Dust Environment Modelling of Comet 67P/Churyumov-Gerasimenko

Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (C–G). Several instruments aboard Rosetta are dedicated to studying various aspects of dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time, impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe the present status of modelling the dust coma of 67P/C–G and predict the speed and flux of dust in the coma, the dust fluence on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C–G is given, because model parameters are derived from this data if possible. For quantities not yet measured for 67P/C–G, we use values obtained for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the in-situ measurements at comet 1P/Halley in 1986. For 67P/C–G, constraining the mass distribution is currently only possible by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production rate of 67P/C–G are those of a fairly typical comet.     

Pickup Ions and Cosmic Rays from Dust in the Heliosphere

The combination of recent observational and theoretical work has completed the catalog of the sources of heliospheric Pickup Ions (PUIs). These PUIs are the seed population for Anomalous Cosmic Rays (ACRs), which are accelerated to high energies at or beyond the Termination Shock (TS). For elements with high First Ionization Potentials (high-FIP atoms: e.g., H, He, Ne, etc.), the dominant source of PUIs and ACRs is from neutral atoms that drift into the heliosphere from the Local Interstellar Medium (LISM) and, prior to ionization, are influenced primarily by solar gravitation and radiation pressure (for H). After ionization, these interstellar ions are pickup up by the solar wind, swept out, and are either accelerated near the TS or beyond it. Elements with low first ionization potentials (low-FIP atoms: e.g., C, Si, Mg, Fe, etc.) are also observed as PUIs by Ulysses and as ACRs by Wind and Voyager. But the low-FIP composition of this additional component reveals a very different origin. Low-FIP interstellar atoms are predominantly ionized in the LISM and therefore excluded from the heliosphere by the solar wind. Remarkably, a low-FIP component of PUIs was hypothesized by Banks (J. Geophys. Res. 76, 4341, 1971) over twenty years prior to its direct detection by Ulysses/SWICS (Geiss et al., J. Geophys. Res. 100(23), 373, 1995) The leading concept for the generation of Inner Source PUIs involves an effective recycling of solar wind on grains near the Sun, as originally suggested by Banks. Voyager and Wind also observe low-FIP ACRs, and a grain-related source appears likely and necessary. Two concepts have been proposed to explain these low-FIP ACRs: the first concept involves the acceleration of the Inner Source of PUIs, and the second involves a so-called Outer Source of PUIs generated from solar wind interaction with the large population of grains in the Kuiper Belt. We review here the observational and theoretical work over the last decade that shows how solar wind and heliospheric grains interact to produce pickup ions, and, in turn, anomalous cosmic rays. The inner and outer sources of pickup ions and anomalous cosmic rays exemplify dusty plasma interactions that are fundamental throughout the cosmos for the production of energetic particles and the formation of stellar systems.     

Effects of lunar and mars dust simulants on HaCaT keratinocytes and CHO-K1 fibroblasts

Exposure to lunar dust during Apollo missions resulted in occasional reports of ocular, respiratory and dermal irritations which showed that lunar dust has a risk potential for human health. This is caused by its high reactivity as well as its small size, leading to a wide distribution also inside habitats. Hence, detailed information regarding effects of extraterrestrial lunar dusts on human health is required to best support future missions to moon, mars or other destinations. In this study, we used several methods to assess the specific effects of extraterrestrial dusts onto mammalian skin by exposing HaCaT keratinocytes and CHO-K1 fibroblasts to dusts simulating lunar or mars soils. These particular cell types were chosen because the skin protects the human body from potentially harmful substances and because a well orchestrated program ensures proper wound healing. Keratinocytes and fibroblasts were exposed to the dusts for different durations of time and their effects on morphology and viability of the cells were determined. Cytotoxicity was measured using the MTT assay and by monitoring culture impedance, while phalloidin staining of the actin cytoskeleton was performed to address structural integrity of the cells which was also investigated by propidium iodide intake. It was found that the effects of the two types of dust simulants on the different features of both cell lines varied to a considerable extent. Moreover, proliferation of HaCaT keratinocytes, as analyzed by Ki67 labeling, was suppressed in sub-confluent cultures exposed to lunar dust simulant. Furthermore, experimental evidence is provided for a delay in regeneration of keratinocyte monolayers from scratch-wounding when exposed to lunar dust simulant. The obtained results will facilitate further investigations of dust exposure during wound healing and will ease risk assessment studies e.g., for lunar lander approaches. The investigations will help to determine safety measures to be taken during extraterrestrial expeditions in order to minimize risks to human health associated with exposure of human skin to dust contaminants.     

