Magnetospheric disturbances associated with the 13 December 2006 solar flare and their ionospheric effects over North-East Asia

We present an observational study of magnetospheric and ionospheric disturbances during the December 2006 intense magnetic storm associated with the 4В/Х3.4 class solar flare. To perform the study we utilize the ground data from North–East Asian ionospheric and magnetic observatories (60–72°N, 88–152°E) and in situ measurements from LANL, GOES, Geotail and ACE satellites. The comparative analysis of ionospheric, magnetospheric and heliospheric disturbances shows that the interaction of the magnetosphere with heavily compressed solar wind and interplanetary magnetic field caused the initial phase of the magnetic storm. It was accompanied by the intense sporadic E and F2 layers and the total black-out in the nocturnal subauroral ionosphere. During the storm main phase, LANL-97A, LANL 1994_084, LANL 1989-046 and GOES_11 satellites registered a compression of the dayside magnetosphere up to their orbits. In the morning–noon sector the compression was accompanied by an absence of reflections from ionosphere over subauroral ionospheric station Zhigansk (66.8°N, 123.3°E), and a drastic decrease in the F2 layer critical frequency (foF2) up to 54% of the quite one over subauroral Yakutsk station (62°N, 129.7°E). At the end of the main phase, these stations registered a sharp foF2 increase in the afternoon sector. At Yakutsk the peak foF2 was 1.9 time higher than the undisturbed one. The mentioned ionospheric disturbances occurred simultaneously with changes in the temperature, density and temperature anisotropy of particles at geosynchronous orbit, registered by the LANL-97A satellite nearby the meridian of ionospheric and magnetic measurements. The whole complex of disturbances may be caused by radial displacement of the main magnetospheric domains (magnetopause, cusp/cleft, plasma sheet) with respect to the observation points, caused by changes in the solar wind dynamic pressure, the field of magnetospheric convection, and rotation of the Earth.     

GNSS-R concept extended by a fine orbit tuning

Small changes in semimajor axis of the orbits selected for the GNSS-R [R as Reflectometry] satellites, so-called fine orbit tuning, known from the ESA’s Gravity and steady-state Ocean Circulation Explorer mission, can dramatically increase the number of nadir and off-nadir reflecting points and, in turn, can enhance the capability of the concept of bistatic altimetry (GNSS Reflectometry) without additional costs. The application of our suggestion is feasible for a satellite which will be equipped by thrusters for the orbit keeping. During the mission lifetime several orbit tunings are feasible, just to transfer from one to another orbit. Then we can study short-periodic or longer-periodic features, according to scientific goals defined for the mission. The shortest cycles (few days), corresponding to the required revisit time (defined by ESA), may be subcycles of much longer cycles (repeat periods).     

聚酰亚胺/无机氧化物复合薄膜的制备与耐原子氧性能

分别以锆酸四丁酯、钛酸四丁酯和正硅酸乙酯为氧化物前驱体,利用溶胶凝胶法制备了一系列聚酰亚胺/无机氧化物复合薄膜,在原子氧地面模拟设备中进行了原子氧暴露实验,原子氧累计通量约为3.1×10²⁰ atom/cm².分别考察了无机氧化物种类和含量对复合薄膜力学性能和耐原子氧性能的影响.结果表明,无机氧化物在聚酰亚胺基体中的分散形态对其力学性能影响很大;原子氧暴露后,聚酰亚胺薄膜表面分别形成了富锆、富钛和富硅的保护层,质量损失率减小,耐原子氧性能明显提高.     

含能热塑性聚氨酯推进剂的能量计算与分析

采用最小自由能法,在标准条件(pc/p0=70∶1)下,比较了用不同软硬段结构的含能热塑性聚氨酯弹性体(ET-PU)作粘合剂的复合推进剂的能量特性,从要获得较高能量水平的观点,排列出了几种ETPU选择的先后次序;计算了含ETPU的各类推进剂的能量特性参数,探讨了ETPU对硝酸酯增塑的复合推进剂和硝胺改性双基推进剂的能量特性的影响规律。结果表明,选用不同ETPU的复合推进剂配方相互间在能量特性上存在着差别,但这种差别并不十分显著,以GAP为软段、TDI为硬段的ETPU,更有利于配方获得较高的能量水平;硝酸酯增塑的ETPU推进剂的理论能量水平高于丁羟推进剂,随增塑比逐渐增大,推进剂的最大理论比冲随之增大,固含量逐步降低;少量ETPU的加入,对硝胺改性双基推进剂的能量特性影响不大,增加Al和RDX含量,更有利于提高含ETPU的硝胺改性双基推进剂的能量水平。     

