太空|TAIKONG 国际空间科学研究所 ISSI-BJ Magazine 北京分部 No. 3 June 2014 FOREWORD

The International Space Science Canada, UK, Germany, Romania, Institute in Beijing (ISSI-BJ) and China. The participants successfully organized a two recognized the very high scientific day forum on “Magnetosphere, value of the mission and raised Ionosphere and Thermosphere constructive comments and (MIT)” in the framework of the suggestions for the project Space Science Strategic Pioneer organization. They concluded Project of the Chinese Academy that the MIT mission has to some of Sciences (CAS), in Beijing on extent complementary objectives IMPRINT October 31 – November 1, 2013. to existing missions. Therefore, The forum discussion covered a the MIT mission is an additional 太空 | TAIKONG broad range of topics: the current excellent example of how the ISSI-BJ Magazine status and overall design of the Chinese Space Science program, MIT mission, scientific objectives, is innovative and challenging, key techniques, potential and complementary to existing international cooperation, and missions. This offers significant future perspectives. It focused opportunities for cooperation on key questions related to the through mission coordination and Address: NO.1 Nanertiao, coupling of the magnetosphere- scientific analysis that places MIT Zhongguancun, Haidian District, ionosphere-thermosphere and and China in a central position Beijing China techniques to develop space- due to its unique objectives Postcode: 100190 borne particle detectors to study and satellite configuration. This Telephone: +86-10-62582811 e.g., the disturbances of the Earth’s TAIKONG magazine provides an Website: www.issibj.ac.cn magnetic field, so called “Magnetic overview of the scientific objectives Storms”. To investigate the and the overall design of the MIT Main Authors coupling of the magnetosphere- project, including spacecraft and ionosphere-thermosphere the MIT instrumentation discussed during Liu Yong, State Laboratory of mission plans a constellation of the forum. Space Weather CAS, China four spacecraft orbiting the Earth at It is a special honour to write the different altitudes, two satellites in Foreword of this published ISSI- Editors the Ionosphere/Thermoshpere and BJ magazine TAIKONG. However, two located in the Magnetosphere. I wish to thank the conveners Ariane Dubost Bonnet This will contribute to a better and organizer of the forum Chi Maurizio Falanga understanding of Space Weather Wang and Yong Liu (National phenomena, and to the formulation Space Science Center, CAS, of predictive models of the near- China), Berndt Klecker (Max Earth space environment. Planck Institute for Extraterrestrial The MIT mission was successfully Physics, Germany), and Andrew incorporated into the background Yau (University of Calgary, study of the Space Science Canada). I also wish to thank Strategic Pioneer Project of the ISSI-BJ staff, Ariane Bonnet, the CAS in 2011, and is now Lijuan En, and Xiaolong Dong, for under scientific and engineering actively und cheerfully supporting background studies. The MIT the organization of the forum. In proposal should be submitted particular I wish to thank Yong to the CAS in 2015 to compete Liu and Berndt Klecker who with in the final selection. MIT is one dedication, enthusiasm, and Front Cover of the candidate missions of the seriousness, conducted the whole Intensive Preparative Study of forum and the editing of this Future Space Science Missions, report. Let me also thank all those which aims at selecting appropriate who participated actively in this new space science missions to be stimulating forum. implemented during the Five-Year Plan period 2016-2020. Prof. Dr. Maurizio Falanga The forum attracted some Beijing 26 scientists from the USA, June 2014

