Solar X-ray Monitor (XSM) on-board Chandrayaan-2 orbiter

The remote X-ray fluorescence spectroscopy is a powerful technique to investigate the elemental abundances in the atmosphere-less planetary bodies. The experiment involves measuring spectra of fluorescent X-rays from lunar surface using a low energy X-ray detector onboard an orbiting satellite. Since the flux of fluorescent X-ray lines critically depend on the flux and spectrum of the incident solar X-rays, it is essential to have simultaneous and accurate measurement of X-ray from both Moon and Sun. In the context of Moon, this technique has been employed since early days of space exploration to determine elemental composition of lunar surface. However, so far it has not been possible to exploit it to its full potential due to various reasons. Therefore it is planned to continue the remote X-ray fluorescence spectroscopy experiment on-board Chandrayaan-2 which includes both lunar X-ray observations and solar X-ray observations as two separate payloads. The lunar X-ray observations will be carried out by Chandra Large Area Soft x-ray Spectrometer (CLASS) experiment; whereas the solar X-ray observations will be carried out by a separate payload, Solar X-ray Monitor (XSM). Here we present the overall design of the XSM instrument, the present development status as well as preliminary results of the laboratory model testing. XSM instrument will have two packages namely – XSM sensor package and XSM electronics package. XSM will accurately measure spectrum of Solar X-rays in the energy range of 1–15 keV with energy resolution ∼200 eV @ 5.9 keV. This will be achieved by using state-of-the-art Silicon Drift Detector (SDD), which has a unique capability of maintaining high energy resolution at very high incident count rate expected from Solar X-rays. XSM onboard Chandrayaan-2 will be the first experiment to use such detector for Solar X-ray monitoring.     

Preliminary Scientific Results of Chang'E-1 Lunar Orbiter: Based on Payloads Detection Data in the First Phase

Chang'E-1 lunar Orbiter was launched by Long March 3A rocket from Xichang Satel-lite Launch Center at 18:05BT(Beijing Time) Oct.24,2007.It is the first step of its ambitious three-stage moon program,a new milestone in the Chinese space exploration history.The primary science objectives of Chang'E-1 lunar orbiter are to obtain three-Dimension(3D) stereo images of the lunar surface,to analyze the distribution and abundance of elements on the surface,to investigate the thickness of lunar soil,evaluate helium-3 resources and other characteristics,and to detect the space environment around the moon.To achieve the above four mission objectives,eight sets of scientific instruments are chosen as the payloads of the lunar orbiter,including a CCD stereo camera(CCD),a Sagnac-based interferometer spectrometer(ⅡM),a Laser Altimeter(LAM),a Microwave Radiometer(MRM),a Gamma-Ray Spectrometer(GRS),an X-ray spectrometer(XRS),a High-Energy Particle Detector(HPD),and two Solar Wind Ion Detectors(SWID).The detected data of the payloads show that all payloads work well.This paper introduces the status of payloads in the first phase and preliminary scientific results.     

X-ray fluorescence spectrometrywith the SELENE orbiter

X-ray fluorescence spectrometry of the Moon using a CCD-based instrument “XRS” is planned with the SELENE (Selenological and Engineering Explorer) orbiter, which will be launched in 2003. In the Apollo 15 and 16 missions, elemental mapping of Mg, Al and Si has been performed at the lunar equatorial regions for only 9% of the total surface. Much improved datasets will be obtained by using the XRS to map most of major elements, for 90% coverage of the total surface, and within 20 km spatial resolution. Key scientific objectives are (a) to measure the global average of lunar surface composition for investigation of the overall properties of lunar crust, (b) to map the rock-type distribution to study the formation and evolution of the crust and the maria, and to speculate the origin of the dichotomy, (c) to survey the chemical pattern of lava flows, or bottoms of craters or basins, for surveying the vertical structure and composition of the lunar crust and mantle. We describe the XRS instrument.     

The high precision gamma-ray spectrometer for lunar polar orbiter SELENE

The high precision gamma-ray spectrometer (GRS) is scheduled to be launched on the lunar polar orbiter of the SELENE mission in 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals as an anticoincidence detector. A Stirling cryocooler was adopted in cooling the Ge detector. The flight model of SELENE GRS has been completed and an energy resolution of 3.0 keV (FWHM) at 1.332 MeV has been achieved. The spectrometer aims to observe nuclear line gamma rays emitted from the lunar surface in a wide energy range from 100 keV to 12 MeV for one year and more to obtain chemical composition on the entire lunar surface. The gamma-ray data enable us to study lunar geoscience problems including crust and mantle composition, and volatile reservoirs at polar regions.     

