New celestial assisted INS initial alignment method for lunar explorer

In the future lunar exploration programs of China, soft landing, sampling and returning will be realized. For lunar explorers such as Rovers, Landers and Ascenders, the inertial navigation system （INS） will be used to obtain high-precision navigation information. INS propagates position, velocity and attitude by integration of sensed accelerations, so initial alignment is needed before INS can work properly. However, traditional ground-based initial alignment methods cannot work well on the lunar surface because of its low rotation rate （0.55°/h）. For solving this problem, a new autonomous INS initial alignment method assisted by celestial observations is proposed, which uses star observations to help INS estimate its attitude, gyroscopes drifts and accelerometer biases. Simulations show that this new method can not only speed up alignment, but also improve the alignment accuracy. Furthermore, the impact factors such as initial conditions, accuracy of INS sensors, and accuracy of star sensor on alignment accuracy are analyzed in details, which provide guidance for the engineering applications of this method. This method could be a promising and attractive solution for lunar explorer＇s initial alignment.

New autonomous celestial navigation method for lunar satellite

Celestial navigation system is an important autonomous navigation system widely used for deep space exploration missions, in which extended Kalman filter and the measurement of angle between celestial bodies are used to estimate the position and velocity of explorer. In a conventional cartesian coordinate, this navigation system can not be used to achieve accurate determination of position for linearization errors of nonlinear spacecraft motion equation. A new autonomous celestial navigation method has been proposed for lunar satellite using classical orbital parameters. The error of linearizafion is reduced because orbit parameters change much more slowly than the position and velocity used in the cartesian coordinate. Simulations were made with both the cartesiane system and a system based on classical orbital parameters using extended Kalman filter under the same conditions for comparison. The results of comparison demonstrated high precision position determination of lunar satellite using this new method.

Micro-arcsecond Celestial Reference Frames:definition and realization——Impact of the recent IAU Resolutions

The adoption of the International Celestial Reference System （ICRS）, based on Very Long Baseline Interferometry （VLBI） observations of extragalactic radiosources by the International Astronomical Union （IAU） since 1998 January 1, opened a new era for astronomy. The ICRS and the corresponding frame, the International Celestial Reference Frame （ICRF）, replaced the Fundamental Catalog （FK5） based on positions and proper motions of bright stars, with the Hipparcos cat- alog being adopted as the primary realization of the ICRS in optical wavelengths. According to its definition, the ICRS is such that the barycentric directions of distant extragalactic objects show no global rotation with respect to these objects; this pro- vides a quasi-inertial reference for measuring the positions and angular motions of the celestial objects. Other resolutions on reference systems were passed by the IAU in 2000 and 2006 and endorsed by the International Union of Geodesy and Geophysics （IUGG） in 2003 and 2007, respectively. These especially concern the definition and re- alization of the astronomical reference systems in the framework of general relativity and transformations between them. First, the IAU 2000 resolutions refined the con- cepts and definition of the astronomical reference systems and parameters for Earth＇s rotation, and adopted the IAU 2000 precession-nutation. Then, the IAU 2006 resolutions adopted a new precession model that is consistent with dynamical theories; they also addressed definition, terminology or orientation issues relative to reference systems and time scales that needed to be specified after the adoption of the IAU 2000 resolutions. An additional IUGG 2007 resolution defined the International Terrestrial Reference System （ITRS） so that it strictly complies with the IAU recommendations. Finally, the IAU 2009 resolutions adopted a new system of astronomical constants and an improved realization of the ICRF. These fundamental changes have led to significant improvements in the fields of astrometry, celestial mechanics, geodynam- ics, geodesy, etc. Of special interest are the improvements in the model for variations in Earth＇s rotation, which, in turn, can provide better knowledge of the dynamics of the Earth＇s interior. These have also contributed to a significant improvement in the accuracy of the ephemerides of the solar system bodies as determined from modern measurements, with a large number of scientific applications. This paper recalls the main aspects of the recent IAU resolutions on reference systems as well as their con- sequences on the concepts, definitions, nomenclature and models that are suitable for the definition, realization and transformation of reference frames at a microarcsecond level.

