Initial orbit determination of BDS-3 satellites based on new code signals

For the two newly launched satellites(PRN number 27 and 28) of the future global BeiDou navigation satellite system(BDS-3), there is no available broadcast ephemeris data and other initial orbit information, but the initial orbit is the fundamental of the comprehensive analysis of the satellites and their signals. Precise orbit determination(POD) also requires determination of a priori initial value with a certain precision in order to avoid problems such as filter divergence during POD. Compared with the Newton iteration method, which relies on the initial value, this study utilizes the Bancroft algorithm to directly solve the nonlinear equations with the advantage of numerical stability. The initial orbits of these two satellites are calculated based on new code signals, and their results are analyzed and discussed. The experimental results show that, with the exception of very few epochs, when the new code signal is utilized, the median and robust variance factor of the observed residuals computed using pseudo-range observations and the solved initial orbits are less than 4 and 2 m, respectively. It also shows that this solution can be used for rapid initial orbit recovery after maneuvers of the new BeiDou satellites.

Research on Autonomous Orbit Determination of Navigation Satellite Based on Crosslink Range and Orientation Parameters Constraining

Autonomous navigation of navigation satellite is di scussed. The method of auto-orbit determination using the crosslink range and o rientation parameters constraining is put forward. On the basis of the analysis of its feasibility, some useful conclusions are given.

High Precision Orbit Determination of CHAMP Satellite

The precision orbit determination of challenging minisatellite payload(CHAMP) satellite was done based on position and navigation data analyst(PANDA) software which is developed in Wuhan University, using the onboard GPS data of year 2002 from day 126 to 131. The orbit accuracy was assessed by analyzing the difference from GFZ post-processed science orbits (PSO), the GPS carrier and pseudo-range data residuals and the satellite laser ranging (SLR) residuals.

A Fast and Accurate LEO Satellite-Based Direct Position Determination Assisted by TDOA Measurements

This paper focuses on the trusted vessel position acquisition using passive localization based on the booming low-earth-orbit(LEO) satellites. As the high signal-to-noise ratio(SNR) reception cannot always be guaranteed at LEO satellites, the recently developed direct position determination(DPD)is adopted. For LEO satellite-based passive localization systems, an efficient DPD is challenging due to the excessive exhaustive search range leading from broad satellite coverage. In order to reduce the computational complexity, we propose a time difference of arrival-assisted DPD(TA-DPD) which minimizes the searching area by the time difference of arrival measurements and their variances. In this way, the size of the searching area is determined by both geometrical constraints and qualities of received signals, and signals with higher SNRs can be positioned more efficiently as their searching areas are generally smaller.Both two-dimensional and three-dimensional passive localization simulations using the proposed TA-DPD are provided to demonstrate its efficiency and validity. The superior accuracy performance of the proposed method, especially at low SNRs conditions, is also verified through the comparison to conventional two-step methods. Providing a larger margin in link budget for satellite-based vessel location acquisition,the TA-DPD can be a competitive candidate for trusted marine location service.

Error Analysis of Orbit Determination for the Geostationary Satellite with Single Station Antenna Tracking Data

In the study, position and velocity values of a geostationary satellite are found. When performing this, a MATLAB algorithm is used for Runge-Kutta Fehlberg orbit integration method to solve spacecraft’s position and velocity. Integrated method is the solution for the systems which mainly work with a single station. Method provides calculation of azimuth, elevation and range data by using the position simulation results found by RKF. Errors of orbit determination are analysed. Variances of orbit parameters are chosen as the accuracy criteria. Analysis results are the indicator of the method’s

Results and Analyses of BDS Precise Orbit Determination with the Enhancement of Fengyun-3C

Global navigation satellite system occultation sounder (GNOS) Fengyun-3C was launched successfully on September 23, 2013, which carried GPS/BDS receiver for the first time. This provides the convenience to study the enhancement results of low earth orbiter satellite (LEO) to BDS precise orbit determination (POD). First the data characteristic and code observation noise of GNOS are analyzed. Then the enhancement experiments in the case of global and regional ground observation stations layout are processed with four POD schemes: BDS single system, GPS/BDS double system, BDS single system with GNOS observations, GPS/BDS double system with GNOS observations. The precision of BDS orbits and clocks are compared via overlapping arcs. Results show that in the case of global station layout the along directional precision of GEO satellite has the biggest improvement, with the improvement percentage 60%. Then the precision of cross direction and the along direction of remaining satellites shows the second biggest improvement. The orbit precision of BDS-only POD in part of observation arcs some satellite even suffers a slight decline. The root mean square (RMS) of overlapping clock difference of visible arcs in GPS/BDS POD experiments improves by 0.1 ns level. As to the experiments of regional station layout with 7 ground stations, the orbit and clock overlapping precision and orbit predicting precision are analyzed. Results show that the predicting precision of BDS GEO satellites in the along direction improves by 85%. The remaining also has a substantial improvement, with the average percentage 21.7%. RMS of overlapping clock difference of visible arcs improves by 0.5 ns level.

