Design and application of solar sailing: A review on key technologies

Solar sail technology has been proposed and developed for space explorations with advantages of low launch cost, no-propellant consumption, and continuous thrust, which has great potentials in earth polar detection, interstellar explorations and etc. The development of solar sail has made significant progress in structural design, manufacturing, materials, orbit transfer, and stability control in the past few decades, which makes meaningful contributions to astronomy, physics, and aerospace science. Technological breakthroughs of Solar Radiation Pressure (SRP) propulsion and interstellar transfer have been achieved in current solar sail missions. However, there are still many challenges and problems need to be solved. This paper attempts to summarize the research schemes and potential applications of solar sailing in space missions from the viewpoint of key technologies, so as to provide an overall perspective for researchers in this field. Analyses of the key technologies of solar sailing system design are provided. Finally, challenges and prospective development of solar sailing are discussed.     

太阳帆材料研究进展

太阳帆飞船由于无需动力等优势近年来引起了各国科学家的研究兴趣,并在深空探测领域具有重要的应用前景.太阳帆的结构设计和材料选择是影响其性能的重要因素,本文结合太阳帆飞行环境的特点,介绍了太阳帆的基本结构和飞行原理,重点针对目前几种比较典型的太阳帆设计,对其支撑材料以及帆面薄膜材料进行了综述,并分析了各种材料和设计的性能特点.     

太阳帆航天器在绕地轨道中的热诱发振动

太阳帆航天器在绕地轨道中将会周期性地进出地球阴影，经历热环境的剧烈变化，在热辐射冲击作用下，太阳帆这种大柔性空间结构的热致响应值得研究。以方形有桅杆式太阳帆为研究对象，考虑热辐射等非线性因素，建立了太阳帆的热-结构耦合动力学模型，分析了太阳帆桅杆-薄膜结构热诱发振动的特点和影响因素。分析结果表明：太阳帆由地球阴影区进入光照区将会发生明显的热诱发振动；随着热流入射角的增大，太阳帆桅杆截面的摄动温度减小，热诱发振动减弱，频率不变；太阳帆桅杆刚度的增大有利于抑制结构热诱发振动的发生；帆膜预应力将会影响太阳帆的热诱发振动，随着桅杆轴力增大，热诱发振动的振幅增大，频率减小，当轴力增大至一定程度，太阳帆的热诱发振动将会发散。     

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.     

Structural dynamic responses of a stripped solar sail subjected to solar radiation pressure

The stripped solar sail whose membrane is divided into separate narrow membrane strips is believed to have the best structural efficiency. In this paper, the stripped solar sail structure is regarded as an assembly made by connecting a number of boom-strip components in sequence. Considering the coupling effects between booms and membrane strips, an exact and semi-analytical method to calculate structural dynamic responses of the stripped solar sail subjected to solar radiation pressure is established. The case study of a 100 m stripped solar sail shows that the stripped architecture helps to reduce the static deflections and amplitudes of the steady-state dynamic response. Larger prestress of the membrane strips will decrease stiffness of the sail and increase amplitudes of the steady-state dynamic response. Increasing thickness of the boom will benefit to stability of the sail and reduce the resonant amplitudes. This proposed semi-analytical method provides an efficient analysis tool for structure design and attitude control of the stripped solar sail.     

太阳帆航天器动力学建模与求解

 太阳帆航天器动力学建模与求解是姿态控制与结构振动抑制的基础,具有重要的理论与工程意义。针对带有控制杆和控制叶片的太阳帆航天器,进行结构的合理简化。应用矢量力学基本原理,推导出考虑弹性振动的太阳帆航天器姿态动力学方程,再对其进行简化,分别得到基于控制叶片和控制杆的两类太阳帆航天器的姿态动力学方程,联立太阳帆支撑杆振动方程,结合非约束模态的定义对运行于超地球同步转移轨道的太阳帆航天器动力学方程进行了求解及分析,结果表明所建立的太阳帆动力学模型可准确地描述柔性太阳帆航天器的动力学特性。     