2 太空|TAIKONG free electrons and positive ions, as INTRODUCTION EARTH’S well as the negative ions at lower The Magnetosphere, Ionosphere IONOSPHERE, altitudes. and Thermosphere (MIT) Forum MAGNETOSPHERE was successfully held in Beijing AND SPACE The medium as a whole is on October 31 – November 1, electrically neutral, which means 2013. This forum was organized WEATHER that there are equal numbers of by the International Space positive and negative charges It is well known that life on Earth is Science Institute-Beijing (ISSI-BJ) within a given volume. Generally, protected by the Earth’s magnetic and sponsored by the National the ionosphere changes field from the hazardous energetic Space Science Center (NSSC) significantly with variation of the particles coming from the deep of the Chinese Academy of solar angle. The ionosphere is space. The outer part of the region Sciences (CAS) and by the State separated into layers, designated controlled by the Earth’s magnetic Key Laboratory of Space Weather. D, E, F1 and F2 during daytime. field is called the magnetosphere. More than 20 scientists from USA, While, the D and F1 regions vanish The magnetosphere spreads from Canada, UK, Germany, Romania at night, and the E region becomes 1000 km above the ground to more and China attended the forum much weaker. The dominant ion than 60’000 km high in the polar (see Appendix). is O+ in the F region and the region and toward the sun. In the MIT is one of the candidate lighter ions H+ or He+ become tail direction, the magnetosphere missions of the Intensive dominant at higher altitudes. extends to a distance over 100 Preparative Study of Future Because this ionized gas co-exists times the Earth’s radius. Figure Space Science Missions, which with the neutral atmospheric gas 1 shows a schematic view of the aims at selecting appropriate to which it is coupled, the ionized/ magnetosphere. new space science missions neutral gas system is more to be implemented during properly considered a partially Inside the magnetosphere are the the 13th Five-Year Plan period ionized gas rather than a medium Earth and its atmosphere. Above (2016-2020). The purpose of consisting of two independent the atmosphere, extending from this mission is to investigate the fluids. The percentage of the about 50 and 100 km above the coupling of the magnetosphere, ionization increases with altitude, sea level to ~1000 km, are the ionosphere and thermosphere and reaches 100 % at around ionosphere and thermosphere, (MIT). The discussion covered 1000 km which is the bottom respectively. Some of the neutral a broad range of topics: the of the magnetosphere. The particles of the high atmosphere history, current status and future understanding of the variability are ionized by radiation from the of the MIT mission, the overall of the ions and neutral gas sun, resulting in free electrons design of the project, scientific in this region has practical and electrically charged atoms objectives, key techniques importance for a real operational and molecules. The ionosphere and potential international need for such predictions to contains a significant number of cooperation. It focused on key aid communication, navigation questions related to the coupling of magnetosphere-ionosphere- thermosphere and techniques to develop space-borne particle detectors. This report provides an overview of the scientific objectives and the overall design of the MIT project, including spacecraft and instrumentation.

Fig 1. A schematic view of Earth’s magnetosphere.

太空|TAIKONG 3 Fig 2. A schematic plot of how space weather affects human beings.

and surveillance systems, and for were destroyed by the space protons. The outer radiation belt is satellite trajectories in low-Earth environment and caused millions dominated by energetic electrons orbit. of people out of contact; the and ions and ranges from 3 ~5 eventual loss is enormous in that Re. The Van Allen Probe has been Most of the satellites circle case. A summary of how space implemented by NASA to explore the Earth in the ionosphere or weather affects human beings is the radiation belt. Japan has also magnetosphere region which is far shown in Figure 2. planned the small satellite mission, from a comfortable incubator. On ERG (Energization and Radiation the contrary, Earth’s ionosphere Although most of the energetic in Geospace) to investigate the and magnetosphere are stormy particles coming from the sun or energetic particles in the radiation regions full of hazardous elements interplanetary space are shielded belt [See Figure 3]. such as energetic particles. by the Earth’s magnetic field, some Despite their small size, energetic of them are still able to penetrate The energetic particles circle the particles travel over a thousand km through the polar region into magnetic field line, and bounce every second. If a Ping-Pong ball the magnetosphere, even to back and forth between the travels at that speed, it carries the the lower ionosphere. During Earth’s North Pole and South Pole kinetic energy of a thousand trains times when the magnetosphere [See Figure 4]. The particles travel traveling at 100 km/hour. If a large is heavily disturbed, electrons very fast so that they complete group of energetic particles hit a and ions can also be energized a back-forth trip in minutes. As spacecraft, they may either charge in the magnetosphere, electrons shown in Figure 4, the ions shift the surface of the spacecraft to a up to relativistic energies. The westward and the electron shift high voltage or penetrate deep region where energetic particles eastward, resulting in a current into the digital unit and modify concentrate is called the radiation circling around the Earth. The its logic status. Both the charging belt. Nowadays, we know that the current distributed in a “ring” and unexpected modification of radiation belt is separated into an region around the Earth so it is logic status can cause damage to inner radiation belt and an outer called the “Ring Current”. The the spacecraft or the instrument radiation belt. The inner radiation current generates a magnetic field onboard. Sometimes the damage belt is at an equatorial distance pointing south on the surface of is unrecoverable or even fatal. between 1 and 2 Earth radii (Re), the Earth, which is opposite to In the past, some satellites and composed of high energy the Earth’s magnetic field on the surface of the Earth. Whenever a disturbance happens in the solar wind, the “Ring Current” intensifies and thus increases the magnetic field it generates, resulting in a reduction of the total magnetic field on the Earth’s surface. The disturbance of Earth’s magnetic field are generally termed as “Magnetic Storm”. The magnetic storm is a very important space weather phenomena and the major research objective of the space weather.

