The BepiColombo/MMO model payload and operation plan

The Institute of Space and Astronautical Science (ISAS) of Japan plans to contribute the Mercury Magnetospheric Orbiter (MMO) to the BepiColombo program, the ESA Cornerstone mission to the planet Mercury. The principal objective of the MMO is to study the magnetic field and magnetosphere of Mercury. The ISAS Mercury exploration working group has performed the definition study of the MMO mission in cooperation with the ESA/ESTEC BepiColombo project team. This paper briefly reviews the scientific objectives, and describes the model payload and its operation plan.     

Optical performance of PHEBUS/EUV detector onboard BepiColombo

BepiColombo, a mission of ESA (European Space Agency) in cooperation with JAXA (Japan Aerospace Exploration Agency), will explore Mercury, the planet closest to the Sun. BepiColombo will launch in 2014 on a journey lasting up to six and a half years; the data gathering phase should occupy a one year nominal mission, with a possible extension of another year. The data which will be brought back from the orbiters will tell us about the Hermean surface, atmospheric composition, and magnetospheric dynamics; it will also contribute to understanding the history and formation of terrestrial planets. The PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) instrument will be flown on MPO: Mercury Planetary Orbiter, one of the two BepiColombo orbiters. The main purpose of the instrument is to reveal the composition and the distribution of the exosphere of Mercury through EUV (Extreme Ultraviolet: 55–155 nm) and FUV (Far Ultraviolet: 145–315 nm) measurements. A consortium composed of four main countries has been formed to build it. Japan provides the two detectors (EUV and FUV), Russia implements the scanning system, and France and Italy take charge of the overall design, assembly, test, integration, and also provide two small NUV (Near Ultraviolet) detectors (for the light from calcium and potassium molecules). An optical prototype of the EUV detector which is identical to the flight configuration has been manufactured and evaluated. In this paper, we show the first spectra results observed by the EUV channel optical prototype. We also describe the design of PHEBUS and discuss the possibility of detecting noble gases in Mercury’s exosphere taking the experimental results so far into account.     

Mercury’s sodium exosphere explored by the BepiColombo mission

The Mercury’s Sodium Atmosphere Spectral Imager (MSASI) on BepiColombo will address fundamental scientific questions pertaining to the Mercury’s sodium exosphere. Together, our measurements on the overall scale will provide ample new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the surface-bounded exosphere. We will compare the four different source mechanisms in preparation for modeling MSASI data and show the feasibility of identifying a process.     

Development of the EUV detector for the BepiColombo mission

An ultraviolet spectrometer, PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) that is loaded onto the Mercury Planetary Orbiter in the BepiColombo mission is under development. The instrument, basically consisting of two spectrophotometers (EUV: 50–150 nm, FUV: 145–330 nm) and one scanning mirror, aims at measuring emission lines from molecules, atoms and ions present in the tenuous atmosphere of Mercury. The detectors employ microchannel plates as 2-D photon-counting devices. In order to enhance the quantum detection efficiencies, the surface of the top microchannel plates of EUV detector is covered with photocathode. This method enables us to identify weak atmospheric signatures such as neon (73.5 nm) and argon (104.8 nm), which could not be detected with conventional detector systems. This paper presents measurements of the performance characteristics of potassium bromide and esium iodide photocathodes, which have been evaluated for use in the EUV channel.     

MEMORIS: a wide angle camera for the BepiColombo mission

MEMORIS (MErcury Moderate Resolution Imaging System) is a wide angle camera (WAC) concept for the ESA mission BepiColombo. The main scientific objectives consist of observing the whole surface of Mercury in the spectral range of 400–1000 nm, with a spatial resolution of 50 m per pixel at peri-Herm (400 km) and 190 m at apo-Herm (1500 km). It will obtain a map of Mercury in stereo mode allowing the determination of a digital elevation model with a panchromatic filter through two different channels. The camera will also perform multispectral imaging of the surface with a set of 8–12 different broad band filters. A third channel dedicated to limb observations will provide images of the atmosphere. MEMORIS will thus monitor the surface and the atmosphere during the entire mission, providing a unique opportunity to study the relationship between surface regions and the atmosphere, as suggested by ground-based observations and theory.     

