柔性太阳翼在轨热分析

卫星的太阳电池翼在轨的温度状况对其性能和可靠性有着重要的影响。相比于刚性太阳翼,柔性太阳翼有着质量轻,综合性能好,结构也较简单等优点。在考虑了地球红外辐射,地球的太阳反照,太阳辐射加热的前提下,以柔性太阳翼为研究对象,利用I-DEAS TMG建立2种太阳电池有限元模型,分析了柔性太阳翼厚度方向的温差,以及不同太阳高度和工作状态对其在轨温度场的影响。分析结果表明,当飞行器绕轨道飞行进入第2个周期后,太阳电池温度场呈现周期变化特性;柔性太阳翼正反两面温度几乎一致,不会因为厚度方向的温差引起热应力;0°太阳高度角分流状态太阳电池温度最高,温度变化最为剧烈;66°太阳高度角工作状态,太阳电池的温度最低,温度变化最为缓慢;电池板面内温差极小。     

The streaming of solar flare particles and plasma in interplanetary space

A review is given of the features of solar particle emissions which cause various terrestrial disturbances. Three types of corpuscular emissions, namely, solar cosmic rays, energetic storm protons and plasma clouds, are associated with intense solar flares. Outward streaming of the solar wind and of beams of enhanced activity originate from the quiescent solar corona. It is shown that these solar particles propagate through interplanetary space, being modulated in a systematic way by existing magnetic fields. Time variations of solar flare particle flux, and their energy spectrum, are discussed.     

Reconstruction of Past Solar Irradiance

Accurate measurements of solar irradiance started in 1978, but a much longer time series is needed in order to uncover a possible influence on the Earth's climate. In order to reconstruct the irradiance prior to 1978 we require both an understanding of the underlying causes of solar irradiance variability as well as data describing the state of the Sun (in particular its magnetic field) at the relevant epochs.Evidence is accumulating that on the time-scale of the solar cycle or less, variations in solar irradiance are produced mainly by changes in the amount and distribution of magnetic flux on the solar surface. The main solar features contributing to a darkening of the Sun are sunspots, while active-region faculae and the network lead to a brightening. There is also increasing evidence for secular changes of the solar magnetic field and the associated of solar brightness variability. In part the behavior of sun-like stars is used as a guide of such secular changes.Under the assumption that solar irradiance variations are due to solar surface magnetism on all relevant time scales it is possible to reconstruct the irradiance with some reliability from today to around 1874, and with lower accuracy back to the Maunder minimum. One major problem is the decreasing amount and accuracy of the relevant data with age. In this review the various reconstructions of past solar irradiance are presented and the assumptions underlying them are scrutinized.     

Solar Variability Over the Past Several Millennia

The Sun is the most important energy source for the Earth. Since the incoming solar radiation is not equally distributed and peaks at low latitudes the climate system is continuously transporting energy towards the polar regions. Any variability in the Sun-Earth system may ultimately cause a climate change. There are two main variability components that are related to the Sun. The first is due to changes in the orbital parameters of the Earth induced by the other planets. Their gravitational perturbations induce changes with characteristic time scales in the eccentricity (～100,000 years), the obliquity (angle between the equator and the orbital plane) (～40,000 years) and the precession of the Earth’s axis (～20,000 years). The second component is due to variability within the Sun. A variety of observational proxies reflecting different aspects of solar activity show similar features regarding periodic variability, trends and periods of very low solar activity (so-called grand minima) which seem to be positively correlated with the total and the spectral solar irradiance. The length of these records ranges from 25 years (solar irradiance) to 400 years (sunspots). In order to establish a quantitative relationship between solar variability and solar forcing it is necessary to extend the records of solar variability much further back in time and to identify the physical processes linking solar activity and total and spectral solar irradiance. The first step, the extension of solar variability, can be achieved by using cosmogenic radionuclides such as ¹⁰Be in ice cores. After removing the effect of the changing geomagnetic field, a 9000-year long record of solar modulation was obtained. Comparison with paleoclimatic data provides strong evidence for a causal relationship between solar variability and climate change. It will be the subject of the next step to investigate the underlying physical processes that link solar variability with the total and spectral solar irradiance.     

