Fuel consumption for interplanetary missions of solar sailing

The orbits of solar sails can be changed by adjusting the sail’s attitude through external control torques.The resulting momentum will be changed,either provided by a typical attitude control subsystem or by a propellantless device.This paper investigates the extra momentum input and fuel consumption for a typical attitude control subsystem.The minimum-time transfer trajectories are designed for two rendezvous missions using both indirect and direct methods,generating continuous and discrete attitude histories,respectively.The results show that the momentum variation is almost wholly due to the solar radiation pressure.The feasibility of using tip-mounted microthrusters for attitude control is evaluated.The results show that less than0.1 kg of propellant are required for an interplanetary transfer mission when pulsed plasma thrusters with a specific impulse of700 s and a thrust of 150 mN are mounted at the tip of a 20 m square solar sail.The fuel consumptions of two transfer missions indicate that a tip-mounted pulsed plasma thruster is a viable technique for the attitude control of a solar sail.     

Evaluation and prediction of the degradation of space Si solar cells induced by a low-earth-orbit radiation environment

Space-graded silicon solar cells are evaluated by 1 MeV and 2 MeV electron-irradiation. The mean degradation of the maximum power (P_max) is presented and analyzed. The degradation at both electron energies has been correlated with the displacement damage dose (D_d). A good linearity between the electron D_d and the mean P_max degradation is obtained. The concept of D_d has also been used to predict the Si solar cell response in a low-earth-orbit (Altitude 799 km, Inclination 99^o) radiation environment, considering the shielded effect of a 120 μ m-thick silica coverglass on reducing the radiation. Compared with the on-orbit data from a Si solar array of a Chinese satellite (duration from April 2007 to July 2010), a good match can be found between the on-orbit data and the predicted results using D_d methodology, indicating the method is appropriate for evaluating the radiation damage of the solar cells, and also to provide a new technique for studying radiation effects on the optoelectronic detectors used in many high energy physics applications, where harsh radiation environments produce damage in optoelectronic device materials.     

不均匀光照条件下太阳能电池串联电路特性分析及GMPPT控制

通过对太阳能电池串联电路的动态特性分析,建立了不均匀光照条件下多峰值出现的充要条件.基于串联电路的工作原理,建立了局部峰值点功率之间的数学关系,确定了最大功率点区间位置的动态判断系数.该方法可快速定位全局最大功率点所在区间,确定该区间的上下边界,将电导增量法的运行初值保持在该区间,能够使其快速准确跟踪到全局最大功率点.该方法利用较少计算和小区间搜索代替全局搜索,具有良好的快速性和准确性.同时该方法改善了区间搜索重启条件使其拥有较强的鲁棒性.     

Application of millimeter-sized polymer cylindrical lens array concentrators in solar cells

A unique method is proposed to encapsulate solar cells and improve their power conversion efficiency by using a millimeter-sized cylindrical lens array concentrator. Millimeter-sized epoxy resin polymer(ERP) cylindrical lens array concentrators are fabricated by the soft imprint technique based on polydimethylsiloxane stamps. The photovoltaic measurements show that millimeter-sized ERP cylindrical lens array concentrators can considerably improve the power conversion efficiency of silicon solar cells. The validity of the proposed method is proved by the coupled optical and electrical simulations. The designed solar cell devices with the advantages of high-efficiency and convenient cleaning are very useful in practical applications.     

Efficient nanocoax‐based solar cells

The power conversion efficiency of most thin film solar cells is compromised by competing optical and electronic constraints, wherein a cell must be thick enough to collect light yet thin enough to efficiently extract current. Here, we introduce a nanoscale solar architecture inspired by a well‐known radio technology concept, the coaxial cable, that naturally resolves this “thick–thin” conundrum. Optically thick and elec‐ tronically thin amorphous silicon “nanocoax” cells are in the range of 8% efficiency, higher than any nanostructured thin film solar cell to date. Moreover, the thin nature of the cells reduces the Staebler–Wronski light‐induced degradation effect, a major problem with conventional solar cells of this type. This nanocoax represents a new platform for low cost, high efficiency solar power. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Oxide semiconductors for solar to chemical energy conversion: nanotechnology approach