近月空间带电粒子环境——“嫦娥1号”“嫦娥2号”观测结果

“嫦娥1号”（CE-1）、“嫦娥2号”（CE-2）都安装了1台太阳高能粒子探测器（High-energetic ParticlesDetectors,HPD）和2台太阳风离子探测器（Solar Wind Ion Detectors,SWIDs）,进行了月球轨道200 km和100 km空间环境探测,获得了月球轨道空间高能带电粒子（质子、电子和重离子）能谱随时间的演化特征、等离子体与月球相互作用特征以及太阳风离子速度、密度和温度参量。空间环境探测数据分析结果表明：太阳活动低年、空间环境扰动水平相对较低、月球处于太阳风中时,近月空间带电粒子环境的基本特征与行星际空间相比变化不大。CE-1、CE-2在轨运行期间,发现了多起0.1～2 MeV能量电子急剧增加事件,这些事件发生在月球从太阳风运动到磁尾的所有空间区域,其中20%的事件伴随着卫星周围等离子体离子加速。模拟和统计研究表明：能量电子急剧增加使得绕月卫星和月球表面电位大幅下降导致了离子加速现象的发生;能量电子总流量大于10¹¹ cm^-2时,绕月卫星和月球表面充电电位可达负的上千伏。此外,月表溅射与反射太阳风离子、太阳风“拾起”离子等空间环境事件的发现,揭示了太阳风离子和月球存在复杂的相互作用过程。     

嫦娥三号巡视器有效载荷

嫦娥三号巡视器配置了全景相机、测月雷达、红外成像光谱仪、粒子激发X射线谱仪四种科学探测有效载荷. 介绍了有效载荷的科学探测任务、系统设计方案和系统组成,描述了各有效载荷的方案设计要点,设计中的主要关注点及主要技术指标等.      

Space-radiation-induced photon luminescence of the Moon

We report on the results of a continuing study of the photon luminescence of the Moon induced by Galactic Cosmic Rays (GCRs) and space radiation from the Sun, using the Monte Carlo program FLUKA. Understanding the space radiation environment is critical to future exploration of the Moon, and this includes photons. The model of the lunar surface is taken to be the chemical composition of soils found at various landing sites during the Apollo and Luna programs, averaged over all such sites to define a generic regolith for the present analysis. This surface model then becomes the target that is bombarded by Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs) or Solar Particle Events (SPEs) above 1 keV in FLUKA to determine the photon fluence albedo produced by the Moon’s surface when there is no sunlight and Earthshine. The result is to be distinguished from the gamma-ray spectrum produced by the radioactive decay of radiogenic constituents lying in the surface and interior of the Moon. From the photon fluence we derive the spectrum which can be utilized to examine existing lunar spectral data and to aid future orbiting instrumentation in the measurement of various components of the space-radiation-induced photon luminescence present on the Moon.     

Recent advances in observations and modeling of the solar ultraviolet and X-ray spectral irradiance

There have been significant, recent advances in understanding the solar ultraviolet (UV) and X-ray spectral irradiance from several different satellite missions and from new efforts in modeling the variations of the solar spectral irradiance. The recent satellite missions with solar UV and X-ray spectral irradiance observations include the X-ray Sensor (XRS) aboard the series of NOAA GOES spacecraft, the Upper Atmosphere Research Satellite (UARS), the SOHO Solar EUV Monitor (SEM), the Solar XUV Photometers (SXP) on the Student Nitric Oxide Explorer (SNOE), the Solar EUV Experiment (SEE) aboard the Thermosphere, Ionosphere, Mesosphere, Dynamics, and Energetics (TIMED) satellite, and the Solar Radiation and Climate Experiment (SORCE) satellite. The combination of these measurements is providing new results on the variability of the solar ultraviolet irradiance throughout the ultraviolet range shortward of 200 nm and over a wide range of time scales ranging from years to seconds. The solar UV variations of flares are especially important for space weather applications and upper atmosphere research, and the period of intense solar storms in October–November 2003 has provided a wealth of new information about solar flares. The new efforts in modeling these solar UV spectral irradiance variations range from simple empirical models that use solar proxies to more complicated physics-based models that use emission measure techniques. These new models provide better understanding and insight into why the solar UV irradiance varies, and they can be used at times when solar observations are not available for atmospheric studies.     

Detection of X-ray fluorescence line feature from the lunar surface

We present the results of an analysis by ASCA (Japanese X-ray astronomy satellite) observation of the lunar surface on July 10th – 11th, 1993. In spite of the fact that the X-ray surface brightness is estimated to be at nearly CXB (Cosmic X-ray Background) level, the X-ray spectrum shows significant deviations in relation to Al-Kα and Si-Kα fluorescence X-rays. According to the intensity ratios of Al/Si (1–2) and Mg/Si(<0.4), the properties of the X-ray spectrum is consistent with an intermediate abundance ratio between highlands and mares (or relatively similar to highland values). However, the X-ray illuminated region on the lunar surface are mainly covered with mare regions and the emission of AlK and SiK fluorescence arises from both day side and night side region of the moon. These facts indicate the existence of X-ray production due to bremsstrahlung, with high energy particles impacting even on the night side.     