Elemental Abundances in the Solar Upper Atmosphere Derived by Spectroscopic Means

The composition of the solar photosphere is believed to be uniform. Indeed a quantity that does not vary with solar surface location or with a particular solar feature, i.e., no observational evidence is available to indicate that the photospheric composition near the solar equator is different from the photospheric composition near the solar poles or that the photospheric composition in quiet regions is different from the composition in active regions. In contrast, the composition of the solar upper atmosphere is not well defined. Solar composition work in recent decades has brought the recognition that there are systematic differences between the composition of the corona and the photosphere and revealed evidence for spatial and time variability in the composition of various coronal features. We review the spectroscopic techniques used and the progress that was made in recent years in deriving the plasma compositions of various solar upper atmosphere structures. This revised version was published online in August 2006 with corrections to the Cover Date.     

Swan Observations of the Solar Wind Latitude Distribution and its Evolution Since Launch

SWAN is the first space instrument dedicated to the monitoring of the latitude distribution of the solar wind by the Lyman alpha method. The distribution of interstellar H atoms in the solar system is determined by their destruction during ionization charge-exchange with solar wind protons. Maps of sky Ly-α emission have been recorded regularly since launch. The upwind maximum emission region deviates strongly from the pattern that would be expected from a solar wind that is constant with latitude. It is divided in two lobes by a depression aligned with the solar equatorial plane, called the Lyman-alpha groove, due to enhanced ionization along the neutral sheet where the slow and dense solar wind is concentrated. The groove (or the anisotropy) is more pronounced in 1997 than in 1996, but it then decreases between 1997 and 1998. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Solar Origin of Corotating Interaction Regions and Their Formation in the Inner Heliosphere

Corotating Interaction Regions (CIRs) form as a consequence of the compression of the solar wind at the interface between fast speed streams and slow streams. Dynamic interaction of solar wind streams is a general feature of the heliospheric medium; when the sources of the solar wind streams are relatively stable, the interaction regions form a pattern which corotates with the Sun. The regions of origin of the high speed solar wind streams have been clearly identified as the coronal holes with their open magnetic field structures. The origin of the slow speed solar wind is less clear; slow streams may well originate from a range of coronal configurations adjacent to, or above magnetically closed structures. This article addresses the coronal origin of the stable pattern of solar wind streams which leads to the formation of CIRs. In particular, coronal models based on photospheric measurements are reviewed; we also examine the observations of kinematic and compositional solar wind features at 1 AU, their appearance in the stream interfaces (SIs) of CIRs, and their relationship to the structure of the solar surface and the inner corona; finally we summarise the Helios observations in the inner heliosphere of CIRs and their precursors to give a link between the optical observations on their solar origin and the in-situ plasma observations at 1 AU after their formation. The most important question that remains to be answered concerning the solar origin of CIRs is related to the origin and morphology of the slow solar wind. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modeling and analysis of solar Doppler difference bias with arbitrary rotation axis

The solar rotation causes the solar Doppler difference bias, which leads to the decline of the velocity measurement accuracy. Modeling and compensation are an effective solution. The limited model with specific geometric direction, where the solar rotation axis is perpendicular to the plane through the Sun, the Earth and Mars, was established. However, in fact, the geometric relationship among the Sun, Mars and the spacecraft is not fully in line with the hypothesis of the model due to the spacecraft orbital angle and the solar rotation axis drift. Thus, this model is not consistent with the fact. In order to solve this problem, a universal solar Doppler difference bias model, which provides the expression with arbitrary rotation axis, is established in this paper. In this method, for any point at the solar surface, four variables including the direction of the solar rotation linear velocity at this point, the distance from this point to the rotation axis, the vector from this point to Mars, and the vector from this point to the spacecraft are calculated. Based on these four variables, the solar Doppler difference bias corresponding to this point is obtained. The theoretical analysis and simulation results demonstrate that the solar Doppler difference bias model with the actual rotation axis is different from that with one of the specific rotation axes. Therefore, it is indispensable to build the proposed model for compensation. Besides, the direction of the solar rotation axis, the spacecraft-Mars-Sun angle and the spacecraft-to-Mars distance are important impact factors for the proposed model.     