Although the root cause of the magnetic storm is the disturbance of the solar wind, the direct cause is the increase (Strengthen) of the Ring Current. If we look closely into the composition of the ring Fig 2. A schematic plot of how space weather affects human beings. current, the protons dominate during the quiet time. During the storm, singly charged oxygen

4 太空|TAIKONG Fig 3. Schematic view of the inner and outer radiation belts

Fig 4. Trajectory of trapped particles in the magnetosphere ions increase and sometime to a in the magnetosphere generally been completely resolved, the dominant ion species if energy is come from either solar wind or upflow of oxygen ions have been taken into account. In this sense, ionosphere. Since the solar wind an interesting question in the the direct cause of the magnetic comes from very hot sun’s surface, community of space physics. storm is the increase of the oxygen most of the oxygen ions lost The oxygen ions put ionosphere ions in the ring current. As a result, most of their electrons, dominant as a good participants in the some space physicist called the oxygen ions are O6+ and O7+. process of magnetic storm, since oxygen ions the “ion source” of the The ionosphere is much colder than the ionosphere was not only magnetic storm. the solar wind, it has abundance disturbed by the storm, but O+ in this region and it is the only also provide the “ion source” Where these oxygen ions come possible source for the O+ions of the storm. The coupling of from and how they transport in the magnetosphere. How the magnetosphere and ionosphere are very interesting questions O+ions transport from the top becomes very strong during the in the space community. Now, ionosphere to the magnetosphere storm time. The oxygen ions in the answer to the first question remains an unanswered question. the magnetosphere also affect is clearly ionosphere. The ions Although the details have not the quiet time magnetosphere.

太空|TAIKONG 5 The periods of sawtooth events, field. The wave ion interaction is which is determined by the quite a complicated process, but THE oscillation mode of quiet time can be analog to surfing in the MAGNETOSPHERE- magnetosphere, correlate with the water. When the particles move IONOSPHERE- percentage of the oxygen ions. together with the wave front, they can obtain energy from the wave. THERMOSPHERE The oxygen ions move up The electrons are much lighter (MIT) MISSION against the gravity, they must than ions so that it is easier for gain enough energy to keep them to fly up along the magnetic SCIENTIFIC OBJECTIVES OF THE moving up to a certain altitude. field and end up with a parallel MIT MISSION The physical processes for them electric field pointing up. The to gain energy actually vary at electric field can acceleration ions The Magnetosphere-Ionosphere- different altitudes as shown in the moving up along the magnetic Thermosphere Coupling Small- Figure 5. At very low altitude, the field. At event higher altitude, the Spacecraft Constellation Mission heating comes from the electrons eccentric force becomes a major is designed to investigate the either from the sunlight ionization acceleration process. The particles physical processes involved in the or the precipitation electrons from circle the magnetic field line like coupling of the MIT system. Its above. These electrons have higher beads on a rode. If the magnetic major scientific objectives are: temperature than other particles in field is disturbed, like the rode 1. Investigate the origin of the ionosphere. At higher altitude, the was shaken, then the particles are outflow ions and their acceleration wave ions interaction and electric accelerated as beads on a shaking mechanisms field parallel to the magnetic rode. 2. Understand the impact of the outflow ions on magnetic storm development 3. Characterize the ionosphere and thermosphere storm caused by magnetic storm 4. Explore key mechanisms for the magnetosphere, ionosphere and thermosphere coupling. We will detail the four points in the following.