Microwave Brightness Temperature and Lunar Son Dielectric Property Retrieve

Among many scientific objectives of lunar exploration, investigations on lunar soil become more and more attractive to the scientists duo to the existence of abundant 3He and ilmenite in the lunar soil and their possible utilization. Although the soil composition determination on the lunar surface is available by visible light spectrometer, γ/X-ray spectrometer etc, the evaluations on the total reserves of 3He and ilmenite in the lunar deep and on the thickness of the lunar soil are still impossible so far. In this paper, the authors first give a rough analysis of the microwave brightness temperature images of the lunar disc observed using the NRAO 12 Meter Telescope and Siberian Solar Radio Telescope; then introduce our researches on the microwave dielectric properties of lunar soil simulators; finally, discuss some basic relations between the microwave brightness temperature and lunar soil properties.     

Hard X-ray source profiles as determined by RHESSI

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has been recording rotationally-modulated X-rays from solar flares since its launch on February 5, 2002. Its 9 grid pairs time-modulate the detected photon flux giving RHESSI spatial information on hard X-rays at 9 logarithmically-spaced angular scales ranging from 2.3 to 183 arcsec. Using the calibrated modulation profiles for a variety of flares, we present new information on the spatial profiles of the hard X-ray structures in flares. We find that the FWHM of cores of single-component flares range from 3 to 11″ in size. Most of the flares in this set show extended emission out to 2 to 3 times the radii of the cores, and these ‘halos’ contain up to 25% of the total flux.     

Mapping lunar surface chemistry: New prospects with the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS.     

中国月球与深空探测有效载荷技术的成就与展望

有效载荷是实现科学目标最直接的工具,其技术手段和水平影响科学目标的可实现程度。简要回顾了中国月球与深空探测的科学目标与有效载荷配置。介绍了"嫦娥1号"和"嫦娥2号"月球环绕探测器中采用的CCD立体相机、干涉式成像光谱仪、激光高度计、微波探测仪、伽马射线谱仪、X射线谱仪、太阳风粒子探测仪、高能粒子探测仪等遥感探测类有效载荷的技术实现、探测结果和取得的成就。同时,也介绍了"嫦娥3号"月球着陆器和巡视器中采用的地形地貌相机、月基光学望远镜、极紫外相机、红外成像光谱仪、粒子激发X射线谱仪、测月雷达等就位和巡视探测类有效载荷的技术实现、探测结果和取得的成就。分析了有效载荷技术的发展趋势,展望了我国未来有效载荷技术的发展。     

Instrument study of the Lunar Dust eXplorer (LDX) for a lunar lander mission

One of the highest-priority issues for a future human or robotic lunar exploration is the lunar dust. This problem should be studied in depth in order to develop an environment model for a future lunar exploration. A future ESA lunar lander mission requires the measurement of dust transport phenomena above the lunar surface. Here, we describe an instrument design concept to measure slow and fast moving charged lunar dust which is based on the principle of charge induction. LDX has a low mass and measures the speed and trajectory of individual dust particles with sizes below one micrometer. Furthermore, LDX has an impact ionization target to monitor the interplanetary dust background. The sensor consists of three planes of segmented grid electrodes and each electrode is connected to an individual charge sensitive amplifier. Numerical signals were computed using the Coulomb software package. The LDX sensitive area is approximately 400 cm². Our simulations reveal trajectory uncertainties of better than 2° with an absolute position accuracy of better than 2 mm.     

Energetic electrons in solar flares as viewed in X-rays

Hard X-ray observations provide the most direct diagnostic we have of the suprathermal electrons and the hottest thermal plasma present in solar flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is obtaining the most comprehensive observations of individual solar flares ever available in hard X-rays. For the first time, high-resolution spectra are available for a large number of flares that accurately display the spectral shape and its evolution and, in many cases, allow us to identify the transition from the bremsstrahlung X-rays produced by suprathermal electrons to the bremsstrahlung at lower energies emitted by thermal plasma. Also, for the first time, images can be produced in arbitrary energy bands above 3–4 keV, and spectra of distinct imaged components can be obtained.I review what we have learned from RHESSI observations about flare suprathermal electron distributions and their evolution. Next, I present computations of the energy deposited by these suprathermal electrons in individual flares and compare this with the energy contained in the hot thermal plasma. I point out unsolved problems in deducing both suprathermal electron distributions and the energy content of the thermal plasma, and discuss possible solutions. Finally, I present evidence that electron acceleration is associated with magnetic reconnection in the corona.     

