Multi-objective optimization of parachute triggering algorithm for Mars exploration

A multi-objective optimization procedure to design parachute triggering algorithm, based on Monte Carlo analysis of flight uncertainties, has been developed in this paper. Most of Mars explorations missions utilize parachute for a safe descent through the lowest of the atmosphere. The parachute triggering algorithm is designed to accommodate the range of off-nominal entry trajectories, and is aimed to parachute opening in certain range of Mach numbers, dynamic pressure and altitude. Our novel algorithm takes the fight uncertainty into the account through Monte Carlo analysis, selects maximization of altitude statistical mean and minimization of Mach number statistical mean as two objectives, then employs multi-objective evolutionary algorithm based on decomposition (MOEA/D), to search the Pareto-front framework. Such a methodology can be implemented on the future design of entry, descent, and landing (EDL) mission.     

Disturbance observer-based robust guidance for Mars atmospheric entry with input saturation

With low-lifting capability taken into account,a robust guidance law for Mars entry vehicles with low lift-to-drag ratios,such as Mars Science Laboratory(MSL),is presented.Consider the nonlinear term in the drag dynamic equation and bounded disturbances as a lumped disturbance,and design a linear disturbance observer(DOB)to estimate it.With the consideration of the control input saturation,an innovative sliding surface and a virtual system are introduced to design the guidance law.Analyses of disturbance observer performance and Lyapunov-based transient performance are also presented.It is shown that the drag tracking error can be adjustable by explicit choices of design parameters.Simulation results confirm the effectiveness of the proposed guidance law.     

Planetary penetrators: Their origins,history and future

Penetrators, which emplace scientific instrumentation by high-speed impact into a planetary surface, have been advocated as an alternative to soft-landers for some four decades. However, such vehicles have yet to fly successfully. This paper reviews in detail, the origins of penetrators in the military arena, and the various planetary penetrator mission concepts that have been proposed, built and flown. From the very limited data available, penetrator developments alone (without delivery to the planet) have required ∼$30M: extensive analytical instrumentation may easily double this. Because the success of emplacement and operation depends inevitably on uncontrollable aspects of the target environment, unattractive failure probabilities for individual vehicles must be tolerated that are higher than the typical ‘3-sigma’ (99.5%) values typical for spacecraft. The two pathways to programmatic success, neither of which are likely in an austere financial environment, are a lucky flight as a ‘piggyback’ mission or technology demonstration, or with a substantial and unprecedented investment to launch a scientific (e.g. seismic) network mission with a large number of vehicles such that a number of terrain-induced failures can be tolerated.     

火星卫星的冻结轨道研究

冻结轨道是一种稳定的轨道,地球、火星、月球的卫星因引力场的南北不对称,都存在冻结轨道.由于主星体引力场的不同,它们卫星的冻结轨道也有不同的特性.地球卫星的冻结执道的偏心率非常小,对卫星遥感非常有利,国内外已有相当多的近地遥感卫星采用这种轨道.月球卫星的冻结轨道偏心率随轨道倾角的不同有很大的变化,对月球卫星冻结轨道的研究...     

21世纪的航天(续)

航天事业在20世纪已取得显著进展和辉煌成就。21世纪即将来临。在21世纪,世界航天如何发展、将取得哪些重大成就,是人们关注的话题。为此,笔者根据有关材料汇编了这份材料,以供参考。共4讲,第一、二讲已刊登在本刊1998年第4期,下面为第三、四讲。     

IMF Direction Derived from Cycloid-Like Ion Distributions Observed by Mars Express