Solar Radiation Pressure Modeling and Application of BDS Satellites

Solar radiation pressure(SRP)model is the basis of high precise orbit determination and positioning of navigation satellites.At present,it is common to see the study of SRP model of BDS satellites.However,the establishment and application of a comprehensive analytical SRP model based on satellite physical parameters are rare.Different from other conservative forces and non-conservative forces,SRP is closely related to the satellite’s physical parameters and in-orbit state.On the basis of the physical mechanism of solar radiation,BDS satellite physical parameters,in-orbit attitude control mode,and so on,a comprehensive analytical model has been studied in this paper.Based on precise ephemeris and satellite laser ranging(SLR)data,the precision of a comprehensive analytical model has been verified.And the precision of orbit determination is at the decimeter level using this comprehensive analytical SRP model.According to the satellite conservation theorem of angular momentum and change of in-orbit telemetry parameters,the difference between a comprehensive analytical model and the actual in-orbit interference force has been analyzed and calculated.The addition of empirical items on the comprehensive analytical model has been proposed.SLR validations demonstrated that the orbit precision of BDS C08 and C10 can be achieved at 0.078 m and 0.084 m respectively.Compared with using the improved CODE empirical model,precision orbit accuracy of them has increased by 0.021 m and 0.045 m respectively.

HOI延迟对LEO卫星简化动力学POD的影响

通常使用无电离层(IF)线性组合(LC)消除低地球轨道(LEO)卫星简化动力学精密定轨(POD)一阶电离层延迟误差,忽略了高阶电离层(HOI)延迟误差。随着LEO卫星POD技术的发展,计算不同轨道高度的HOI延迟并探索其变化已成为进一步提高POD精度的重要手段。首先,使用国际参考电离层-2016(IRI-2016)和国际地磁参考场第13代(IGRF-13)模型,计算电离层穿刺点(IPP)位置和地磁场强度。其次,使用平滑星载GNSS数据计算电离层斜路径总电子含量(STEC)。然后,分别计算GOCE、GRACE-A和SWARM-A/B卫星的二阶和三阶电离层延迟。最后,评估了HOI延迟对LEO卫星重叠轨道分析、卫星激光测距(SLR)检核和精密科学轨道(PSO)比较结果的影响。实验结果表明:HOI延迟对LEO卫星简化动力学POD的影响大约在毫米至厘米的数量级上;HOI延迟对LEO卫星简化动力学POD外符合精度的影响分别达到0.92,0.22,0.21和0.18 mm;随着LEO卫星轨道高度的增加,HOI延迟对LEO卫星简化动力学POD的影响减小。

广播星历旋转误差对低轨星载BDS-3/GPS实时精密定轨影响分析

基于LT-01A卫星星载BDS-3/GPS观测值进行了星载实时精密定轨研究,并重点分析了广播星历旋转误差对实时定轨精度的影响。通过赫尔默特转换评估了所选时段内GPS和BDS-3广播星历轨道旋转误差,显示BDS-3广播星历旋转误差可达-8.7 mas,平均量级较GPS大约2.5倍。BDS-3广播星历经旋转改正后,轨道切向、法向均方根(RMS)误差从25 cm左右提升至10 cm量级,提升幅度超过50%。因此,基于星载BDS-3以及BDS-3/GPS联合的实时定轨精度受BDS-3星历旋转误差影响严重,且主要作用于切向和法向。经过旋转改正后,单独BDS-3实时定轨在切向、法向、径向RMS分别为21.0 cm、10.7 cm及11.2 cm,其切向和法向精度比改正前分别提升15.0%和31.8%;BDS-3与GPS联合定轨进一步提升切向精度至19.4 cm。得益于BDS-3广播星历较高的精度,单BDS-3以及BDS-3/GPS联合的实时定轨在旋转改正前的三维RMS分别为31.9 cm和29.2 cm,较单GPS实时定轨分别提升9.1%和16.8%;添加旋转改正后,其定轨精度分别提升至26.7 cm和25.0 cm,较单GPS实时定轨分别提升22.6%和27.5%。

Schmidt算法在导航卫星自主定轨中的应用

针对现有导航卫星自主定轨采用的等效观测Kalman滤波算法精度难以进一步提升的问题,本文将顾及卫星间状态量协方差信息的Schmidt分布式算法应用于自主定轨,给出了逐观测量处理的Schmidt分布式算法测量更新和时间更新计算公式,提出了采用平方根滤波方法解决Schmidt分布式算法用于星间链路定轨时协方差阵非负定问题。仿真和实测数据自主定轨结果表明,相比等效观测分布式滤波算法,本文方法能够有效提升自主定轨精度。