1. Investigate the origin of the outflow ions and their acceleration mechanisms

It has been stated that acceleration is needed for ions to flow out of ionosphere into magnetosphere and the different mechanisms boost ions at different altitudes. A lot of questions remain unanswered in the acceleration processes for outflow ions.

At lower altitude, what is the major source of the outflow ions, the cusp region on the day side or the aurora region on the night side? What is the dominant acceleration Fig 5. The acceleration mechanisms of ions at different altitudes. mechanism at all different altitudes? Does the dominant mechanism change with the solar

6 太空|TAIKONG wind condition? Over 6000 km, very good opportunity to further ions immediately increase at the the parallel electric is considered the study of all these questions start of magnetic storm. Current as a good candidate to accelerate and clarify some of the remaining theory cannot explain the sudden upflow ions, but how the electricity disagreements. increase. is formed was a still a question. It Another important question is the has been demonstrated that the origin of the energetic oxygen ions 2. Understand the impact of the formation of parallel electric field in the ring current during storm outflow ions on magnetic storm was related to the waves caused time. We have stated that the development by precipitation electrons. More oxygen ions from the ionosphere details of the physics need to be provide more energy than protons During storm time, the sudden revealed on how the precipitation in the ring current. However, increase of oxygen ratio in ring electron, electromagnetic waves how these oxygen ions transport current is a puzzle, so is the impact and parallel electric field are related. into the ring current remains of increased oxygen ions on ring Over 10000 km, some scientists unknown. The current explanation current. The intense ion upwelling believed that the eccentric force is that the oxygen ions flow to the from the ionosphere into the contribute over 50 % of the energy magnetic tail along the magnetic magnetosphere is so strong that to the ions, but other showed that field and they drift to the ring ionospheric O+ can dominate eccentric force can only provide current region. It takes hours for the high altitude ion pressures. about 10 % of the total energy ionospheric oxygen ions to reach This alters magnetospheric gain. The implementation of the the ring current. Observations dynamics by modifying magnetic MIT mission will provide us with a have shown that ratio of oxygen reconnection both on the dayside

Fig 6. Multi-fluid simulation of magnetosphere with and without oxygen ions on the left and right panels separately. In the upper panels, a plasmoid is released at 2h50m into the simulation. The lower panels show the simulation at 4h45m. The red lines in the panels demonstrate the magnetic field lines. The results shows that magnetosphere with oxygen ions are more unstable than without.

太空|TAIKONG 7 and on the night side. Figure 6 investigated for decades. However, changing the thermospheric shows multi-fluid simulations there are still many unknowns. composition. Because these of the magnetosphere with heavier molecules increase the ion protons only (Left Panel) and both During storm time, a large recombination rate, ion density protons and oxygen (Right Panel). amount of energy was injected decreases in the region of strong When adding a tailward plasma into magnetosphere from heating. Joule heating also can flow at the magnetic tail, the the solar wind, and then from change the pressure gradient and magnetosphere near with protons the magnetosphere into the redirect the neutral winds, which only is stable and the flow has little ionosphere and thermosphere. spread the depleted ionosphere to impact on the near earth space, There are three discrete ways for a larger area in the lower latitudes. say the inner magnetosphere magnetosphere to deposit energy That is the general understanding and the ring current region. On and momentum: precipitation of the negative phase of the the contrary, the magnetosphere aurora electron and protons, ionosphere. However, there with proton and oxygen ions are joule heating and ion drag. The are a lot of questions remain disturbed by the plasma flow and precipitation particle heating, unanswered about the how the magnetic field configuration is which is only from 10 to 20 geomagnetic storm causes significantly modified, especially gigatwatts during quiet time, ionospheric and thermospheric the field in the near Earth space. increases to over 100 gigawatts storm. Uncertainties in estimating The additional oxygen ions control during storm time. However, the Joule heating and lack the processes near the magnetic previous studies showed that of neutral wind data are the tail and make the magnetosphere particle heating contribute only major hurdles for a better more unstable. to a small portion of energy understanding of the ionosphere source. The precipitation electron and thermosphere interaction. 3. Investigate the origin of and protons ionize part of Whether there are other causes the outflow ions and their the atmosphere and increase for the negative phase besides acceleration mechanisms the atmosphere conductivity. the neutral composition change The electric field from the remains unknown. The ionosphere During a geomagnetic storm, the magnetosphere causes ion drift in and thermosphere system is quite near Earth space including the the ionosphere. As the ions move different from the magnetosphere ionosphere and thermosphere can through the thermosphere, they due to the existence of neutral be disturbed. The thermospheric exchange energy with the neutrals particles and collision. The system density increases significantly in the forms of Joule heating is more complicated, and shows and quickly at high altitude; the and neutral wind acceleration very puzzling character during peak electron density in the F2 or deceleration (kinetic energy). storm time. The proposed MIT region of the ionosphere is also Joule heating, which contributes mission can address these issues modified, and it either increases or hundreds of gigawatts to the with an instrument such as UV decreases, depending on the local ionosphere/thermosphere, is due imager, which can record O² and time, season and latitude. to the magnetosphere convection N² composition. Such an imager electric field and increased can provide an instant global view The understanding of ionosphere conductivity. Ion drag can either of the ionospheric density and and thermosphere response to transport energy into or from the help track ionospheric response geomagnetic storm is important neutral particles depending on to geomagnetic storms. This kind not only for scientific interest directions and magnitudes of the of imaging data is invaluable to but also for great practical ion drift and the neutral wind. both scientific research and space value. The low orbit satellites The neutral gases are forced to weather applications. decay more rapidly as a result follow the ions through collisions. of the denser thermosphere. It should be noted here that the 4. Explore key mechanisms for The disturbed ionosphere may ionosphere is very collisional at the magnetosphere, ionosphere, affect satellite communication, lower altitude, contrary to the and thermosphere coupling GPS positioning and even power collionless magnetosphere. transportation facilities on the The auroral current circuit ground. How geomagnetic storm Joule heating can cause upwelling is assumed to include (1) a causes ionospheric storm and and lead to heavier molecules O² magnetospheric generator at high thermospheric storm has been and N² moving to higher altitudes altitude, which provides energy