Although the Mars Express (MEX) does not carry a magnetometer, it is in principle possible to derive the interplanetary magnetic field (IMF) orientation from the three dimensional velocity distribution of pick-up ions measured by the Ion Mass Analyser (IMA) on board MEX because pick-up ions' orbits, in velocity phase space, are expected to gyrate around the IMF when the IMF is relatively uniform on a scale larger than the proton gyroradius. During bow shock outbound crossings, MEX often observed cycloid distributions (two dimensional partial ring distributions in velocity phase space) of protons in a narrow channel of the IMA detector (only one azimuth for many polar angles). We show two such examples. Three different methods are used to derive the IMF orientation from the observed cycloid distributions. One method is intuitive (intuitive method), while the others derive the minimum variance direction of the velocity vectors for the observed ring ions. These velocity vectors are selected either manually (manual method) or automatically using simple filters (automatic method). While the intuitive method and the manual method provide similar IMF orientations by which the observed cycloid distribution is well arranged into a partial circle (representing gyration) and constant parallel velocity, the automatic method failed to arrange the data to the degree of the manual method, yielding about a 30° offset in the estimated IMF direction. The uncertainty of the derived IMF orientation is strongly affected by the instrument resolution. The source population for these ring distributions is most likely newly ionized hydrogen atoms, which are picked up by the solar wind.     

利用CRISM数据探测火星表面含水矿物及其演化

火星表层矿物识别是了解火星大气环境变化、表层地质环境的关键因素。通过确定火星表层矿物,分析矿物特性,了解火星的环境状态、地质演化以及火星的未来适居性。火星勘测轨道器(Mars reconnaissance orbiter,MRO)上搭载的紧凑型侦察成像仪(compact reconnaissance imaging spectrometer for Mars,CRISM)是针对火星矿物探测的最新的高光谱成像仪,以很高的光谱分辨率覆盖可见光至近红外波段,为火星表面的矿物分布及区域填图提供了可能。通过光谱匹配及计算CRISM光谱参数综合产品,分析了火星Jezero以及Holden撞击坑内的矿物成分及其演化。Jezero与Holden因其复杂而关键的地质特征,被列为火星2020登陆任务的备选登陆点。对这两个地点的矿物探测与填图分析不仅可进一步分析火星典型地质特征以及演化,而且还可以为未来的火星登陆点分析提供现实意义。在研究区域已检测到与水成蚀变相关的含水硅酸盐类以及碳酸盐类与含水硫酸盐类。水合矿物增加了这些区域曾经含水的可能性,且矿物的多样性表明研究区地质环境经历了不同的变化,其中Jezero地区不同于火星的绝大多数地区从中性环境到酸性环境的演化,有可能经历了从中性环境到碱性环境的演化。     

行星着陆自主导航与制导控制研究现状与趋势

行星着陆自主导航与制导控制技术是行星着陆过程的核心技术之一,关系到行星着陆任务的成败。本文基于未来火星和小天体着陆对自主导航与制导控制技术的发展需求,阐述了进一步开展自主导航与制导控制研究的必要性,围绕行星着陆过程环境特点,分析了自主导航与制导控制技术所遇到的挑战,随后概括了行星着陆自主导航与制导控制所涉及的关键技术,并综述了关键技术的研究现状。最后对我国未来行星着陆探测自主导航与制导控制技术的发展方向进行了展望。     

集成火星进入弹道的开伞过程动力学特性研究

针对火星探测任务设计阶段的需求,提出集成再入弹道、开伞过程仿真一体化设计方法。首先,利用质点动力学模型,计算质点弹道,进行探测器进入过程的飞行轨迹仿真,获得开伞初始状态。其次,基于任意拉格朗日-欧拉（ALE）方法,建立开伞过程的流固耦合（FSI）动力学模型,进行典型工况开伞过程数值模拟,分析开伞动压和马赫数对降落伞充气过程的影响。数值模拟开伞过程伞衣几何外形变化和降落伞的流固耦合动力学行为,得到开伞过载变化曲线、伞衣阻力面积变化等典型特征参数。计算结果表明,降落伞开伞动力学的数值仿真方法为火星再入、减速和着陆（EDL）过程的概念设计提供了一定的参考依据。     

火星进入段自主导航技术研究现状与展望

基于国际上成功着陆的火星探测任务和未来火星着陆探测技术的发展需求,阐述了火星进入段自主导航的必要性。首先总结了火星进入段自主导航技术的研究现状与发展趋势,随后分析了火星进入段自主导航的特点以及所面临的挑战,并概括了火星进入段自主导航所涉及的关键技术。最后对我国未来火星探测任务进入段的自主导航技术发展方向进行了展望。