一种高精度星载磁强计系统级标定方法

星载三轴磁强计经常被用于卫星在轨的姿态确认与修正,为提高其在轨磁场测量精度,提出了一种高精度的星载磁强计系统级标定方法。首先,引入了光学棱镜基准,完成了参照磁强计磁轴的正交性自校准。随后,利用二乘法完成了三轴零磁环境模拟系统线圈系数校准,再利用参照磁强计完成了三轴零磁环境模拟系统磁轴正交性标定,从而获得高精度的空间磁环境地面模拟系统。最后,利用三轴零磁环境模拟系统与卫星正交性对应关系,完成了星载磁强计的标定。试验结果表明:经过标定后,三轴零磁环境模拟系统非正交度优于0.01°,星载磁强计标定误差优于10 nT,为星载磁强计系统地面标定试验验证提供了新途径。

双星跟飞测高卫星在轨初步验证

卫星测高反演重力场的常规做法是利用海面高差求解垂线偏差,进一步计算海洋重力异常和海洋大地水准面高等信息。显然,提高海面高差的测量精度可以直接提升海洋重力场的反演精度。本文给出了双星跟飞卫星测高原理,通过轨道设计使双星星下点跨轨间距(即分辨率)在1′左右,双星同时测量沿其轨道的海面高差及跨轨的星间海面高差,此时轨道径向误差表现为星间或单星历元间的相对轨道径向误差,而与大气传播和地球物理效应等有关的改正项,对于地面轨间距只有1′的双星近似相等,其在海面高差中几无体现,因此海面高差的精度相比于传统的单星测量将有显著提高。利用测高A/B双星的实际观测数据,初步验证了相对轨道径向误差和海面高差中的8项改正的差值误差。结果表明,对于定标阶段约25 km的星下点间距,干对流层、湿对流层、电离层、固体潮、极潮和逆大气压等改正项的差值误差均在5 mm量级;海潮改正差值、海况偏差差值中分别有约1 cm和2 cm的残留误差;对于业务轨道约2 km的星下点间距,相对轨道径向误差约为3 mm,除了海况偏差差值有约0.52 cm的残留误差,其他改正项的差值误差均小于0.05 cm,可完全忽略不计。

面向导航增强的低轨卫星钟差确定及预报方法研究

低轨导航增强是未来导航发展的重要趋势,而高精度低轨卫星钟差是实现低轨导航增强的必要条件。基于Sentinel-6A卫星,对低轨卫星钟差特性进行了分析,给出了钟差确定方法及影响因素,介绍了顾及钟差特性的低轨卫星钟差预报方法。实验表明,低轨卫星钟差含有多个周期项,给低轨卫星建模和预报带来了困难。与使用运动学定轨模型相比,基于简化动力学的定轨模型可显著提升低轨卫星钟差精度;当基于运动学模型确定低轨卫星钟差时,相较于使用GPS单系统数据,多GNSS观测数据可提升低轨卫星钟差精度。研究表明,基于GPS和Galileo观测的Sen-tinel-6A卫星钟差精度相较于GPS单系统钟差精度改善了36%,同时,所使用的GNSS产品精度与低轨卫星钟差精度密切相关。利用顾及卫星钟差特性的低轨卫星钟差预报方法,当预报时长小于1min,低轨卫星钟差预报精度(预报与解算值之差的RMSE)在0.1ns之内,当预报时长小于5min,预报精度在0.3ns之内,随着预报时长的增长,预报精度显著下降。

一种适用于北斗三号星间扩展用户的定轨算法

针对北斗卫星导航系统星间链路网络扩展服务航天器的精密轨道确定及时间同步需求,提出了基于多项式轨道拟合方法的轨道确定与时间同步算法,克服了传统算法中使用北斗星间链路双向测量数据必须具备初始轨道和钟差等先验信息的约束,可有效拓宽北斗星间链路使用场景。该算法以多项式表达航天器一段时间的轨道和钟差,并使用星间双向测量数据基于最小二乘算法迭代估计多项式系数,从而完成航天器轨道和钟差解算。利用北斗三号星间链路在轨实测数据的试验表明定轨和时间同步精度均在0.12 m以内,有效验证了该算法的正确性。

双线程滑动窗口多系统GNSS超快精密定轨实现及评估

全球导航卫星系统(GNSS)超快精密定轨为GNSS实时应用提供了高精度空间基准。基于天地协同定位、导航与授时(PNT)网络服务中心实现了四系统GNSS卫星超快精密定轨,并对定轨结果进行精度评价。介绍了天地协同PNT网络的概念内涵以及网络服务中心部署的超快精密定轨软件架构和详细功能,并针对实时应用需求提出了一种双线程滑动窗口超快精密定轨策略。最后利用重叠弧段比较、与外部轨道产品比较以及卫星激光测距(SLR)检核3种方式对定轨结果进行了精度评价。结果表明,与武汉大学分析中心的最终事后精密轨道产品相比,四系统GNSS MEO卫星预报6 h弧段的径向均方根(RMS)误差整体在2~5 cm水平,BDS2 IGSO卫星最小一维RMS误差在10~15 cm水平;GPS和Galileo卫星的SLR检核残差均值在1~3 cm水平,标准差在3~6 cm水平,能够满足后续厘米级实时应用对空间基准的精度需求。

