Thermal Properties of Icy Surfaces in the Outer Solar System

The thermal properties of airless icy surfaces are providing a wealth of information on their regolith structure after eons of space weathering. Numerous observations of the thermal cycles of Jupiter and Saturn icy satellites or Centaurs and TNOs have been acquired in the latest decades thanks to the Galileo and Cassini missions and to the Spitzer and Herschel telescopes. These observations and the latest developments on thermophysical modeling which have been achieved to link the thermal inertia to the regolith structure are reviewed here. Measured thermal inertias of these surfaces covered with water ice are very low, roughly between about 1 and 100 J/m²/K/s^1/2. Often interpreted as due to unconsolidated or highly porous regoliths, these low values may result from a composition of amorphous ice or from the roughness of grains defacing contacts in a regolith of normal compaction. Taken together, thermal inertias appear to increase with probed depth and to decrease with heliocentric distance. This latter effect can be easily reproduced if heat transfer is dominated by radiation in pores, despite low temperatures, because the conduction through grains is limited, either due to the presence of amorphous ice or because of the roughness of grains.     

Spectroscopy of Icy Moon Surface Materials

Remote sensing of icy objects in the outer solar system relies upon availability of appropriate laboratory measurements. Surface deposits of specific substances often provide our most direct route to understanding interior composition, thereby informing theories of endogenic surface modification, exogenic surface processing and processes involving exchange of material with the interiors. Visible to near-infrared reflectance spectra of properly prepared compounds are required to enable retrieval of surface abundances through linear and nonlinear mixture analysis applied to spacecraft observations of icy bodies. This chapter describes the techniques, conditions and approaches necessary to provide reference spectra of use to theoretical models of icy satellite surface compositions, and summarizes the current state of knowledge represented in the published literature.     

真空环境中多层隔热材料的隔热性能

通过对一典型多层隔热材料在真空环境下的系列隔热性能实验和分析,分析了多层隔热材料层间温度差(Δt)的分布趋势,揭示了多层隔热材料在不同层间隔热性能的优劣特性及其变化规律。实验结果证明:多层隔热材料的层间温度差(Δt)变化呈U型分布趋势;外层隔热性能优于中间层的隔热性能,4层以内18层以外层间气流状态接近分子流,隔热性能较好,温度差(Δt)大;中间各层气流处于非稳态,隔热性能稍差,温度差(Δt)小;靠近加热板一侧层间温度差小于低温一侧。     

玄武岩纤维/ 氨酚醛树脂防热材料的性能

采用丁异戊橡胶作为主体材料,从补强体系、硫化体系和增塑剂三个方面分析了它们对橡胶高低 温性能、耐老化性能和耐压性能的影响。粒径小、结构度高的炭黑和气相白炭黑并用可有效改善橡胶的力学性 能;硫磺含量在0. 8% ~1. 3%使得硫化橡胶既具备较好的高低温性能又兼顾较好的耐老化性能;增塑剂可有 效调整橡胶硬度和耐压性能。并对研制的丁异戊橡胶弹性材料及其柔性接头构件耐高低温性能及耐压性能进 行分析。结果表明,弹性材料高低温剪切性能及耐压性能表征结果能初步反映柔性接头构件的摆动性能及耐 压性能。     

纳米隔热材料热辐射特性的理论计算

高温下纳米隔热材料内热辐射的影响将显著增强,其热辐射特性对热辐射传热有很大影响。为了认识高温纳米隔热材料的热辐射特性,采用Mie理论建立了掺杂纤维增韧剂和遮光剂的纳米隔热材料热辐射特性理论计算方法,编写了纳米隔热材料热辐射特性计算程序,对某纳米隔热材料的热辐射特性进行了理论研究,得到了光谱衰减系数、光谱散射反照率以及全光谱平均辐射特性参数及散射相函数。理论模拟结果表明:在3～9.5μm波长范围内,纳米隔热材料对热辐射具有强烈的衰减作用,对3～7μm的热辐射呈现强烈的散射特征,对7～9.5μm的热辐射,随波长增大散射特征逐渐减弱,对9.5μm的热辐射呈现较强的吸收特征。在300～1 300 K,该纳米隔热材料全光谱平均衰减系数>5×104 m-1,平均散射反照率>0.96,具有较强的前向散射特征,这些特征来源于遮光剂粒子,增韧剂影响很小。     

热防护材料表面催化特性研究进展

随着高超声速飞行器的发展,高焓离解环境下热防护材料所承受的气动热载荷在很大程度上受到材料表面催化特性的影响。根据高焓服役环境特征和热防护材料表面催化特性的发展现状,重点综述了材料表面催化反应机理和不同尺度的催化模型,分析、比较了催化特性地面测试与评价方法以及典型热防护材料表面催化特性的影响因素,简要总结了国内现阶段相关催化特性研究的初步成果,并在此基础之上提出了催化特性测试与表征方法的不足和后续研究的重点方向,为有效改进热防护材料表面催化特性试验测试技术、准确预测高超声速飞行器气动热环境,从而实现热防护系统的精细化设计提供指导。     

Characteristics of Icy Surfaces

The surfaces of the Solar System’s icy satellites show an extraordinary variety of morphological features, which bear witness to exchange processes between the surface and subsurface. In this paper we review the characteristics of surface features on the moons of Jupiter, Saturn, Uranus and Neptune. Using data from spacecraft missions, we discuss the detailed morphology, size, and topography of cryovolcanic, tectonic, aeolian, fluvial, and impact features of both large moons and smaller satellites.     

