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.

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.

A Novel Ephemeris Model for Martian Moons Incorporating Their Free Rotation

High-precision ephemerides not only support space missions,but can also be used to study the origin and future of celestial bodies.In this paper,a coupled orbit-rotation dynamics model that fully takes into account the rotation of the Martian moons is developed.Phobos and Deimos’rotations are first described by Eulerian rotational equations,and integrated simultaneously with the orbital motion equations.Orbital and orientational parameters of Mars satellites were simultaneously obtained by numerical integration for the first time.In order to compare the differences between our newly developed model and the one now used in the ephemerides,we first reproduced and simulated the current model using our own parameters,and then fit it to the Institut de Mécanique Céleste et de Calcul deséphémérides ephemerides using least-square procedures.The adjustment test simulations show Phobos and Deimos’orbital differences between the refined model and the current model are no more than 300 m and125 m,respectively.The orientation parameters are confirmed and the results are in good agreement with the International Astronomical Union results.Moreover,we simulated two perturbations(main asteroids and mutual torques)which were not included in our refined model,and find that their effects on the orbits are completely negligible.As for the effect on rotation,we propose to take care of the role of mutual attraction in future models.

天问二号星载光学观测小行星(469219)Kamo`oalewa轨道精度仿真分析

中国小行星探测任务—天问二号将于2025年发射升空,其探访的第一个目标,小行星(469219)Kamo`oalewa(又称2016 HO3),是一颗与地球共轨的近地小天体,有着极高的运动演化研究价值.目前小行星(469219)Kamo`oalewa只有有限的地基观测资料,限制了其轨道精度.搭载光学载荷的天问二号在抵近Kamo`oalewa的过程中,预计将获得大量的星载光学观测数据.这将大大改善小行星(469219)Kamo`oalewa只有地基光学观测数据,无2021年后的公开观测资料的状况.通过仿真带有一定轨道误差的天问二号的光学观测数据,完成对小行星(469219)Kamo`oalewa定轨预报精度的任务前评估.精度评估使用协方差分析法和数值比较法,在考虑的可能观测精度范围内,预估天问二号光学观测数据能使小行星(469219)Kamo`oalewa定轨精度整体提升至15 km以内,并且分析了两种精度评估方法结果的差异与特性.

SpaceX星链卫星发布星历的研究

面对星链卫星(Starlink)严重干扰正常航天活动的现状,美国太空探索(SpaceX)公司发布的星链星历给星链卫星的相关研究带来契机,但缺乏明确说明也给进一步使用带来困难.分析星历文件后发现该星历基本是未来3d的预报轨道,平根数研究表明星历文件的前部分是至少考虑20阶非球形引力摄动的外推轨道,后部分是考虑J2项摄动的设计轨道,星历包含协方差信息,分析发现停泊和工作轨道卫星的星历在前1 d的精度优于2km,抬升阶段卫星星历的精度在半天不到的时间内迅速增长至数公里,通过发布星历的设计轨道可以更加精确地分析星链星座构型,尤其是各卫星的设计定点位置,有助于星链卫星的识别和跟踪.研究为星链星历的广泛应用提供有益参考,为星链卫星的机动检测和碰撞预警提供依据.

Updating the orbital ephemeris of the dipping source XB 1254–690 and the distance to the source

XB 1254-690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254-690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254-690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M2 = 0.42 ± 0.04 M for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 Mo. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6±0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking.

Experiment on diffuse reflection laser ranging to space debris and data analysis

Space debris poses a serious threat to human space activities and needs to be measured and cataloged. As a new technology for space target surveillance, the measurement accuracy of diffuse reflection laser ranging （DRLR） is much higher than that of microwave radar and optoelectronic measurement. Based on the laser ranging data of space debris from the DRLR system at Shanghai Astronomical Observatory acquired in March-April, 2013, the characteristics and precision of the laser ranging data are analyzed and their applications in orbit determination of space debris are discussed, which is implemented for the first time in China. The experiment indicates that the precision of laser ranging data can reach 39 cm-228 cm. When the data are sufficient enough （four arcs measured over three days）, the orbital accuracy of space debris can be up to 50 m.