Research on the Changes of Celestial Tide-generating Force and the Outgoing Long-wave Radiation before the Lushan (China) M_S7.0 Earthquake

Calculation of tidal changes reveals that the MS 7. 0 Lushan County,Sichuan,China,earthquake of April 20,2013 occurred at the minimum phase point of tidal force. It indicates that the seismogenic fault on which the tidal force acts on is of thrust type. The outgoing long-wave radiation( OLR) is the energy radiating from the Earth as infrared radiation at low energy to space. According to the tidal cycle,abnormal OLR change is analyzed based on NOAA satellite data around the whole of China before and after the earthquake. The result shows that the OLR changed evidently with the tide force change.Temporally,the change went through the course: initial OLR rise → s trengthening →reaching abnormal peak → a ttenuation → r eturning to normal; in space,the abnormal area was distributed along the Longmenshan fault and evolved as: scattering→ c onvergent→ s cattering. The process is similar to the change process of rock breaking under stress loading. It indicates that the celestial tidal force can trigger earthquakes when the tectonic stress reaches the critical break point of an active fault and the OLR anomaly is proportional to the seismic tectonic stress change. It is of practical value to combine OLR and tidal force anomaly with earthquake precursor studies.

Electromagnetic Field Created by Rotation of Celestial Bodies

The observed correlation of the angular momenta Lik and magnetic moments μlm of celestial bodies (the Sun, planets and stars) was discussed by many authors but without any explanation. In this paper, a possible explanation of this phenomenon is suggested. It is shown that the function satisfies Maxwell equations and can be considered as a function which determines the electro-magnetic properties of rotating heavy bodies. The Riklm is the Riemann tensor, which determines the gravitational field of the body, rg is the gravitational radius of the body, and η is the constant which has to be determined by observations. The field Φlm describes the observed correlation. It explains the stability of magnetic field of white dwarfs and neutron stars despite the ohmic dissipation. The function Φl0 describes the electric field created by rotating heavy bodies. The presented theory does not contradict any existed experiments and observations.

The present status and prospects in the research of orbital dynamics and control near small celestial bodies

Small celestial body exploration is of great significance to deep space activities. The dynamics and control of orbits around small celestial bodies is of top priority in the exploration research. It includes the modeling of dynamics environment and the orbital dynamics mechanism. This paper introduced state-ofthe-art researches, major challenges, and future trends in this field. Three topics are mainly discussed： the gravitational field modeling of irregular-shaped small celestial bodies, natural orbital dynamics and control, and controlled orbital dynamics. Finally, constructive suggestions are made for China’s future space exploration missions.

A New Celestial Mechanics Dynamics of Accelerated Systems

We present in this text the research carried out on the dynamic behavior of non-inertial systems, proposing new keys to better understand the mechanics of the universe. Applying the field theory to the dynamic magnitudes circumscribed to a body, our research has achieved a new conception of the coupling of these magnitudes, to better understand the behavior of solid rigid bodies, when subjected to multiple simultaneous, non-coaxial rotations. The results of the research are consistent with Einstein’s theories on rotation;however, we propose a different mechanics and complementary to classical mechanics, specifically for systems accelerated by rotations. These new concepts define the Theory of Dynamic Interactions (TDI), a new dynamic model for non-inertial systems with axial symmetry, which is based on the principles of conservation of measurable quantities: the notion of quantity, total mass and total energy. This theory deduces a general equation of motion for bodies endowed with angular momentum, when they are subjected to successive non-coaxial torques.

Notes on the Motion of Celestial Bodies

A novel method for the computation of the motion of multi-body systems is proposed against the traditional one, based on the dynamic exchange of attraction forces or using complex field equations, that hardly face two-body problems. The Newton gravitational model is interpreted as the emission of neutrino/gravitons from celestial bodies that combine to yield a cumulative flux that interacts with single bodies through a momentum balance. The neutrino was first found by Fermi to justify the energy conservation in β decay and, using his model;we found that the emission of neutrino from matter is almost constant independently from the nuclides involved. This flux can be correlated to Gauss constant G, allowing the rebuilding of Newton law on the basis of nuclear data, the neutrino weight and the speed of light. Similarly to nature, we can therefore separate in the calculations the neutrino flux, that represents the gravitational field, is dependent on masses and is not bound to the number of bodies involved, from the motion of each body that, given the field, is independent of the mass of bodies themselves. The conflict between exchanges of forces is avoided, the mathematics is simplified, the computational time is reduced to seconds and the stability of result is guaranteed. The example of computation of the solar system including the Sun and eight planets over a period of one to one hundred years is reported, together with the evolution of the shape of the orbits.

