通信卫星推力器可靠性评估方法

针对通信卫星推力器服役寿命长、试验费用高、寿命试验所得数据通常较少等具体特点,提出一种推力器极少失效数据可靠性评估和寿命预测方法,并建立不同试验工况下试验信息的相互折算原则,有效解决了通信卫星推力器的高精度可靠性评估难题.对某型推力器脉冲试验和稳态试验数据进行了处理,分别给出其同步轨道运行可靠性和转移轨道运行可靠性评估结果.      

Numerical modeling of spacecraft electric propulsion thrusters

There is a clear current trend towards the replacement of small chemical thrusters used for spacecraft control by electric propulsion thrusters. These thrusters use a variety of mechanisms to convert electrical power into thrust and, in general, provide superior specific impulse in comparison to chemical systems. Electric propulsion has been under development for the last 40 yr, and almost all thrusters are designed based on experience and experimentation. The present article considers the progress made in numerical simulation of electric propulsion thrusters. Due to the wide range of such devices, attention is restricted to electric propulsion thruster types that are presently in use by orbiting spacecraft. The physical regimes created in these thrusters indicate that a variety of numerical methods is required for accurate numerical simulation ranging from continuum formulations to kinetic approaches. Successes of numerical simulation models are demonstrated through specific examples. It is concluded that numerical simulations can be expected to play a more prominent role in the design and evolution of future electric propulsion thrusters.     

卫星姿控发动机混合物羽流场分区耦合计算研究

研究求解喷管内流场N-S方程数值计算方法,发展基于N-S方程物面边界滑移流理论计算技术。提出求解羽流核心区轴对称DSMC模拟方法与远场三维DSMC仿真方案,发展多组元混合物羽流DSMC仿真方法。研究求解卫星姿控发动机内外近场、远场、倒流区和物面相互作用影响区多流域流场分区耦合计算技术,建立了一套用于求解混合物燃气羽流及对太阳电池帆板与卫星体表面撞击污染影响数值模拟方法。通过对分别安装于某在轨卫星不同位置两个典型姿控发动机燃气五组元混合物羽流计算研究及相关结果对比分析,证实本文数值方法可靠性。     

基于章动原理实施推力器标定

为了保证在实施大的变轨过程中卫星的安全，必须进行推力器对偶性检验。卫星设计部门和地面工作人员根据卫星的特点，利用姿态数据及章动原理建立了一套标定推力器对称性的方法。此方法在地球同步三轴稳定卫星轨道维持过程中得到实际检验，效果良好。     

Direct drive options for electric propulsion systems

Power processing units (PPUs) in an electric propulsion system provide many challenging integration issues. The PPU must provide power to the electric thruster while maintaining compatibility with all of the spacecraft power and data systems. Inefficiencies in the power processor produce heat, which must be radiated to the environment in order to ensure reliable operation. Although PPU efficiencies are generally greater than 0.9, heat loads are often substantial. This heat must be rejected by thermal control systems which generally have specific masses of 15-30 kg/kW. PPUs also represent a large fraction of the electric propulsion system dry mass. Simplification or elimination of power processing in a propulsion system would reduce the electric propulsion system specific mass and improve the overall reliability and performance. A direct drive system would eliminate all or some of the power supplies required to operate a thruster by directly connecting the various thruster loads to the solar array. The development of concentrator solar arrays has enabled power bus voltages in excess of 300 V which is high enough for direct drive applications for Hall thrusters such as the Stationary Plasma Thruster (SPT). The option of solar array direct drive for SPTs is explored to provide a comparison between conventional and direct drive system mass     

Electrodynamic forces in tethered satellite systems. I. Systemcontrol

Part I of this work deals with the use of electrodynamic forces for control of tethered satellite system. A system formed by two massive end-bodies connected to each other by a current carrying tether is to be kept in an Earth-pointing orientation by means of joint actions of thrusters on one of the end-bodies and electrodynamic forces acting on the tether     

动量轮在轨状态可靠性贝叶斯网络建模与评估

卫星动量轮在轨运行环境复杂,并且无失效数据,难以利用传统方法进行可靠性建模与评估。为此,提出一种利用贝叶斯网络融合动量轮各种试验信息及轴温和电流等遥测数据的可靠性建模与评估方法。基于失效分析建立贝叶斯网络拓扑结构,根据试验数据估计网络参数,而后,通过贝叶斯网络的推理得到动量轮可靠度的点估计和区间估计,并利用在轨遥测数据实时评估动量轮可靠性,获得动量轮可靠性变化趋势比较明显的遥测数据取值区间。该方法对动量轮实时状态监控具有一定的理论和实践意义。     

