末端带集中质量的可伸展挠性附件与航天器姿态耦合动力学分析

结构复杂的航天器带有几十米、上百米大型挠性附件,附件末端还带有大质量刚体.大型挠性附件在空中展开时,其伸展运动、弹性振动和航天器的姿态运动相互耦合.为研究附件伸展和振动对航天器姿态的影响并设计有效的控制器,有必要建立可伸缩挠性附件与航天器姿态耦合动力学模型.为此,利用动量矩定理推导出末端带集中质量的可伸缩柔性附件与航天器姿态耦合动力学方程,研究了带末端质量附件的伸展运动对航天器姿态及对附件挠性振动的影响.附件匀速伸展,用Runge-Kutta法对系统进行数学仿真,仿真结果表明:伸展过程姿态角误差增大,附件振幅增大,附件频率不断降低,并且末端质量越大时,在相同长度处附件频率越小,增加了控制的难度.对末端带集中质量的挠性附件和中心刚体进行主动控制能有效抑制挠性附件的振动,满足姿态角精度要求.     

航天器太阳帆板伸展过程最优控制的粒子群优化算法

讨论航天器太阳帆板伸展过程中航天器姿态运动的最优控制问题。利用多体动力学方法导出带太阳帆板航天器姿态运动方程。在系统角动量为零的情况下,带太阳帆板航天器系统的姿态运动控制问题可转化为无漂移系统的非完整运动规划问题。在非完整运动规划中引入粒子群优化算法,通过控制太阳帆板伸展运动可同时获得航天器姿态的期望位形。数值仿真表明,该方法对太阳帆板伸展过程中航天器主体姿态控制是有效的。     

带伸展柔性附件航天器的动力响应

推导了带伸展柔性附件航天器的时变系数动力学方程。对比了用刚性模型和柔性模型处理这类问题的区别,柔性模型的姿态角速度围绕刚性模型姿态角速度曲线振荡,因此用刚性模型可以近似地预测角速度的运动趋势。分析了附件自由振动和受简谐激励、脉冲激励时对航天器姿态的影响。指出了一些独特的动力学行为：齐次解的非瞬态特性、脉冲响应的渐强振动、简谐激励的非稳态特性、瞬时共振的延续和加强。这些特性的存在会导致航天器姿态的剧烈运动和附件的破坏     

低轨道下运行的卫星-太阳帆板系统的刚-柔-热耦合动力学建模

传统地考虑热效应的卫星-太阳帆板动力学模型只考虑太阳直接辐射热流的影响,仅适用于高轨道运行的航天器。以低轨道下运行的卫星-太阳帆板系统为研究对象,提出了一种通用的分析其在宇宙空间各种热流作用下刚-柔-热耦合动力学特性的建模方法。考虑太阳帆板热变形、卫星的姿态运动和太阳帆板受到的各种辐射的热流密度之间的耦合关系,分别给出了太阳直接辐射热流、地球红外辐射热流以及地球反照辐射热流的计算公式。将系统视为中心刚体-悬臂梁模型,首先建立了悬臂梁的热传导方程,然后通过引入考虑热应变的应力-应变关系,用虚功原理建立了卫星-太阳帆板多体系统的考虑热效应的动力学方程,对热传导方程和动力学方程联立求解。对低轨道下运行的卫星-太阳帆板系统进行了数值仿真分析,分析了考虑地球红外辐射和地球反照辐射热流对热振动的影响,以及考虑刚-柔-热耦合效应对系统动力学特性的影响,并给出了系统热振动稳定时特征参数的范围。     

计入姿态的绳系卫星概周期振动

建立了计入子星姿态的绳系卫星系统非线性动力学模型,研究了状态保持阶段系统的动力学行为。因计入子星姿态运动,导致子星高频振动与系绳低频摆动耦合,使得面内绳系卫星系统成为快-慢时变的非线性振动系统。应用变量分离和多尺度方法,获得了绳系卫星系统在平衡位置附近的概周期运动。结果表明,计入子星姿态的面内绳系卫星系统表现为概周期振动。     