面向低空无人机运行的高精度卫星测速算法

针对无人机在城市低空环境下运行时存在多径误差导致星基导航测速精度较差的问题,提出一种利用卫星方位角加权和多普勒观测值辅助的优化测速算法。该算法融合多普勒观测值与载波相位观测值优势,根据无人机低空运行环境特点构建基于卫星方位角的加权模型,有效削弱了多路径效应对测速精度的影响,并通过抗差卡尔曼滤波提升速度估计的鲁棒性。基于实测数据的算法评估结果表明,该算法的测速精度较传统TDCP算法在2种场景下的三维速度分别提升了32.23%、10.37%、50.39%和10.20%、30.19%、31.54%,证明了该算法的有效性。

LEO星载GPS实时精密定轨伪模糊度随机过程参数优化

提出在定轨策略及其他变量不变的情况下,使用一种数值步进的搜索比较方法,以确定伪模糊度随机过程参数的最优设置。使用GRACE-C、SWARM-A两颗LEO卫星2021年doy92~101共10 d的GPS数据及同时段的CNT、MADOCA两种实时精密星历产品,以模拟在轨实时精密定轨的方式,对伪模糊度随机过程参数开展优化实验。结果表明,在伪模糊度参数最优值方案下,两颗LEO卫星的实时精密定轨三维位置误差(RMS)约为4.62~7.56 cm,相比于传统模糊度浮点解方案,使用CNT和MADOCA产品的实时定轨精度分别平均提升约39.15%和29.61%。

基于RBFNN的双星协同仅测角定轨方法

针对空间非合作目标空间态势感知任务中弱可观测无源定轨状态的快速捕获问题,提出了一种基于径向基函数神经网络(RBFNN)的双星协同稀疏无源测角定轨方法。首先,在限制性三体问题的假设下建立了考虑地球非球形J2项摄动的轨道动力学模型和赤经赤纬测量模型。然后,构建了基于RBFNN的双星协同仅测角定轨框架,设计了训练数据集生成器、数据预处理方法和RBFNN结构。最后,利用地球静止轨道任务进行了数值仿真验证,并对测角频率等参数的定轨敏感性进行分析。仿真结果表明,在240 s内仅进行三次角度观测的条件下,该模型对初始相对距离估计的平均绝对百分比误差约为0.36%,目标轨道速度的估计误差在米/秒量级,可实现高精度的超短弧段稀疏无源测量定轨。

卫星导航多干扰源直接定位方法

卫星导航信号到达地面时非常微弱,容易受到各种干扰,给用户带来一定的影响;针对此种情况,面向卫星导航系统多干扰源定位场景,传统两步定位算法受参数估计精度影响较大,DPD_MVDR算法虽然改进了MUSIC算法需要估计目标数这一缺点,但由于使用固定网格分辨率,定位精度与计算复杂度二者无法兼得;针对上述问题,提出一种改进DPD_MVDR的直接定位方法,在直接定位这一关键技术上运用自适应网格细化,其最大优势在于只对干扰源位置附近的网格实现多级细化,能很好地兼顾定位精度与计算复杂度,避免了传统穷举搜索带来的巨大计算复杂度;首先使用DPD_MVDR算法在粗网格下进行位置初始估计,然后在估计位置处进行迭代自适应网格细化,在降低计算复杂度的同时,提高定位精度;仿真表明,改进算法在100 m网格分辨率下计算复杂度明显降低且较DPD_MVDR算法定位精度得到明显提高;适用于对定位精度和定位实时性均有一定要求的场景。

FCM测站定权的LAGEOS-2卫星精密定轨影响分析

由于卫星激光测距(satellite laser ranging, SLR)台站的测距精度和稳定性存在差异,精密定轨中需要对不同性能的台站赋予不同权重。本文将模糊C均值(fuzzy C-means, FCM)聚类定权应用于LAGEOS-2精密定轨,并比较原始测站定权和FCM定权对轨道精度的影响。结果表明:1)相较于原始测站定权,FCM定权更能反映各SLR台站的性能,提高定轨精度和观测值数量;2)对于ILRS四个质量分析机构,原始测站定权下JCET发布的质量报告在定轨精度上略优于其他中心,采用FCM定权后,以4个机构发布的质量报告进行定轨的结果在同一水平,轨道精度为4.83~4.86 cm。