8 太空|TAIKONG significant when the electric field is small. One specific example is the so called Harang region, near midnight, which plays a key role in the substorm cycle. The plasma convection reversal boundary here is located deep inside the auroral oval and the electric field can remain small over fairly large areas around this boundary.

The major scientific objectives focus on the heating, acceleration and transport processes of ions in the polar regions and on their impact on the ring current and radiation belts. Because of the dynamic nature of these processes that also vary with altitude, it is imperative to cover with MIT altitudes from a few 100 km to several earth radii. This will be accomplished with 4 spacecraft in polar orbits as described below. This constellation of 4 spacecraft will also provide an excellent platform for the exploration of auroral electrodynamics, in particular for the investigation of the auroral acceleration region at altitudes of ~1 Re and for the investigation of the influence of neutral winds on auroral electrodynamics. Systematic studies on the influence of the neutral, thermospheric winds on auroral electrodynamics will be made possible as well.

THE ORBITS OF THE MIT Fig 7. The Orbits of the four spacecraft of the MIT Constellation mission. SPACECRAFT to the system, mainly as Poynting both low altitude satellites and one flux, (2) the auroral acceleration of the high altitude satellites, will The mission plans a constellation regionaround 1 Re altitude, where provide as well ample information composed of four satellites the Poynting energy is converted for systematic studies. MIT will orbiting the Earth at three different into particle energy, mainly of also enable a close examination altitudes as shown in Figure 7. The recipitating electrons, and (3) of the neutral winds’ influence spacecraft on the higher orbit are the ionospheric load, where the on auroral electrodynamics. called MA and MB. They are in a energy is dissipated. MIT will While this influence is in general polar orbit of 2Re×8Re, with the provide a unique opportunity disregarded, since the equivalent orbital phase adjusted such to have to investigate this current electric field of the neutral winds MA and MB at the same time at circuit systematically, by triple is typically small compared to the apogee and perigee, respectively. conjunction event studies. Double auroral electric field, the effect of The low-altitude spacecraft are conjunctions, between one or the neutral winds can become called ITA and ITB with a polar orbit

太空|TAIKONG 9 Table 1 Instrumentation on MIT Magnetosphere Satellite-A (MA) / Magnetosphere Satellite-B (MB)

Table 2 Instrumentation on MIT Ionosphere/Thermosphere Satellite-A (ITA) / Ionosphere/Thermosphere Satellite-B (ITB)