Research career of an astronomer who has studied celestial mechanics

Celestial mechanics has been a classical field of astronomy. Only a few astronomers were in this field and not so many papers on this subject had been published during the first half of the 20th century. However, as the beauty of classical dynamics and celestial mechanics attracted me very much, I decided to take celestial mechanics as my research subject and entered university, where a very famous professor of celestial mechanics was a member of the faculty. Then as artificial satellites were launched starting from October 1958, new topics were investigated in the field of celestial mechanics. Moreover, planetary rings, asteroids with moderate values of eccentricity, inclination and so on have become new fields of celestial mechanics. In fact I have tried to solve such problems in an analytical way. Finally, to understand what gravitation is I joined the TAMA300 gravitational wave detector group.

Proposal of New Criteria for Celestial Mechanics

Based on a new interpretation on the behavior of rigid bodies exposed to simultaneous non-coaxial rotations, we have developed a hypothesis: the Theory of Dynamics Interactions, which can be applied to understand celestial mechanics. We have analyzed the velocity and acceleration fields generated in a rigid body with intrinsic angular momentum, when exposed to successive torques, to assess new criteria for this speeds coupling. In this context, reactions and inertial fields take place, which cannot be justified by means of classical mechanics. We believe that the results obtained after the analysis of dynamics fields systems accelerated by rotation will allow us to conceive a new perspective in celestial dynamics, astrometry, stellar dynamics and galactic astronomy, unknown up to date. After carrying out ample research, we have come to the conclusion that there still exists an unstructured scientific area under the present general assumptions and, more specifically, in the area of dynamic systems submitted to rotational accelerations. The aim of this paper is to present information of the surprising results obtained, and to attract the interest towards the investigation of this new area of knowledge in rotational non-inertial dynamics, and its multiple and remarkable scientific applications.

Quaternion methods and models of regular celestial mechanics and astrodynamics

This paper is a review,which focuses on our work,while including an analysis of many works of other researchers in the field of quaternionic regularization.The regular quaternion models of celestial mechanics and astrodynamics in the Kustaanheimo-Stiefel(KS)variables and Euler(Rodrigues-Hamilton)parameters are analyzed.These models are derived by the quaternion methods of mechanics and are based on the differential equations of the perturbed spatial two-body problem and the perturbed spatial central motion of a point particle.This paper also covers some applications of these models.Stiefel and Scheifele are known to have doubted that quaternions and quaternion matrices can be used efficiently to regularize the equations of celestial mechanics.However,the author of this paper and other researchers refuted this point of view and showed that the quaternion approach actually leads to efficient solutions for regularizing the equations of celestial mechanics and astrodynamics.This paper presents convenient geometric and kinematic interpretations of the KS transformation and the KS bilinear relation proposed by the present author.More general(compared with the KS equations)quaternion regular equations of the perturbed spatial two-body problem in the KS variables are presented.These equations are derived with the assumption that the KS bilinear relation was not satisfied.The main stages of the quaternion theory of regularizing the vector differential equation of the perturbed central motion of a point particle are presented,together with regular equations in the KS variables and Euler parameters,derived by the aforementioned theory.We also present the derivation of regular quaternion equations of the perturbed spatial two-body problem in the Levi-Civita variables and the Euler parameters,developed by the ideal rectangular Hansen coordinates and the orientation quaternion of the ideal coordinate frame.This paper also gives new results using quaternionic methods in the perturbed spatial restricted three-body problem.

Giorgio Vasari’s Celestial Utopia of Whimsy and Joy:Constellations,Zodiac Signs,and Grotesques

This study elaborates on the decoration of the ceiling in the refectory of the former Monteoliveto monastery in Naples,today part of the church of Sant’Anna dei Lombardi.It consists of three parts:an explanation of the ceiling design with its geometrical configurations of circles,octagons,hexagons,ovals,and squares;an iconographical analysis solely focusing on the ceiling decoration,which consists of grotesques,constellations,and zodiac signs;and a discussion of some of the literary and visual sources employed in the decoration.The Florentine Mannerist painter Giorgio Vasari,aided by several assistants,renovated and painted the ceilings between 1544 and 1545.Don Giammateo d’Anversa,the Abbot General of the Monteolivetan Order in Naples,composed the iconographical program with the assistance of insightful suggestions from the Florentine Monteolivetan prior Don Miniato Pitti,who was Vasari’s patron and friend as well.This oversight inspired Vasari to paint a celestial utopia of hilarity and whimsicality on the Neapolitan ceiling,thus leavening the other imagery,which combined both religious and secular representations of moral virtues and divine laws.

