Spacecraft Design-for-Demise implementation strategy & decision-making methodology for low earth orbit missions

Space missions designed to completely ablate upon an uncontrolled Earth atmosphere reentry are likely to be simpler and cheaper than those designed to execute controlled reentry. This is because mission risk (unavailability) stemming from controlled reentry subsystem failure(s) is essentially eliminated. NASA has not customarily implemented Design-for-Demise meticulously. NASA has rather approached Design-for-Demise in an ad hoc manner that fails to entrench Design-for-Demise as a mission design driver. Thus, enormous demisability challenges at later formulation stages of missions aspired to be demisable are evident due to these perpetuated oversights in entrenching Design-for-Demise practices. The investigators hence propose a strategy for a consistent integration of Design-for-Demise practices in all phases of a space mission lifecycle. Secondly, an all-inclusive risk-informed, decision-making methodology referred to as Analytic Deliberative Process is proposed. This criterion facilitates in making a choice between an uncontrolled reentry demisable or controlled reentry. The authors finally conceive and synthesize Objectives Hierarchy, Attributes, and Quantitative Performance Measures of the Analytical Deliberative Process for a Design-for-Demise risk-informed decision-making process.     

Atmospheric reentry hemisphere prediction for prograde orbits using logical disjunction

A unique logic-based algorithm for atmospheric reentry hemisphere prediction is presented for spacecraft in low-eccentricity, prograde low Earth orbits at altitudes of 300 km and lower. Using two-line element (TLE) data for initial orbit conditions, coupled with coarse estimates for spacecraft aerodynamic characteristics, the algorithm relies on logical disjunction operations based on a dual analysis of histogram and two-weighted Gaussian probability density function (PDF) fits of predicted reentry latitude data. The algorithm requires the execution of a series of parametric simulations to determine the reentry hemisphere for variations in spacecraft aerodynamic coefficients and drag reference area. When implemented, the algorithm yields accurate hemisphere predictions on average 15 days from reentry as demonstrated by historical reentry cases from 1979 to 2018. All reentry cases were selected to demonstrate the algorithm’s ability to deliver accurate reentry hemisphere predictions for spacecraft with varying physical size and mass, and reentering during different periods of solar cycle activity.     

谈风险管理在航天器研制中的应用

风险管理是航天计划/项目管理的重要组成部分。在航天型号研制中，国际上都十分重视风险的管理，在型号研制工作中都制定风险管理计划，并已有一套系统的做法。文章介绍了在航天项目中风险管理的内容、要求和过程，并介绍了一些国际上应用的情况。     

用四元数法建立卫星返回运动方程组

通常坐标系间的转换关系及角运动的描述采用欧拉角方法,但该方法的描述在角运动方程中存在不定解问题;在卫星的返回再入过程中,角度变化范围很大,有时很难避开奇点。采用四无数法,可根本解决奇点问题,有效地提高计算的精度和速度。在此基础上,文章建立了卫星返回运动的方程组。     

Computational methods for reentry trajectories and risk assessment

The trajectory modeling of uncontrolled satellites close to reentry in the atmosphere is still a challenging activity. Tracking data may be sparse and not particularly accurate, the objects’ complicate shape and unknown attitude evolution may render difficult the aerodynamic computations and, last but not the least, the models used to predict the air density at the altitudes of interest, as a function of solar and geomagnetic activity, are affected by significant uncertainties.After a brief overview of the relevance of the risk related to satellite reentries and debris survival down to the ground, the paper describes some of the methods and techniques developed in support of the reentry predictions carried out for civil protection purposes. An appropriate management of the intrinsic uncertainties of the problem is in fact critical for the dissemination of the information, avoiding, as much as possible, misunderstandings and unjustified alarm.Special attention is paid to the evaluation of the risk, the availability of orbit determinations, the uncertainties of the residual lifetime estimation, and the definition of reentry and risk windows. When possible, the discussion is supported by real data, results and examples, often based on the authors’ direct experience and researches.     

基于自适应伪谱法的高超声速飞行器再入轨迹优化

针对高超声速飞行器再入轨迹优化问题,建立考虑地球自转的三自由度再入运动方程,以美国通用空天飞行器为对象建立再入约束模型。采用Legendre-Gauss-Radau配点对3种典型优化问题:最大纵程、最大横程及最小航迹角变化率问题进行离散,将连续时间最优控制问题转化为非线性规划问题。基于Legendre多项式近似理论,引入衰减系数构建相对误差估计关系式,并以此提出一种有效的自适应网格重构策略。最终获得了3种典型再入轨迹优化问题的最优解。仿真结果表明,该算法的求解结果与变步长Runge-Kutta-Fehlberg法积分一致。相比传统自适应伪谱法,其配点和区间分配更合理,迭代次数少,求解速度高,且对人工参数不敏感。      

