关于脉冲星脉冲到达时间转换方程

较详细地介绍了脉冲星脉冲到达时间（TOA）转换方程,讨论了脉冲星TOA转换方程在航天器导航算法中的具体应用问题。同时,对导航用的脉冲星脉冲TOA转换方程与地面射电计时观测用的脉冲星脉冲TOA转换方程进行了比较研究。     

基于X射线脉冲星的航天器自主导航算法分析

脉冲星自转非常稳定,可以用作时间标准,许多脉冲星的空间位置、自行、距离、自转周期及其导数等天体测量参数和天体物理参数都能被精确测定.由于脉冲星能够同时提供时间信号和空间位置坐标,安装在航天器上的脉冲星导航系统能够实现航天器的自主导航.首先根据航天器轨道动力学方程预测航天器的位置,再通过航天器上观测的脉冲到达时间和预报的脉冲到达时间之差,应用Kalman滤波计算航天器位置估计的误差,从而对航天器的位置进行修正.最后,分析初始误差、脉冲到达时间测量精度、脉冲星个数对导航精度的影响.     

关于X射线脉冲星自主导航的位置观测方程

在X射线脉冲星自主导航(XNAV)中,位置观测方程表达了X光子到达航天器的时刻(TOA)和航天器位置的关系.具体讨论时,一般用TOA和"时间基准"的差值代替TOA,用太阳系质心系中的位置矢量表示航天器的位置."时间基准"可以取X光子到达太阳系质心(SSB)的真实时间,也可以取X光子到达SSB的"等效时间".讨论了基于这两种时间基准的位置观测方程,给出了时间精度为0.1 ns的位置观测方程,分析了其中各项的物理意义.     

脉冲星在空间飞行器定位中的应用

利用脉冲星钟模型能高精度地预报脉冲星脉冲到达太阳系质心的时间。基于脉冲星时、空参考架可实现各类空间飞行器的自主导航。讨论了脉冲星钟的模型和脉冲星导航系统的框架结构,描述了脉冲星导航的基本原理和算法。指出脉冲星导航系统对脉冲星脉冲到达探测器时刻的测量精度,是决定空间飞行器位置解算精度的关键因素。脉冲星导航观测采用的原子钟如果足够稳定,则空间飞行器位置的解算方法可以简化。在脉冲星导航系统计时观测精度达到或优于几十微秒量级时,脉冲星视差、相对论效应的影响是不可忽略的。对脉冲星导航系统开发设计中的关键技术和进一步研究的主要问题进行了初步分析和讨论。     

X射线脉冲星导航可用目标源研究

脉冲星具有自转非常稳定的特性,在空间自主导航中有重要的应用前景.选择和研究一组适合于脉冲星导航使用的候选目标源非常重要,决定脉冲星导航精度的主要因素有:导航目标源X射线流量强度、目标源的位置精度和旋转参数精度.对可用于导航的一些X射线源进行了讨论研究,并对最适合做导航研究的转动能驱动的X射线脉冲星进行统计分析.     

基于脉冲星计时的航天器自主定位误差估计方法

目前很多学者希望从"X射线脉冲星自主导航"的导航算法研究入手,利用数据分析或仿真进行验证.其中关于航天器自主定位的误差估计方法、误差量级和各种影响因素的讨论,并没有在给定详细初始条件的基础上系统性地说明问题.为了分析上述问题,需从天体测量学的角度出发,对自主定位的各种误差源及其影响因素进行探讨和误差量级的估计.首先,由...     

脉冲星钟模型精度分析

毫秒脉冲星具有很高的自转稳定性,利用脉冲星自转极其稳定的特性可以开展许多应用研究,如:脉冲星时间标准的建立、宇宙背景引力波的探测、X射线脉冲星导航应用等等.利用国际脉冲星计时阵(International Pulsar Timing Array,IPTA)中J0437-4715和J1713+0743 2颗源的实测数据开展脉冲星钟模型参数精度分析和脉冲到达时间(Time Of Arrival,TOA)预报精度研究.通过研究得知,目前脉冲星自转频率测量精度为10-15Hz,频率1阶导数测量精度为10~(-23)s~(-2),且自转参数测量精度随观测时间跨度每4–5 yr提高1个量级.另外,利用J0437-4715 10 yr观测数据建立的钟模型,其脉冲到达时间预报偏差4.8 yr之内可保持在1μs之内.因此,利用该脉冲星建立时间标准用于校准原子时,可以使原子时相对于地球时(Terrestrial Time,TT)的偏差在4.8 yr之内小于1μs.     

