Response of a pentagonal PZT element as a component of a 4π-real-time detector

The detector characteristics of a pentagonal element were studied by colliding it with hypervelocity micro-particles. A charge-sensitive amplifier was developed for the element of its capacitance ∼10 nF. The output amplitudes were expressed as a linear function of the momentum at collision. Empirical formulas obtained from on-ground experiments could be used for the calibration of the detector. The pentagonal element was potential to measure the momentum during collision from the output amplitude. A set of electrodes on the surface was used to confirm the measurement of the coordinates at collision. A possible application of this pentagonal element on a real-time dust detector was discussed.     

The GFZ real-time GNSS precise positioning service system and its adaption for COMPASS

Motivated by the IGS real-time Pilot Project, GFZ has been developing its own real-time precise positioning service for various applications. An operational system at GFZ is now broadcasting real-time orbits, clocks, global ionospheric model, uncalibrated phase delays and regional atmospheric corrections for standard PPP, PPP with ambiguity fixing, single-frequency PPP and regional augmented PPP. To avoid developing various algorithms for different applications, we proposed a uniform algorithm and implemented it into our real-time software. In the new processing scheme, we employed un-differenced raw observations with atmospheric delays as parameters, which are properly constrained by real-time derived global ionospheric model or regional atmospheric corrections and by the empirical characteristics of the atmospheric delay variation in time and space. The positioning performance in terms of convergence time and ambiguity fixing depends mainly on the quality of the received atmospheric information and the spatial and temporal constraints. The un-differenced raw observation model can not only integrate PPP and NRTK into a seamless positioning service, but also syncretize these two techniques into a unique model and algorithm. Furthermore, it is suitable for both dual-frequency and sing-frequency receivers. Based on the real-time data streams from IGS, EUREF and SAPOS reference networks, we can provide services of global precise point positioning (PPP) with 5–10 cm accuracy, PPP with ambiguity-fixing of 2–5 cm accuracy, PPP using single-frequency receiver with accuracy of better than 50 cm and PPP with regional augmentation for instantaneous ambiguity resolution of 1–3 cm accuracy. We adapted the system for current COMPASS to provide PPP service. COMPASS observations from a regional network of nine stations are used for precise orbit determination and clock estimation in simulated real-time mode, the orbit and clock products are applied for real-time precise point positioning. The simulated real-time PPP service confirms that real-time positioning services of accuracy at dm-level and even cm-level is achievable with COMPASS only.     

End-to-end validation process for the INTA-Nanosat-1B Attitude Control System

This paper describes the end-to-end validation process for the Attitude Control Subsystem (ACS) of the satellite INTA-NanoSat-1B (NS-1B). This satellite was launched on July 2009 and it has been fully operative since then. The development of its ACS modules required an exhaustive integration and a system-level validation program. Some of the tests were centred on the validation of the drivers of sensors and actuators and were carried out over the flying model of the satellite. Others, more complex, constituted end-to-end tests where the concurrency of modules, the real-time control requirements and even the well-formedness of the telemetry data were verified. This work presents an incremental and highly automatised way for performing the ACS validation program based on two development suites and an end-to-end validation environment. The validation environment combines a Flat Satellite (FlatSat) configuration and a real-time emulator working in closed-loop. The FlatSat is built using the NS-1B Qualification Model (QM) hardware and it can run a complete version of the on-board software with the ACS modules fully integrated. The real-time emulator, running on an industrial PC, samples the actuation signals and emulates the sensors signals to close the control loop with the FlatSat. This validation environment constitutes a low-cost alternative to the classical three axes tilt table, with the advantage of being easily configured for working under specific orbit conditions, in accordance with any of the selected tests. The approach has been successfully applied to the NS-1B in order to verify different ACS modes under multiple orbit scenarios, providing an exhaustive coverage and reducing the risk of eventual errors during the satellite's lifetime. The strategy was applied also during the validation of the maintenance and reconfiguration procedures required once the satellite was launched. This paper describes in detail the complete ACS validation process that was performed and it shows the most relevant errors detected and fixed during testing. Finally it summarises some of the most significant conclusions.     

A heuristic design method for attitude stabilization of magnetic actuated satellites

In this paper a heuristic design strategy for stabilizing the satellite attitude has been proposed. It is assumed that the satellite is actuated by a set of mutually perpendicular magnetic coils. Using well-known Lyapunov direct stability method it is shown that the proposed controller causes to a global asymptotic stable system for all near polar orbits. The design procedure is based on analyzing of the conceptual effects of magnetic coils on the satellite attitude motion. Considering these effects lead to some intuitive results which determine the global stabilizing control law. The performance and robustness of the designed controller against actuators saturation and quantization error have been verified using a real-time-hardware–software in-loop (RTHSIL) simulation results. These results show that the global stability can be achieved although some disturbances and restrictions exist. This stabilizing controller can be simply combined with a linear explicit model predictive controller (EMPC) to achieve a full three-axis control law.     