基于差分进化算法的再入可达域快速计算#br#

针对高升阻比高超飞行器再入可达域计算问题,提出了基于差分进化算法和倾侧角插值相结合的混合求解方案。通过设计罚函数和适应度函数极值化将再入过程等式约束和不等式约束添加到优化指标。为了减小参数化倾侧角剖面的搜索空间,利用带约束的差分进化算法求解满足再入过程约束和终端约束的再入轨迹。在分别得到最大横向航程和最大纵向航程的倾侧角剖面后,利用插值法快速生成倾侧角指令集,进而实现再入可达域的快速计算。以高升阻比飞行器CAV H为对象,设计仿真算例,结果表明,该混合优化求解方案易于实现且具有良好的可操作性。     

Reentry survival analysis of tumbling metallic hollow cylinder

The survival of orbital debris reentering the Earth’s atmosphere is considered. The numerical approach of NASA’s Object Reentry Survival Analysis Tool (ORSAT) is reviewed, and a new equation accounting for reradiation heat loss of hollow cylindrical objects is presented. Based on these, a code called Survivability Analysis Program for Atmospheric Reentry (SAPAR) has been developed, and the new equation for reradiation heat loss is validated. Using this equation in conjunction with the formulation used in ORSAT, a comparative case study on the Delta-II second stage cylindrical tank is given, demonstrating that the analysis using the proposed equation is in good agreement with the actual recovered object when a practical value for thermal emissivity is used. A detailed explanation of the revised formulation is given, and additional simulation results are presented. Finally, discussions are made to address the applicability of the proposed equation to be incorporated in future survival analyses of orbital debris.     

基于雷诺数的大气阻力模型在飞行器再入预报中的应用

随着对空间技术服务需求的增加和空间碎片主动移除技术的实现,未来空间碎片将以数量多、质量大、难分解等特点频繁再入大气层,给地面人员和财产安全造成更多威胁.因此,亟需对火箭体等大型航天器的大气再入进行预警,然而因缺乏合适的大气阻力系数模型难以实现高精度的大气再入预报.为此,在简化航天器模型的基础上引入基于雷诺数的大气动力模...     

深空探测返回舱着陆冲击动力学分析

为分析深空探测返回舱着陆冲击动力学问题,首先建立包括返回舱及着陆土壤在内的全柔体着陆冲击动力学分析模型,并利用"神舟号"载人飞船着陆冲击试验数据对土壤模型进行修正;然后利用非线性动力分析软件LS-DYNA对深空探测返回舱着陆冲击过程进行仿真分析。通过典型着陆工况计算,得到了返回舱着陆过程中姿态变化、应力分布、关键点加速度响应曲线及冲击能量分配等。仿真结果可为深空探测返回舱结构优化设计、着陆姿态选择及地面试验等研究提供参考。     

浅论回收型卫星气动外形设计

本文首先简要介绍回收型卫星重返大气层概貌。从工程设计角度出发论述卫星再入舱气动外形设计依据,评述美、苏两国现有空间再入飞行器外形的特点,然后论述卫星再入舱与导弹再入弹头的主要差别,指出再入舱特有的主要空气动力学问题。最后展望回收型卫星气动外形未来发展趋势,推荐一种有发展前途的新型再入舱气动外形—平头双锥体。     

一种低轨废弃目标的捕获与回收方案

如何清除轨道上日益增多的废弃目标已成为国内外航天活动无法回避的现实问题和迫切需解决的问题.针对低轨道大型废弃目标回收问题,基于天基回收技术的概念,提出了一种新型组合式柔性捕获回收方案.使用空间绳网捕获废弃目标后通过充气式增阻离轨方式进行被动离轨,再利用充气式进入减速技术(inflatable entry deceler...     

基于星下点机动的再入飞行器离轨规划

针对约束再入点地理位置的再入飞行器离轨问题,提出了一种基于星下点机动的离轨规划方法。再入飞行器的离轨轨道设计受到飞行器当前轨道状态和再入点参数的约束。首先,基于轨道飞行原理,建立了一般椭圆轨道冲量模型下离轨制动参数和再入点参数的关系,分析了最优离轨的推力施加原则;其次,在考虑地球自转的前提下,提出了直接离轨必要条件,针对约束再入点经纬度的问题,完善了利用非线性规划优化方法确定有限推力模型下离轨点位置的策略,同时给出了符合燃料最优目标的离轨制动参数;最后,探讨了一般情况下初始轨道不满足直接离轨必要条件时,为满足星下点约束而进行的轨道机动施加策略。      

再入飞行器末端能量管理段纵向剖面优化方法

摘要： 对于轨道再入飞行器,根据各阶段飞行特性和任务的不同被分为初期再入、末端能量管理以及进场着陆几个阶段.本文提出一种末端能量管理段航程及纵向剖面优选方法,通过对不同的初始航程和纵向剖面进行递推,以阻力板控制裕度最大为优化目标,选出最适应飞行器升阻特性的航程以及相应的高度动压剖面.考虑初始状态误差及气动特性偏差条件下的六自由度仿真验证所设计的纵向剖面的鲁棒性.     