CHES: A Space-borne Astrometric Mission for the Detection of Habitable Planets of the Nearby Solar-type Stars

The Closeby Habitable Exoplanet Survey(CHES) mission is proposed to discover habitable-zone Earth-like planets of nearby solar-type stars(~10 pc away from our solar system) via microarcsecond relative astrometry.The major scientific objectives of CHES are:to search for Earth Twins or terrestrial planets in habitable zones orbiting100 FGK nearby stars;further to conduct a comprehensive survey and extensively characterize nearby planetary systems.The primary payload is a high-quality,low-distortion,high-stability telescope.The optical subsystem is a coaxial three-mirror anastigmat(TMA) with a 1.2 m-aperture,0°.44 × 0°.44 field of view and 500 nm-900 nm working wave band.The camera focal plane is composed of a mosaic of 81 scientific CMOS detectors each with4 k × 4 k pixels.The heterodyne laser interferometric calibration technology is employed to ensure microarcsecond level(1 μas) relative astrometry precision to meet the requirements for detection of Earth-like planets.The CHES satellite operates at the Sun-Earth L2 point and observes all the target stars for 5 yr.CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on microarcsecond astrometry from space.This will definitely enhance our understanding of the formation of diverse nearby planetary systems and the emergence of other worlds for solar-type stars,and finally provide insights to the evolution of our own solar system.

Variable stars in M37

The CCD photometric observations of open star cluster M37(NGC 2099) were carried out up to a limiting magnitude of V ～ 20 in both B and V filters to search for variable stars using a 2k×4k CCD and the 1.3 m telescope at the Vainu Bapu Observatory, Kavalur.A total of 314 stars were in the first observing run, out of which 60 were identified as variables.Eight out of the identified 60 variables are classified as W UMa binary stars.For model fitting, we used PHOEBE based on the W-D code to estimate the physical parameters of these newly detected W UMa binaries that theoretically best match the observed light curves.

The principle of a navigation constellation composed of SIGSO communication satellites

The Chinese Area Positioning System （CAPS）, a navigation system based on geostafionary orbit （GEO） communication satellites, was developed in 2002 by astronomers at Chinese Academy of Sciences. Extensive positioning experiments of CAPS have been performed since 2005. On the basis of CAPS, this paper studies the principle of a navigation constellation composed of slightly inclined geostationary orbit （SIGSO） communication satellites. SIGSO satellites are derived from GEO satellites which are near the end of their operational life by inclined orbit operation. Considering the abundant frequency resources of SIGSO satellites, multi-frequency observations could be conducted to enhance the precision of pseudorange measurements and ameliorate the positioning performance. A constellation composed of two GEO satellites and four SIGSO satellites with an inclination of 5° can provide service to most of the territory of China with a maximum position dilution of precision （PDOP） over 24 h of less than 42. With synthetic utilization of the truncated precise code and a physical augmentation factor in four frequencies, the navigation system with this constellation is expected to obtain comparable positioning performance to that of the coarse acquisition code of the Global Positioning System （GPS）. When the new method of code-carrier phase combinations is adopted, the system has the potential to possess commensurate accuracy with the precise code in GPS. Additionally, the copious frequency resources can also be used to develop new anti-interference techniques and integrate navigation and communication.

New upper limit on the cosmological constant from solar system dynamics

The cosmological constant A is the simplest model for explaining the dark energy which supposedly drives the observed accelerated expansion rate of the Universe. Together with the concept of cold dark matter, it satisfactorily accommo- dates a wealth of observations related to cosmology. Due to its assumed constancy throughout the Universe, A might also affect the dynamics of the planets in the so- lar system, although with extremely small effects. However, modern high-precision ephemerides provide a promising tool for constraining it. Using the supplementary advances in the perihelia provided by current INPOP10a and EPM2011 ephemerides, we obtain a new upper limit on A in the solar system when the Lense-Thirring ef- fect due to the Sun＇s angular momentum and the uncertainty of the Sun＇s quadrupole moment are properly taken into account. These two factors were mostly absent in pre- vious works dealing with A. We find that INPOP10a yields an upper limit of A = （0.26±1.45） × 10^-43 m^-2 and EPM2011 gives A = （-0.44 4±8.93） × 10^-43 m^-2. Such bounds are about 10 times less than previously estimated results.