Navigating BepiColombo during the weak-stability capture at Mercury

BepiColombo is scheduled for launch in August 2013 and to arrive after a nearly six-year long transfer at Mercury in June 2019. The trajectory has a number of challenging elements: a launch with Soyuz/Fregat into a geostationary transfer orbit, followed by a lunar flyby, long low-thrust arcs and five more planetary flybys (one at the Earth, two at Venus and two at Mercury). At arrival the low thrust arcs reduce the approach velocity so much that BepiColombo passes by the Sun–Mercury Lagrange points L₁ and L₂ and gets weakly captured in a highly eccentric orbit around Mercury in case the orbit insertion manoeuvre would fail.This paper describes the navigation strategy during the final phase. Five trajectory correction manouevres during the last 65 days requiring up to 20 m/s (3σ) are proposed. With this strategy it is possible to navigate BepiColombo safely through the weak-stability boundary of Mercury and to reach the target periherm with a precision of 11 km.     

METHIS: Mercury thermal infrared spectrometer

The BepiColombo mission to Mercury is devoted to the thorough exploration of Mercury and its environment, with the aim to understand the processes of planetary formation and evolution in the hottest part of the protoplanetary nebula. This mission represents an unique opportunity for the European community to extend the understanding of the Solar Nebula evolution from its outer edge – ideally represented by comets – to its inner and warmer edge. Obviously this exploration asks for a detailed knowledge of the main constituents of the matter present in the different Solar System areas. Spectroscopy is a powerful tool to acquire this knowledge. We have participated with a large consortium of European researchers to the development of the Rosetta imaging spectrometer. We propose here to use our experience to develop a newly designed spectrometer to investigate the mineralogical composition of the Mercurial surface. Given the particular thermodynamical situation of the Mercurial surface, we have developed a concept that combines a medium IR low spectral resolution imager with a moderate spectral resolution NIR point spectrometer. The main goal of METHIS is to provide the mineralogical characterisation of the surface with sufficient spectral resolution in a scientifically diagnostic spectral range.     

Development of an extreme ultraviolet imaging spectrometer for the BepiColombo mission

Extreme and far ultraviolet imaging spectrometers are proposed for the low-altitude orbiter of the BepiColombo mission. The UV instrument, consisting of the two spectrometers with common electronics, aims at measuring (1) emission lines from molecules, atoms and ions present in the Mercury’s tenuous atmosphere and (2) the reflectance spectrum of Mercury’s surface. The instrument pursues a complete coverage in UV spectroscopy. The extreme UV spectrometer covers the spectral range of 30–150 nm with the field of view of 5.0°, and the spectrum from 130 to 430 nm is obtained by the far UV spectrometer. The extreme UV spectrometer employs multi-layer coating technology to enhance its sensitivity at particular emission lines. This technology enables us to identify small ionospheric signatures such as He II (30.4 nm) and Na II (37.2 nm), which could not be detected with conventional optics.     

基于预测校正法的低升阻比飞船再入轨迹设计

对低升阻比飞船高速再入地球大气层的轨迹规划问题,提出了基于数值预测校正NPC(Numeric Predictor-Corrector)法的预测制导方法,并用时间替代能量作为自变量从而规避奇异问题;由飞船再入的3自由度运动方程推导纵向平面内的运动方程,并使用预测-校正方法获得倾侧角数值;同时通过设计横向漏斗确定倾侧角的符号,最终得到当前需要的倾侧角.仿真结果表明,该方法能根据不同的再入条件得出对应的再入轨迹和倾侧角变化规律,其动压、热流率、过载也符合再入要求.     

航天器近距离导引轨迹规划仿真系统设计

以航天器近距离导引轨迹规划仿真验证为目标,对基于Visual C+ +,Vega Prime和Matlab的联合仿真系统进行开发研究.首先,建立了数学模型.然后,利用Matlab对所建立的数学模型进行优化求解,得到追踪航天器近距离机动时的位置、速度等信息.并通过Multigen Creator软件建立卫星等对象的模型,使用Vega Prime进行视景仿真.之后,采用Visual C+ +进行系统集成,建立基于三者相结合的仿真验证系统.最后,以椭圆参考轨道下近距离交会的连续推力式燃料最优轨迹规划为例,验证了该联合仿真系统.     

Laboratory calibration measurements of a piezoelectric lead zirconate titanate cosmic dust detector at low velocities

A cosmic dust monitor for use onboard a spacecraft is currently being developed using a piezoelectric lead zirconate titanate element (PZT). Its characteristics of the PZT sensor is studied by ground-based laboratory impact experiments using hypervelocity particles supplied by a Van de Graaff accelerator. The output signals obtained from the sensor just after the impact appeared to have a waveform that was explicitly related to the particle’s impact velocity. For velocities less than ∼6 km/s, the signal showed an oscillation pattern and the amplitude was proportional to the momentum of the impacting particle. For higher velocities, the signal gradually changed to a single waveform. The rise time of this single waveform was proportional to the particle’s velocity for velocities above ∼6 km/s. The present paper reports on results for the low velocity case and especially discusses the effect of an outer coating of the sensor with a paint, which is used to reduce heating by solar radiation.     