动态构造网管中被管对象的可视化扩展

随着互联网规模的不断扩大和网络应用的日益丰富,传统网管已经难以适应对大型、异构、动态变化的网络和种类繁多的网络应用的管理需要.动态构造的网络管理是一种新型的网络管理模式,被管对象的扩展是动态构造网管中的重要组成部分.提出了被管对象的可视化扩展方法.通过在管理人机交互界面上构造一棵MOS(被管对象集)树,并提供一系列的编辑工具,供设备厂商和应用开发商可视化定义其设备和应用所实现的MOS模块.这些模块以具有正确语法格式的MOS文件的形式提交给网管系统,由动态MOS编译将其加载到系统中,系统通过对其的访问实现被管对象和管理功能的关联及扩展.     

动力增程型高超声速飞行器的再入轨迹规划

为研究飞行过程中的动力装置启动时刻及燃料消耗情况,对轨迹进行优化,进而提出一种动力增程型弹道的再入模式。推导Sanger弹道的解析解,分析得到高超声速飞行器再入航程最优所必须的迎角及初始速度取值条件等相关前提,利用该结论设计动力装置的启动方式使航程最远、燃料利用率最大。将轨迹设计为Sanger弹道和拟平衡滑翔弹道相结合的混合弹道:再入前期利用助推器间隔点火的方式形成等高类周期跳跃弹道以保证足够远的航程; 再入后期采用拟平衡滑翔弹道,将最优控制问题转化为复杂多约束非线性规划问题,性能指标综合考虑了轨迹平滑和航程。仿真实现了所提出的动力增程型再入弹道; 并在燃料充足、弹道倾角取值合适的条件下,得到“打水漂”弹道形式,该弹道能量损失极慢,具有足够远的飞行能力。仿真表明,与不同点火方式及求解方法得出的弹道相对比,所提动力增程型再入弹道具有3.47~3.84倍的航程、1.04~1.18倍的末端动能以及4.47~15.79倍的燃料利用率。      

空间目标在天基光学探测中的特性分析与仿真

分析了空间目标的分布及几何特性,研究了空间目标光学特性与天基探测系统、太阳以及目标自身参数的关系,提出了空间目标光学特性仿真的思路,建立的天基空间目标光学特性分析系统可以计算并绘制相对距离、太阳相位角及目标星等变化曲线.由于很难获取准确的空间目标实际光度数据,文中提出了对仿真结果的验证方法.通过对仿真结果的分析,得出了天基空间目标光学探测的特点,为天基光学探测和识别的研究提供了参考.      

Predicting the vulnerability of spacecraft components: Modelling debris impact effects through vulnerable-zones

The space environment around the Earth is populated by more than 130 million objects of 1 mm in size and larger, and future predictions shows that this amount is destined to increase, even if mitigation measures are implemented at a far better rate than today. These objects can hit and damage a spacecraft or its components. It is thus necessary to assess the risk level for a satellite during its mission lifetime. Few software packages perform this analysis, and most of them employ time-consuming ray-tracing methodology, where particles are randomly sampled from relevant distributions. In addition, they tend not to consider the risk associated with the secondary debris clouds. The paper presents the development of a vulnerability assessment model, which relies on a fully statistical procedure: the debris fluxes are directly used combining them with the concept of vulnerable zone, avoiding the random sampling the debris fluxes. A novel methodology is presented to predict damage on internal components. It models the interaction between the components and the secondary debris cloud through basic geometrical operations, considering mutual shielding and shadowing between internal components. The methodologies are tested against state-of-the-art software for relevant test cases, comparing results on external structures and internal components.     

航天系统快速风险分析法

风险分析是大型工程,特别是具有高风险的航天系统可行性研究、案论证和方案评审等的主要内容之一。已经开发的对费用、进度、性能进行综合风险分析的计算机软件,如GERT,VERT,RISNET,SLAM 等,要求分析人员经过专门的培训,且工作量大,使用不便。文章给出了等风险轮廓线法、风险参数法和概率事件分析法三种快速、简便的风险分析方法,适合于一般工程技术人员,特别是管理人员在实际工作中应用。     

考虑禁飞区规避的预测校正再入制导方法

针对升力式高超声速飞行器再入滑翔侧向制导问题,提出了一种考虑禁飞区规避的预测校正制导方法.纵向制导采用落点误差预测与指令校正相结合的方式,不断更新倾侧角的幅值,实时修正轨迹纵程.侧向制导设计了一种倾侧角反转逻辑的切换机制,利用航向角误差走廊和航向角导向区域控制飞行器的侧向运动.CAV-H再入滑翔飞行器制导仿真实例表明,该方法不依赖于标准再入轨迹,能够导引飞行器规避禁飞区约束.Monte Carlo仿真验证表明,在随机初始扰动和误差存在的情况下,该制导方法具有良好的鲁棒性.