Ultralight deployable booms for solar sails and other large gossamer structures in space

Future solar sail spacecraft which do not need any rocket motors and propellants are a promising option for long-term exploration missions in the solar system. However, they will require ultralight reflective foils and deployable booms which will allow for the unfolding of huge sails. The achievement of an acceptable ratio of reflective sail area and structural mass, which results in a still small, but significant acceleration under the photon pressure of sunlight, is extremely challenging. The same challenging deployment technique is required for the unfolding of large reflector membranes or antennas (gossamer structures). The key elements are the booms which must be stowable in a very small envelope before they reach their destination in space. Such booms were developed by DLR and have been successfully tested under zero-g-conditions during a parabolic flight campaign in February 2009. It could be convincingly demonstrated that the unfolding process is both controllable and reproducible. The booms consisted of two co-bonded omega-shaped carbonfiber half shells with 0.1 mm wall thickness each and had a weight of only 62 g per meter. Two different deployment technologies were tested, one based upon an inflatable 12 μm thick polymer hose inside the boom, the other one using an electromechanical uncoiling device at the tip of each boom. In the latter case, the uncoiling devices will radially fly away from the spacecraft, such that they become “expendable deployment mechanisms” and their mass does not count any more for the spacecraft mass that needs to be accelerated or actively controlled.     

太阳帆航天器研究及其关键技术综述

综述了国内外关于太阳帆航天器的研究成果。介绍了太阳帆航天器的构型与材料、姿态控制、轨道控制及任务分析、试验验证及动力学仿真分析等的研究进展,讨论了太阳帆航天器轻质高强度帆体、折叠储存与展开控制、结构设计、姿态控制、地面试验及在轨演示验证,以及测试与诊断等关键技术,分析了未来太阳帆航天器的发展趋势。     

火星探测器降落伞拉直过程中的“绳帆”现象研究

针对火星探测器降落伞在拉直过程中出现的“绳帆”现象,以及火星探测器降落伞开伞前初始参数和大气密度与地球环境下的差异,建立了火星探测器降落伞拉直过程的数学模型,研究了火星环境下,伞包弹射速度、开伞前进入器的攻角、开伞马赫数以及大气密度对“绳帆”现象的影响。研究结果表明,选择较大的伞包弹射速度,并将开伞前进入器的攻角严格限定在较小范围内,将有利于避免或降低“绳帆”现象的发生。这一研究结果可为我国实施火星探测时减速着陆系统的设计分析提供一定参考。     

Analysis of dynamic behaviour of inflatable booms in zigzag and modified zigzag folding patterns

The deployment behaviour of inflatable booms with zigzag and modified zigzag folding patterns is experimentally and theoretically investigated in this paper with the aim to deploy the booms as the actuator for future deployable large-scale membrane structures. Regarding the experimental approach, the stable deployment of a modified zigzag folding pattern is demonstrated, and the relation between stable and unstable deployment behaviour is considered in relation to air pressure and flow rate. In terms of the theoretical approach, the folding process and deployment behaviour are simulated using commercially available software (PAM-CRACH and PAM-SAFE). To create folding lines from the zero stress condition in the case of analytical inflatable boom models, the stress distribution and the shapes of the folding lines are considered for the initial self-deployment behaviour and deployment behaviour using the uniform pressure method. From the folding experiments and the results of folding analyses and UPM, the deployment behaviour of inflatable boom models in zigzag and modified zigzag folding patterns is compared by using the finite point-set method. For the sequential deployment behaviour, which is difficult to replicate, the uniform pressure method is used for the calculations, and the relation between inlet air flow and stable deployment behaviour is discussed through comparison of the experimental and analytical results.     

IKAROS太阳帆的关键技术分析与启示

分析了国外太阳帆的发展现状,重点论述了世界上首次成功飞行的太阳帆——太阳辐射驱动星际风筝航天器（IKAROS）的总体设计、材料设计、空间展开和姿态控制等关键技术,以及中国开展太阳帆和空间大型展开结构的总体设计、空间展开、姿态控制、空间环境适应性等关键技术,提出了系统开展以太阳帆为代表的大型轻质展开结构研制与应用的建议。     

Dynamics of the orbiter based construction of structural components for space platforms

A relatively general formulation for studying liberational dynamics of a large class of spacecraft during deployment of arbitrarily oriented beam and plate type flexible members has been developed by the authors. The formulation is applicable to a variety of missions ranging from deployment of antennas, booms and solar panels to manufacturing of trusses for space platforms using the Space Shuttle. The governing nonlinear, nonautonomous and coupled equations of motion are extremely difficult to solve even with the help of a computer, not to mention the cost involved. To get some appreciation as to the complex interaction between flexibility, deployment and attitude dynamics as well as to help pursue stability and control analyses, the procedure is applied to the Space Shuttle based deployment of plate-like members. Results suggest substantial influence of the flexural rigidity of the appendages, deployment velocity, initial conditions, and appendage orientation on the system response. Deployment maneuvers in conjunction with a typical controlled time history of permissible liberational rates suggest flexible plate members to be stable. In general, the instability is triggered through roll excitation leading to unbounded yaw due to coupling. The results should prove useful in planning of the Orbiter based experiments aimed at studying dynamics and control of flexible, deployable structural components needed in construction of space platforms.     