Automated design architectures for co-orbiting spacecraft swarms for planetary moon mapping

This work describes the design and optimization of spacecraft swarm missions to meet spatial and temporal visual mapping requirements of missions to planetary moons, using resonant co-orbits. The algorithms described here are a part of Integrated Design Engineering and Automation of Swarms (IDEAS), a spacecraft swarm mission design software that automates the design trajectories, swarm, and spacecraft behaviors in the mission. In the current work, we focus on the swarm design and optimization features of IDEAS, while showing the interaction between the different design modules. In the design segment, we consider the coverage requirements of two general planetary moon mapping missions: global surface mapping and region of interest observation. The configuration of the swarm co-orbits for the two missions is described, where the participating spacecraft have resonant encounters with the moon on their orbital apoapsis. We relate the swarm design to trajectory design through the orbit insertion maneuver performed on the interplanetary trajectory using aero-braking. We then present algorithms to model visual coverage, and collision avoidance in the swarm. To demonstrate the interaction between different design modules, we relate the trajectory and swarm to spacecraft design through fuel mass, and mission cost estimations using preliminary models. In the optimization segment, we formulate the trajectory and swarm design optimizations for the two missions as Mixed Integer Nonlinear Programming (MINLP) problems. In the current work, we use Genetic Algorithm as the primary optimization solver. However, we also use the Particle Swarm Optimizer to compare the optimizer performance. Finally, the algorithms described here are demonstrated through numerical case studies, where the two visual mapping missions are designed to explore the Martian moon Deimos.     

航天器交会计算机视觉系统测距求解新算法

对航天器交会对接最终逼近段应用的计算机视觉系统,提出目标航天器标志点测距求解新算法.该方法根据标志点构型几何特征,建立非线性测距方程组并构造加权目标函数,按最小二乘问题,采用Gauss-Newton数值迭代法求解测距最佳值.获得测距后,即可应用四元数估算法(QUEST)确定相对姿态与相对位置.对非共面标志点构型(如3点T型与5点锥型)和共面标志点构型(如正方形、矩形、菱形),目标函数均含标志点间距比率关系项;对共面构型,目标函数还包含共面条件项.对共面标志点四边形构型,利用对角线交点的虚影像坐标确定测距求解迭代初值.大量模拟计算结果表明,提出的测距求解算法对共面与非共面各种标志点构型普遍适用,满足最终逼近段相对状态确定要求.      

航天器构型重构技术研究进展与展望

航天器构型重构技术是航天器在轨服务等重大空间任务必须突破的关键技术之一,将对新一代航天器系统的设计与研发产生深远影响。首先,给出了航天器构型重构的内涵及分类;其次基于主结构变构型等多种典型技术,对构型重构技术的研究现状进行了系统的总结和探讨;随后基于标准化模块设计等方法,给出了航天器构型重构技术体系;接着从支持航天器故障排除等方面出发,对构型重构技术的应用前景进行了归纳;最后,总结了构型重构技术的总体研究进展,并对其未来发展进行了展望。     

月面无人自动采样返回飞行程序设计与实现

针对嫦娥五号飞行程序多舱段、多任务、系统控制复杂的设计特点和难点,采用传统的飞行程序设计方法工作量大,状态控制困难,很难满足任务要求。提出了一种新的基于状态转移的方法对飞行程序进行系统建模,首先将整个飞行过程分解成若干模块状态机;然后针对每个模块状态机的功能划分为状态触发器、评估器、执行器和确认器,并分别开展建模设计;最后通过状态触发器和确认器将各个功能模块进行连接,形成整个飞行程序的有限状态机描述。相比传统方法,该方法具有通用性、可扩展性和可复用性等特点,对于规范飞行程序设计,描述复杂的飞行任务过程有很大的优势。采用该方法对嫦娥五号飞行程序进行了建模和设计,并给出了典型飞行过程的设计结果。在轨飞行试验结果表明,该方法可以满足飞行任务的要求,确保了嫦娥五号在轨飞行控制任务圆满成功。     

航天器热故障诊断专家系统推理机的设计

航天器在飞行过程中,经常发生各种故障,因此需要充分进行地面模拟试验.在航天器地面热试验的故障分析过程中,除了形成了可供故障诊断用的规则以外,还得到了许多具体的事例.后者很难用规则来准确地描述,但却是人类专家最珍贵的经验,必须加以利用.据此提出了基于事例推理和基于规则推理的混合推理机制,给出了具体的流程图,并就两种推理给出了相应的冲突消解策略.     