10 太空|TAIKONG of 500 km x 1500 km and a period INSTRUMENTATION ONBOARD energy range covering more than of 1/9 of the MA /MB spacecraft. THE HIGH-ALTITUDE SPACECRAFT 5 orders of magnitude requires If MA, MB and ITA and ITB start MA AND MB two electron sensors and three ion from the North Pole, after half a sensors as summarized below. period of MA, both MA and MB are The two high-altitude spacecraft located at the South Pole. The ITA will provide simultaneous Low-Energy Electron and ITB spacecraft complete 4.5 measurements in the polar Measurements orbits at the same time, providing regions of the Earth at altitudes High time resolution with 3D now measurements over the between 1 and 7 Re. The scientific coverage can be achieved on a South Pole. This configuration with objectives of the MIT mission spinning spacecraft with a spherical 4 spacecraft at 3 different altitudes require the determination of analyzer in top-hat configuration in the polar regions provides ideal the 3D distribution functions of as schematically shown in Figure coverage for the investigation electrons and ions with high time 8. This sensor design was first of transport and acceleration resolution (1 spin) over a large proposed about 20 years ago and processes of ions and electrons energy range, covering energies since then successfully used for during quiet times and during from the ionospheric source at low electron and ion measurements magnetic storms. energies (~eV) up to the energy on many missions (e.g. FAST, of accelerated particles in the ring Cluster). The energy per charge current (~500 keV/e). In order to of the particles is determined by MIT unambiguously determine the sweeping a voltage on the inner source of the particles, it is also hemisphere (positive for electrons, INSTRUMENTATION mandatory to measure the mass negative for ions, see lower panel), per charge composition of the and only particles in a narrow The instrumentation proposed for ions over a wide energy range, energy window that depends MIT has state-of-the art capability to distinguish between ions on the voltage setting, and on to measure the electric and of magnetospheric origin (e.g. the spacing and the radius of the magnetic fields, the cold plasma He+, O+) and solar wind origin spherical analyzer hemispheres, and neutral wind, 3D ion and (e.g. He²+, O⁶+, O⁷+). The large can pass the analyzer and are then electron distribution functions, low-energy neutral particles and UV from the aurora, utilizing identical instruments onboard the two high altitude (MA/MB) and low altitude (ITA/ITB) spacecraft, respectively. The high-altitude spacecraft MA/MB are spin-stabilized with a spin period of 6 seconds. The low-altitude spacecraft are 3-axis stabilized. A summary of all MIT instruments is provided for MA/ MB in Table 1 and for ITA/ITB in Table 2. In the following chapters only the particle instrumentation (indicated by colour background in the Tables) will be discussed in some detail, because this was the main emphasis of the MIT Forum.

Fig 8. Schematic view of the spherical analyzer in Top-Hat configuration for the measurement of 3D velocity distribution functions of electrons on MIT.

太空|TAIKONG 11 M/Q = (E/Q)* / (E/M) (see also Figure 9). The TIMS sensor is now under development at NSSC and a prototype is expected to be ready for tests in May 2014.

Energetic Ion Composition Analyzer (EICA)