不平衡飞轮的扰动特性

高精度航天器对指向精度有极高的要求,飞轮是卫星姿态控制环节中不可或缺的执行部件,在研制和装备过程中,不可避免地具有微量的偏心或动不平衡,在姿态机动和稳定控制的过程中,飞轮的旋转会产生干扰力。将动静不平衡质量作为航天器的一部分,推导出完整航天器动力学姿态方程,进行动力学仿真,并根据完整的姿态动力学方程简化分析仿真结果。研究发现动静不平衡质量在飞轮高速转动时,对姿态均有影响,动不平衡质量对姿态的影响与安装位置关系很小,而静不平衡质量呈现线性关系,且两者对姿态的影响满足线性叠加。单轴转动时,指向精度的长周期变化只与飞轮的固有特性有关,与转速的大小无关。多轴转动时,姿态会振荡或发散,与初始相位有关;但对姿态的影响不满足单轴转动的叠加。     

卫星重力梯度数据用于精化地球重力场的研究

确定厘米级大地水准面和发展超高阶地球重力场模型是现代物理大地测量的主要科学目标之一。卫星重力梯度测量的实现将为这一目标做出重大贡献。文章着重评述这一领域的研究进展，并讨论利用卫星重力梯度数据精化地球重力场的若干理论和方法问题。     

卫星精确定向的模型参考鲁棒控制器设计

本文建立了圆轨道卫星的姿态动力学模型,并进行了线性化,分析了传感器噪声对卫星姿态角和姿态角速度的影响,采用加权函数法设计了模型参考鲁棒H-inf控制器,并通过DK迭代求解,仿真证明当存在传感器测量误差和模型不确定时,卫星能够跟踪参考模型,鲁棒H-inf 控制系统具有良好的性能。     

带挠性附件卫星刚柔耦合姿态动力学建模与仿真

研究了带挠性附件卫星姿态运动与附件弹性变形运动之间的耦合效应.在计及挠性附件变形位移场耦合作用的基础上,利用假设模态,采用Kane方法建立了卫星刚柔耦合姿态动力学一次近似模型.通过数值仿真,表明了本文模型比传统零次近似模型更能准确的预测星体的姿态运动和挠性体的动力学行为.     

绳系卫星收放控制地面实验研究

根据天-地动力学相似原理,设计了圆轨道绳系卫星面内运动地面实验系统。该系统的特色在于:利用气垫和喷气模拟卫星系统的空间动力学环境,如重力梯度和Coriolis力。基于计算机视觉和无线局域网技术,构建了在线测控子系统。根据在线优化及滚动时域控制理论,设计了绳系卫星反馈控制器。所设计的反馈控制律并非以解析形式给出,而是利用Legendre伪谱和非线性规划方法在线计算开环最优轨道来确定。最后,通过示例实验对控制器性能和地面实验系统的有效性进行了考核和验证。     

空间卷曲折叠管充气控制展开动力学研究

充气展开管是大型空间充气展开结构的基本支撑部件,该文针对柔性卷曲折叠管,采用刚体平面运动理论分析了有无阻尼控制的展开过程,并提出了分段式充气控制体积有限元模型,模拟了空间环境下卷曲折叠管的展开动力学。最后对卷曲折叠管在阻尼控制下进行了充气展开测试,试验结果与数值模拟结果相一致。这表明:采取一定控制展开的卷曲折叠管能作为空间充气展开结构的控制展开方式;数值模拟是有效的,可为空间环境下的展开过程提供一定依据。     

阻尼器对卫星太阳翼锁定冲击力矩影响的研究

本文在卫星太阳翼系统建模的基础上,利用多体动力学分析软件MSC.ADAMS对太阳翼展开过程进行了动力学仿真分析,通过展开过程中对帆板之间的冲击力矩变化进行考察,分析了阻尼器在不同位置的情况下,锁定过程中的锁定冲击力矩的变化,评估阻尼器的抑振效果,从而确定阻尼器安装的最佳位置。     

重力对大型环形可展天线展开动力学的影响研究

受限于火箭尺寸,大型星载环形天线在发射时收拢,入轨后在零重力环境下展至工作态。然而在地面实验重力环境下,克服重力的悬吊卸载系统并不能完全抵消重力场的全部影响,导致地面实验难以准确预测在轨展开动力学行为。因此,有必要借助仿真深入对比分析地面上重力加卸载展开与太空中无重力展开的动力学异同。该文基于柔性多体动力学的仿真方法,建立了天线在零重力和重力加卸载系统两种工况下的全尺寸展开动力学模型。仿真结果不但复现了地面实验的非同步展开现象,而且系统地给出了天线在整个展开历程中所有杆件载荷和驱动力的变化规律。并进一步基于能量分析,半解析地研究了重力对驱动力的影响。该文的研究不但有助于理解大型网状天线的展开动力学,为天线的机构设计、优化和地面实验设计提供技术支撑,而且提出的建模方法和得到的认识也可用于研究和理解其他大型网状天线。     