Cubesat solar sail 3-axis stabilization using panel translation and magnetic torquing

A Cubesat mission with a deployable solar sail of 5 meter by 5 meter in a sun-synchronous low earth orbit is analyzed to demonstrate solar sailing using active attitude stabilization of the sail panel. The sail panel is kept parallel to the orbital plane to minimize aerodynamic drag and optimize the orbit inclination change caused by the solar pressure force normal to the sail surface. A practical control system is proposed, using a combination of small 2-dimensional translation of the sail panel and 3-axis magnetic torquing which is proved to have sufficient control authority over the gravity gradient and aerodynamic disturbance torques. Miniaturized CMOS cameras are used as sun and nadir vector attitude sensors and a robust Kalman filter is used to accurately estimate the inertially referenced body rates from only the sun vector measurements. It is shown through realistic simulation tests that the proposed control system, although inactive during eclipse, will be able to stabilize the sail panel to within ±2° in all attitude angles during the sunlit part of the orbit, when solar sailing is possible.     

RCD太阳帆航天器人工平动点轨道保持与控制

针对航天器平动点轨道保持问题,研究了含有反射率控制设备(RCD)的太阳帆航天器在日地系共线人工平动点处的轨道保持与控制,同时降低因频繁改变航天器姿态所带来的振动问题。首先,基于太阳帆圆型限制性三体问题,计算了RCD型太阳帆人工平动点位置,给出了太阳帆共线人工平动点三阶Halo轨道,并将其作为参考轨道;然后,将太阳帆动力学方程线性化,采用跟踪控制输出的方法对线性模型进行控制;最后,通过合理选择控制变量矩阵,将控制律代入非线性模型中进行轨道保持控制。仿真结果表明,通过控制RCD太阳帆反射率设备参数及姿态角,实现了长时间的Halo轨道保持,同时大幅减小了太阳帆姿态角的改变,从而减小了帆面振动,为太阳帆航天器长期轨道任务的实现提供了良好的理论依据。     

太阳帆航天器被动姿态控制研究

针对由有效载荷、太阳帆和4个控制叶片所组成的太阳帆航天器系统,从物理模型出发,利用欧拉方程建立了姿态动力学模型,并通过数值仿真对太阳帆航天器基于控制叶片的对日定向性能进行了研究。研究结果表明,在行星际飞行中太阳帆航天器可以通过使控制叶片保持偏置来保持姿态稳定。     

Artificial equilibrium points and bi-impulsive maneuvers to observe 243 Ida

In the restricted three-body problem, the traditional Lagrange points L₁ and L₂ are the only equilibrium points near the asteroid 243 Ida. The thrust generated by a solar sail over a spacecraft enables the existence of new artificial equilibrium points, which depend on the position of the spacecraft with respect to the asteroid and the attitude of the solar sail. Such equilibrium points generate new spots to observe the body from above or below the plane of motion. Such points are very good observational locations due to their stationary condition. This work provides a preliminary analysis to observe Ida through the use of artificial equilibrium points as spots combined with transfer maneuvers between them. Such combination can be used to observe the asteroid from more different points of view in comparison to fixed ones. The analyses are made for a spacecraft equipped with a solar sail and capable of performing bi-impulsive maneuvers. The solar radiation pressure is used both to maintain the equilibrium condition and to reduce the costs of the transfers and/or to create transfers with longer duration. This is a new aspect of the present research, because it combines the continuous thrust with initial and final small impulses, which are feasible for most of the spacecraft, because the magnitudes of the impulses are very low. These combined maneuvers may reduce the transfer times of the maneuvers in most of the cases, compared with the maneuvers based only on continuous thrust. Several options involved in these transfers are shown, like to minimize the fuel spent ($\mathrm{\Delta }\mathit{v}$) as a function of the transfer time or to extend the duration of the travel between the points. Extended transfer times can be useful when observations are required during the transfers.     