The present work considers the application of oxide semiconductors in the conversion of solar energy into the chemical energy required for water purification (removal of microbial cells and toxic organic compounds from water) and the generation of solar hydrogen fuel by photoelectrochemical water splitting. The first part of this work considers the concept of solar energy conversion by oxide semiconductors and the key performance-related properties, including electronic structure, charge transport, flat band potential and surface properties, which are responsible to the reactivity and photoreactivity of oxides with water. The performance of oxide systems for solar energy conversion is briefly considered in terms of an electronic factor. The progress of research in the formation of systems with high performance is considered in terms of specific aspects of nanotechnology, leading to the formation of systems with high performance. The nanotechnology approach in the development of high-performance photocatalysts is considered in terms of the effect of surface energy associated with the formation of nanostructured system on the formation of surface structures that exhibit outstanding properties. The unresolved problems that should be tackled in better understanding of the effect of nanostructures on properties and performance of oxide semiconductors in solar energy conversion are discussed. This part is summarised by a list of unresolved problems of crucial importance in the formation of systems with enhanced performance. This work also formulates the questions that must be addressed in order to overcome the hurdles in the formation of oxide semiconductors with high performance in water purification and the generation of solar fuel. The research strategy in the development of oxide systems with high performance, including photocatalysts for solar water purification and photoelectrodes for photoelectrochemical water splitting, is considered. The considerations are focused on the systems based on titanium dioxide of different defect disorder as well as its solid solutions and composites.     

An identifier-actor-optimizer policy learning architecture for optimal control of continuous-time nonlinear systems

An intelligent solution method is proposed to achieve real-time optimal control for continuous-time nonlinear systems using a novel identifier-actor-optimizer(IAO)policy learning architecture.In this IAO-based policy learning approach,a dynamical identifier is developed to approximate the unknown part of system dynamics using deep neural networks(DNNs).Then,an indirect-method-based optimizer is proposed to generate high-quality optimal actions for system control considering both the constraints and performance index.Furthermore,a DNN-based actor is developed to approximate the obtained optimal actions and return good initial guesses to the optimizer.In this way,the traditional optimal control methods and state-of-the-art DNN techniques are combined in the IAO-based optimal policy learning method.Compared to the reinforcement learning algorithms with actor-critic architectures that suffer hard reward design and low computational efficiency,the IAO-based optimal policy learning algorithm enjoys fewer user-defined parameters,higher learning speeds,and steadier convergence properties in solving complex continuous-time optimal control problems(OCPs).Simulation results of three space flight control missions are given to substantiate the effectiveness of this IAO-based policy learning strategy and to illustrate the performance of the developed DNN-based optimal control method for continuous-time OCPs.     

Effectiveness of full spectrum light soaking on solar cell degradation analysis

This study examined the effect of UV-spectrum light soaking on solar cell degradation tests. An indoor light soaking test was evaluated over three different spectral ranges: “UV only”, “UV blocked” and “Full spectrum”. a-Si:H and poly-crystalline silicon solar cell technologies were studied by light soaking tests with the same optical filter configurations.The I–V measurement results demonstrated that “UV only” irradiated solar cells exhibited the smallest output power degradation, which was only half of a percent variation compared with the full spectrum light soaking case. Using a filter that excluded the effect of the UV spectral range on light soaking, the “UV blocked” case also exhibited a significant output power degradation of the solar cells. A comparative analysis of the solar cell response, based on the I–V characteristics and the diode ideality factor under these different light soaking spectra, demonstrated the importance of the full spectrum light soaking test in the evaluation of the long-term performance of solar cells.     

