任务轨道设计

本文首先说明太空任务与轨道设计的关系，接着介绍轨道的基本性质。从地球重力势的观点看各种常用的绕地轨道，包括地球和太阳同步轨道及Molniya轨道。从扰动的观点看常用的星际轨道，包括LISA，ASTROD，SOHO轨道。最后对星际轨道设计，说明二点边界值问题的数值解法，飞掠星体的应用，最佳化的考虑，并用以设计2015年发射的ASTROD初步任务轨道。     

ASTROD 1中的望远镜前指量研究

单航天器激光天文动力学空间计划ASTROD1是激光天文动力学ASTROD的第一步,通过发射绕太阳的无拖曳航天器,并且当航天器处于太阳背面附近时,与地面站进行深空激光测距,以执行科学任务。该文计算了ASTROD12015年的轨道、提出了判断轨道精度是否满足任务需要的方法、分析了地球和航天器的位置同望远镜前指量之间的关系并且给出了望远镜前指量的结果。     

行星际电子及重核对ASTROD Ⅰ测试质量充电过程模拟的研究

在LISA,ASTROD I和ASTROD之类用于探讨引力波天文、天文动力学和相对论测试的深空激光探测计划中,暴露在空间粒子环境中的无拖曳测试质量将会受各种带电粒子的影响而带电,引起库伦力和洛伦兹力干扰,从而影响实验数据的精度.在先前的工作中,已用GEANT4工具包模拟了银河宇宙射线中质子和氦核以及太阳高能粒子事件对测试质量的充电过程.文章里,参数化了行星际电子和主要种类的重核,并模拟了由测试质量块在行星际电子和C,H,O等重核环境中的充电速率.行星际电子源主要是木星和银河,而重核主要来自于银河宇宙射线.经过模拟计算, ASTROD Ⅰ测试质量由行星际电子引起的充电速率大约是行星际质子在太阳活动最小值时的9%,在太阳活动最大值时的28%.行星际重核相对于行星际质子在太阳活动最小值和最大值时的贡献分别约是0.83%和1.64%.     

ASTROD-GW轨道设计

激光天文动力学引力波探测任务ASTROD-GW(ASTROD[AstrodynamicalSpace Test of Relativity Using Optical Devices Optimized for Gravitation WaveDetection)是ASTROD专注于探测引力波的优化方案,其航天器轨道在日地拉格朗日点L_3、L_4、L_5附近,构成一个接近等边的三角形阵列,干涉臂长约为2.6×10~8 km,其可探测的引力波波长可达LISA(Laser Interferometer Space Antenna)的52倍.文中综述ASTROD-GW轨道的设计和优化方法.轨道经优化后,其臂长差(在激光干涉测量中可称为干涉差)10 yr内的变化为10~(-4) AU量级、3个臂长方向的多普勒速度小于4 m/s,均小于LISA的要求,因此LISA发展的激光测距技术可用于ASTROD-GW.     

ASTROD-GW时间迟延干涉

ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitation Wave detection)是ASTROD专注于引力波探测的优化方案,组成任务的3个航天器分别位于日地拉格朗日点L3、L4和L5点附近,组成臂长为2.6× 108 km的干涉阵列.根据优化得到的ASTROD-GW 20 yr任务轨道,利用CGC2.7 (CGC:Center for Gravitation and Cosmology)星历,采用适当数值计算的方法,对引力波探测中所用到的时间迟延干涉路径进行分析和计算.     

行星际电子及重核对ASTRODI测试质量充电过程模拟的研究

在LISA,ASTRODI和ASTROD之类用于探讨引力波天文、天文动力学和相对论测试的深空激光探测计划中,暴露在空间粒子环境中的无拖曳测试质量将会受各种带电粒子的影响而带电,引起库伦力和洛伦兹力干扰,从而影响实验数据的精度．在先前的工作中,已用GEANT4工具包模拟了银河宇宙射线中质子和氦核以及太阳高能粒子事件对测试质量的充电过程．文章里,参数化了行星际电子和主要种类的重核,并模拟了由测试质量块在行星际电子和C,H,O等重核环境中的充电速率．行星际电子源主要是木星和银河,而重核主要来自于银河宇宙射线．经过模拟计算,ASTRODI测试质量由行星际电子引起的充电速率大约是行星际质子在太阳活动最小值时的9％,在太阳活动最大值时的28％．行星际重核相对于行星际质子在太阳活动最小值和最大值时的贡献分别约是0．83％和1．64％．     