Convex optimization of asteroid landing trajectories driven by solar radiation pressure

High-area/mass ratio landers driven by Solar Radiation Pressure (SRP) have potential applications for future asteroid landing missions. This paper develops a new convex optimization-based method for planning trajectories driven by SRP. A Minimum Landing Error (MLE) control problem is formulated to enable planning SRP-controlled trajectories with different flight times. It is transformed into Second Order Cone Programming (SOCP) successfully by a series of different convexification technologies. A trust region constraint and a modified MLE objective function are used to guarantee the convergence performance of the optimization algorithm. Thereafter, the SRP-driven trajectory optimal control problem is converted equivalently into a sequence of convex optimal control problems that can be solved effectively. A set of numerical simulation results has verified the effectiveness and feasibility of the proposed optimization method.     

Angular velocity determination of spinning solar sails using only a sun sensor

The direction of the sun is the easiest and most reliable observation vector for a solar sail running in deep space exploration. This paper presents a new method using only raw measurements of the sun direction vector to estimate angular velocity for a spinning solar sail. In cases with a con-stant spin angular velocity, the estimation equation is formed based on the kinematic model for the apparent motion of the sun direction vector;the least-squares solution is then easily calculated. A performance criterion is defined and used to analyze estimation accuracy. In cases with a variable spin angular velocity, the estimation equation is developed based on the kinematic model for the apparent motion of the sun direction vector and the attitude dynamics equation. Simulation results show that the proposed method can quickly yield high-precision angular velocity estimates that are insensitive to certain measurement noises and modeling errors.     

Solar sail trajectories with piecewise-constant steering laws

Solar sails have much attracted the interest of the scientific community as an advanced low-thrust propulsion means capable of promoting the reduction of mission costs and the feasibility of missions that are not practically accessible via conventional propulsion because of their large ΔV requirements. To reduce the overall flight time, a given mission is usually analyzed in the framework of a minimum time control problem, with the employment of a continuous steering law. The aim of this paper is to investigate the performance achievable with a piecewise-constant steering law whose aim is to substantially reduce the complex task of reorienting the sail over the whole mission. Unlike previous studies based on direct approaches, here we use an indirect method to optimally select the sail angle within a set of prescribed values. The corresponding steering law translates the results available for continuous controls to the discrete case, and is able of producing trajectories that are competitive in performance with the optimum variable direction program.     

翼梢帆片－机翼非定常气动力计算研究

本文应用偶极子网格法，数值研究矩形机翼与它三对翼梢帆片的干扰非定常气动力。数值结果表明，由于帆片的干扰效应，使翼梢区域剖面的升压系数分布发生畸变，在１／４弦长附近出现凹坑。干扰升压随振荡频率的增大而增大。在定常和低频振荡的范围内，帆片对机翼气动力的干扰贡献比帆片本身的贡献大，随着振荡频率的增大后者的贡献逐渐变得重要起来。     

混合小推力航天器轨道保持高性能滑模控制

针对采用太阳帆、太阳电混合小推力推进的航天器，研究了其在日心悬浮轨道的保持控制问题。为解决已有控制方法中未综合考虑内部未建模动态和外部未知扰动的问题，以及进一步提高系统控制性能，设计了一种高性能滑模控制策略。首先，考虑模型不确定性，建立了混合小推力航天器在日心悬浮轨道柱面坐标系的动力学方程；其次，基于改进型条件积分滑模面和径向基（RBF）神经网络设计了控制律，结合自适应方法在线估计不确定参数；接着，将求取的虚拟控制量在推进剂最优条件下转换成实际控制量，即太阳帆姿态角和太阳电推进力；最后，数值仿真验证了上述设计方法提高了系统鲁棒性，减小了轨道位置超调，并且混合推进相比于单一太阳帆推进，在更短收敛时间内控制精度提高了4个数量级，相比于单一太阳电推进，一年可以节省约89.6%的推进剂。     

翼尖帆片的优化设计

本文提出了带翼尖帆片的非共面机翼气动力计算以及帆片参数优化计算方法。文中采用涡格法研制了一种有效的非共同气动力计算程序，采用Ｐｏｗｅｌｌ方法进行优化计算，以获得最优的帆片配置方案。设计了某运输机的翼尖帆片，计算了升力和阻力系数，其结果与风洞试验值基本一致。计算和风洞试验结果表明，翼尖帆片对减少机翼的诱导阻力具有明显效果，本文的方法可供翼尖帆片初步设计应用。     

FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results

Recent spectroscopic measurements from instruments on the Solar and Heliospheric Observatory (SOHO) find that the coronal composition above a polar coronal hole is nearly photospheric. However, similar SOHO observations show that in coronal plasmas above quiet equatorial regions low-FIP elements are enhanced by a factor of ≈ 4. In addition, the process of elemental settling in coronal plasmas high above the solar surface was shown to exist. Measurements by the Ulysses spacecraft, which are based on non-spectroscopic particle counting techniques, show that, with the exception of He, the elemental composition of the fast speed solar wind is similar to within a factor of 1.5 to the composition of the photosphere. In contrast, similar measurements in the slow speed wind show that elements with low first ionization potential (FIP < 10 eV) are enhanced, relative to the photosphere, by a factor of 4-5. By combining the SOHO and Ulysses results, ideas related to the origin of the slow speed solar wind are presented. Using spectroscopic measurements by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument on SOHO the photospheric abundance of He was determined as 8.5 ± 1.3% (Y = 0.248). This revised version was published online in June 2006 with corrections to the Cover Date.     

Novel orbit-attitude combination mode for solar power satellites to reduce mass and fuel

Solar power satellite receives great attention because it can release the energy crisis and environmental problems in the future. However, the launch and maintenance costs are tremendous due to the large system mass and large fuel consumption to counteract space perturbations. To reduce mass and fuel, a novel quasi-Sun-pointing attitude in Sun-frozen orbit is proposed. The Sun-frozen orbit has a nonzero eccentricity vector that always points towards the Sun. The quasi-Sun-pointing attitude is a periodic solution of the Sun-pointing attitude angle. Although about 3 % electricity must be given up because of the variation of Sun-pointing attitude angle, little control action is required to deal with the solar radiation pressure and gravity-gradient torque. The algorithm to obtain initial conditions is proposed. The influences of system parameters and structural flexibilities are studied. Simulation results reveal that the quasi-Sun-pointing attitude in Sun-frozen orbit dramatically reduce fuel consumption, the dry mass, and complexity of the control system. In addition, structural vibration is hardly induced by the gravity-gradient torque. Thus, the bending stiffness as well as the mass of the supporting structure can be reduced.     

离轨帆弹性桅杆力学性能分析

采用有限元分析软件ABAQUS分析弹性桅杆几何参数对其力学性能的影响,为离轨帆弹性桅杆设计提供一定的理论依据。结果表明:增加壳体厚度、保持弧长不变,减小曲率半径以及增大壳体截面圆心角都能有效提高离轨帆自动展开能力及弹性桅杆支撑刚度;弹性桅杆的弯曲内部应力只与材料属性、曲率半径、缠绕半径以及壳体厚度有关;曲率半径减小、壳体厚度增加都会增大弹性桅杆的弯曲内部应力,有可能会导致弹性桅杆在缠绕时发生塑性变形。因此,在对弹性桅杆设计时,需综合考虑弹性桅杆几何参数对其展开能力以及缠绕性能的影响。     

硬式空中加油装置运动建模与仿真研究

针对由加油机和硬式加油伸缩管构成的硬式空中加油多体动力学系统,在已有的加油机运动仿真模型的基础上,考虑加油机的尾流场扰动作用,采用基于拉格朗日方程的速度传递矩阵法,建立了系统运动仿真模型。通过运动仿真,对伸缩管的动态特性和系统的紊流扰动响应特性进行了研究。仿真结果表明,硬管的动态响应特性较差、阻尼偏小,且俯仰运动与偏航运动耦合,需控制系统予以改善并实现解耦操纵;轻微的紊流对硬管的姿态具有较明显的扰动作用,通过稳定加油机的航迹,能够显著改善硬式加油装置的抗紊流特性。