嫦娥四号着陆区织女陨坑电场环境数值模拟

由于太阳紫外、X射线和太阳风粒子作用，近月表形成尘埃等离子体环境，而月表陨坑地形使得这种尘埃等离子体环境更为复杂.本文以位于嫦娥四号着陆区的织女陨坑为研究对象，基于高程数据构造了该陨坑的三维模型.根据太阳-月球关系和陨坑地理坐标信息，计算了陨坑白天任意时刻的有效太阳辐照度分布，探讨了不同时刻陨坑内外的光照面积占比，得到陨坑随地方时而发生的遮蔽效应特征.同时，基于月表充电方程计算了织女陨坑在不同地方时条件下的平衡表面电势、德拜鞘高度和电场强度分布，发现陨坑自身遮蔽效应对坑内电场环境影响十分明显.以坑底中心为例，讨论了地方时和纬度对类织女陨坑的平衡表面电势、德拜鞘高度及电场强度的影响，结果表明三者变化特征均以正午时刻及赤道为界呈对称分布，越接近12:00LT或者越接近赤道，坑底中心的平衡表面电势和电场强度越高，德拜鞘高度越低.      

神舟3号飞船上太阳辐射测量

2002年3月至9月间，用3台太阳辐照度绝对辐射计(SIAR)组装的太阳常数监测器在神舟3号飞船轨道舱上测量了太阳辐照度．改进了SIAR辐射计的锥腔结构，把电加热丝埋在薄锥腔壁中间，提高了绝对精度．采用了用宽视场辐射计飞船在轨运动中太阳扫过其视场期间进行测量的方法，测量值与美国EOS上ACRIM Ⅲ测量数据的最大偏差在0．2％以内．     

月球仍然活跃的构造、火成和内部特征等证据

月球尽管被作为类地行星演化的最终形态的代表,被认为在25亿年前已经完全冷却,根据阿波罗时 代以来、特别是近十余年的月球轨道器和着陆器获得的关于月球构造、火成活动、月震和内部结构等多种证据,表明月球从深层内部到表面仍然活跃,尚未彻底冷却“死亡”。这将完全改变人们关于月球演化历史和状态的观念。     

Origin and location of chromospheric evaporation in flares

Observation of two flares obtained with the Solar Maximum Mission spectrometers indicate that at flare onset the emission in soft (3.5 – 8 keV) and hard (16 – 30 keV) X-rays is predominant at the footpoints of the flaring loops. Since, at the same time, blue-shifts are observed in the soft X-ray spectra from the plasma at temperature of 10⁷ K, we infer that material is injected at high velocity into the coronal loops from the footpoints. These areas are also the sites of energy deposition, since their emission in hard X-rays is due to non-thermal electrons penetrating in the denser atmosphere. Hence, chromospheric evaporation occurs where energy is deposited. During the impulsive phase, the configuration of the flare region changes indicating that the flaring loop is progressively filled by hot plasma.     

The Neupert effect and new RHESSI measures of thetotal energy in electrons accelerated in solar flares

It is believed that a large fraction of the total energy released in a solar flare goes initially into acceleratedelectrons. These electrons generate the observed hard X-ray bremsstrahlung as they lose most of their energy by coulomb collisions in the lower corona and chromosphere. Results from the Solar Maximum Mission showed that there may be even more energy in accelerated electrons with energies above 25 keV than in the soft X-ray emitting thermal plasma. If this is the case, it is difficult to understand why the Neupert Effect — the empirical result that for many flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission — is not more clearly observed in many flares. From recent studies, it appears that the fraction of the released energy going into accelerated electrons is lower, on average, for smaller flares than for larger flares. Also, from relative timing differences, about 25% of all flares are inconsistent with the Neupert Effect. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating the Neupert Effec since it covers soft X-rays down to 3 keV (when both attenuators are out of the field of view) and hard X-rays with keV energy resolution, arcsecond-class angular resolution, and sub-second time resolution. When combined with the anticipated observations from the Soft X-ray Imager on the next GOES satellite, these observations will provide us with the ability to track the Neupert Effect in space and time and learn more about the relation between plasma heating and particle acceleration. The early results from RHESSI show that the electron spectrum extends down to as low as 10 keV in many flares, thus increasing the total energy estimates of the accelerated electrons by an order of magnitude or more compared with the SMM values. This combined with the possible effects of filling factors smaller than unity for the soft X-ray plasma suggest that there is significantly more energy in nonthermal electrons than in the soft X-ray emitting plasma in many flares.