle is described first, followed by a detailed presentation of this ¿dual-band search-coil¿ (DBSC) that will be part of the plasma wave instrument (PWI) onboard the Mercury magnetospheric orbiter (MMO) of the ESA-JAXA mission BepiColombo dedicated to the exploration of the plasma environment of planet Mercury.

The mass spectrum analyzer (MSA) onboard BEPI COLOMBO MMO: Scientific objectives and prototype results

BEPI COLOMBO is a joint mission between ESA and JAXA that is scheduled for launch in 2014 and arrival at Mercury in 2020. A comprehensive set of ion sensors will be flown onboard the two probes that form BEPI COLOMBO. These ion sensors combined with electron analyzers will allow a detailed investigation of the structure and dynamics of the charged particle environment at Mercury. Among the ion sensors, the Mass Spectrum Analyzer (MSA) is the experiment dedicated to composition analysis onboard the Mercury Magnetospheric Orbiter (MMO). It consists of a top-hat for energy analysis followed by a Time-Of-Flight (TOF) section to derive the ion mass. A notable feature of MSA is that the TOF section is polarized with a linear electric field that provides an enhanced mass resolution, a capability that is of importance at Mercury since a variety of species originating from the planet surface and exosphere is expected. MSA exhibits two detection planes: (i) one with moderate mass resolution but a high count rate making MSA appropriate for plasma analysis, (ii) another with a high (above 40) mass resolution though a low count rate making it appropriate for planetology science. Taking advantage of the spacecraft rotation, MSA will provide three-dimensional distribution functions of magnetospheric ions, from energies characteristic of exospheric populations (a few eVs or a few tens of eVs) up to the plasma sheet energy range (up to ∼40 keV/q) in one spin (4 s).

The Plasma Wave Investigation (PWI) onboard the BepiColombo/MMO: First measurement of electric fields, electromagnetic waves, and radio waves around Mercury

The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft includes the plasma and radio wave observation system called Plasma Wave Investigation (PWI). Since the receivers for electric field, plasma waves, and radio waves are not installed in any of the preceding spacecraft to Mercury, the PWI will provide the first opportunity for conducting in-situ and remote-sensing observations of electric fields, plasma waves, and radio waves in the Hermean magnetosphere and exosphere. These observations are valuable in studying structure, dynamics, and energy exchange processes in the unique magnetosphere of Mercury. They are characterized by the key words of the non-MHD environment and the peculiar interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM 2P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10 MHz for the electric field and from 0.3 Hz to 640 kHz for the magnetic field. From 2008, we will start the development of the engineering model, which is conceptually consistent with the flight model design. The present paper discusses the significance and objectives of plasma/radio wave observations in the Hermean magnetosphere, and describes the PWI sensors, receivers and their performance as well as the onboard data processing.

YThe Mercury sodium atmospheric spectral imager for the MMO spacecraft of Bepi-Colombo

The Mercury Sodium Atmosphere Spectral Imager (MSASI) on the Mercury Magnetospheric Orbiter (MMO) of the JAXA/ESA Bepi-Colombo (BC) Mission will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral region near the sodium D 2 emission (589 nm), a major constituent of the Mercury exosphere. A single high-resolution Fabry–Perot etalon is used in combination with a narrow-band interference filter to achieve a compact and efficient instrument design. The etalon and filter are extremely stable with respect to long-term aging and temperature variations. Full-disk images of the planet are obtained by means of a single-axis scanning mirror in combination with the spin of the MMO spacecraft. This paper presents an overview of the MSASI and the design of the Fabry–Perot interferometer used as its spectral analyser. It is concluded that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments. (2) The thermally stable etalon design is based on concepts, designs and materials that have a good space heritage. (3) The MSASI instrument will achieve a high signal-to-noise ratio (SNR) (>10) in the range of 2 K–10 M Rayleigh.

The fluxgate magnetometer of the BepiColombo Mercury Planetary Orbiter

The magnetometer (MAG) on the Mercury Planetary Orbiter (MPO) of the joint European–Japanese BepiColombo mission to planet Mercury is a low-noise, tri-axial, dual-sensor, digital fluxgate instrument with its sensors mounted on a 2.8-m-long boom. The primary MPO/MAG science objectives are to determine the spatial and temporal structure of the magnetic field in the Hermean system, in particular the structure and origin of the intrinsic magnetic field of Mercury. MPO/MAG has a dynamic measurement range of ± 2000 nT with a resolution of 2 pT during operation along the near-polar orbit of the MPO spacecraft around Mercury. MPO/MAG is designed to provide measurements with rates between 0.5 and 128 vectors/s. In cooperation with its sister magnetometer instrument, MMO/MGF on board the BepiColombo Mercury Magnetospheric Orbiter (MMO), MPO/MAG will be able to distinguish between temporal and spatial magnetic field variations in the magnetically closely coupled Hermean system.

Scientific objectives and instrumentation of Mercury Plasma Particle Experiment (MPPE) onboard MMO

Mercury is one of the least explored planets in our solar system. Until the recent flyby of Mercury by MESSENGER, no spacecraft had visited Mercury since Mariner 10 made three flybys: two in 1974 and one in 1975. In order to elucidate the detailed plasma structure and dynamics around Mercury, an orbiter BepiColombo MMO (Mercury Magnetospheric Orbiter) is planned to be launched in 2013 as a joint mission between ESA and ISAS/JAXA. Mercury Plasma Particle Experiment (MPPE) was proposed in order to investigate the plasma/particle environment around Mercury. MPPE is a comprehensive instrument package for plasma, high-energy particle and energetic neutral atom measurements. It consists of seven sensors: two Mercury electron analyzers (MEA1 and MEA2), Mercury ion analyzer (MIA), Mercury mass spectrum analyzer (MSA), high-energy particle instrument for electron (HEP-ele), high-energy particle instrument for ion (HEP-ion), and energetic neutrals analyzer (ENA). Since comprehensive full three-dimensional simultaneous measurements of low to high-energy ions and electrons around Mercury as well as measurements of energetic neutral atoms will not be realized before BepiColombo/MMO's arrival at Mercury, it is expected that many unresolved problems concerning the Mercury magnetosphere will be elucidated by the MPPE observation.

Magnetic field investigation of Mercury's magnetosphere and the inner heliosphere by MMO/MGF

The Mercury magnetospheric orbiter (MMO) of the Japanese–European BepiColombo mission carries a dual-sensor magnetometer, MMO/MGF. The sensors are of the classical fluxgate type mounted on a boom. For redundancy, each sensor carries its own electronics and is connected to a different data processing unit. MMO/MGF can sample the magnetic field at a rate of up to 128 Hz. The resulting comparatively high time resolution of the magnetic field measurements, i.e., down to 8 ms, will be necessary when studying the dynamics of and processes within the Hermean magnetosphere, since the Mariner 10 observations have shown that their typical time scales are much shorter than in the Earth's magnetosphere, by about a factor of 30. The high time resolution will also be very useful for studying the evolution of the still young solar wind plasma as well as interplanetary shocks at 0.3–0.46 AU. Of course, MMO/MGF is also well-prepared to assist the sister magnetometer aboard the Mercury planetary orbiter, MPO/MAG, in measuring Mercury's intrinsic magnetic field, in particular by helping to distinguish between temporal fluctuations and spatial variations.