The energetic ion composition analyzer will cover the energy range ~50 keV/e to 500 keV/e and provide mass per charge resolution to identify the dominant ions in the ring current (H+, He+, O+). The EICA discriminates the ion composition by measuring the ion flight time in the instrument, which is similar with the work Fig 9. Schematic view of the TIMS and SIA sensors for the measurement of 3D principle of TIMS. The Start signal velocity distribution functions of H+, He+ and O+. is provided via the secondary electrons produced by the ions counted at the exit by suitable large energy range requires two penetrating through the carbon detectors (e.g. channeltrons or separate sensors, the Thermal Ion foil. The Stop signal is provided via microchannelplates (MCP)). The Mass Spectrometer (TIMS) and the the secondary electrons produced top-hat configuration (upper Suprathermal Ion Analyzer (SIA), by the ions hitting on the solid panel) provides an instantaneous covering different energy ranges state detector. The ion energy 360° coverage. Mounting the as shown in Table 1. This operating is measured by the solid state sensor perpendicular to the spin principle was successfully used detector. The design of EICA is axis provides 3D coverage in halve onboard the FAST, Equator-S and similar with the Suprathermal Ion a spin period. The Low Energy the four Cluster spacecraft and is Telescope (SIT) on STEREO ( Figure Electron Analyzer use the top- shown schematically in Figure 8. 10). The development of EICA is hat configuration with detector The energy per charge of the ions is supposed to be an international of microchannel plates and cover measured by sweeping a negative collaboration between NSSC and the energy range from 30 eV to 50 voltage on the inner hemisphere IEAP (Institute of Experiment and keV, with an angular resolution of of the analyzer. At the analyzer Applied Physics) of Christian Albert 22.5°x11.25°. exit the ions are accelerated by a University in Germany. high voltage (~15 kV for MIT) and Thermal and Suprathermal Ion enter the time-of-flight section Composition Measurements via a thin carbon foil (~3.5 mg/ cm2). Ions penetrating the carbon The scientific objectives of the MIT foil generate secondary electrons mission require the determination that provide a Start signal at a of the 3D distribution functions MCP at the exit of the time-of- of ions over the large energy flight section. The Stop signal is range of ~ 1eV/e to ~50 keV/e, provided by the ions that also hit with sufficient mass per charge the MCP. The energy per mass resolution to identify H+, He+, (E/M) of the ions can be derived and O+. The state-of-the-art from the length of the flight path configuration to accomplish and from the flight time t = Stop- this task is the combination of a Start, typically in the range of ~2 hemispherical top-hat analyzer – 20 ns/cm in this energy range. Fig 10. The SIT instrument on board with time-of-flight measurement The mass per charge (M/Q) of the STEREO (image credit: UCB/SSL) and post-acceleration. The ions can then be computed from

12 太空|TAIKONG Fig 11. The cross section of EPD

Energetic Particle Detector (EPD) as well as the in-situ determination signals measured by the four of density, temperature and adjacent collectors. The Langmuir The energetic particle detector velocity of the cold plasma and Probes developed by NSSC for (EPD) will cover the energy range neutral wind at low altitudes. the sounding rockets have been between 50 keV and 4 MeV for Furthermore, the payload includes launched successfully in 2011 ions (predominantly protons) and an energetic particle detector to and 2013. The development of 50 keV to 400 keV for electrons, measure precipitating electrons the prototype of Langmuir Probe, respectively. The sensor design and ions at low altitudes as well as a RPA and IDM for the China Seismo- is based on a solid state detector far UV spectrograph for the remote Electromagnetic Satellite has (SSD) telescope where electrons measurement of aurora generated already been finished. are swept out of the ion telescope by precipitating particles. by a magnet and protons Neutral Atmosphere Analyzer below~400 keV are stopped in the Cold Plasma Analyzer (CPA) (NATA) electron telescope by a thin foil (Figure 11). The design is similar Instrumentation for the The Neutral Atmosphere Analyzer to the SEPT sensor onboard the determination of the parameters consists of 4 sensors for the STEREO spacecraft that has been of the cold plasma in near-Earth measurement of density (1 successfully operated for more orbit have been developed since sensor), composition (1 sensor) than 7 years. The prototype of EPD the early times of spaceflight and velocity of the neutral wind for MIT will be ready for test in May, in the 1960s and are now in a in the direction of the velocity 2014. very advanced state. Electron vector of the spacecraft (1 density and temperature will be sensor), and perpendicular to INSTRUMENTATION ONBOARD measured with Langmuir probes it (1 sensor). The measurement THE LOW-ALTITUDE SPACECRAFT and the ion parameters density, of velocity in the spacecraft ITA AND ITB temperature, and composition direction the sensor design is will be determined with Retarding based on a recent development The main purpose of the low- Potential Analyzers (RPA) and Ion for the US minisatellite C/NOFS altitude spacecraft ITA/ITB is Drift Meters (IDM). The electron (Communication/Navigation the investigation of the physical and ion density and temperature Outage Forecast System), condition and dynamic processes are calculated from the voltage- launched in 2008. The density in the source region of the ions current curves achieved by and composition sensors are that are subsequently observed sweeping voltages applied on the heritage from Tiangong-1, the throughout the magnetosphere. Langmuir Probes and Retarding Chinese manned space station. These observations require the Potential Analyzer, respectively. The velocity parallel to the satellite measurement of electric and The Ion drift velocity is calculated flying is measured from the energy magnetic fields and wave spectra, from the ratio of the current of the neutral wind particles.

