Simulation study for the determination of the lunar gravity field from PRARE-L tracking onboard the German LEO mission

A simulation study has been performed at GFZ Potsdam, which shows the anticipated improvement of the lunar gravity field model with respect to current (LP150Q model) or near-future (SELENE) knowledge in the framework of the planned German Lunar Explorations Orbiter (LEO) mission, based on PRARE-L (Precise Range And Range-rate Equipment – Lunar version) Satellite-to-Satellite (SST) and Satellite-Earth-Satellite (SEST) tracking observations. It is shown that the global mean error of the lunar gravity field can be reduced to less than 0.1 mGal at a spatial resolution of 50 km. In the spectral domain, this means a factor of 10 (long wavelengths) and some 100 (mid to short wavelengths) improvement as compared to predictions for SELENE or a factor of 1000 with respect to LP150Q. Furthermore, a higher spatial resolution of up to 28 km seems feasible and would correspond to a factor of 2–3 improvement of SELENE results. Moreover, PRARE-L is expected to derive the low-degree coefficients of the lunar gravity field with unprecedented accuracy. Considering long mission duration (at least 1 year is planned) this would allow for the first time a precise direct determination of the low-degree tidal Love numbers of the Moon and, in combination with high precision SEST, would provide an experimental basis to study relativistic effects such as the periselenium advance in the Earth–Moon system.     

自主姿态测量最优算法研究

针对利用地球重力场和磁场矢量观测进行自主姿态测量的应用问题,提出了一种新的最优递推估计算法。该算法采用卡尔曼滤波框架,利用加权统计线性回归并结合自适应滤波技术进行测量更新,与现有方法相比,在提高测量精度的同时,增加了同步提供姿态速率信息的功能。仿真结果表明,新算法的姿态估计精度比目前常用的直接计算方法提高近两倍。     

相对轨道自主确定方法的改进

编队飞行卫星相对轨道的确定具有重要意义。本文提出一种完全自主的定轨方案,在利用星间测量信息实现编队飞行卫星自主定轨的基础上,引入太阳敏感器测量信息,利用扩展卡尔曼滤波算法提高环绕星相对轨道确定精度。仿真结果验证了这种导航方案和算法的有效性。     

多姿态敏感器测量的信息融合定姿方法研究

基于最优融合估计理论,给出并证明了多敏感器组合姿态确定系统状态最优融合估计形式。设计了基于信息分配的多信息融合联合滤波器结构和算法,分析估计性能,讨论了决定联合滤波器融合的性能信息分配因子选择方法,提出了一种基于协方差阵特征值平方分解的动态自适应信息分配因子确定方法。以某卫星多姿态敏感器组合测量为例,推导了卫星姿态确定的误差状态方程和各子系统的量测方程及观测阵。仿真结果表明：采用联合滤波器对多敏感器卫星姿态确定系统进行信息融合能改善定姿精度,有效抑制滤波发散,并提高整个系统的运算与收敛速度。     

基于EKF容错滤波方法的编队卫星相对轨道自主确定

为避免因卫星测量野值导致的相对轨道估计与滤波精度下降,提出了一种基于残差正交性的扩展Kalman滤波（EKF）容错滤波算法的编队卫星相对轨道确定方法。根据卫星相对运动与相对位置量测方程,用残差序列方差的迹实现对野值的剔除及在线修正,保证滤波器有较强的鲁棒性、稳定性和精度。仿真结果表明：该法简单、有效,有较高的理论和工程应用价值。     

航空发动机单机技术状态寿命控制及应用

提出了按单机技术状态确定在役航空发动机寿命的技术体系框架及相关管理手段,在航空发动机维修领域首次突破了传统的机群定时翻修理念,实现了寿命确定从宏观到微观的变革;应用这种新的寿命管理办法,有效地延长了多型发动机的使用寿命。     

GPS single-frequency orbit determination for low Earth orbiting satellites

The determination of high-precision orbits for Low Earth Orbiting (LEO) satellites (e.g., CHAMP, GRACE, MetOp-A) is based on dual-frequency tracking data from on-board GPS (Global Positioning System) receivers. The two frequencies allow it to eliminate the first order ionosphere effects. Data screening and precise orbit determination (POD) procedures are optimized under the assumption of the availability of two frequencies.     

Variability study of the crest-to-trough TEC ratio of the equatorial ionization anomaly around 120°E longitude

In this paper, latitudinal profiles of the vertical total electron content (TEC) deduced from the dual-frequency GPS measurements obtained at ground stations around 120°E longitude were used to study the variability of the equatorial ionization anomaly (EIA). The present study mainly focuses on the analysis of the crest-to-trough TEC ratio (TEC-CTR) which is an important parameter representing the strength of EIA. Data used for the present study covered the time period from 01 January, 1998 to 31 December, 2004. An empirical orthogonal function analysis method is used to obtain the main features of the TEC-CTR’s diurnal and seasonal variations as well as its solar activity level dependency. Our results showed that: (1) The diurnal variation pattern of the TEC-CTR at 120°E longitude is characterized by two remarkable peaks, one occurring in the post-noon hours around 13–14 LT, and the other occurring in the post-sunset hours around 20–21 LT, and the post-sunset peak has a much higher value than the post-noon one. (2) Both for the north and south crests, the TEC-CTR at 120°E longitude showed a semi-annual variation with maximum peak values occurring in the equinoctial months. (3) TEC-CTR for the north crest has lower values in summer than in winter, whereas TEC-CTR for the south crest does not show this ‘winter anomaly’ effect. In other words, TEC-CTR for both the north and south crests has higher values in the northern hemispheric winter than in the northern hemispheric summer. (4) TEC-CTR in the daytime post-noon hours (12–14 LT) does not vary much with the solar activity, however, TEC-CTR in the post-sunset hours (19–21 LT) shows a clear dependence on the solar activity, its values increasing with solar activity.     

CHAMP and GRACE accelerometer calibration by GPS-based orbit determination

Current and planned Earth observation missions are equipped with highly sensitive accelerometers. Before using the data, the instrument has to be calibrated by determining scale and bias parameters for each axis. Here, the accelerometer measurements are used in a GPS-based reduced-dynamic orbit determination approach, replacing the non-gravitational force models, and nominally daily calibration parameters are estimated. Additional empirical accelerations are estimated to account for deficiencies in the applied force models. This method is applied to 5 years of CHAMP and GRACE data, resulting in an orbit precision at the level of a few centimeters. In along-track direction the calibration parameters can be estimated freely, scale factors of 0.96 ± 0.014 and 0.95 ± 0.015 are obtained for GRACE A and B, and 0.85 ± 0.024 for CHAMP. A constant scale factor results in the smoothest bias series, with clear trends and occasional jumps. In radial and cross-track direction tight constraints to a priori biases have to be applied. Furthermore, the determined orbits are analyzed with respect to reference trajectories, and SLR, phase and KBR residuals are presented.     

星敏感器与地平仪组合定姿建模与仿真

根据用星敏感器和地平仪组合的姿态确定算法建立的星敏感器和地平仪测量模型,以及采用的记忆衰减最小二秉滤渡的定姿估计模型,基于RT-LAB实时仿真平台和MATLAB/Simulink数字仿真平台进行了仿真.结果表明:星敏感器和地平仪组合定姿精度较高;用RT-LAB平台进行实时仿真具有方便、高效、精确和开放等优点.