航天器交会最终逼近段相对姿态估计与控制

对航天器交会对接最终逼近段,给出姿态运动学方程统一形式以及相对姿态动力学方程;除了应用交会航天器的绝对姿态运动方程进行相对姿态估计(间接法)外,还直接应用相对姿态运动方程进行相对姿态估计(直接法);阐述相对姿态控制的相平面法与四元数反馈法的设计方法.相平面控制法应用常值推力,针对小姿态角机动的特点,将相对姿态通道解耦为3个独立的二阶子系统,设计相平面推力方向切换函数;四元数反馈法应用简化的基于本征轴旋转的线性二阶系统,选择相对四元数与角速率反馈增益系数,确定控制力矩.此外,对相对姿态估计与控制方法进行模拟计算与比较.理论分析与模拟计算结果表明:应用扩展Kalman滤波的相对姿态间接估计法与直接估计法是有效的,后者有可能简化估计算法;相平面控制法与四元数反馈法均可有效实现相对姿态控制,前者应用常值推力(推力方向与姿态反馈有关),较易实现,但动力消耗较大,后者按控制力矩随姿态反馈量而变,动力消耗较小.      

Dynamics and control of spacecraft hovering using the geomagnetic Lorentz force

To achieve hovering, a spacecraft thrusts continuously to induce an equilibrium state at a desired position. Due to the constraints on the quantity of propellant onboard, long-time hovering around low-Earth orbits (LEO) is hardly achievable using traditional chemical propulsion. The Lorentz force, acting on an electrostatically charged spacecraft as it moves through a planetary magnetic field, provides a new propellantless method for orbital maneuvers. This paper investigates the feasibility of using the induced Lorentz force as an auxiliary means of propulsion for spacecraft hovering. Assuming that the Earth’s magnetic field is a dipole that rotates with the Earth, a dynamical model that characterizes the relative motion of Lorentz spacecraft is derived to analyze the required open-loop control acceleration for hovering. Based on this dynamical model, we first present the hovering configurations that could achieve propellantless hovering and the corresponding required specific charge of a Lorentz spacecraft. For other configurations, optimal open-loop control laws that minimize the control energy consumption are designed. Likewise, the optimal trajectories of required specific charge and control acceleration are both presented. The effect of orbital inclination on the expenditure of control energy is also analyzed. Further, we also develop a closed-loop control approach for propellantless hovering. Numerical results prove the validity of proposed control methods for hovering and show that hovering around low-Earth orbits would be achievable if the required specific charge of a Lorentz spacecraft becomes feasible in the future. Typically, hovering radially several kilometers above a target in LEO requires specific charges on the order of 0.1 C/kg.     

多舱段载人航天器CO2去除系统性能仿真分析

多舱段载人航天器通常由主控舱段利用舱间通风对组合体空气环境参数进行集中控制.利用Ecosimpro建立了一种多舱段载人航天器CO₂去除系统性能仿真分析模型,包括舱体模块、乘员模块、CO₂净化模块、舱间通风模块,并对三舱段载人航天器CO₂去除系统性能进行了计算分析.结果表明,当净化装置进风量为0.007 2 kg/s,非主控舱段驻留人数达到6人时,会造成非主控舱段CO₂分压超出700 Pa的指标上限.此时增大舱间通风量对降低非主控舱段CO₂分压的效果并不明显,有效的控制方式是增大净化装置进风量.当净化装置进风量增加至0.011 3 kg/s时,非主控舱段CO₂分压可降至700 Pa以下.该工作有助于加快载人航天器空气环境控制系统的设计和改进流程.     

探月飞船预测-校正再入制导律设计

针对以第二宇宙速度返回的探月飞船再入制导律设计问题,采用一种数值预测一校正的预测制导法,分析了飞船配平攻角的飞行特性,建立了再入三自由度运动方程。进而详细介绍了预测一校正及其纵向、横向制导律的基本原理。通过标准初始状态、有误差初始状态两种条件下的仿真分析,表明这种预测一校正制导律在满足各种约束的条件下,不仅能够达到较高的精度,而且对初始误差具有良好的鲁棒性,能够应付再入时各种不确定性因素的影响。