太空|TAIKONG 13 The velocity perpendicular to presently implemented for the design and development of the satellite flying is measured four spacecraft of NASA’s MMS some payload. All the scientists from the neutral particles density (Magnetospheric Multiscale) joining the forum agree that it is variation with the position of the mission, expected to be launched an exciting mission for the space sweeping baffle before a density at the end of 2014. Active potential community, implementing it will sensor. The design of velocity control will be important for largely upgrade space physics sensors is similar with WATS on MIT MA/MB and it is planned to study in China. We expect that it DE-2 satellite. The prototype of implement this technique on will be selected during the 13th Neutral Wind Analyzers for MIT will MIT MA/MB in an international five-year plan for launch. be ready for test in May, 2014. cooperation with the team that is presently working on the SPACECRAFT CHARGING EFFECTS implementation for MMS

The conductive surface of a RECOMMENDATIONS FOR spacecraft in sunlight will charge PAYLOAD OPTIMIZATION up due to the combined effects of the plasma environment and (1) In the discussion of the MIT of emitted photoelectrons. The instrumentation the importance of spacecraft charge will depend on active spacecraft potential control the spacecraft configuration and for low-energy measurements on the density and temperature was stressed. It was suggested to of the plasma environment. evaluate in a model calculation, Spacecraft at altitudes of MIT MA/ in cooperation with the team MB are typically positively charged involved in the design of the with spacecraft potential values spacecraft control device, the varying in the range of a few range of potentials expected volts up to 10s volts. This variable for the MIT MA/MB orbit and potential would severely limit the spacecraft configuration and capability to measure the velocity the beam current necessary for distribution of particles at low controlling the potential. energies: because of the repelling (2) It was discussed that in the potential for positive charged low altitude orbit of MIT ITA/ITB particles (ions), energies below precipitating low-energy ions the spacecraft potential would be and electrons are possibly even cut-off. With positive spacecraft more important than electrons potential, negative charged and ions above 50 keV, measured particles (electrons) would with EPD in the model payload. It be accelerated, thus severely was suggested to investigate the distorting electron energy spectra implementation of low-energy at low energies. ion and electron measurements onboard ITA/ITB, possibly using The effect of spacecraft charging models of the TIMS and LEEA can be mitigated by an active instruments that are already in the spacecraft potential control that model payload of MA/MB. uses, for example, the emission of a positively charged ion SUMMARY beam. Dependent on the plasma environment and the beam The MIT mission is proposed by current, the spacecraft potential the State Key Laboratory of Space can be controlled. This technique, Weather to study key questions utilizing an indium beam of ~5 for the understanding of the space keV, has been successfully used weather. Now we are able to finish on several missions (Equator-S, the background model study Cluster, Double Star TC-1) and is which includes the orbit, spacecraft

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Participants

Chi Wang National Space Science Center, China Berndt Klecker Max-Planck-Institute, Germany Wenbin Wang University Corporation for Atmospheric Research, USA Paul Song University of Massachusetts Lowell, USA Malcolm Dunlop Imperial College London, UK Octav Marghitu Institute of Space Science, Romania Robert Rankin University of Alberta, Canada Qiugang Zong Peking University, China Jiuhou Lei University of Science and Technology of China, China Bin Miao University of Science and Technology of China, China Zhenpeng Su University of Science and Technology of China, China Zhigang Yuan Wuhan University, China Quanqi Shi Shandong University, China Qinghe Zhang Shandong University, China Hongqiao Hu Polar Research Institute of China, China Cao Jinbin Beihang University, China Yong Liu National Space Science Center, China Jinrong Cai National Space Science Center, China Jianhua Zheng National Space Science Center, China Jiyao Xu National Space Science Center, China Jianqiang Shi National Space Science Center, China Linggao Kong National Space Science Center, China Binzheng Zhang Dartmouth College, USA Liying Qian University Corporation for Atmospheric Research, USA Qian Wu University Corporation for Atmospheric Research, USA En Lijuan International Space Science Institute - Beijing, China Ariane Bonnet International Space Science Institute - Beijing, China