空间热载荷作用下星载天线耦合动态影响分析

为了研究空间热载荷对星载天线刚柔耦合多体系统的扰动,根据抛物反射面几何特征,采用壳体单元有限元离散化法,并考虑壳体厚度方向上的温度变化,建立了有限元列式的热传导方程;引入与应变能有关的耦合项,利用拉格朗日法推导了星载天线系统的大范围刚柔耦合动力学方程,研究了温度载荷对星载天线多体系统的动力学特性影响。仿真结果表明:空间热效应引起了动态的温度载荷,与结构变形发生耦合,诱发耦合颤振,加剧柔性反射面的弹性振动,造成卫星姿态和天线指向的扰动,严重影响了星载天线的指向精度。结论对星载天线指向精度的分析与控制具有重要的理论价值及工程实际意义。     

航天器可展开支撑杆的研制及其收拢展开特性研究

复合材料豆荚杆是一种质量轻、刚度较大、收拢效率高、展开过程可靠的可展开管状杆结构。本工作对豆荚杆进行优化设计,并对多种豆荚杆试件进行性能测试与评估,选取其中综合性能优异的材料体系研制了2m长豆荚杆样机。利用研制的豆荚杆收展控制机构对豆荚杆的收拢-展开性能进行了测试,结果显示玻璃布/FEB豆荚杆可实现多次收拢-展开,其综合性能可基本满足空间可展开结构的性能需求。     

空间望远镜层合材料镜片展开过程非线性动力学行为分析

为了研究空间望远镜柔性子镜展开过程对镜片型面精度和望远镜系统的扰动问题,以花瓣式可展开空间望远镜抛物层合镜片为研究对象,基于绝对节点坐标法,采用考虑初始形态曲率的曲壳单元对镜片的形变位移进行描述,表征了层合镜片几何非线性关系与材料非线性关系下的应变和应力关系。利用虚功原理推导了傍瓣子镜展开过程的耦合动力学方程,考虑了镜片弹性变形与大范围运动的耦合作用。针对使用的曲壳单元和传统建模方式,分别对镜片展开过程进行仿真分析,结果表明使用绝对节点坐标法更有利于描述柔性体大变形与大范围运动的耦合,壳单元在描述曲壳结构时更加精确。铰链驱动力矩能够激发镜片的振荡,特别是在多镜片同时展开时,多柔体的耦合作用会严重影响镜面的型面精度,进而扰动卫星本体的姿态。结论对空间望远镜的镜面精度和姿态精度的分析与控制具有理论价值和工程实际意义。     

Satellite-to-satellite tracking and satellite gravity gradiometry (Advanced techniques for high-resolution geopotential field determination)

The purpose of satellite-to-satellite tracking (SST) and/or satellite gravity gradiometry (SGG) is to determine the gravitational field on and outside the Earth's surface from given gradients of the gravitational potential and/or the gravitational field at satellite altitude. In this paper both satellite techniques are analysed and characterized from a mathematical point of view. Uniqueness results are formulated. The justification is given for approximating the external gravitational field by finite linear combination of certain gradient fields (for example, gradient fields of single-poles or multi-poles) consistent to a given set of SGG and/or SST data. A strategy of modelling the gravitational field from satellite data within a multiscale concept is described; illustrations based on the EGM96 model are given.     

Satellite attitude stabilization using fluid rings

The three-dimensional attitude stabilization of a satellite using fluid rings is proposed in the present paper. The general formulation of the system that comprises a satellite and three fluid rings, one on each axis, is obtained through Euler’s moment equations. The linearized system model is derived and the stability conditions are obtained. Linear control laws and nonlinear control laws based on sliding mode control techniques are developed for fluid control torques. The numerical simulation of the governing nonlinear equations of motion of the system along with stability analysis establishes the feasibility of achieving desired attitude stabilization of the satellite. The fluid controllers are successful in stabilizing the attitude of the satellite in presence of high attitude disturbance torques and intermittent actuators’ failures. In the case of sudden attitude disturbance torques, the nonlinear fluid controllers outperform the linear fluid controllers with virtually no effect on the satellite attitude response. The proposed attitude stabilization method may find applications in future satellite missions.     