New upper limits on deviation from the inverse-square law of gravity in the solar system:a Yukawa parameterization

New physics beyond the standard model of particles might cause deviation from the inverse-square law of gravity. In many theoretical models of modified gravity, it is parameterized by the Yukawa correction to the Newtonian gravitational force in terms of two parameters α and λ. Here α is a dimensionless strength parameter and A is a length scale. Using the supplementary advances in perihelia provided by INPOP10a and EPM2011 ephemerides, we obtain new upper limits on the deviation from the inverse-square law when the uncertainty of the Sun＇s quadrupole moment is taken into account. We find that INPOP10a yields the upper limits as α =- 3.1× 10-11 and λ= 0.15 au, and EPM2011 gives α = 5.2 × 10-11 and λ=- 0.21 au. In both of them, α is at least 10 times less than the previous results.

Precession effects on a liquid planetary core

Motivated by the desire to understand the rich dynamics of precessionally driven flow in a liquid planetary core, we investigate, through numerical simulations, the precessing fluid motion in a ro- taring cylindrical annulus, which simultaneously possesses slow precession. The same problem has been studied extensively in cylinders, where the precessing flow is characterized by three key parameters： the Ekman number E, the Poincar6 number Po and the radius-height aspect ratio F. While in an annulus, there is another parameter, the inner-radius-height aspect ratio T, which also plays an important role in controlling the structure and evolution of the flow. By decomposing the nonlinear solution into a set of inertial modes, we demonstrate the properties of both weakly and moderately precessing flows. It is found that, when the precessional force is weak, the flow is stable with a constant amplitude of kinetic energy. As the precessional force increases, our simulation suggests that the nonlinear interaction be- tween the boundary effects and the inertial modes can trigger more turbulence, introducing a transitional regime of rich dynamics to disordered flow. The inertial mode u111, followed by u113 or u112, always dominates the precessing flow when 0.001 ≤Po ≤ 0.05, ranging from weak to moderate precession. Moreover, the precessing flow in an annulus shows more stability than in a cylinder which is likely to be caused by the effect of the inner boundary that restricts the growth of resonant and non-resonant inertial modes. Furthermore, the mechanism of triadic resonance is not found in the transitional regime from a laminar to disordered flow.

Preliminary limits on deviation from the inverse-square law of gravity in the solar system:a power-law parameterization

New physics beyond the standard model of particles might cause a deviation from the inverse-square law of gravity. In some theories, it is parameterized by a power-law correction to the Newtonian gravitational force, which might originate from the simultaneous exchange of particles or modified and extended theories of gravity. Using the supplementary advances of the perihelia provided by INPOP 10a （IMCCE, France） and EPM2011 （IAA RAS, Russia） ephemerides, we obtain preliminary limits on this correction. In our estimation, we take the Lense-Thirring effect due to the Sun＇s angular momentum into account. The parameters of the power-law correction and the uncertainty of the Sun＇s quadrupole moment are simultaneously estimated with the method of minimizing X2. From INPOP10a, we find N - 0.605 for the exponent of the power-law correction. However, from EPM2011, we find that, although it yields N = 3.001, the estimated uncertainty in the Sun＇s quadrupole moment is much larger than the value given by current observations. This might be caused by the intrinsic nonlinearity in the power-law correction, which makes the estimation very sensitive to the supplementary advances of the perihelia.

JPL行星历表的比较及评估

鉴于美国宇航局(NASA)喷气推进实验室(JPL)研发的一系列行星历表在深空导航、行星际探测等各个方面的广泛应用,有必要就其内容、适用范围、实现和维护进行比较.针对我国未来有望开展的金/火星深空探测任务,以DE405、DE421以及DE423为例,分析了动力学模型及其所采用的观测数据的不同.通过评估上述不同版本历表的精度和性能,着重讨论了不同历表对环金/火星探测器的影响并给出使用上的建议:对于金星探测任务而言,建议使用DE423;对于火星探测任务而言,建议使用DE421或DE423.

