Some novel aspects of cometary research

In spite of numerous observations and intense theoretical work already accomplished, many important questions concerning comets remain unsolved. The origin of comets is far from being elucidated. The nature of comets, of their nuclei seems to be reasonably described by the model of Whipple, yet their very structure and constitution remain hypothetical. The complex internal dynamics of active comets awaits a detailed explanation. One of the outstanding problems pertains to the very nature of the residual material remaining after the outgasing of the cometary nucleus. The problem is connected with the presence of organic matter, of their constituents as well as aggregates important to the development of life and to the hypothetical influence of such ingredients on the evolution of its forms already existing on some celestial bodies.It is obvious that irrespective to the recently devised methods and instruments new developments are needed. The paper attempts to show some novel ways of exploration of comets by the use of astronautical means. Recommendations for the realization of such future cometary missions are presented.     

The determination of ice composition with instruments on cometary landers

The determination of the composition of materials that make up comets is essential in trying to understand the origin of these primitive objects. The ices especially could be made in several different astrophysical settings including the solar nebula, protosatellite nebulae of the giant planets, and giant molecular clouds that predate the formation of the solar system. Each of these environments makes different ices with different composition. In order to understand the origin of comets, one needs to determine the composition of each of the ice phases. For example, it is of interest to know that comets contain carbon monoxide, CO, but it is much more important to know how much of it is a pure solid phase, is trapped in clathrate hydrates, or is adsorbed on amorphous water ice. In addition, knowledge of the isotopic composition of the constituents will help determine the process that formed the compounds. Finally, it is important to understand the bulk elemental composition of the nucleus. When these data are compared with solar abundances, they put strong constraints on the macro-scale processes that formed the comet. A differential scanning calorimeter (DSC) and an evolved gas analyzer (EGA) will make the necessary association between molecular constituents and their host phases. This combination of instruments takes a small (tens of mg) sample of the comet and slowly heats it in a sealed oven. As the temperature is raised, the DSC precisely measures the heat required, and delivers the gases to the EGA. Changes in the heat required to raise the temperature at a controlled rate are used to identify phase transitions, e.g., crystallization of amorphous ice or melting of hexagonal ice, and the EGA correlates the gases released with the phase transition. The EGA consists of two mass spectrometers run in tandem. The first mass spectrometer is a magnetic-sector ion-momentum analyzer (MAG), and the second is an electrostatic time-of-flight analyzer (TOF). The TOF acts as a detector for the MAG and serves to resolve ambiguities between fragments of similar mass such as CO and N2. Because most of the compounds of interest for the volatile ices are simple, a gas chromatograph is not needed and thus more integration time is available to determine isotopic ratios. A gamma-ray spectrometer (GRS) will determine the elemental abundances of the bulk cometary material by determining the flux of gamma rays produced from the interaction of the cometary material with cosmic ray produced neutrons. Because the gamma rays can penetrate a distance of several tens of centimeters a large volume of material is analyzed. The measured composition is, therefore, much more likely to be representative of the bulk comet than a very small sample that might have lost some of its volatiles. Making these measurements on a lander offers substantial advantages over trying to address similar objectives from an orbiter. For example, an orbiter instrument can determine the presence and isotopic composition of CO in the cometary coma, but only a lander can determine the phase(s) in which the CO is located and separately determine the isotopic composition of each reservoir of CO. The bulk composition of the nucleus might be constrained from separate orbiter analyses of dust and gas in the coma, but the result will be very model dependent, as the ratio of gas to dust in the comet will vary and will not necessarily be equal to the bulk value.     

Some fluid dynamic problems in the studies of planetary collisions with cometary comas

The flow field in a cometary coma varies from free molecular flow to transition flow and finally to continuum flow. General discussions of these flow regimes with two-phase effects are given. Some numerical results of similarity solution of a strong shock propagation in a two-phase flow are presented.     

Role of sample return and sample science in low cost missions

Sample return is an essential component of solar system exploration. Samples provide a unique data set that is critical for understanding formation and evolution of our solar system. This uniqueness is based on the scale of observations, precision of measurements, the ability to modify experiments as logic and technology dictate, and the ability to use instruments free of the constraints on mass, power, reliability, and data rate of flight instruments. Advances in analytical capabilities in recent years enable fundamental measurements to be made on extremely small samples, greatly reducing mass constraints on robotic sample return spacecraft. Sample studies provide irreplaceable ground truth for remotely-sensed data on planetary surfaces and fit within a variety of architectures for human exploration of the solar system.     