纳米计量学的基础技术组件

为了满足ASTROD激光宇航动力学任务慨念计划的高精度要求 ,以及实现新质量标准 ,我们开始进行次纳米激光测长与纳米定位控制的研究。本文将回顾我们在清华大学与工研院测量中心的研究成果 ,介绍如何利用外差式激光干涉仪、挠性微动台与压电陶瓷 ,进行次纳米激光测长与纳米定位控制。此研究成果将做为ASTROD计划中 ,无拖曳航天技术的研发基础。之后讨论如何将纳米定位控制系统与扫描穿隧显微镜进行整合 ,完成计量型扫描穿隧显微镜 ,进一步将微结构的测量尺寸直接追溯至长度标准。     

圆周运动天体轨道半径的相对论效应

从理论上探讨圆周运动天体轨道半径的相对论效应,并应用于行星际飞船与人造地球卫星的情形。结果表明,在这两种情形中,均存在着可观测的效应。     

星际气体之谜

星系中除了恒星,还有一个重要的组成部分就是恒星间的星际介质。星际介质又叫星际物质,包括气体、尘埃、磁场、宇宙线等。天文学家们最先关注的就是无处不在的星际气体。     

星际尘埃研究现状与进展

由于星际尘埃的广泛存在和其在恒星与行星系统的形成、星系以及整个宇宙演化中的重要作用,星际尘埃的研究成为当今天体物理领域的热点前沿课题。该文从尘埃与电磁场相互作用的观测证据出发,系统地介绍了星际消光(包括吸收和散射)、星际红外辐射、星际偏振等的研究现状,讨论了星际元素减损,以及行星际尘埃和陨石中的前太阳尘埃等问题。从相应的观测证据中,可以得到关于星际尘埃的丰度、化学组成、尺寸和形状的信息。该文还对当前比较流行的三种尘埃模型(硅酸盐-石墨-PAHs模型、硅酸盐核-碳有机耐熔质壳层模型和多孔尘埃模型)进行了讨论与比较,对该研究领域中待解决的问题也作了简要的概括。     

Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I)—a class-M fundamental physics mission proposal for cosmic vision 2015–2025: 2010 Update

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals.For this mission, accurate pulse timing with an ultra-stable clock, and a drag-free spacecraft with reliable inertial sensor are required. T2L2 has demonstrated the required accurate pulse timing; rubidium clock on board Galileo has mostly demonstrated the required clock stability; the accelerometer on board GOCE has paved the way for achieving the reliable inertial sensor; the demonstration of LISA Pathfinder will provide an excellent platform for the implementation of the ASTROD I drag-free spacecraft. These European activities comprise the pillars for building up the mission and make the technologies needed ready. A second mission, ASTROD or ASTROD-GW (depending on the results of ASTROD I), is envisaged as a three-spacecraft mission which, in the case of ASTROD, would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth, or in the case of ASTROD-GW, would be dedicated to probe gravitational waves at frequencies below the LISA bandwidth to 100?nHz and to detect solar g-mode oscillations. In the third phase (Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD bandwidth. This paper on ASTROD I is based on our 2010 proposal submitted for the ESA call for class-M mission proposals, and is a sequel and an update to our previous paper (Appouchaux et al., Exp Astron 23:491?C527, 2009; designated as Paper I) which was based on our last proposal submitted for the 2007 ESA call. In this paper, we present our orbit selection with one Venus swing-by together with orbit simulation. In Paper I, our orbit choice is with two Venus swing-bys. The present choice takes shorter time (about 250?days) to reach the opposite side of the Sun. We also present a preliminary design of the optical bench, and elaborate on the solar physics goals with the radiation monitor payload. We discuss telescope size, trade-offs of drag-free sensitivities, thermal issues and present an outlook.     

Astrodynamical Space Test of Relativity Using Optical Devices I (ASTROD I)—A class-M fundamental physics mission proposal for Cosmic Vision 2015–2025

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.

Design of ASTROD-GW Orbit

The ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity Using Optical Devices] Optimized for Gravitation Wave Detection), the mission of the laser astrodynamical gravitational wave detection, is the scheme of optimality of the gravitational wave detection on which the ASTROD is concentrated. Its spacecraft orbits form a triangular array close to an equilateral triangle in the vicinity of the solar-terrestrial Lagrangian points L₃, L₄ and L₅. The length of the interference arm is about 2.6 × 10⁸ km and the detectable wavelength of the gravitational wave is 52 times larger than that detected by the LISA (Laser Interferometer Space Antenna). In this article, the design and optimization method of the ASTROD-GW orbit are summarized. After the orbit is optimized, the variation in the arm length difference (which can be called the interference difference in laser interferometry) within 10 years is in the order of magnitude of 10⁻⁴ AU. The Doppler velocities in the three arm length directions are smaller than 4 m/s, and all of them are less than that required by the LISA. Therefore the laser ranging techniques developed by the LISA can be applied to the ASTROD-GW.     