Electrostatic particle collection in vacuum

Lunar grains accumulate charges due to solar-based ionizing radiations, and the repelling action of like-charged particles causes the levitation of lunar dust. The lunar dust deposit on sensitive and costly surfaces of investigative equipment is a serious concern in lunar explorations. Inspired by electrostatic precipitators (ESPs), the Electrostatic Lunar Dust Collector (ELDC) was proposed for collecting already charged lunar dust particles to prevent the lunar dust threat. As the conditions for terrestrial counterparts are not valid in the lunar environment, equations developed for terrestrial devices yield incorrect predictions in lunar application. Hence, a mathematical model was developed for the ELDC operating in vacuum to determine its collection efficiency. The ratios of electrical energy over potential energy, kinetic energy over potential energy and the ratio of ELDC dimensions were identified to be the key dimensionless parameters. Sensitivity analyses of the relevant parameters showed that depending on ELDC orientation, smaller particles would be collected more easily at vertical orientation, whereas larger particles were easier to collect in a horizontal ELDC configuration. In the worst case scenario, the electrostatic field needed to be 10 times stronger in the vertical mode in order to adequately collect larger particles. The collection efficiency was very sensitive to surface potential of lunar dust and it reached the maximum when surface potential was between 30 and 120 V.     

基于模糊滑模的月球车驱动控制

研究了运行于自然环境、具有小滑移率及小失配角、六轮独立驱动的摇臂式月球车驱动控制问题。针对以月球车车轮滑移率、方向轮失配角为输人及以月球车车体平动速度、转动速度为输出的动力学方程，利用模糊滑模控制方法设计月球车车轮滑移率，方向轮失配角的控制律．实现月球车的跟踪控制，理论分析及仿真结果表明．基于模糊滑模的月球车动力学系统驱动控制方法是可行的，在实际应用中是有效的。     

水泥立窑除尘技术的现状与趋势

本文首先在论述大型水泥企业除尘技术经验的基础上，介绍了几种新型除尘技术和设备，最后介绍了国内外先进的电除尘技术。     

Response of a pentagonal PZT element as a component of a 4π-real-time detector

The detector characteristics of a pentagonal element were studied by colliding it with hypervelocity micro-particles. A charge-sensitive amplifier was developed for the element of its capacitance ∼10 nF. The output amplitudes were expressed as a linear function of the momentum at collision. Empirical formulas obtained from on-ground experiments could be used for the calibration of the detector. The pentagonal element was potential to measure the momentum during collision from the output amplitude. A set of electrodes on the surface was used to confirm the measurement of the coordinates at collision. A possible application of this pentagonal element on a real-time dust detector was discussed.     

中国月球探测任务轨道确定技术及发展综述

月球探测器的轨道确定是完成月球探测任务的基础,在我国月球探测任务的引领下,在我国深空测控体系发展的同时,轨道确定技术也得到了快速的进步。从时空参考框架和动力学模型两个方面介绍了我国月球探测任务轨道确定技术的发展过程,基于时空参考框架的优化及动力学模型的改进,我国月球探测器的轨道确定能力及精度也不断提升,这对于当前及后续的月球探测任务都有很好的借鉴意义。     

月球粒子辐射环境探测现状

月球表面没有磁场的保护,粒子辐射是人类在月球活动的重要风险要素。概述了月球的辐射环境以及辐射来源,并介绍了月球探测的现状,特别提及了近年来几个较为典型的月球辐射探测实例及其探测结果;介绍了我国“嫦娥4号”上搭载的月表中子与辐射剂量探测仪（Lunar Lander Neutron&Dosimetry,LND）的科学目标及其技术指标。LND的科学目标主要包括：载人登月辐射剂量的测量、月球南极艾特肯盆地水含量的测量、艾特肯盆地FeO含量的测量,以及为日球层科学的研究提供依据。     

月球着陆器着陆过程动力学分析

以哈尔滨工业大学宇航空间机构及控制研究中心研制的四腿桁架式月球着陆器样机为研究对象,通过简化模型,导出了着陆器着陆过程中各个着陆脚和着陆器质心在惯性坐标系中的位置坐标方程,以此位置坐标方程为依据得到了着陆器准静态稳定性条件.通过分析着陆器与月面着陆时瞬态动力学行为,得到了着陆器在此瞬态的各动力学参数的计算公式,以此为依据,并离散时间变量,给出了可以程序化实现整个动态着陆过程动力学模拟的计算过程,为进一步研究着陆过程动力学行为奠定了基础.