99-1985 - c 11/3/99 LQG controller design using GUI:...

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c 11/3/99 LQG controller design using GUI: Application to antennas and radio-telescopes Erin Maneria and Wodek Gawronskib a Montana State Universiv, Bozeman, MT 5971 9, USA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91 I09 Abstract The Linear Quadratic Gaussian (LQG) algorithm as presented in Refs.[l] and [2] has been used to control the JPL’s beam wave-guide [2], and 70-m [3] antennas. This algorithm signlJicantly improves tracking precision in a wind disturbed environment. Based on this algorithm and the implementation experience a Matlab based Graphical User Interface (CUI) was developed to design the LQG controllers applicable to antennas and radiotelescopes. The GUI is described in this paper. It consists of two parts: the basic LQG design and the Jne-tuning of the basic design using a constrained optimization algorithm. The presented GUI was developed to simplljj the design process, to make the design process user-friendly, and to enable design of an LQG controller for one with a limited control engineering background. The user is asked to manipulate the GUI sliders and radio buttons to watch the antenna performance. Simple rules are given at the GUI display. 1
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4 1. Introduction The NASA Deep Space Network (DSN) antennas serve as a communication tools for the space exploration. DSN antennas are located at three complexes: in California, Spain, and Australia. Viewed from outer space, the DSN complex looks like a cluster with one large (70-meter), and several smaller (34-meter) antennas. Antennas are the source of radio signals carrying commands and data to guide the actions of a spacecraft. As the Earth turns, the cluster begins to disappear over one edge, to be replaced by another at the opposite edge, which continues as the source of radio signals to the spacecraft. It is equally true that the same antennas arelistening to anysignal sent Earthward by a spacecraft. The very tiny amount of radio energy from the spacecraft is collected and focussed by the precision quasi-parabolic dish antennas into microwave equipment which amplifies it in low-noise amplifiers that operate at temperatures near absolute zero. From these amplifiers, the signal passes on to other equipment that eventually transforms it into a' replica of the data that originated on the spacecraft. Thus, the DSN is a data communication service that accepts a stream of data to be transported to a spacecraft and delivers another stream of data that originated on the spacecraft. An example of the NASNJPL beam-wave guide (BWG) antenna with 34-meter dish is shown in Fig.1. The antenna can rotate with respect to the azimuth (vertical) and elevation (horizontal) axes. Rotation in azimuth is accomplished by moving the entire structure on a circular azimuth track Precision pointing of the narrow signal to the spacecraft is critical, especially when making initial contact without having a received signal for reference. The required precision is proportional to the beamwidth of the signal, which is 22 millidegrees at S- band, 5.9
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99-1985 - c 11/3/99 LQG controller design using GUI:...

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