SiO_2气凝胶材料的制备、性能及其低温保温隔热应用

由于SiO2气凝胶独特的纳米多孔结构,使其具有诸多其他材料所不能比拟的优异性能,比如极高的孔隙率和比表面积、极低的热导率及密度等特性。这些优异的性能使得SiO2气凝胶在高效保温隔热、隔声等领域具有极大的应用潜力。本文阐述了SiO2气凝胶的溶胶-凝胶制备过程及其机理,分别对SiO2气凝胶的热学、力学、光学和疏水性能的研究进展进行了概述,同时分析了气凝胶的微观结构与上述性能之间的关系,并介绍了SiO2气凝胶在低温保温隔热领域的应用现状和前景。     

Evolution of Icy Satellites

Evolutionary scenarios for the major satellites of Jupiter, Saturn, Neptune, and Pluto-Charon are discussed. In the Jovian system the challenge is to understand how the present Laplace resonance of Io, Europa, and Ganymede was established and to determine whether the heat being radiated by Io is in balance with the present tidal dissipation in the moon. In the Saturnian system, Enceladus and Titan are the centers of attention. Tidal heating is the likely source of activity at the south pole of Enceladus, although the details of how the heating occurs are not understood. An evolutionary scenario based on accretion and internal differentiation is presented for Titan, whose present substantial orbital eccentricity is not associated with any dynamical resonance. The source and maintenance of methane in Titan’s present atmosphere remain uncertain. Though most attention on the Saturnian moons focuses on Titan and Enceladus, the mid-size satellites Iapetus, Rhea, Tethys, and the irregular satellite Phoebe also draw our interest. An evolutionary scenario for Iapetus is presented in which spin down from an early rapidly rotating state is called upon to explain the satellite’s present oblate shape. The prominent equatorial ridge on Iapetus is unexplained by the spin down scenario. A buckling instability provides another possible explanation for the oblateness and equatorial ridge of Iapetus. Rhea is the only medium-size Saturnian satellite for which there are gravity data at present. The interpretation of these data are uncertain, however, since it is not known if Rhea is in hydrostatic equilibrium. Pluto and Charon are representative of the icy dwarf planets of the Kuiper belt. Did they differentiate as they evolved, and do either of them have a subsurface liquid water ocean? New Horizons might provide some answers when it arrives at these bodies.     

纳米隔热材料的热导率变化规律

为认识和掌握纳米隔热材料的热导率变化规律,以正硅酸乙酯(TEOS)为硅源、炭黑为遮光剂、石英纤维为增强体,采用溶胶-凝胶工艺结合超临界干燥技术制备了纳米隔热材料,并采用热导率测试仪、N_2吸附-脱附、SEM、激光粒度仪对材料进行了表征。测试结果表明:未添加炭黑的材料常压热导率随表观密度的变化以203 kg/m^3为分界点,分界点之前随表观密度的增大线性降低,分界点之后则随表观密度的增大线性升高,并且后一阶段较前一阶段变化快。孔隙率相同时,常压热导率随炭黑含量的增加先降低后稍有升高,极限真空热导率逐渐降低,而常压条件下的气相热导率增大。在半对数坐标系中,气相热导率随环境气压的下降而降低,并且依据降低速率可以划分为三个阶段,101.325～30 kPa之间下降最快,且变化值约为6 mW/(m·K);30～0.1 kPa之间下降较快,且变化值约为2 mW/(m·K);0.1～0.01 kPa之间下降最慢,且基本可以忽略不计。材料常压热导率最低值为16.62 mW/(m·K),添加5wt%的炭黑后可以进一步降低至14.50 mW/(m·K)。     

航天器热控材料的应用和发展

介绍了航天器热控系统对材料的要求以及应用的情况，并根据航天器总体和热控技术的需求，对热控材料的发展提出初步的建议。     

界面导热材料研究进展

综述了导热脂、导热胶黏剂、导热橡胶、导热胶带及相变材料等几类界面导热材料(TIMs)的组成成分、制备方法、主要性能、应用领域及其优化设计方法,并对国内外界面导热材料的发展进行了展望。     

高效隔热材料结构与性能研究

以陶瓷隔热瓦和纳米隔热材料为研究对象,揭示了高效隔热材料结构与性能的关系.研究结果表明:随着密度的增加,隔热材料室温热导率和力学性能随之增加;陶瓷隔热瓦平面方向和厚度方向的结构和性能存在明显差异;复合纳米结构后,材料的隔热性能明显提高;室温热导率从43 mW/(m·K)降低至36 mW/(m·K);添加少量功能添加物后,材料的高温隔热性能进一步提高,高温考核中背面温度从668℃降低到576℃.同时介电常数从2.2％增加到6.6％;通过气相超临界工艺在材料表面接枝有机基团,材料表面疏水状态发生显著变化,材料具备了防水和低吸潮的特性.     

