Dual attitude and parameter estimation of passively magnetically stabilized nano satellites

The attitude determination capability of a nano satellite is limited by a lack of traditional high performance attitude sensors, a result of having small budgets for mass and power. Attitude determination can still be performed on a nano satellite with low fidelity sensors, but an accurate model of the spacecraft attitude dynamics is required. The passive magnetic stabilization systems commonly employed in nano satellites are known to introduce uncertainties in the parameters of the attitude dynamics model that cannot easily be resolved prior to launch. In this paper, a batch estimation problem is formulated that simultaneously solves for the attitude of the spacecraft and performs parameter estimation on the magnetic properties of the magnetic materials using only a measurement of the solar vector. The estimation technique is applied to data from NASA Ames Research Center's O/OREOS nano satellite and the University of Michigan's RAX-1 nano satellite, where clear differences are detected between the magnetic properties as measured before launch and those that fit the observed data. To date this is the first known on-orbit verification of the attitude dynamics model of a passively magnetically stabilized spacecraft.     

A simplified approach to uncertainty quantification for orbits in impulsive deflection scenarios

For the majority of near-Earth Asteroid (NEA) impact scenarios, optimal deflection strategies use a massive impactor or a nuclear explosive, either of which produce an impulsive change to the orbit of the object. However, uncertainties regarding the object composition and the efficiency of the deflection event lead to a non-negligible uncertainty in the deflection delta-velocity. Propagating this uncertainty through the resulting orbit will create a positional uncertainty envelope at the original impact epoch. We calculate a simplified analytic evolution for impulsively deflected NEAs and perform a full propagation of uncertainties that is nonlinear in the deflection delta-velocity vector. This provides an understanding of both the optimal deflection velocities needed for a given scenario, as well as the resulting positional uncertainty and corresponding residual impact probability. Confidence of a successful deflection attempt as a function of launch opportunities is also discussed for a specific case.     

DPOD2014: A new DORIS extension of ITRF2014 for precise orbit determination

To support precise orbit determination of the altimetry missions, the International DORIS Service (IDS) regularly estimates the DPOD (DORIS terrestrial reference frame for Precise Orbit Determination) solution which includes mean positions and velocities of all the DORIS stations. This solution is aligned to the current realization of the International Terrestrial Reference Frame (ITRF) and so, can be seen as a DORIS extension of the ITRF. In 2016, moving to the IDS Combination Center, the DPOD construction scheme changed. The new DPOD solution is produced from a DORIS cumulative position and velocity solution. We present the new methodology used to compute DPOD2014 and its validation procedure. In order to present geophysical applications and interpretations of these results, we show two examples: (1) the Gorkha earthquake (M7.8 – April 2015) generates a 3-D mis-positioning of nearly 55?mm of the EVEB DORIS station at the Everest base camp 90?km from the epicenter. (2) Applying the results the DPOD2014 realization, we show that the most recent vertical velocity of Thule, Greenland is similar to that observed between 2006 and 2010, indicating further ongoing ice mass loss in the Thule region of northwest Greenland.     

双站跟踪模式下“嫦娥4号”中继星定轨仿真分析

位于地月平动点的探测器因为较差的观测几何,需要地基USB/UXB与天文VLBI长时间的联合跟踪数据获取稳定精确的轨道。提出了利用中国深空网双站共视跟踪平动点探测器,获取双程、三程测距及VLBI测量数据,解算探测器精确轨道的模式。以"鹊桥"卫星为分析对象,首先评估中国深空网对"鹊桥"的跟踪能力。然后分析不同观测组合模式下的定轨计算精度。结果表明:双站共视约束下,深空站每天对"鹊桥"跟踪弧长大于5 h;使用长于6 h的双站跟踪数据进行定轨,系统差的解算更有利于轨道精度提升;跟踪时长超过2天时,必须在轨道解算的同时估计光压系数,并有望实现优于百米的轨道精度。     

修正容积卡尔曼滤波数据域直接定位算法

为解决数据域直接定位（DPD）算法面临的计算压力,提高算法效率,提出一种基于修正的容积卡尔曼滤波（MCKF）的DPD算法。首先,融合各观测信号波达方向信息,利用子空间数据融合方法建立一种基于间接观测量的DPD滤波模型;然后,根据模型特点设计MCKF算法进行求解,解决间接观测量带来的噪声累积问题;最后,对算法计算量进行分析和对比,说明计算效率的提升。仿真结果表明,所提算法与基于最大似然遍历搜索和遗传算法的DPD算法相比,在相同的估计性能下,计算量下降明显,时效性显著提升,增加了算法实用价值。     

一种成像敏感器对月定姿算法

成像敏感器根据月像来确定卫星对月姿态角。分析了月球光学系统成像模型以及卫星两轴姿态角与月像边缘曲线方程的关系，利用分析结果并结合月像边缘点的曲线拟合提出了一种新的卫星对月定向姿态确定方法。此算法克服了非零姿态月像边缘的非圆现象并且在部分月像下也可完成姿态确定，仿真工作显示了新算法的有效性。     

一种有效提高CE-1卫星卸载前后精密星历衔接精度的定轨策略

主要讨论了动量轮卸载对嫦娥一号卫星绕月轨道的影响以及这种影响对其精密星历衔接段精度的影响,分析了不同轨道改进策略下的精密星历衔接弧段的精度,认为使用2~3d的弧段进行轨道改进及卸载计算能得到较高精度的搭接星历,并通过使用实测数据进行定轨改进计算进行了验证,结果表明,该策略可以使星历衔接精度在沿迹方向(T)提高至优于100m量级。     

NPF算法在X射线脉冲星导航中的应用研究

针对X射线脉冲星导航中航天器模型的强非线性、高阶模型不确定性等问题,提出应用非线性预测滤波(NPF)算法实时估计航天器的轨道信息。首先,建立具有模型不确定性的X射线脉冲星导航定轨指标函数,优化得到满足指标函数最小的系统模型误差值,通过降低模型不确定性的影响来提高航天器自主定轨精度。对STK生成的“火星探路者”和“金星快车”及“北斗一号”三种航天器轨道数据进行分析,仿真结果表明,该算法比EKF算法具有更高的定轨精度,能够满足深空以及近地轨道航天器的自主定轨精度指标要求。     

一种星载激光测距仪姿态的确定方法及误差分析

激光测距仪与立体测绘相机在对地目标定位方面具有较强的互补性,将两者结合可以获取较高的地面目标三维定位精度。利用激光测距仪辅助立体测绘相机实现全球大比例尺无控测图是当今测绘卫星的发展方向。激光测距仪的定位精度主要受俯仰角和侧摆角的影响,由于失重、热交变、微振动等外界环境的影响以及激光器发射激光束存在自身抖动,星载激光测距仪的激光出射方向是不断变化的。为实现高精度地面目标定位,满足大比例尺测绘需求,需要对激光出射方向进行精确测量。文章提出了一种基于足印记录相机的激光测距仪姿态确定方法,该方法采用足印记录相机、地相机图像联合处理的技术,解决了激光测距仪姿态角和激光指向高精度确定问题。通过误差分析,该方法能够满足1︰10 000比例尺定位精度的要求。