Fault Tolerant Attitude Synchronization Control during Formation Flying

It is necessary for precise satellite formations to keep each satellite in accurate relative attitude synchronization and to maintain relative angular velocity synchronization. An adaptive fuzzy terminal sliding mode control is proposed for a formation flying tracking system which includes acquisition, tracking, and pointing. The relative attitude of the leader and follower spacecraft under gravity gradient torque and external periodic disturbances is controlled by four reaction wheels. First, a terminal sliding mode controller is used to obtain stable and fast tracking. Then, the adaptive fuzzy logic system is used to approximate and learn the system uncertainty with the online fault and time-varied external disturbances. The system is proved to be stable, and the parameters are proved to be bounded under the control scheme, using a Lyapunov methodology. Finally, simulation results (under actuator faults like wheel failure and wheel degradation) show that the proposed control method has the advantages of high tracking accuracy, low computation load, robustness, and ease of engineering application.     

Operational Monitoring of Daily Crop Water Requirements at the Regional Scale with Time Series of Satellite Data

This work presents a simple, cost-effective, and operational approach to monitor crop water requirements at the regional scale for water management and monitoring purposes. The recommended Food and Agricultural Organization of the United Nations methodology (FAO-56) calculates crop evapotranspiration using crop-specific coefficients (Kc), which vary according to the crop type, health, and phenological stage. This approach, though widely applied for irrigation planning, cannot always match the appropriate crop coefficient with the actual crop phenological stage and health condition, especially in anomalous situations. Previous research demonstrated that crop coefficients and spectral vegetation indexes are correlated. Recent studies have used this relationship with high-resolution satellite data from different sensors to provide information to irrigation advisory services. However, high-resolution data are not feasible for an operational and routine monitoring of water consumption and needs. This paper tests the usefulness of time series of coarse resolution satellite data such as those collected by the moderate-resolution imaging spectroradiometer (MODIS) sensor, to monitor crop coefficients temporal and spatial variability and therefore crop water needs at the regional scale taking advantage of the peculiar characteristics offered by MODIS in terms of high temporal resolution and preprocessed products availability. The outlined methodology takes into account the actual growing stage of the crops and nearly real-time vegetation variations, overcoming some limitations of the traditional FAO approach while preserving the maximum operability. The analysis was carried out in the South Milan agricultural area on data referring to 2003 and 2004. The results agreed with those of other studies and proved to be able to account for the anomalous conditions of the summer in 2003. These results were then compared with those obtained using the traditional FAO crop coefficient curves built with data collected during field campaigns in the same years in rice fields. Constraints, limitations, and possible uses are discussed.     

Thermoplastic–Carbon Fiber Composites Could Aid Solar-Based Power Generation: Possible Support System for Solar Power Satellites

Solar power has merit as a renewable source of energy; it is the largest asset available for consumption on Earth and is limitless. There have been many ideas proposed to beam solar power to Earth; all have been dependent upon the provision of a backing frame to support solar panels, photovoltaic cells, and transmission. This paper suggests one type of rigid deployable skeletal structure and its material of manufacture to form the backing frame of solar panel systems; the structure takes the form of a skeletal double-layer tetrahedral system. The composite material is polyethersulphone thermoplastic polymer reinforced with carbon fiber (CF). This paper also discusses the hostile environment of space in relation to the fiber-reinforced polymer (FRP) composite material, with special reference to the thermal response. Finally, it suggests the alternate possibility of using a rigidized inflatable flexible skeletal structure and, as far as is possible, compares (a)?the relative cost of transferring the two structures to low Earth orbit from Earth, and (b)?the cost of solar energy relative to other forms of energy.     

LabVIEW环境下绘制GPS卫星星座图和卫星运行轨迹的方法

为了分析GPB卫星星座变化对姿态解算状态(Attitude Type)的影响，笔者在LabVIEW平台上开发了一套软件，可以从GPS接收的数据中提取出卫星信息，形成卫星星座图，并能画出卫星的历史轨迹图。     

A review of Ka and Ku band propagation measurements on satellite paths made at the bt laboratories in the U.K.

Measurements of slant-path attenuation and crosspolar discrimination, obtained from four satellite measurement programmes carried out at the BT Laboratories, Martlesham Heath, England, are described. The measurements covered frequencies in the range 11.3 GHz to 30 GHz, path elevations ranging from 8.3° to 29.9°, and were made using both circularly and linearly polarized signals. Cumulative distributions, derived from the measured data, are extrapolated to frequencies of 12.5, 14.3, 19.8 and 29.7 GHz and then combined to give statistics for a database of more than 20 years.     

New Approach to Satellite Formation-Keeping: Exact Solution to the Full Nonlinear Problem

This paper presents a new, simple, and exact solution to the formation keeping of satellites when the relative distance between the satellites is so large that the linearized relative equations of motion no longer hold. We employ a recently proposed approach, the Udwadia-Kalaba approach, which makes it possible to explicitly obtain the desired control function without making any approximations related to the nonlinearities in the underlying dynamics. We use an inertial frame of reference to describe the motion of a satellite and since no approximations are made, the results obtained apply to situations even when the distance between the satellites is arbitrarily large. The paper deals with a projected circular formation, but the methodology in this paper can be applied to any desired configuration or orbital requirements. Numerical simulations confirm the brevity and the accuracy of the analytical solution to the dynamical control problem developed herein.     

SATSRP经费分配模型及其软件结构设计

提出了卫星应用技术科研项目评审的指标体系，并利用ＡＨＰ的Ｆｕｚｚｙ扩展，建立了一种新的ＧＡＨＰ赋权优化模型，给出了卫星应用技术科研项目经费分配模型及其软件设计的目标与功能模块结构。     

基于星载GPS卫星编队可视化仿真系统

针对研究星载GPS编队卫星自主导航算法及模型对编队的影响,为实际编队提高导航定位精度,结合数据库系统编制出了关于星载GPS编队卫星仿真系统。在分析卫星编队相对导航运动规律基础上,利用OPENGL及数据库技术对星载GPS空间圆编队,车轮式编队和水平圆编队进行了三维可视化仿真,给出了设计过程。考虑到编队卫星需要接收GPS信号进行自主导航,利用GPS星座可见性分析方法,实现星载GPS编队卫星的GPS星座选择。三维可视化仿真结合STK进行了验证。仿真系统已作为编队方案设计、编队飞行相对导航仿真算法设计的基础工具,还为将来各种航天器编队飞行应用技术及航天器对接技术提供可靠的试验基础数据和技术依据。     

星站差分GPS在数字罗经安装/校准中的应用

针对传统罗经安装或校准测量方法操作复杂、耗时长、投入大,且不适用与船舶浮动状态下船艏向测量的缺点,提出采用星站差分GPS测船艏向的方法。工程实例表明,星站差分GPS测艏向的方法适用于专业海洋调查船的罗经安装与罗经校准值的获取。