X射线脉冲星自主导航的光传播时间方程

详细讨论了X射线脉冲星自主导航系统的广义相对论效应,采用DSX体系的后牛顿近似方法,计算出1PN度规下的光线弯曲轨迹和时间延缓以及2PN度规下的引力延缓,得到X射线脉冲自主导航的高精度测量方程.     

基于卡尔曼滤波的脉冲星计时研究

脉冲星是高速自转的中子星,其自转周期稳定,不受人为干扰破坏,可作为绝对时间的参考量.论文提出一种基于卡尔曼滤波算法的脉冲星授时方法,以太阳某同步轨道为例,对基于卡尔曼滤波的钟差控制以及脉冲星星表误差和脉冲到达时间(TOA)测量精度对授时精度的影响进行了仿真分析.结果表明,该方法可以有效消除星载时钟钟差并抑制其随时间的增加,解决了航天器搭载低成本时钟精度不能满足要求的问题.     

脉冲星计时技术及其应用

简述脉冲星发现和计时观测的概况。文中概述脉冲星计时的物理模型和计算用的各种钦件,特别是全球广泛应用的TEMPO2软件,并描述脉冲星计时阵的概念和国际脉冲星计时阵。对脉冲星计时观测应用:建立脉冲星时标、改进行星历表(包括外行星质量测定和海外天体的发现)、检测引力波、测定脉冲星的旋转和天体测量参数、脉冲星自主导航、相对论引力理论的验证等作了介绍。最后,对我国开展此项工作的情况给予简要描述,并提出若干建议。     

Algorithm Analysis of Autonomous Navigation of Spacecraft Based on X-ray Pulsars

A pulsar has the very stable rotation and can be used as the time standard. The astrometric parameters and astrophysical parameters of many pulsars, such as the spatial position, proper motion, distance, rotation period and its derivative, etc., can be all accurately determined. Since the pulsar can provide the time signal and the coordinates of its spatial position simultaneously, the pulsar navigation system installed on a spacecraft enables the autonomous navigation of the spacecraft to be realized. Firstly, the position of the spacecraft is predicted based on the equation of orbit dynamics of the spacecraft and then the Kalman filtering is applied to calculating the estimation error of the spacecraft position through the difference between the pulse arrival time observed on the spacecraft and the predicted pulse arrival time, thereby modifying the position of the spacecraft. Finally, the effects of the initial error, measuring accuracy of the pulse arrival time and number of pulsars on the navigation accuracy are analyzed.     

Autonomous optical navigation using nanosatellite-class instruments: a Mars approach case study

This paper examines the effectiveness of small star trackers for orbital estimation. Autonomous optical navigation has been used for some time to provide local estimates of orbital parameters during close approach to celestial bodies. These techniques have been used extensively on spacecraft dating back to the Voyager missions, but often rely on long exposures and large instrument apertures. Using a hyperbolic Mars approach as a reference mission, we present an EKF-based navigation filter suitable for nanosatellite missions. Observations of Mars and its moons allow the estimator to correct initial errors in both position and velocity. Our results show that nanosatellite-class star trackers can produce good quality navigation solutions with low position (\(<300\,\text {m}\)) and velocity (\(<0.15\,\text {m/s}\)) errors as the spacecraft approaches periapse.     