Analysis and pre-development of an imaging spectrometer for in-situ cometary soil analysis on-board the esa rosetta mission

The CIVA-M instrument, a highly integrated infrared/visible microscope for the Rosetta mission (ESA — 2003) is presented. It will enable scientists to study in great detail the composition of the Wirtanen Comet: minerals, organic compounds and ices. A monochromator will illuminate a cometary sample, drilled from the comet sub-surface (≈40cm). An infrared detector will give an image of the sample for each wavelength, from 1 to 4μm with a spectral resolution of 6nm and a spatial resolution of 50 μm. In order to analyze accurately spectra a signal to noise ratio of 50 is needed (for ALBEDO = 0.04). We will use a 128×128 elements photovoltaic mercury cadmium telluride bi-dimensional array working at intermediate temperature (110K to 150K), from the French company SOFRADIR. At such relatively high temperature the critical parameter is the dark current: it limits the exposure time, preventing a high signal to noise ratio. I am in charge of the electronic board, which is the interface between the detector and the on-board processor. Some preliminary results obtained with this board, on a test detector, are then discussed.     

样品容器火工解锁冲击试验研究

某航天器的样品容器在火工解锁过程中,出现了解锁后向前冲击移动的现象。为充分掌握样品容器在轨火工解锁过程中冲击影响情况,开展了解锁冲击分析及试验验证。根据动量守恒定律,推算了样品容器在轨火工解锁的理论冲击移动距离,并开展了3次地面验证试验。计算结果和试验结果均表明,样品容器的冲击移动距离小于12 mm的指标要求,因此不会影响在轨样品转移任务的顺利实施。     

Electric transfer optimization for mars sample return mission

The aim of this paper is to analyse an alternative scenario for Mars Sample Return Orbiter mission, where electric propulsion is used for Earth-Mars and Mars-Earth heliocentric cruises and for Mars orbit insertion / escape transfers, whereas chemical propulsion is used for final Mars rendezvous. The problem consists in minimizing the initial vehicle mass to obtain a specific final dry mass in reasonable time. The planetocentric phases correspond to continuous low-thrust trajectories, spiraling around Mars between a low orbit and the influence sphere altitude. The heliocentric phases consist of a succession of low-thrust and coasting arcs with specific departure and arrival conditions at the Earth. For these two types of transfer, efficient optimal control tools exist based on Pontryagin's maximum principle. Thanks to the coordination between planetocentric and heliocentric phases, the solution obtained with these two separate tools gives a good upper bound of the optimal solution in terms of propellant consumption and duration. This optimization procedure is described and finally applied to the proposed mission. The numerical results are presented and compared with the baseline chemical mission solution. The electric option could allow to decrease the spacecraft departure mass but may lead to rather long mission duration.     

大型振动试验的辅助支撑系统设计

给出了解决大型振动试验中静支撑和稳定性问题的方法及悬挂辅助支撑系统的设计过程和使用范围。     

Mainbelt asteroid reconnaisance and sample return using solar electric propulsion

Reconnaisance of asteroids has thus far been accomplished on a limited scale. The scientific community has expressed interest in conducting long-term reconnaisance of multiple mainbelt asteroids and returning a sample from a mainbelt asteroid, with Ceres and Vesta the targets of greatest interest. This work presents results of preliminary feasibility studies of these missions. Since propellant requirements are prohibitively large with chemical propulsion, solar electric propulsion was assumed here. Multiple opportunities for Ceres/Vesta reconnaisance missions and Vesta sample returns were found which appear to be feasible in the next decade.     

紧固件的抽样检验

从统计抽样的基本概念出发,分析了航天产品常用的紧固件抽样检验的规则并对抽样方案作了详细地介绍。     

MarcoPolo-R: Near-Earth Asteroid sample return mission selected for the assessment study phase of the ESA program cosmic vision

This paper presents the sample return mission to a primitive Near-Earth Asteroid (NEA) MarcoPolo-R proposed to the European Space Agency in December 2010. MarcoPolo-R was selected in February 2011 with three other missions addressing different science objectives for the two-year Assessment Phase of the Medium-Class mission competition of the Cosmic Vision 2 program for launch in 2022. The baseline target of MarcoPolo-R is the binary NEA (175706) 1996 FG3, which offers an efficient operational and technical mission profile. A binary target also provides enhanced science return. The choice of a binary target allows several scientific investigations to occur more easily than through a single object, in particular regarding the fascinating geology and geophysics of asteroids. MarcoPolo-R will rendezvous with a primitive, organic-rich NEA, scientifically characterize it at multiple scales, and return a bulk sample to Earth for laboratory analyses. The MarcoPolo-R sample will provide a representative sample from the surface of a known asteroid with known geologic context, and will contribute to the inventory of primitive material that is probably missing from the meteorite collection. The MarcoPolo-R samples will thus contribute to the exploration of the origin of planetary materials and initial stages of habitable planet formation, to the identification and characterization of the organics and volatiles in a primitive asteroid and to the understanding of the unique geomorphology, dynamics and evolution of a binary asteroid that belongs to the Potentially Hazardous Asteroid (PHA) population.     