Structured H∞ Control for Spacecraft with Flexible Appendages

Spacecraft with large flexible appendages are characterized by multiple system modes. They suffer from inherent low-frequency disturbances in the operating environment that consequently result in considerable interference in the operational performance of the system. It is required that the control design ensures the system’s high pointing precision, and it is also necessary to suppress low-frequency resonant interference as well as take into account multiple performance criteria such as attitude stability and bandwidth constraints. Aiming at the comprehensive control problem of this kind of flexible spacecraft, we propose a control strategy using a structured H-infinity controller with low complexity that was designed to meet the multiple performance requirements, so as to reduce the project cost and implementation difficulty. According to the specific resonant mode of the system, the design strategy of adding an internal mode controller, a trap filter, and a series PID controller to the structured controller is proposed, so as to achieve the comprehensive control goals through cooperative control of multiple control modules. A spacecraft with flexible appendages (solar array) is presented as an illustrative example in which a weighted function was designed for each performance requirement of the system (namely robustness, stability, bandwidth limit, etc.), and a structured comprehensive performance matrix with multiple performance weights and decoupled outputs was constructed. A structured H-infinity controller meeting the comprehensive performance requirements is given, which provides a structured integrated control method with low complexity for large flexible systems that is convenient for engineering practice, and provides a theoretical basis and reference examples for structured H-infinity control. The simulation results show that the proposed controller gives better control performance compared with the traditional H-infinity one, and can successfully suppress the vibration of large flexible appendages at 0.12 Hz and 0.66 Hz.     

Plasmon enhanced light trapping in thin film GaAs solar cells by Al nanoparticle array

Light trapping is a crucial factor to enhance the performance of thin film solar cells. For effective light trapping, we introduced Al nanoparticle array on the top and rear surface of thin film GaAs solar cells. The effect of both array on the optical absorption and current density of solar cells is investigated by using finite difference time domain (FDTD) method. The optimization process of top and rear array in solar cells is done systematically. The results indicate that by plasmonic action of arrays, the optical absorption is significantly enhanced and optimized structure yields a current density of 25.77 mA/cm². These enhancements are mainly attributed to surface plasmon effects induced by Al nanoparticles and the light grating properties of the arrays.     

太阳能光伏-温差发电驱动的新型冰箱模型设计与热力学分析

结合太阳能电池温度特性和温差发电特点,设计了一套新的太阳能光伏发电-温差发电驱动的冰箱模型,该模型包括太阳能光伏电池、半导体温差发电模块、电源控制系统等.根据负载用电需求,做出了光伏发电系统的设计方案.采用热力学基本理论,对该模型进行了工作效率及 火 用 效率的分析.结果发现:能效比COP达到了2.73(一般 冰箱COP为2左右), 火 用 效率也达到42.5%.同时,该系统模型环境效益明显,可以减排CO₂ 1394.2 kg,SO₂     

Low-thrust trajectory optimization of asteroid sample return mission with multiple revolutions and moon gravity assists

Near-Earth asteroids have gained a lot of interest and the development in low-thrust propulsion technology makes complex deep space exploration missions possible. A mission from low-Earth orbit using low-thrust electric propulsion system to rendezvous with near-Earth asteroid and bring sample back is investigated. By dividing the mission into five segments, the complex mission is solved separately. Then different methods are used to find optimal trajectories for every segment. Multiple revolutions around the Earth and multiple Moon gravity assists are used to decrease the fuel consumption to escape from the Earth. To avoid possible numerical difficulty of indirect methods, a direct method to parameterize the switching moment and direction of thrust vector is proposed. To maximize the mass of sample, optimal control theory and homotopic approach are applied to find the optimal trajectory. Direct methods of finding proper time to brake the spacecraft using Moon gravity assist are also proposed. Practical techniques including both direct and indirect methods are investigated to optimize trajectories for different segments and they can be easily extended to other missions and more precise dynamic model.     

Fuel quality and operational issues for polymer electrolyte membrane (PEM) fuel cells

Polymer electrolyte membrane (PEM) fuel cells are susceptible to degradation due to the catalyst poisoning caused by CO present in the fuel above certain limits. Although the amount of CO in the fuel may be within the permissible limit, the fuel composition (% CO₂, CH₄, CO and H₂O) and the operating conditions of the cell (level of gas humidification, cell temperature and pressure) can be such that the equilibrium CO content inside the cell may exceed the permissible limit leading to a degradation of the fuel cell performance. In this study, 50 cm² active area PEM fuel cells were operated at 55–60 °C for periods up to 250 hours to study the effect of methane, carbon dioxide and water in the hydrogen fuel mix on the cell performance (stability of voltage and power output). Furthermore, the stability of fuel cells was also studied during operation of cells in a cyclic dead end / flow through configuration, both with and without the presence of carbon dioxide in the hydrogen stream. The presence of methane up to 10% in the hydrogen stream showed a negligible degradation in the cell performance. The presence of carbon dioxide in the hydrogen stream even at 1–2% level was found to degrade the cell performance. However, this degradation was found to disappear by bleeding only about 0.2% oxygen into the fuel stream.     