Review of Radiation Damage to Silicon Solar Cells

This paper reviews a large number of silicon solar cell irradiation experiments performed over the last 10 years, including 1-MeV and energy spectrum electron studies, and low-(100-keV) and high-energy (up to 155-MeV) proton studies on bare and covered silicon solar cells of several types. The results of satellite flight experiments on individual solar cells are also presented, as well as data from complete solar arrays and data on the new high-efficiency solar cells. Experimental evidence indicates that the percentage of degradation is smaller in thin solar cells than in thick ones, and that cells with high resistivity (10 ?·cm) degrade less than cells with lower resistivity (1 ?·cm). It is shown that high-efficiency silicon solar cells produced at COMSAT Laboratories and pilot production groups of these cells retain most of their increased power output under irradiation. It is emphasized that all surfaces and edges of the solar cells must be completely shielded from the large flux protons in the space environment. Insufficiencies in the published data are noted in certain areas, and recommendations for additional research are presented. Finally, an extensive bibliography is included.     

考虑局部遮挡的太阳能无人机能源控制

针对太阳能无人机在飞行状态下可能出现的太阳能电池局部遮挡情况,开展相应的太阳能电池最大功率点追踪算法和能源控制研究。通过将发光亮度引入相对吸引力计算过程对萤火虫算法进行改进,实现了局部阴影情况下太阳能电池最大功率点的高效追踪。以此为基础,设计了考虑局部遮挡情况下太阳能无人机的太阳能电池/蓄电池混合能源状态机控制规则。以"蒲公英I"无人机为例,建立了太阳能电池阵列模型,开展了考虑局部遮挡情况下太阳能电池最大功率点追踪仿真实验;基于"蒲公英I"飞行剖面,开展了考虑局部遮挡情况的混合能源控制仿真试验。研究结果表明：改进的萤火虫算法可以实现在局部阴影情况下太阳能电池最大功率点的有效跟踪,与萤火虫算法相比收敛时间更短、且功率波动幅度更小;采用改进萤火虫算法和状态机能源管理策略,在考虑局部遮挡的飞行状态下可以实现太阳能电池/蓄电池之间的合理功率分配与控制。     

Global solar magnetic field evolution inferred from geomagnetic variations

I have analyzed geomagnetic disturbance index C9, mean solar magnetic field observed at Stanford Solar Observatory for the interval January 13, 1976 – December 30, 1993. It has been established a good correspondence between high-intensity geomagnetic recurrent and solar magnetic field patterns during whole period analyzed. A surprising thing is that the behavior of the solar mean field and interplanetary medium in the latest two solar cycles is very similar. Geomagnetic activity variations actually could serve as an ecliptic monitor of solar magnetic field structure and its evolution.     

Dynamic analysis of spinning solar sails at deployment process

The spinning deployment process of solar sails is analyzed in this study.A simplified model is established by considering the out-of-plane and in-plane motions of solar sails.The influences of structure parameters,initial conditions,and feedback control parameters are also analyzed.A method to build the geometric model of a solar sail is presented by analyzing the folding process of solar sails.The finite element model of solar sails is then established,which contains continuous cables and sail membranes.The dynamics of the second-stage deployment of solar sails are simulated by using ABAQUS software.The influences of the rotational speed and out-of-plane movement of the hub are analyzed by different tip masses,initial velocities,and control parameters.Compared with the results from theoretical models,simulation results show good agreements.     