试验运载器姿控总体优化设计技术

试验运载器在姿控动力系统空间布置紧张、控制力臂有限的情况下，要实现初始起控阶段大初始姿态偏差及气动干扰条件下的稳定控制，以及有效载荷释放阶段的多通道多次连续大角度调姿控制，给姿控系统的设计造成了困难。为此，通过鸭式直接力控制方案设计、多通道连续大角度调姿方案设计等技术，设计出了满足任务要求且性能良好的姿控总体方案。     

薄膜充气管展开模拟试验

根据多体理论中凯恩方法建立的折叠充气管模型,模拟研究了V形折叠充气管的充气展开动力学特性.由管内气压变化与充气展开时间的关系,分析了不同充气速率和初始展开角时展开加速度与时间的关系.结果表明:该模拟方法有效,展开加速度与充气速率总体成正比.另发现,为改善充气管的展开动力学性能,需控制特定展开角度范围内的加速度波动.     

推力矢量发动机燃气舵舵间干扰的数值分析

通过求解N-S方程,对某空空导弹燃气舵在不同状况下的三维湍流干扰流场进行数值仿真,得到了燃气舵在不同舵偏角下绕流流场的复杂波系结构,计算了测量舵在无干扰舵和有干扰舵情况下升力和阻力等参量随舵偏角的变化曲线。所得舵间干扰相对误差不超过2%,与实际要求相吻合。结果表明,所采用的流动模型和数值模拟方法对燃气舵的气动性能进行预示是有效的。     

基于拟欧拉角描述的上面级姿态控制律设计

上面级在多星部署过程中将涉及大角度姿态机动问题,卫星释放所引起的质心横移将给上面级姿态控制带来困难。根据系统质心的横移情况,在上面级体坐标系中确定矢量喷管的平衡位置,进而确定出矢量喷管指向指令方向时的上面级姿态。调制姿态四元数可以得到描述上面级姿态偏差的拟欧拉角及相应的拟欧拉角速度,在拟欧拉角描述的上面级姿态运动模型的基础上,选择合适的滑模面,构造变结构控制律。仿真结果表明,该控制律可对上面级姿态进行控制,进而实现对矢量喷管指向的间接控制,喷管摆角的限幅不会影响姿态控制的过程。     

European Sail Tower SPS concept

Based on a DLR-study in 1998/99 on behalf of ESA/ESTEC called “System Concepts, Architectures and Technologies for Space Exploration and Utilization (SE&U)” a new design for an Earth-orbiting Solar Power Satellite (SPS) has been developed. The design is called “European Sail Tower SPS” and consists mainly of deployable sail-like structures derived from the ongoing DLR/ESA solar sail technology development activity. Such a SPS satellite features an extremely light-weight and large tower-like orbital system and could supply Europe with significant amounts of electrical power generated by photovoltaic cells and subsequently transmitted to Earth via microwaves. In order to build up the sail tower, 60 units - each consisting of a pair of square-shaped sails - are moved from LEO to GEO with electric propulsion and successively assembled in GEO robotically on a central strut. Each single sail has dimensions of 150m × 150 m and is automatically deployed, using four diagonal light-weight carbon fiber (CFRP) booms which are initially rolled up on a central hub. The electric thrusters for the transport to GEO could also be used for orbit and attitude control of the assembled tower which has a total length of about 15 km and would be mainly gravity gradient stabilized. Employing thin film solar cell technology, each sail is used as a solar array and produces an electric power in orbit of about 3.7 MW_e. A microwave antenna with a diameter of 1 km transmits the power to a 10 km rectenna on the ground. The total mass of this 450 MW SPS is about 2100 tons. First estimates indicate that the costs for one kWh delivered in this way could compete with present day energy costs, if launch costs would decrease by two orders of magnitude. Furthermore, mass production and large numbers of installed SPS systems must be assumed in order to lower significantly the production costs and to reduce the influence of the expensive technology development. The paper presents the technical concept and an economic assessment as well as results of a recent solar sail deployment ground demonstration at DLR's facilities in Cologne.     