Time-delay Interferometry for ASTROD-GW

ASTROD-GW(ASTROD[Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitational Wave detection) is an optimization of ASTROD to focus on the detection of gravitational waves. Three spacecraft in the mission are positioned respectively in the vicinity of the Sun- Earth Lagrange points L3, L4 and L5. They form a nearly equilateral interferometerarray with the arm lengths of about 260 million kilometers. A set of optimized 20-yr mission orbits of the ASTROD-GW spacecraft are worked out by us. And with this, we have performed the numerical simulation of time-delay interferometry under the CGC2.7 (CGC: Center for Gravitation and Cosmology) ephemeris framework.     

Trajectory Analysis and Design for A Jupiter Exploration Mission

The trajectory design for a Jupiter exploration mission is investigated in this paper. The differences between the Jupiter exploration trajectory and the Mars or Venus exploration trajectory are mainly concerned about. Firstly, the selection of the Jupiter-centered orbit is analyzed based on the Galileo Jupiter mission. As for the Earth-Jupiter transfer orbit, the fuel consumption of the direct transfer is too large. So the energy-saving technologies such as the planetary gravity assist should be used for the trajectory to the Jupiter. The different sequences of planetary gravity assists are examined by applying the Particle Swarm Optimization (PSO). According to the searched result, the Venus-Earth-Earth sequence (VEEGA) is the most effective one for the Jupiter mission. During the Jupiter mission, the spacecraft will pass though the main asteroid belt between the orbits of Mars and Jupiter, and may encounter multiple asteroids. Therefore the Jupiter mission is able to combine with the main-belt asteroid flyby mission. The design method of the intermediate asteroid flyby trajectory is also considered. At last, an entire trajectory for the Jupiter mission launched in 2023 is presented.     

木星探测轨道分析与设计

研究了与木星探测相关的轨道设计问题.重点关注木星探测轨道与火星、金星等类地行星探测轨道的不同及由此带来的轨道设计难点.首先分析了绕木星探测任务轨道的选择.建立近似模型讨论了向木星飞行需要借助多颗行星的多次引力辅助,对地木转移的多种行星引力辅助序列,使用粒子群算法搜索了2020年至2025年之间的燃料最省飞行方案并对比得到了向木星飞行较好的引力辅助方式为金星-地球-地球引力辅助.结合多任务探测,研究了航天器在飞向木星途中穿越主小行星带飞越探测小行星的轨道设计.最后,给出2023年发射完整的结合引力辅助与小行星多次飞越的木星探测轨道设计算例.     

Boundary-value problem formulations for computing invariant manifolds and connecting orbits in the circular restricted three body problem

We demonstrate the remarkable effectiveness of boundary value formulations coupled to numerical continuation for the computation of stable and unstable manifolds in systems of ordinary differential equations. Specifically, we consider the circular restricted three-body problem (CR3BP), which models the motion of a satellite in an Earth–Moon-like system. The CR3BP has many well-known families of periodic orbits, such as the planar Lyapunov orbits and the non-planar vertical and halo orbits. We compute the unstable manifolds of selected vertical and halo orbits, which in several cases leads to the detection of heteroclinic connections from such a periodic orbit to invariant tori. Subsequent continuation of these connecting orbits with a suitable end point condition and allowing the energy level to vary leads to the further detection of apparent homoclinic connections from the base periodic orbit to itself, or the detection of heteroclinic connections from the base periodic orbit to other periodic orbits. Some of these connecting orbits are of potential interest in space mission design.     

Quasi-terminator orbits near primitive bodies

Quasi-terminator orbits are introduced as a class of quasi-periodic trajectories in the solar radiation pressure (SRP) perturbed Hill dynamics. These orbits offer significant displacements along the Sun-direction without the need for station-keeping maneuvers. Thus, quasi-terminator orbits have application to primitive-body mapping missions, where a variety of observation geometries relative to the Sun (or other directions) can be achieved. This paper describes the characteristics of these orbits as a function of normalized SRP strength and invariant torus frequencies and presents a discussion of mission design considerations for a global surface mapping orbit design.