The Solar Wind in the Outer Heliosphere

The solar wind evolves as it moves outward due to interactions with both itself and with the circum-heliospheric interstellar medium. The speed is, on average, constant out to 30 AU, then starts a slow decrease due to the pickup of interstellar neutrals. These neutrals reduce the solar wind speed by about 20% before the termination shock (TS). The pickup ions heat the thermal plasma so that the solar wind temperature increases outside 20–30 AU. Solar cycle effects are important; the solar wind pressure changes by a factor of 2 over a solar cycle and the structure of the solar wind is modified by interplanetary coronal mass ejections (ICMEs) near solar maximum. The first direct evidences of the TS were the observations of streaming energetic particles by both Voyagers 1 and 2 beginning about 2 years before their respective TS crossings. The second evidence was a slowdown in solar wind speed commencing 80 days before Voyager 2 crossed the TS. The TS was a weak, quasi-perpendicular shock which transferred the solar wind flow energy mainly to the pickup ions. The heliosheath has large fluctuations in the plasma and magnetic field on time scales of minutes to days.     

Physical reasons and consequences of a three-dimensionally structured heliosphere

In this article we have discussed reasons both of solar and of interstellar origin giving rise to a pronounced three-dimensional structure of the expanding solar wind and thus of the global configuration of the heliosphere. Our present observational knowledge on these structurings is reviewed, and all attempts to theoretically model these solar wind structures are critically analysed with respect to their virtues and flaws. It is especially studied here by what mechanisms interstellar imprints on the actual type of solar wind expansion can be envisaged. With concern to this aspect it hereby appears to be of eminent importance that the solar system maintains a relative motion with a submagnetosonic velocity of about 23km/sec with respect to the ambient magnetized interstellar medium corresponding to a magnetosonic Mach number of about 0.5.A heliopause closing the distant heliospheric cavity within a solar distance of about 100AU on the upwind side and opening it into an largely extended tail on the downwind side results as a first consequence from this relative motion. As a second consequence an asymmetric heliospheric shockfront with upwind distances smaller than downwind distances by ratios between 1/3 and 2/3 is most likely provoked which gives rise to at least two important upwind-downwind asymmetric processes influencing the supersonic solar wind expansion downstream from the shock: the anomalous cosmic ray diffusion into the solar wind, and high energetic jet electrons originating at the shock and moving inwards up to an inner critical point at around 20AU. As we shall demonstrate both processes are influencing the solar wind expansion beyond 20AU, however, more efficiently in the upwind hemisphere as compared to the downwind hemisphere. In the region inside 20AU other mechanisms are operating to propagate the interstellar imprint on the solar wind expansion further downstream into the inner heliosphere because here even the original solar wind electrons, in view of the solar wind bulk velocities, behave as a subsonic plasma constituent which can modify the solar wind solutions by means of an appropriate detuning of the circumsolar electric polarisation field. We give quantitative estimates for these effects.What concerns the theory of a solar wind expansion into a counterflowing ambient interstellar medium, some flaws of the present theoretical attempts are identified impeding that the interstellar influence on the actual solar wind solutions can become visible. We thus conclude that there is a clear need for three-dimensional and time-dependent solar wind models with a free outflow geometry taking into account the multisonicity of the solar wind plasma with different eigenmodes for a perturbation propagation.     

Solar cosmic rays

The first observations of solar cosmic rays were made simultaneously by many investigators at worldwide cosmic-ray stations in the periods of powerful chromospheric flares on February 28 and March 7, 1942. The discovery of these and the investigation of cosmic-ray solar-daily variations with maximum time near noon led some authors (Richtmyer and Teller, 1948; Alfvén, 1949, 1950) to a model of apparent cosmic-ray solar origin. We present here the results of the properties of solar cosmic rays from ground events (experimental and theoretical investigations). We also discuss important information from solar experimental data relating to these ground events observed in September and October 1989 and May 1990. Some experimental evidence of acceleration processes in associated phenomena with flares and long-term (solar cycle) variation of the average flux of solar cosmic rays is discussed as also cornal and interplanetary propagation, and that in the terrestrial magnetosphere. Note that the energy spectrum of solar cosmic rays varied very strongly from one flare to another. What are the causes of these phenomena? What is the nature of chemical and isotopic contents of solar cosmic rays? How can its changes occur in the energy spectrum and chemical contents of solar cosmic rays in the process of propagation? Is it possible to recalculate these parameters to the source? What makes solar cosmic rays rich in heavy nucleus and³He? The important data about electrons, positrons, gamma-quanta and neutrons from flares will be discussed in a subsequent paper (Dorman and Venkatesan, 1992). The question is: What main acceleration mechanism of solar flare and associated phenomena are reliable? These problems are connected with the more general problem on solar flare origin and its energetics. In Dorman and Venkatesan (1993) we will consider these problems as well as the problem of prediction of radiation hazard from solar cosmic rays (not only in space, but also in the Earth's atmosphere too).     