聚光光强对光伏电池阵列输出性能的影响

基于槽式聚光热电联供系统,深入分析晶硅电池阵列和砷化镓电池阵列在高倍聚光下的输出特性及输出功率的影响因素.研究结果表明,聚光光强下砷化镓电池阵列输出性能优于晶硅电池阵列,高光强会导致光伏电池禁带宽度变窄,短路电流成倍增加,增加输出功率,但同时耗尽层复合率变大,开路电压降低,制约阵列的输出功率;高光强还引起电池温度升高,电池阵列串联内阻增加.分析表明聚光作用下电池阵列串联内阻对输出功率影响巨大,串联内阻从0 Ω增加1 Ω,四种电池阵列输出功率分别损失67.78%,74.93%,77.30%和58.01%. 关键词： 热电联供 太阳电池阵列 串联内阻 输出功率     

一种新方法制备硅/聚(3, 4-乙撑二氧噻吩)核/壳纳米线阵列杂化太阳能电池

采用气相聚合法制备了有机/无机杂化的硅/聚3, 4-乙撑二氧噻吩核/壳纳米线阵列(SiNWs/PEDOT)太阳能电池. 相对平面结构Si/PEDOT太阳能电池, SiNWs/PEDOT太阳能电池的能量转换效率提升了7倍, 达到3.23%.对比分析反射光谱、I-V曲线及外量子效率的实验结果, 发现SiNWs/PEDOT太阳能电池性能改进的主要原因可归结为: 气相聚合法能够有效地制备出SiNWs/PEDOT电池的核/壳纳米线阵列结构, 使得器件具有高光捕获、高比结面积和高电荷收集效率. 关键词： Si/PEDOT核/壳纳米线结构 太阳能电池 气相聚合     

Status of single-model optical fiber standardization in the electronic industries association (EIA)

This paper introduces and analyzes revolutionary laser system architecture capable of dramatically reducing the complexity of laser systems while simultaneously increasing capability. The architecture includes three major subsystems. The first is a phased array of laser sources. In this article, we discuss diode-pumped fiber lasers as the elements of the phased array, although other waveguide lasers can also be considered. The second provides wavefront control and electronics beam steering, as described in an IEEE Proceedings article on “Optical Phased Array Technology” [1]. The third is subaperture receiver technology. Combining these three technologies into a new laser systems architecture results in a system that has graceful degradation, can steer to as wide an angle as individual optical phased array subapertures, and can be scaled to high power and large apertures through phasing of a number of subapertures. Diode-pumped fiber lasers are appealing as laser sources because they are electrically pumped, efficient, relatively simple, and scalable to significant power levels (over 100 Watts has been demonstrated from a single diode-pumped fiber laser) [2]. The fiber laser design also lends itself to integration into a phased array. Fiber lasers have been phased. Initial phasing demonstrations have been at low power and were conducted by taking a single source, dividing it into multiple fibers, then phasing them together. To develop this technology further we need to use independent fiber lasers or fiber amplifiers, seeded by a common source, and to increase laser power. As we increase laser power, we will have to learn to cope with nonlinearities in the laser amplifiers. Optical Phased Array technology has demonstrated steering over a 90-degree field of regard [4], although this approach used additional optical components. If we use straightforward optical phased array beam steering without additional optics we can steer with high efficiency to about one-third λ/d, where d is the smallest individually addressable element. The one-third factor depends on the efficiency threshold. For example, if we use 1.5 μm light, and 5 μm center-to-center spacing, we can steer with high efficiency to about ±6 degrees, or a field of regard of 12 degrees. Last, we need to develop a subaperture receive technology. This can be a pupil plane receiver, an image plane receiver, or some combination of the approaches. When we have matured each individual technology and combined them into new laser systems architectures, we will have the ability to build simpler and more capable laser systems. The vision for an integrated, phased array laser concept is to enable a new class of laser systems with significant advantages, including high-efficiency, all-electric laser source; all waveguide beam transport; wavefront control at the sub-aperture level (enabling wavefront compensation, conformal apertures, and wide-angle electronic beam steering); random access beam pointing over wide angles; multiple simultaneous beam generation and control; and graceful degradation.     