Analysis of the Precision of Pulsar Time Clock Modeltwo

Millisecond pulsars have a very high rotation stability, which can be applied to many research fields, such as the establishment of the pulsar time standard, the detection of gravitational wave, the spacecraft navigation by using X-ray pulsars and so on. In this paper, we employ two millisecond pulsars PSR J0437-4715 and J1713+0743, which are observed by the International Pulsar Timing Array (IPTA), to analyze the precision of pulsar clock parameter and the prediction accuracy of pulse time of arrival (TOA). It is found that the uncertainty of spin frequency is 10^?15 Hz, the uncertainty of the first derivative of spin frequency is 10^?23 s^?2, and the precision of measured rotational parameters increases by one order of magnitude with the accumulated observational data every 4～5 years. In addition, the errors of TOAs within 4.8 yr which are predicted by the clock model established by the 10 yr data of J0437-4715 are less than 1 μs. Therefore, one can use the pulsar time standard to calibrate the atomic clock, and make the atomic time deviate from the TT (Terrestrial Time) less than 1 μs within 4.8 yr.     

Comparison of three filters in asteroid-based autonomous navigation

At present,optical autonomous navigation has become a key technology in deep space exploration programs.Recent studies focus on the problem of orbit determination using autonomous navigation,and the choice of filter is one of the main issues.To prepare for a possible exploration mission to Mars,the primary emphasis of this paper is to evaluate the capability of three filters,the extended Kalman filter(EKF),unscented Kalman filter(UKF) and weighted least-squares(WLS) algorithm,which have different initial states during the cruise phase.One initial state is assumed to have high accuracy with the support of ground tracking when autonomous navigation is operating; for the other state,errors are set to be large without this support.In addition,the method of selecting asteroids that can be used for navigation from known lists of asteroids to form a sequence is also presented in this study.The simulation results show that WLS and UKF should be the first choice for optical autonomous navigation during the cruise phase to Mars.     

The Model of Radio Two-way Time Comparison between Satellite and Station and Experimental Analysis

Time synchronization between satellite and station is the key technique of satellite navigation system and the foundation of realization of satellite navigation and positioning. Aiming at solving the problems of time synchronization, we have discussed a new method of radio two-way time comparison between satellite and station, deduced in detail the reduction model of up- and down-link pseudo ranges between satellite and station, and provided a practical calculation model of clock error between satellite and station. By calculating the differences between up- and down-link pseudo ranges, this method has eliminated the influences of common errors, such as the tropospheric delay, satellite ephemeris errors, ground station coordinates errors and so on. The ionospheric delay relevant to signal frequency is also weakened largely, thus this improves the accuracy of time comparison greatly. Finally, experimental analysis is conducted by using observational data, and the results show that the accuracy of radio two-way time comparison between satellite and station can attain about 0.34 ns, which validates the correctness of theoretical method and model.     

Long-term Clock Bias Prediction Based on An ARMA Model

The long-term and reliable prediction of satellite clock bias (SCB) is an important prerequisite for realizing the satellite autonomous navigation and orbit determination. Considering the shortcomings of the quadratic polynomial model (PM) and gray system model (GM) in the long-term prediction of SCB, a new prediction method of SCB based on an ARMA (Auto-Regressive Moving Average) model is proposed to represent the variation characteristics of SCB more accurately. In this paper, a careful precision analysis of the 90-day SCB prediction is made to verify the feasibility and validity of this proposed method by using the IGS (International GNSS Service) clock data. According to the variation characteristics of each satellite clock, the pattern recognition, modeling and prediction of SCB are conducted, and the detailed comparison is made with the other three models at the same time. The results show that adopting the ARMA model can effectively improve the accuracy of long-term SCB prediction.     

On the Equation of Position Measurement of XNAV

The equation of position measurement of XNAV (X-ray pulsar-based autonomous navigation) reveals the relation between the time of arrival (TOA) of an X-ray photon and the spacecraft position at this moment. In specific dis- cussions of navigation, the TOA is generally replaced by the difference between the TOA and a preset “time reference”, and the spacecraft position is expressed by the position vector in the barycentric system of the solar system. The “time reference” may be the true TOA at the solar-system barycenter (SSB), or an “equivalent TOA” at SSB. As the true TOA at SSB is difficult to obtain, the “equivalent TOA” is more convenient for navigation. The equations of position measurement based on the two kinds of “time reference” are discussed, the equa- tion based on the “equivalent TOA”, which has the time accuracy of 0.1 ns, is given, and the physical meanings of the every term in which are analyzed.