薄膜充气管充气展开特性试验

用展开导轨消除因重力产生的摩擦力,在不同充气速率与初始展开角条件下对薄膜材料充气管的充气展开特性进行了试验研究,获得了展开角,以及展开加速度和内气压的变化规律。试验及分析结果表明:充气管的充气膨胀与展开相互独立,充气膨胀过程近似为等压增容过程,折叠部位的气压变化特性与整体气压变化特性差异明显。     

太阳帆航天器移位轨道设计

研究了太阳帆日心移位轨道的稳定性、控制律设计及轨道拼接。将柱坐标形式的太阳帆动力学方程在参考移位轨道附近线性化,得到线性变分方程。分析线性变分方程的特征值在复数平面上的位置就可以得到移位轨道的稳定性条件。设计了太阳帆日心移位轨道的控制律,并证明了控制律满足稳定性条件。该控制律仅要求太阳帆在移位轨道飞行时姿态角α保持不变。此外,太阳帆移位轨道可以与开普勒轨道相互转化,也可以与移位轨道之间相互拼接。     

Decentralized sliding-mode control for spacecraft attitude synchronization under actuator failures

This paper examines attitude synchronization and tracking problems with model uncertainties, external disturbances, actuator failures and control torque saturation. Two decentralized sliding mode control laws are proposed and analyzed based on algebraic graph theory. Using Barbalat׳s Lemma, it is shown that the control laws guarantee each spacecraft approaches the desired time-varying attitude and angular velocity while maintaining attitude synchronization among the other spacecraft in the formation. The first controller is designed in the presence of model uncertainties, external disturbances, and actuator failures. The results are extended to the case with control input saturation in the second controller. Both control laws do not require online identification of failures. Numerical simulations are presented to show the effectiveness of the proposed attitude synchronization and tracking approaches.     

基线平面布局的GPS定姿算法

ＧＰＳ定姿线性化算法需要载体的姿态初值和迭代运算，提出一种适用于基线平面布局的矩阵元素求解算法，它不需初值和迭代计算，计算量小，运算速度快，特别适用于载体大角度姿态机动的情形。用ＴＡＮＳＶｅｃｔｏｒＧＰＳ接收机进行了实验，取得了较满意的结果。     

大型挠性空间结构的变结构控制

本文从ＬＦＳＳ的相对阶为２的特点出发设计了用于ＬＦＳＳ的镇定控制的变结构控制器,从而避免了主导极点的选择（模态截断）,解决了“控制溢出”问题。以太阳帆板展开过程中航天器姿态控制为例,作了计算机仿真。     

纯磁控微小卫星的姿态捕获控制研究

针对纯磁控微小卫星姿态捕获问题,提出了一种基于姿态角和姿态角速度反馈的磁
矩能量控制律。利用Matrosov定理证明了该控制律具有一致渐近稳定性,能够保证星体最终
稳定到唯一的零轨道姿态角平衡位置。结合某在研低轨纳星,分析了气动力矩作用下星体大
角度姿态捕获的纯磁控性能。仿真结果表明,所设计的能量控制律具有一致渐近稳定特性,
考虑气动力矩影响时可在一个轨道周期内完成纳星姿态捕获,控制精度较高。该控制律具有
较好的工程应用前景,对于低成本微小卫星的研制是一个有益的探索。     

运载器饱和非线性姿态控制系统稳定性分析

简要介绍了用描述函数分析饱和非线性系统稳定性的方法，然后在此基础上给出了适合于工程的饱和非线性系统稳定裕度的定义，研究了舵偏角不满足近似关系时，正弦函数非线性对姿控系统稳定性的影响，最后计算了某运载器的伺服机构处于饱和状态时姿态控制系统的稳定裕度。     

充气太阳能帆板展开动力学数值模拟预报

充气太阳能帆板是一种通过气体驱动支撑管展开的新型太阳能帆板。首先简要介绍其研究进展，然后针对充气展开支撑管，提出了分段式充气体积控制模型，基于LS—DYNA模拟了空间环境下Z型折叠充气太阳能帆板在支撑管无约束与有轴向约束控制时的展开过程，分析了支撑管每折叠段的气压变化，上横板的动力学特性以及基板的平面外振动，预报了展开过程中支撑管与基板的接触碰撞，并通过悬吊式展开试验验证了计算结果。结果表明，本文计算能够预报充气太阳能帆板在空间展开的动力学特性。     

一种冷热交变环境下太阳帆应力保持方法

针对冷热交变环境导致太阳帆内部应力剧烈变化的问题,基于形状记忆合金(SMA)弹簧提出了太阳帆的张拉方案和薄膜应力保持恒定的方法,该方法利用形状记忆合金在高低温下的刚度非线性特性,有效补偿薄膜和支撑杆之间的间隙变化,以使薄膜内部应力基本保持恒定。针对六边形构型太阳帆开展了数值仿真,首先建立了太阳帆的热分析模型和力学分析模型,获取了高低温工况下的温度场。然后通过热致变形分析得到薄膜与支撑杆在高低温工况下的间隙变化,据此确定形状记忆合金弹簧的参数。最后对太阳帆在高低温工况下的薄膜内部应力进行了验证。