Attitude control of a satellite with redundant thrusters

Redundant thrusters are generally used for a reliable attitude control system. Also, redundant thrusters yield a better performance if they are used appropriately. In this paper, the authors propose an efficient redundancy management algorithm to reduce the fuel consumption. The algorithm is based on a linear programming problem which is a constrained optimization problem. For the algorithm, a cost function is defined as a quantity related to the fuel consumption for a maneuver. The independent variables are the thrusters' on-times which are control input variables of a satellite dynamic model. The advantage of the proposed method is verified by numerical examples. The examples show that the proposed method consumes less fuel than an existing method for a given maneuvering command. A sub-optimal algorithm is also discussed for an onboard computation. The proposed algorithm is applied to two maneuvers: move-to-rest and rest-to-rest. This is verified by a numerical simulation.     

离子推力器极少数据可靠性评估方法

针对只有两台离子推力器进行寿命试验,试验结果为极少失效数据的情况,建立了一种离子推力器整机可靠性评估方法.通过引入区间统计量的概念,充分开发从最后一个失效数据继续试验到没有发生产品失效这一重要试验信息,由高斯-马尔科夫定理计算出寿命分布参数的最佳线性无偏估计,并给出离子推力器可靠度和寿命的单侧置信下限.最后,对美国NASA研制的型号为XIPS-13的离子推力器进行可靠性评估,得出了其寿命需求10000h的可靠度单侧置信下限为0.87及给定可靠度为0.9时的寿命单侧置信下限为9024.6h,该方法精度较高,便于工程应用.      

卫星姿控发动机喷管羽流撞击效应试验

在高超声速低密度风洞中试验研究了卫星姿控发动机喷管羽流对平板模型的撞击效应,包括气动力和气动热效应。试验气体为加热的氮气。对两个卫星姿态控制发动机喷管的十种实验状态进行了测量。测出了平行于喷管轴线的平板模型上的压力分布和温度变化及处于喷管上方后流区的挡板的温度变化,给出了平板模型上的气动力和气动热分布规律,并判断是否形成后流区。测量结果表明,试验结果可靠,具有工程应用价值,能为姿控发动机在卫星上的布局提供参考。     

敏捷卫星的联合执行机构控制策略

 针对对地观测敏捷卫星大角度快速机动、高控制精度的任务需求,提出了联合推力器与飞轮作为执行机构的控制策略。该控制策略综合利用2种执行机构的优点:推力器以前馈的形式提供机动过程中所需的主要力矩以实现航天器大角度的快速机动,而飞轮以反馈的形式提供精准的控制力矩以提高机动过程中的姿态控制精度。为补偿由于初始状态偏差和推力器输出力矩不准确所带来的控制误差,采用变结构控制设计了2种姿态跟踪控制器,使航天器能够渐进地跟踪上参考轨迹。并对姿态机动控制过程中,飞轮力矩及转速可能出现的饱和问题作了相应的修正。仿真结果表明了所提控制策略及所设计控制算法的可行性和有效性。     

Uses of electrodynamic forces in tethered satellite systems. II.Orbit-transfer

Part II of this work presents electrodynamic forces used for orbit transfer. The system presented in Part I is to be transferred to a new orbit of a different radius while maintaining a nearly Earth-pointing orientation at all times. The maneuver is to be performed with electrodynamic forces without the use of thrusters. To accomplish this mission, the notion of synchronized impulses, that is, running electric current through the tether at precalculated instants and amplitudes, is presented     

基于双状态卡方故障检测的组合导航系统

故障检验与隔离是利用联邦滤波实现组合导航系统安全可靠运行的关键技术。针对常规残差卡方检验法对于慢变故障检验效果差,以及状态卡方检验受到初值误差、系统噪声和建模误差影响导致子系统被频繁隔离的问题,提出一种改进的SINS/GPS/ADS/DVL组合导航系统故障检验算法。该算法采用2个状态推进器交替地对滤波数据进行重置,避免状态递推器被未检测出来的故障污染。实验结果表明,改进的算法能够有效提高故障检验的灵敏度,增强组合导航系统的可靠性。     

Ion engine grids: Function,main parameters,issues, configurations,geometries, materials and fabrication methods

Ion optics are crucial components of ion thrusters and the study of the different ion extraction solutions used since the beginning of the electric propulsion era is essential to understand the evolution of ion engines. This work describes ion engine grids' main functions, parameters and issues related to thermal expansion and sputter erosion, and then introduces a review of ion optics used for significant launched and tested ion thrusters since 1970. Configurations, geometries, materials and fabrication methods are analyzed to understand when typical ion thrusters use two or three grids, what are the thicknesses and aperture sizes of the screen, accelerator and decelerator grids, why molybdenum and carbon-based materials such as pyrolytic graphite and carbon–carbon are the best available options for ion optics and what is the manufacturing method for each material.     