灰色模型修正及其在实时GPS卫星钟差预报中的应用研究

在GPS实时精密单点定位中,卫星钟差的实时可靠预报是实现GPS实时高精度单点定位的关键之一.星载GPS原子钟频率高,非常敏感,极易受到外界及其本身因素的影响,从而很难掌握其复杂细致的变化规律,这些属性符合灰色系统理论的特点.因此,考虑将钟差的变化过程看作一个灰色系统.在探讨二次多项式和灰色模型卫星钟差预报局限性基础上,提出了利用改进的灰色模型实时预报GPS卫星钟差的研究,最后利用3个不同时段的GPS卫星钟差资料进行不同采样间隔钟差预报精度分析、灰色模型指数系数与预报精度的关系、与二次多项式预报精度比较分析,总结不同卫星钟差类型与模型指数系数的一般关系,并与IGS最终钟差星历产品比较,验证本文提出的改进预报模型的可行性和有效性.为实时GPS动态精密单点定位提供较高精度的卫星钟差产品.

卫星钟差预报模型中周期项的选取方法及性能分析

针对卫星钟差预报(SCB)中周期项选取方法存在的问题,在分析卫星钟周期波动特性的基础上,给出了正确的周期项选取方法,并与现有方法进行了比较.利用IGS(International GNSS Service)的卫星钟差数据,比较分析了二次多项式加周期项模型与传统模型的预报精度.从理论上分析了周期项对传统模型的改善程度及适用条件.结果表明:按照提出方法得到的周期项更符合实际,将其应用于钟差预报时能获得更高的预报精度,大量仿真实验还表明卫星钟周期性波动相对较大时周期项对传统模型有明显改善.

导航卫星历书参数拟合算法研究

对导航卫星历书问题进行了综合研究,并结合J_2项分析解,提出了两套新的历书参数拟合方法和用户算法,与正常算法不同的是:8参数历书拟合算法以(?)=-3/2J_2等(R_e^2)/(p^2)n cos i隐性直接代替历书参数Ω_1;在用户算法中对MEO卫星以ω_k=ω_0-ω_1·(Δt/2-t_k),对高轨卫星以ω_k=ω_0-ω_1·(Δt/2-t_k)/2修正历书参数ω_k,其中ω_1=(A_2)/(p^2)n(2-5/2sin^2 i).9参数历书拟合算法在8参数的基础上增加了一个历书参数(?)=(T_Err_n-T_Err_0)/Δt/α参数,在用户算法中以ω_k=ω_0-ω_1·(Δt/2-t_k),M_k=M_0+n·t_k-(?)·(Δt/2-t_k)修正ω_k和M_k.通过多组模拟轨道和IGS精密轨道的历书拟合实验,结果表明,新8参数历书拟合方法具有参数少、迭代收敛速度快、对MEO卫星拟合精度高等优点;新9参数历书拟合算法,迭代收敛快,拟合精度优于其他算法.

相对论天文参考系的回顾与展望

国际天文联合会(IAU)在1991年和2000年分别通过了关于相对论天文参考系的重要决议。特别是2000年的决议,以两个互相等价的相对论N体多参考系理论:Brumberg-Kopeikin体系和Damour-Soffel-Xu体系为基础,构造了严格且自洽的一阶后牛顿(1PN)的局部参考系和全局参考系,并给出了相应的坐标变换规则。IAU2000决议发表后的10多年里,已经开始应用在一些高精度的天体测量数据处理模型中,但是其工程化应用还没有得到广泛实现,特别是目前为止我国没有将其应用到具体的天文观测或者空间探测计划中。因此有必要对IAU的相对论天文参考系理论做一个系统的解读。首先介绍了IAU在1991年给出的一个简单的相对论参考系决议;随后在第3章和第4章详细讨论了Brumberg-Kopeikin理论和Damour-Soffel-Xu体系;接着,详细给出了IAU2000年大会关于相对论参考系的决议内容;最后,讨论了IAU2000决议的工程化应用、近10多年来的理论发展以及对未来的展望。

国际地球自转服务(IERS)评介

回顾了建立国际地球自转服务(IERS)的历史过程,简述了IERS机构各部门的设置及其作用。着重介绍了IERS重建的理由和过程以及新IERS机构的组成。最后给出IERS成果对现有科学研究的作用和意义。