弱引力小天体的自主捕获与相对导航方法

远距离自主捕获与近距离高精度自主相对导航是小天体探测任务中的关键问题,并且目标尺寸越小,问题越突出。首先,针对数万千米到数千千米远距离范围内的星空背景暗弱目标难以识别的问题,提出综合利用运动学和亮度的全自主捕获和识别方法,可以实现距离大范围变化的快速准确捕获,具备了3万千米以远捕获10等星暗弱目标的能力;其次,针对数千到数十千米范围交会段视线测量可观性不足的问题,提出基于视线和轨迹机动一体化设计的相对导航方法,在考虑燃料消耗的前提下有效地提高了轨迹可观性,实现了交会段优于5%精度的相对位置导航;最后,针对近距离不规则小天体表面附近的相对导航问题,提出基于图像陆标和点云特征相结合的光学导航方法,可同时适应阳照区和阴影区的探测需求,并结合基于多源数据融合的弱引力小天体重力场反演方法,进一步提高近距相对导航的精度,近距采样相对位置优于1 m,相对速度优于1 cm/s。对所提出的方法进行了数学和物理的仿真验证。提出的方法有效解决了小天体探测中的高精度相对导航问题,也能适用于数十米量级直径大小和明暗快速交替变化的小天体着陆探测任务。

基于空间目标异步观测的惯导误差快速确定

针对惯性/天文组合导航系统中大的初始状态误差影响惯导误差收敛速度的问题,在星相机观测具有先验位置信息的有限空间目标的辅助下,提出一种基于目标-恒星角距异步测量的惯导误差在线快速确定方法。首先,在星相机光轴旋转角度和视场角大小受限的情况下,设计了通过异步照相观测方式获取有效空间目标参考信息的方案;其次,在利用惯导误差状态传播模型实现异步测量信息同步处理的基础上,构建基于空间目标与恒星之间角距的非线性最小二乘优化模型,避免了星相机的光轴扰动和安装误差对测量精度的影响;最后,基于高斯牛顿法设计了两轮迭代优化估计惯导位置误差和速度误差的方法。蒙特卡洛仿真结果表明,所提方法利用对空间目标和恒星的有限观测信息,可以有效估计惯导位置误差和速度误差,在初始位置误差约十千米量级的情况下,可以估计补偿约97.73%的位置误差以及66.25%的速度误差,优化求解误差参数的计算耗时为0.0160 s。

面向天文多普勒差分测速的太阳/行星光谱对生成方法

为了提供天文多普勒差分测速所需的同步太阳/行星光谱对,提出了一种变分自编码器(VAE)和对偶生成对抗网络(Dual GAN)相融合的VAE-Dual GAN。首先,实测太阳光谱经过VAE编码到隐空间,实现了光谱到光谱域的扩充;然后,由Dual GAN将隐空间映射到伪行星光谱;最后,利用伪行星光谱生成重构太阳光谱。此外,利用编码和生成重建损失加强对网络的约束。VAE-Dual GAN利用Dual GAN的转换学习能力完成了两个光谱域的转换,生成同步太阳/行星光谱对。实验结果表明,VAE-Dual GAN可生成高质量的太阳/行星光谱对,将天文多普勒差分测速精度提高60%以上。

从天涯比邻到天体比邻:科幻电影美学新范畴

在交通工具不发达的古代,“海内存知己,天涯若比邻”的诗句寄托了让真挚情感超越空间束缚的心愿。现代交通技术的迅猛发展逐渐抚平了传统时代因为距离遥远而萌生的惆怅。科幻电影进而在幻想未来科技应用的过程中揭示了“天体比邻”的意蕴。古人对“天涯比邻”进行过多种阐释。相关思路延伸到科幻电影构思中,形成了有关“天体比邻”的三类九种创意,即着眼于人的宇宙志向开拓、地外生物入梦、星际联系建立,着眼于物的交通工具改进、理念投契证明,着眼于事的艺术技巧创新、移民文化投射、怀旧情感抒发。作为科幻电影美学的范畴,“天体比邻”不仅可用以诠释相关影片的审美心理,而且可以作为科幻情境下中国话语与中国叙事体系的范畴起作用。