The Solar Dynamo

Observations relevant to current models of the solar dynamo are presented, with emphasis on the history of solar magnetic activity and on the location and nature of the solar tachocline. The problems encountered when direct numerical simulation is used to analyse the solar cycle are discussed, and recent progress is reviewed. Mean field dynamo theory is still the basis of most theories of the solar dynamo, so a discussion of its fundamental principles and its underlying assumptions is given. The role of magnetic helicity is discussed. Some of the most popular models based on mean field theory are reviewed briefly. Dynamo models based on severe truncations of the full MHD equations are discussed.     

Resonance in a coupled solar-climate model

The 11–year solar activity cycle is magnetic in origin and is responsible for small changes in solar luminosity and the modulation of the solar wind. The terrestrial climate exhibits much internal variability supporting oscillations with many frequencies. The direct effect of changing solar irradiance in driving climatic change is believed to be small, and amplification mechanisms are needed to enhance the role of solar variability. In this paper we demonstrate that resonance may play a crucial role in the dynamics of the climate system, by using the output from a nonlinear solar dynamo model as a weak input to a simplified climate model. The climate is modelled as oscillating about two fixed points (corresponding to a warm and cold state) with the weak chaotically modulated solar forcing on average pushing the solution towards the warm state. When a typical frequency of the input is similar to that of the chaotic climate system then a dramatic increase in the role of the solar forcing is apparent and complicated intermittent behaviour is observed. The nonlinear effects are subtle however, and forcing that on average pushes the solution towards the warm state may lead to increased intervals of oscillation about either state. Owing to the intermittent nature of the timeseries, analysis of the relevant timeseries is shown to be non-trivial.     

The Solar Noble Gas Record in Lunar Samples and Meteorites

Lunar soil and certain meteorites contain noble gases trapped from the solar wind at various times in the past. The progress in the last decade to decipher these precious archives of solar history is reviewed. The samples appear to contain two solar noble gas components with different isotopic composition. The solar wind component resides very close to grain surfaces and its isotopic composition is identical to that of present-day solar wind. Experimental evidence seems by now overwhelming that somewhat deeper inside the grains there exists a second, isotopically heavier component. To explain the origin of this component remains a challenge, because it is much too abundant to be readily reconciled with the known present day flux of solar particles with energies above those of the solar wind. The isotopic composition of solar wind noble gases may have changed slightly over the past few Ga, but such a change is not firmly established. The upper limit of ~5% per Ga for a secular increase of the 3He/4He ratio sets stringent limits on the amount of He that may have been brought from the solar interior to the surface (cf. Bochsler, 1992). Relative abundances of He, Ne, and Ar in present-day solar wind are the same as the long term average recorded in metallic Fe grains in meteorites within error limits of some 15-20%. Xe, and to a lesser extent Kr, are enriched in the solar wind similar to elements with a first ionisation potential < 10 eV, although Kr and Xe have higher FIPs. This can be explained if the ionisation time governs the FIP effect (Geiss and Bochsler, 1986). This revised version was published online in June 2006 with corrections to the Cover Date.     

太阳能无人机关键技术分析

介绍了当前太阳能无人机的发展现状,主要分析了太阳能无人机在设计、制造过程中所涉及到的各种关键技术,指出了需要突破的技术难点,包括轻质、高效太阳能电池的研制与应用技术、能量储存与能量控制系统、太阳能无人机机体平台设计技术。认为太阳能无人机作为航空科学技术与新能源技术相结合的产物,其研制过程需将气动、结构、推进、优化等多学科技术紧密结合。