共查询到20条相似文献,搜索用时 31 毫秒
1.
The effect of a constant synchronization error on PN systems has been studied by Gill [1]. His results are generalized here for random synchronization errors, and extended to PSK systems using decision directed channel measurements [2]. In both cases, it is shown that the effect of random synchronization errors is to reduce the effective input signal power and to introduce an additional self-noise. The effect is minimized when the synchronization error has zero mean and can easily be evaluated in terms of circuit parameters. 相似文献
2.
3.
4.
在综述了各种成象跟踪算法的基础上,给出了一种新的适于飞行力学自动目标跟踪算法的基本思想和方法步骤。研究和控制利用成像跟踪算法获取比例导引律中视线角速度和导弹怀目标间相对速度的方法,并结合导弹飞行控制数学模型,提出了一种基于成像跟踪的比例导引律实现方法。 相似文献
5.
Strategies for in-orbit calibration of drag-free control systems 总被引:3,自引:0,他引:3
Michel Silas Guilherme Waldemar Castro Leite Filho Stephan Theil 《Aerospace Science and Technology》2008,12(5):365-375
Drag-Free Satellites (DFS) are a class of scientific satellite missions designed for research on fundamental physics as well as geodesy. They consist, basically, of a small inner satellite (test mass) located in a cavity inside a larger satellite, the normal one. The Drag-Free Attitude Control System (DFACS) is the most complex technology on-board these satellites. This key technology allows the residual accelerations on experiments on board the satellites to be significantly reduced. In order to achieve this very low disturbance environment (for some missions <10−14 g) the drag-free control system has to be optimized. This optimization process is required because of uncertainties in system parameters that demand a robustness of the control system. This paper will present approaches for in-orbit calibration of drag-free control systems. The discussion includes modeling, with scale factors and cross couplings, possible excitation signals, comparison of different parameter identification/estimation methods as well as simulation results. 相似文献
6.
The electric power system for the Boeing 777 is comprised of two independent electrical systems, the main and the backup. The main electric system includes two engine-driven integrated drive generators, a generator driven by the auxiliary power unit, three generator control units, and a bus power control unit. The backup electric system includes two engine-drive generators and one integrated converter/control unit to provide the redundancy of electrical sources equivalent to a three-engine airplane. Automation of the system is achieved by the use of state-of-the-art, microprocessor-based control units that perform system control, protection, and built-in-test functions. Each control unit has redundant two-way communication through an ARINC 629 communication bus that requires significantly fewer discrete wires than similar systems, allowing considerable reduction of the interface circuits and reduction in weight 相似文献
7.
In low pulse-repetition frequency (PRF) pulse radars, signal-to-noise ratio (SNR) is usually calculated on a per pulse basis and this value is then multiplied by the number of pulses integrated to obtain the SNR for a given duration of target illumination. In high PRF pulse Doppler radars, SNR is usually calculated by using the centerline power of the transmitted signal spectrum as the target return power because the centerline is kept in the receiver and returns of the PRF lines are notched out [1]. We show here that both methods of SNR calculations are entirely equivalent for matched transmit-receive radar systems. 相似文献
8.
Kwangil Ko Robertazzi T.G. 《IEEE transactions on aerospace and electronic systems》2004,40(2):695-705
A new analytical model for equal allocation of divisible computation and communication load is developed. Equal allocation of load is attractive in multiple processor systems when real time information on processor and link capacity that is necessary for optimal scheduling is not available. The model includes a detailed accounting of solution reporting time. Equal allocation scheduling is compared with sequential scheduling and a new type of multi-installment scheduling. Aerospace applications include the processing of satellite imagery, radar, and sensor networks. 相似文献
9.
10.
This paper provides an overview of the Space Station configuration and summarizes the requirements, architecture, and significant challenges associated with the electrical power system (EPS). The Space Station configuration was baselined during the systems design review (SDR) process in March, 1994. The current configuration includes the addition of Russia as an international partner, resulting in major changes to the assembly sequence, pressurized module complement, and overall power architecture. The Russian contributions to the power system architecture, as well as an-overview and development status of the US provided elements is presented. Finally, a planned flight demonstration of solar dynamic power system on the Mir as part of the first phase of US/Russian cooperation in human space flight is described 相似文献
11.
12.
《Air & Space Europe》1999,1(1):55-57
The NASA, the FAA and Eurocontrol have initiated programs of research and development to provide flight crew, air line operators and air traffic managers with automation aids to increase capacity in enroute and terminal areas, to support the goals of safe, flexible, predictable and efficient operations, and to ensure, and to enhance the safety of operations in the response to demands for capacity enhancement. Achievement of these goals is enabled by increased precision of knowledge of aircraft and asset position in space and time, by increased density and bandwidth of transmitted information among the airspace assets and users, and by increased service and information to the flight deck, ATC and airline operations centers. These aiding technologies are intended to support exploitation of timely and dynamic information on atmospheric hazards, traffic fluctuations, and airspace utilization. These systems are intended to support the human operators who maintain the authority and responsibility for safe, efficient operations through cognitive aiding technologies, to serve as cognitive orthoses (Reason, 1988) [12]. 相似文献
13.
Woods L.M. Ribelin R. Armstrong J.H. 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(10):20-24
Future spacecraft and high-altitude airship (HAA) solar array technologies will require high array specific power (W/kg), which can be met using thin-film photovoltaics (PV) on lightweight and flexible substrates [1]. Thin-film array technology, with thin-film specific array support structure, begin to exceed the specific power of crystalline multi-junction arrays with thin-film device efficiencies as low as 8.5% [2]. Thin-film PV devices have other advantages in that they are more easily integrated into HAAs, and are projected to be much less costly than their crystalline PV counterparts. Furthermore, it is likely that only thin-film array technology will be able to meet device specific power requirements exceeding 1 kW/kg (photovoltaic and integrated substrate/blanket mass only). 相似文献
14.
15.
16.
超声速主流中横向喷流场的激波—旋涡结构的数值模拟 总被引:3,自引:2,他引:3
本文利用NND格式,通过求解NS方程,对二维超声速主流中横向喷流干扰流场进行了数值模拟,计算清楚地给出了激波结构、回流区和混合层。本文计算得到的激波结构和实验相当一致。最有兴趣的是由于喷流的干扰,主流在喷口前发生主涡分叉,观察到三个流向旋转涡和两个反流向旋转涡;在喷口后的背风区,存在具有低压和回流区的尾迹。 相似文献
17.
18.
19.
Resolution as a function of aperture length in the presence of phase errors is investigated with the aid of the spatial power spectral density. Numerical calculations are made for power spectra thought to be appropriate for phase errors due to atmospheric turbulence. Both Gaussian and uniform illumination are considered, and the results obtained here are compared with those reported by Brown and Riordan [2]. 相似文献