单组元发动机热回浸现象的理论分析

用有限元法数值分析了通讯卫星上用于姿态和轨道控制的单组元发动机的热回浸现象。计算表明,燃烧室工作后的热量主要是通过支撑圆杆的热回浸和辐射而散失的。所得模拟结果还说明,工程设计中采用毛细管输送燃料,确实能有效地阻止发动机工作后燃烧室中的热量通过输料管传到电磁阀,可充分保证电磁间的安全。     

Performance enhancement using power beaming for electric propulsionEarth orbital transporters

Power requirements for an electric propulsion Earth orbital transport vehicle (EOTV), which can effectively deliver large payloads using much less propellant than chemical transfer methods, are addressed. The power beaming concept is described. Arcjets, magnetoplasmadynamic (MPD) thrusters, and ion engines are covered. Power supply characteristics are discussed for nuclear, solar and power-beaming systems. Operational characteristics are given for each, as are the effects of the power supply alternative on the overall craft performance. Because of its modular nature, the power beaming can meet the power requirements of all three electric propulsion types. Commonality of approach allows different electric propulsion approaches to be powered by means of a single power supply approach. Power beaming exhibits better flexibility and performance than onboard nuclear or solar power systems     

Particle simulation of grid system for krypton ion thrusters

The transport processes of plasmas in grid systems of krypton (Kr) ion thrusters at different acceleration voltages were simulated with a 3D-PIC model, and the result was compared with xenon (Xe) ion thrusters. The variation of the screen grid transparency, the accelerator grid current ratio and the divergence loss were explored. It is found that the screen grid transparency increases with the acceleration voltage and decreases with the beam current, while the accelerator grid current ratio and divergence loss decrease first and then increase with the beam current. This result is the same with Xe ion thrusters. Simulation results also show that Kr ion thrusters have more advantages than Xe ion thrusters, such as higher screen grid transparency, smaller accelerator grid current ratio, larger cut-off current threshold, and better divergence loss characteristic. These advantages mean that Kr ion thrusters have the ability of operating in a wide range of current. Through comprehensive analyses, it can be concluded that using Kr as propellant is very suitable for a multi-mode ion thruster design.     

离子推力器加速栅寿命概率性分析

交换电荷离子对加速栅极的溅射腐蚀是离子推力器的关键失效模式之一,基于交换电荷离子对加速栅溅射腐蚀的物理机理,对离子推力器加速栅工作寿命进行了概率性建模。利用该模型对20cm Xe离子推力器加速栅寿命和其达到预期寿命的可靠度进行了评估。结果显示加速栅的寿命近似服从高斯分布,当推力器工作环境压力近似6.7×10-3Pa时,加速栅工作寿命达到3kh的可靠度为0.9352。     

空间绳系机器人逼近目标协调控制方法

 为了节省空间绳系机器人的末端执行装置在逼近目标卫星过程中推力器所使用的燃料,本文提出一种利用推力器、反作用轮及空间系绳的协调控制方法。首先利用二次型最优控制器(LQR)算法计算出末端执行装置逼近目标所需的理想轨道控制力,然后利用模拟退火算法将所需轨道控制力优化分配到推力器及空间系绳,同时利用时间延迟算法通过反作用轮补偿空间系绳产生的姿态干扰力矩。仿真结果表明,利用该协调控制方法能显著节省末端执行装置上推力器的燃料消耗,有效抑制空间系绳协调控制力产生的姿态干扰,使末端执行装置保持相对稳定的姿态。     

Flexible piloted Mars missions using the TIHTUS engine

The present investigation points out the potential of continuously propelled spacecraft for piloted Mars missions and compares them to impulsive propulsion (chemical and nuclear thermal) and ballistic trajectories. Although the results are related to piloted Mars missions, the stated issues raised hold true for a broad range of space missions. It is demonstrated that the use of impulsive propulsion leads to inflexible missions and may result in long total mission durations. Meanwhile, the use of continuous electric propulsion not only guarantees short total mission durations of Mars missions with moderate masses but also results in highly flexible missions. These criteria can be met with a continuous electric propulsion system that provides a thrust level of 100 N and 3000 s of specific impulse. Great potential lies in electric hybrid thrusters. The high-power, two-stage hybrid plasma thruster TIHTUS is currently being developed at the Institute of Space Systems (IRS). Its technology including preliminary laboratory testing results are presented.