The JUSTSAP experiment on STS-95

An instrumented flow cell in the form of a cylinder with differentially heated end walls and adiabatic sidewalls was flown on STS-95 as the Japan-US Thermal Science Accelerometer Project (JUSTSAP). The purpose of the experiment was to map disturbances in the thermal field during the course of a Shuttle mission in order to correlated them with various mission events and to determine if any global transport could be detected from second order, non-zero time average flows resulting from periodic accelerations (g-jitter). Significant disturbances in the thermal field were noted each time the Shuttle changed attitude, such as the maneuver to -Z solar inertial, which is done periodically for thermal conditioning. Burns from the main thrusters associated with the launch and retrieval of the Spartan satellite produced overturning flows, as might be expected. During extended periods in which the attitude was held constant, the perturbations to the thermal field correlate extremely well with calculated accelerations from gravity gradient and drag. Fair agreement was found between the observed temperature perturbations and those predicted from a modification of the analytical model developed by Bejan and Tien (B&T) for the flow and heat transfer in an infinite cylinder with a constant axial thermal gradient. A full three-dimensional computational fluid dynamic analysis with more realistic thermal boundary conditions provided better agreement after adjustments were made to account for the heat flow away from the measuring thermistors. Once calibrated with a reliable thermal model, the flow cell was found to serve as a high-precision accelerometer, capable of measuring the quasi-steady acceleration with a sensitivity of better than 0.1 micro-g in the presence of the higher amplitude g-jitter typical of Shuttle operations. Further, it was found that the gravity gradient acceleration accounted for virtually all of the observed quasi-steady accelerations during such extended periods. The thermal response time of the JUSTSAP was too slow to expect to see the effects of fluctuating first order flows resulting from the vibrational environment of the Shuttle. However, an indication of a change in the thermal field near the ends of the flow cell was seen during periods of crew exercise that may possibly be attributed to circulating eddies resulting from the higher order terms in the momentum equation. At higher amplitudes, these second order effects can produce non-zero time average flows of a global nature, as can the start-up transients in first-order periodic flows. No such effects were observed, thus it is possible to place an upper limit on the integrated power spectral density of the vibrational environment experienced as well as the nature of the start-up transients of the periodic flows.     

The JUSTSAP experiment on STS-95

An instrumented flow cell in the form of a cylinder with differentially heated end walls and adiabatic sidewalls was flown on STS-95 as the Japan-US Thermal Science Accelerometer Project (JUSTSAP). The purpose of the experiment was to map disturbances in the thermal field during the course of a Shuttle mission in order to correlated them with various mission events and to determine if any global transport could be detected from second order, non-zero time average flows resulting from periodic accelerations (g-jitter).Significant disturbances in the thermal field were noted each time the Shuttle changed attitude, such as the maneuver to -Z solar inertial, which is done periodically for thermal conditioning. Burns from the main thrusters associated with the launch and retrieval of the Spartan satellite produced overturning flows, as might be expected. During extended periods in which the attitude was held constant, the perturbations to the thermal field correlate extremely well with calculated accelerations from gravity gradient and drag. Fair agreement was found between the observed temperature perturbations and those predicted from a modification of the analytical model developed by Bejan and Tien (B&;T) for the flow and heat transfer in an infinite cylinder with a constant axial thermal gradient. A full three-dimensional computational fluid dynamic analysis with more realistic thermal boundary conditions provided better agreement after adjustments were made to account for the heat flow away from the measuring thermistors.Once calibrated with a reliable thermal model, the flow cell was found to serve as a high-precision accelerometer, capable of measuring the quasi-steady acceleration with a sensitivity of better than 0.1 micro-g in the presence of the higher amplitude g-jitter typical of Shuttle operations. Further, it was found that the gravity gradient acceleration accounted for virtually all of the observed quasi-steady accelerations during such extended periods. The thermal response time of the JUSTSAP was too slow to expect to see the effects of fluctuating first order flows resulting from the vibrational environment of the Shuttle. However, an indication of a change in the thermal field near the ends of the flow cell was seen during periods of crew exercise that may possibly be attributed to circulating eddies resulting from the higher order terms in the momentum equation. At higher amplitudes, these second order effects can produce non-zero time average flows of a global nature, as can the start-up transients in first-order periodic flows. No such effects were observed, thus it is possible to place an upper limit on the integrated power spectral density of the vibrational environment experienced as well as the nature of the start-up transients of the periodic flows.