小天体柔性着陆任务规划的动态时间约束推理方法

针对小天体柔性着陆任务规划中的复杂耦合时间约束一致性推理效率问题,建立任务规划时间约束网络,通过划分时间约束类型,设计约束动态添加策略,提出动态弧一致时间约束推理方法,限制新添加约束的传播范围,局部求解时间网络一致性,实现规划过程中时间约束网络一致性的高效维护。最后,构建小天体着陆规划场景,生成着陆任务规划活动及时间约束。仿真结果表明,与现有时间约束推理方法相比,所提出方法提高了时间约束推理效率,进而可为小天体柔性着陆任务规划提供支撑。

小天体智能附着技术研究进展

面向小天体探测与开发稳健附着的需求,结合国内外小天体附着探测任务,分析了小天体智能附着技术的需求,综述了目前的研究进展。回顾了小天体附着探测的相关工程任务、介绍了小天体传统的刚性附着模式与新型智能柔性附着的概念、梳理了小天体智能附着技术的需求,在此基础上从动力学、任务规划、感知、导航、制导与控制等方面归纳总结了智能附着技术的研究进展,对小天体附着技术的发展趋势进行了展望。

近地小行星轨道误差的统计分析

精确确定近地小行星轨道是近地天体监测预警工作的重要部分之一,然而由于观测弧长、观测精度以及力模型的制约,不同目标存在不同的轨道误差,基于JPL(Jet Propulsion Laboratory)小天体数据库中3万多颗近地小行星的轨道数据,对其轨道根数误差开展了统计分析研究。发现近地小行星轨道半长径误差存在双峰分布现象,且产生的原因与观测弧段的分布有关。研究了半长径误差与观测弧长的关系,得到了拟合优度达0.90的回归方程,进一步将绝对星等参数考虑在内,采用BP(Back Propagation)神经网络训练方法对观测始末时间跨度、轨道周期、绝对星等。半长径误差搭建了参数训练网络,该方法使得拟合优度进一步提升至0.96,能够快速合理地对近地小行星半长径误差进行评估。此外,对比了观测弧长对半长径误差、偏心率误差、倾角误差的影响,发现3者随观测弧长增加的改进程度存在差异,最后,还对比分析了半长径与轨道倾角误差分布随轨道倾角的变化,发现倾角误差分布特征与观测精度的选择效应有关。这些统计分析工作有助于增加对近地小行星轨道误差分布规律的认识,为进一步改进近地小行星轨道精度提供参考。

利用固体潮研究岩石天体的深部结构

经过地球物理学的长足发展,我们有着丰富的手段来研究地球的内部结构.然而对于地球之外的其他天体,研究其内部结构的手段却仍然十分有限,往往依赖于轨道探测器、着陆器以及天文观测获取的大地测量数据.在这之中,固体潮对研究其内部结构有着重要的意义.固体潮汐形变和其带来的潮汐耗散提供了关于行星内部结构,尤其是深部核幔边界及核心部分的关键信息.本文将全面地对利用固体潮汐参数(包括潮汐勒夫数及潮汐品质因子)研究岩石天体的深部结构进行综述.首先对固体潮的基本理论、潮汐参数以及黏弹性模型进行了介绍,建立了天体内部结构参数与其外部固体潮汐响应之间的关系.之后对现有利用固体潮汐参数研究水星、金星、火星及月球这些岩石天体的内部结构的工作进行了回顾与总结,可以发现固体潮汐参数是一种对天体深部结构进行约束的有效手段.本文进一步提供了未来探测任务获取的高精度数据对研究天体深部结构的贡献.然而,目前固体潮汐参数对天体深部结构研究中也存在一些问题.例如不同黏弹性模型之间耗散强度的差异性问题、黏弹性模型的短周期实验数据和宏观长周期理论计算结果之间的不匹配问题等.本文也针对这些问题进行了讨论和分析,并对未来的研究方向进行了展望.