Array gain for a cylindrical array with baffle scatter effects

Cylindrical arrays used in sonar for passive underwater surveillance often have sensors surrounding a cylindrical metal baffle. In some operational sonars, the phones in each stave (i.e., each line of phones aligned with the cylinder axis) are hardwired together so that the array is equivalent to a baffled circular array of directional elements, where each element corresponds to a line array of omnidirectional phones steered to broadside. In this paper a model is introduced for computing the array gain of such an array at high frequencies, which incorporates baffle scatter using infinite, rigid cylinder scattering theory, and with ambient noise described by an angular spectral density function. In practice the phones are often offset from the baffle surface, and the acoustic field sampled by the staves is distorted at high frequencies due to interference between the incident and scattered fields. Examples are given to illustrate the resulting array gain degradation, using three noise distributions that are frequently used in sonar performance modeling: three-dimensional isotropic, two-dimensional isotropic, and surface dipole noise.     

Minimally radiating sources for personal audio

In order to reduce annoyance from the audio output of personal devices, it is necessary to maintain the sound level at the user position while minimizing the levels elsewhere. If the dark zone, within which the sound is to be minimized, extends over the whole far field of the source, the problem reduces to that of minimizing the radiated sound power while maintaining the pressure level at the user position. It is shown analytically that the optimum two-source array then has a hypercardioid directivity and gives about 7 dB reduction in radiated sound power, compared with a monopole producing the same on-axis pressure. The performance of other linear arrays is studied using monopole simulations for the motivating example of a mobile phone. The trade-off is investigated between the performance in reducing radiated noise, and the electrical power required to drive the array for different numbers of elements. It is shown for both simulations and experiments conducted on a small array of loudspeakers under anechoic conditions, that both two and three element arrays provide a reasonable compromise between these competing requirements. The implementation of the two-source array in a coupled enclosure is also shown to reduce the electrical power requirements.     

Mean occurrence frequency and temporal risk analysis of solar particle events

The protection of astronauts from space radiation is required on future exploratory class and long-duration missions. For the accurate projections of radiation doses, a solar cycle statistical model, which quantifies the progression level within the cycle, has been developed. The resultant future cycle projection is then applied to estimate the mean frequency of solar particle events (SPEs) in the near future using a power law function of sunspot number. Detailed temporal behaviors of the recent large event and two historically large events of the August 1972 SPE and the November 1960 SPE are analyzed for dose-rate and cumulative dose equivalent at sensitive organs. Polyethylene shielded “storm shelters” inside spacecraft are studied to limit astronauts’ total exposure at a sensitive site within 10 cSv from a large event as a potential goal that fulfills the ALARA (as low as reasonably achievable) requirement.     

Displacement damage analysis and modified electrical equivalent circuit for electron and photon-irradiated silicon solar cells

Solar modules and arrays are the conventional energy resources of space satellites. Outside the earth's atmosphere, solar panels experience abnormal radiation environments and because of incident particles, photovoltaic (PV) parameters degrade. This article tries to analyze the electrical performance of electron and photon-irradiated mono-crystalline silicon (mono-Si) solar cells. PV cells are irradiated by mono-energetic electrons and poly-energetic photons and immediately characterized after the irradiation. The mean degradation of the maximum power (P_max) of silicon solar cells is presented and correlated using the displacement damage dose (D_d) methodology. This method simplifies evaluation of cell performance in space radiation environments and produces a single characteristic curve for P_max degradation. Furthermore, complete analysis of the results revealed that the open-circuit voltage (V_oc) and the filling factor of mono-Si cells did not significantly change during the irradiation and were independent of the radiation type and fluence. Moreover, a new technique is developed that adapts the irradiation-induced effects in a single-cell equivalent electrical circuit and adjusts its elements. The “modified circuit” is capable of modeling the “radiation damage” in the electrical behavior of mono-Si solar cells and simplifies the designing of the compensation circuits.