月球样品自动封装技术的可行性探讨

月球样品自动封装技术是在月表环境下,实现样品容器自动开合、密封、锁紧的技术。我国的探月工程三期和国外的月球取样任务具有明显的技术区别,所以月球样品的封装也必须符合自身的技术特点。文章通过借鉴国外成功经验和我国探月技术的特点,提出了一种月球样品封装技术方案,并对该封装技术方案的实现进行了分析,同时还考虑了月球环境因素的影响。     

Investigation of phase transition-based tethered systems for small body sample capture

This paper summarizes the modeling, simulation, and testing work related to the development of technology to investigate the potential that shape memory actuation has to provide mechanically simple and affordable solutions for delivering assets to a surface and for sample capture and possible return to Earth. We investigate the structural dynamics and controllability aspects of an adaptive beam carrying an end-effector which, by changing material equilibrium phases, is able to actively decouple the end-effector dynamics from the spacecraft dynamics during the surface contact phase. Asset delivery and sample capture and return are at the heart of several emerging potential missions to small bodies, such as asteroids and comets, and to the surface of large bodies, such as Titan.     

Conceptual study and key technology development for Mars Aeroflyby sample collection

Conceptual study of Mars Aeroflyby Sample Collection (MASC) is conducted as a part of the next Mars exploration mission currently entertained in Japan Aerospace Exploration Agency. In the mission scenario, an atmospheric entry vehicle is flown into the Martian atmosphere, collects the Martian dust particles as well as atmospheric gases during the guided hypersonic flight, exits the Martian atmosphere, and is inserted into a parking orbit from which a return system departs for the earth to deliver the dust and gas samples. In order to accomplish a controlled flight and a successful orbit insertion, aeroassist orbit transfer technologies are introduced into the guidance and control system. System analysis is conducted to assess the feasibility and to make a conceptual design, finding that the MASC system is feasible at the minimum system mass of 600 kg approximately. The aerogel, which is one of the candidates for the dust sample collector, is assessed by arcjet heating tests to examine its behavior when exposed to high-temperature gases, as well as by particle impingement tests to evaluate its dust capturing capability.     

未老化NEPE推进剂/衬层粘接试件拉伸失效模式研究

采用原位拉伸扫描电镜观测不同温度下NEPE推进剂/衬层粘接界面裂纹扩展规律,得出不同温度下裂纹产生位置均出现在推进剂和衬层连接处,且裂纹的扩展存在相互竞争关系;粘接性能较好时,粘接界面的好坏主要取决于推进剂/衬层界面附近推进剂性能。重点考察了会引起推进剂"脱湿"的HMX界面,利用纳米压痕仪及动态力学实验,得出当推进剂中含NPBA时,HMX周围存在一高模量层,且该高模量层的动态储能模量与温度呈反向关系。该高模量层的存在或消失会引起推进剂在宏观性能上发生变化,进而影响推进剂/衬层试件宏观力学性能。     

System design of the Hayabusa 2—Asteroid sample return mission to 1999 JU3

The Japan Aerospace Exploration Agency is currently developing the second asteroid sample return mission, designated as Hayabusa 2. Following the successful return of Hayabusa from the asteroid “Itokawa”, Hayabusa 2 is designed as a round-trip mission to the asteroid “1999 JU3”. The 1999 JU3 is a C-type asteroid, which is believed to contain organic matter and hydrated minerals. Thus, it is expected that successful sample collection will provide additional knowledge on the origin and evolution of the planets and, in particular, the origin of water and organic matter. The current mission scenario will enable the spacecraft to reach 1999 JU3 in the middle of 2018 and perform an asteroid proximity operation for 1.5 years. Three touch downs for sampling and one 2-m-class crater generation by means of a high-speed impact operation are planned during the asteroid proximity operation. The samples are to be brought back to the Earth by a re-entry capsule. The present paper describes the system design of Hayabusa 2, some key technical challenges of the mission, and the development status.     

样品温度对原子氧环境下ITO/Kapton/Al涂层性能变化的影响

文章利用原子氧环境地面模拟设备对航天器用材料ITO/Kapton/Al开展了原子氧环境试验研究。研究中选择的原子氧积分通量为9.1×1019 atoms/cm2,试验真空度为10-2 Pa量级,样品温度分别选取为25℃、70℃、100℃、120℃和150℃,研究样品温度对原子氧环境模拟试验可能造成的影响。试验后利用高精度微量电子天平对样品进行了质量损失测试并计算了材料的反应率,利用TEMP 2000A便携热发射率测试仪和LPSR 300便携光谱太阳吸收率测试仪分别对样品的发射率和太阳吸收比进行了测试。通过试验及分析发现:ITO膜对基底材料的保护较好,材料在试验后质量损失较少,原子氧反应率较低;样品温度的变化对ITO/Kapton/Al材料的质量损失影响较小,但对材料的热物理性质影响较大。