3D-Cf / Mg 复合材料的热残余应力研究

采用随动硬化有限元模型,研究了三维碳纤维增强镁基复合材料(3D-Cf/Mg)基体热残余应力的大小、分布以及不同工艺处理对热残余应力的影响。同时,对复合材料进行了高、低温处理,利用XRD定性分析了处理前后复合材料基体热残余应力的变化。计算结果表明:经过-196℃低温处理后,复合材料基体的平均Mises热残余应力由169.06 MPa减小至55.29 MPa;高温处理后,基体平均热残余应力几乎不变。该结果与实验结果吻合,证明了低温处理能明显降低复合材料基体的热残余应力。     

挠性充液航天器超近程逼近段动力学建模与控制

超近程逼近过程中,服务航天器为刚柔液耦合的复杂系统,单摆等液体晃动模型不再适用,对这种工况下的航天器进行了动力学建模与控制的研究。采用虚功率原理推导了一种新的适用于三轴推力作用下的液体晃动等效模型,通过引入相对位置导引矢量与相对位置误差矢量,建立了相对轨道误差动力学模型,结合相对姿态动力学模型,得到超近程逼近段的刚柔液耦合的相对轨道姿态动力学模型。针对模型存在的不确定性和未知干扰,设计了基于滑模估计器的相对姿轨耦合控制律。通过数学仿真验证了控制律的有效性,仿真中的晃动结果与Flow-3D结果能够吻合,验证了晃动模型的合理性。     

An alternative representation of the relative motion: The local orbital elements

The study of the relative motion between two very-close non-massive objects has been usually done through Hill equations. More recent approaches use the differences of orbital elements to extrapolate relative motion. In this paper, we present another possible representation of the relative motion. This representation takes advantage of the very particular most common relative trajectory: the ellipse. Our representation induces a better temporal comprehension of the motion but it also provides the topology of the natural relative motions. Our approach is useful for circular and slightly eccentric reference orbits.     

Onboard orbit determination using GPS observations based on the unscented Kalman filter

Spaceborne GPS receivers are used for real-time navigation by most low Earth orbit (LEO) satellites. In general, the position and velocity accuracy of GPS navigation solutions without a dynamic filter are 25 m (1σ) and 0.5 m/s (1σ), respectively. However, GPS navigation solutions, which consist of position, velocity, and GPS receiver clock bias, have many abnormal excursions from the normal error range for space operation. These excursions lessen the accuracy of attitude control and onboard time synchronization. In this research, a new onboard orbit determination algorithm designed with the unscented Kalman filter (UKF) was developed to improve the performance. Because the UKF is able to obtain the posterior mean and covariance accurately by using the second-order Taylor series expansion through the sampled sigma points that are propagated by using the true nonlinear system, its performance can be better than that of the extended Kalman filter (EKF), which uses the linearized state transition matrix to predict the covariance. The dynamic models for orbit propagation applied perturbations due to the 40 × 40 geo-potential, the gravity of the Sun and Moon, solar radiation pressure, and atmospheric drag. The 7(8)th-order Runge–Kutta numerical integration was applied for orbit propagation. Two types of observations, navigation solutions and C/A code pseudorange, can be used at the user’s discretion. The performances of the onboard orbit determination were verified using real GPS data of the CHAMP and KOMPSAT-2 satellites. The results of the orbit determination were compared with the precision orbit ephemeris (POE) of the CHAMP and KOMPSAT-2 satellites.     

基于SOC的卫星姿轨控系统通用电模拟器设计

在某型卫星地面电联试过程中,对该卫星的姿态轨道控制系统进行接口分析及信号统计,针对其接口复杂性、信号多样性的特点,提出采用片上系统(Systemona Chip,SOC)芯片对所有部件模拟器进行通用化设计。文中给出了该型卫星通用型电模拟器硬件平台设计方案以及陀螺、反作用轮和通用接口模块的硬件配置说明,针对该型卫星姿态轨道控制系统电联试要求,对所有部件按真实接口配置成电模拟器,形成通用接口箱、敏感器电模拟器箱和执行机构电模拟器箱,并通过CAN(Controller Area Network)总线接入闭环仿真,对太阳捕获、地球捕获及正常模式进行了仿真测试,仿真结果表明通用电模拟器满足设计要求,对其他卫星的地面电联试有很好的参考价值。     

q-一致光滑Banach空间中的严格伪压缩映像

提出一种不用投影算子的修正的Mann遮代的循环算法,用于逼近q-一致光滑的Banach空间中有限个严格伪压缩映像的公共不动点,并证明了算法的强收敛性。本结论推广了Kim等和Zhang等关于非扩张映像的相应结果。