Carrier-Doppler-based real-time two way satellite frequency transfer and its application in BeiDou system

Two-way satellite time and frequency transfer (TWSTFT) method is valuable for precise time and frequency transfer. The frequency could be directly transferred by utilizing two-way carrier Doppler measurement. This method requires each station observing both its own and associated station’s transponder signals transferred by satellite. In BeiDou system (BDS), the reference station and the field station construct a two-way link via a GEO satellite, and the field station sends pseudorange and carrier phase information to the reference station by transmission signal, in order to achieve real time TWSTFT. This paper analyzes the theory of carrier Doppler based TWSTFT (called CD-TWSTFT), and validates it by using on line data of BDS. The results demonstrated that the performance of CD TWSTFT is much better than code based TWSTFT in short-term frequency transfer and almost same at long-term frequency transfer.     

最优双冲量交会问题的数学建模与数值求解

基于普适变量法研究了两个共面轨道的最优双冲量交会问题。具体地,基于求解Lambert问题的普适变量法,在将给定时间段划分初始飘移阶段、轨 道转移阶段与终端停泊阶段的前提下,对两圆轨道及两拱线相同的椭圆轨道的最优双冲量交 会问题分别进行了优化数学建模,并利用数学软件Lingo进行了数值求解。数值结果表明,划分给定时间段可以得到更优解。
     

Micro VAX—Ⅱ计算机专用实时接口设备

在实时数字仿真系统中,实时接口设备是仿真机和控制系统实物间的界面,它的性能直接影响着实时数字仿真的精度。本文简要介绍了专为MicroVAX—Ⅱ计算机研制的DSI-4型专用实时接口设备的构成、各功能板的设计,以及DSI-4专用实时接口的工作过程和使用方法。应该指出的是:只要改变连接计算机的总线接口板,DSI-4专用实时接口还可以方便地与其它计算机(例如,CompaQ386机)组成实时数字仿真系统。     

分布式仿真系统实体节点分配问题实时求解算法

分布式仿真系统中,如何使计算节点彼此间通信量尽可能小,是实体节点分配问题研究的内容。针对该问题提出一种基于规则的启发式两阶段实时求解算法。第一阶段构建最小期望事件数量的目标分配模型并进行求解,即根据连通图理论将原问题分解为多个子问题,结合缓存、分治和过滤优选策略,设计递归算法求解子问题,最后得到覆盖所有实体的事件最小集。第二阶段实现分箱算法,将最小集中单个事件关联的实体尽量分配至相同计算节点,最终得到实体节点分配关系。实际应用表明,相比常见的顺序分配策略,该算法能显著减小分布式仿真系统的跨节点网络通信,从而提升仿真效率。该算法还能在秒级耗时生成分配方案,特别适用于包含大量实体的复杂场景分布式仿真。     

基于LabVIEW和光纤传感器的液漏监测系统设计

针对传统液漏传感器检测精度低、空间分辨率小以及不能实时监测多点位液漏等问题，利用LabVIEW设计了一个基于光纤传感器的液漏监测系统。整个系统包括传感器和上位机两个部分。其中，光纤带式传感器负责采集漏水点的信号，其传感功能的实现基于侧向耦合效应。LabVIEW上位机负责实时监测多点位液漏状态，实现了采集数据的处理、存储和显示功能。上位机和传感器之间采用USB接口通信。实验结果表明，该系统能够对8 m区域范围内，160个点位的漏水状态实时精确定位及报警，漏检率≤10 %，位置精度介于±25 mm，较传统液漏传感系统，其空间分辨率提升了10 %。对于当前设备存在的漏检和误报的问题，给出了误差分析及改进思路。通过LabVIEW实时显示多点位漏水状态，能够提高工作效率，适用于对漏水监测有较高要求的场合。     

Real-time modular dynamic modeling for compression system of altitude ground test facilities

Modeling of a centrifugal compressor is of great significance to surge characteristics and fluid dynamics in the Altitude Ground Test Facilities (AGTF). Real-time Modular Dynamic System Greitzer (MDSG) modeling for dynamic response and simulation of the compression system is introduced. The centrifugal compressor, pipeline network, and valve are divided into pressure output type and mass flow output type for module modeling, and the two types of components alternate when the system is established. The pressure loss and thermodynamics of the system are considered. An air supply compression system of AGTF is modeled and simulated by the MDSG model. The simulation results of mass flow, pressure, and temperature are compared with the experimental results, and the error is less than 5%, which demonstrates the reliability, practicability, and universality of the MDSG model.