Geology of the Icy Satellites

In the last 25 years, the explorations of the Voyager and Galileo missions have resulted in an entirely new view of the icy worlds orbiting the giant outer planets. These objects show a huge diversity in their characteristics, resulting from their formation histories, internal processes and interactions with their space environments. This paper will review the current state of knowledge about the icy satellites and discuss the exciting prospects for the upcoming Cassini/Huygens mission as it begins a new era of exploration of the Saturn satellite system.     

Chemical Composition of Icy Satellite Surfaces

Much of our knowledge of planetary surface composition is derived from remote sensing over the ultraviolet through infrared wavelength ranges. Telescopic observations and, in the past few decades, spacecraft mission observations have led to the discovery of many surface materials, from rock-forming minerals to water ice to exotic volatiles and organic compounds. Identifying surface materials and mapping their distributions allows us to constrain interior processes such as cryovolcanism and aqueous geochemistry. The recent progress in understanding of icy satellite surface composition has been aided by the evolving capabilities of spacecraft missions, advances in detector technology, and laboratory studies of candidate surface compounds. Pioneers 10 and 11, Voyagers I and II, Galileo, Cassini and the New Horizons mission have all made significant contributions. Dalton (Space Sci. Rev., 2010, this issue) summarizes the major constituents found or inferred to exist on the surfaces of the icy satellites (cf. Table 1 from Dalton, Space Sci. Rev., 2010, this issue), and the spectral coverage and resolution of many of the spacecraft instruments that have revolutionized our understanding (cf. Table 2 from Dalton, Space Sci. Rev., 2010, this issue). While much has been gained from these missions, telescopic observations also continue to provide important constraints on surface compositions, especially for those bodies that have not yet been visited by spacecraft, such as Kuiper Belt Objects (KBOs), trans-Neptunian Objects (TNOs), Centaurs, the classical planet Pluto and its moon, Charon. In this chapter, we will discuss the major satellites of the outer solar system, the materials believed to make up their surfaces, and the history of some of these discoveries. Formation scenarios and subsequent evolution will be described, with particular attention to the processes that drive surface chemistry and exchange with interiors. Major similarities and differences between the satellites are discussed, with an eye toward elucidating processes operating throughout the outer solar system. Finally we discuss the outermost satellites and other bodies, and summarize knowledge of their composition. Much of this review is likely to change in the near future with ongoing and planned outer planet missions, adding to the sense of excitement and discovery associated with our exploration of our planetary neighborhood.     

尖化前缘高导热材料防热分析

针对飞行器高超声速飞行时严重的气动加热环境,提出疏导式热防护结构( TPS),为飞行器前缘提供热防护.采用有限元法和有限体积法,分别对在特定工况下飞行的尖化前缘固体域和流体域进行计算,验证了前缘内嵌高导热材料的防热效果,其中来流马赫数为6.5时,头部壁面最高温度下降了13.6％,尾部最低温度升高了16.7％,实现了热流...     

低密度材料防热机理及热响应数值模拟

介绍了用于飞船返回舱的低密度材料防热机理及热响应数值模拟方法.采用分层模型建立多层结构一维热传导方程,计算了低密度材料温度分布,并与电弧加热器试验结果作了比较,两者符合较好.     

航天飞行器热防护系统及防热材料研究现状

随着航天技术发展,飞行器的飞行速度更快,服役环境更加恶劣,有效的热防护系统是保证飞行器安全飞行的关键系统之一。本文综述了被动防热系统、主动防热系统和半被动防热系统3类热防护系统在航天飞行器上的应用现状,重点介绍了金属基复合材料、碳基复合材料、陶瓷基复合材料、树脂基复合材料和气凝胶材料,5类防热材料在航天领域的应用发展情况,并提出了航天飞行器未来热防护的发展趋势。     

多层反射纳米隔热材料的制备及性能研究

制备了超薄纳米隔热材料和高反射金属箔,并组合成多层反射纳米隔热材料.结果表明:制备的超薄纳米隔热材料表面平整、厚度小于0.5 mm,材料的孔和粒径为纳米尺度;制备的金属膜结构紧密,厚度满足设计要求,在中心波长附近平均反射率高于95%.典型多层反射纳米隔热材料室温热导率为16 mW/(m·K).     

一种新型蜂窝夹层结构防热材料

针对实际使用的热环境要求,提出了多种防热结构材料及结构方案.通过石英灯加热试验对其防热性能进行了考核验证.考察了防热涂层、样件结构形式以及材料种类对试验件防热性能的影响.结果表明,防热涂层可显著降低防热试验件的背温,最高降幅达241℃;相对于传统的玻璃纤维/酚醛层压板结构,在满足防热要求的同时,新型蜂窝夹层结构的面密度较低,仅为层压板的50％左右,具有明显的减重优势,其中聚酰亚胺面板的蜂窝夹层结构的面密度仅为酚醛玻璃钢面板夹层结构的80％,其表面加防热涂层样件的背温仅为246℃.