Study On Techniques Of Precision Measurement In Assembly Of Spacecraft Antenna

Spacecraft antenna is an important part of spacecraft, because all the communication between the spacecraft and the earth and other aerocrafts must be transformed through spacecraft antennas. Spacecraft antenna assembly measurement is the first and right way to guarantee the antenna performing in the best state. At present, theodolites are usually used to measure spacecraft antenna, in its assembly, to obtain the parameters of position and direction of spacecraft antenna with respect to the spacecraft itself. Traditionally, theodolites must be strictly leveled before measurement, thus the measurement accuracy is always limited by the leveling error of the instruments, which is existing for ever.Measurement efficiency may be also limited because of the long time leveling of theodolites. Aiming at the existing problems in the measurement of spacecraft antenna assembly, the following significant research work will be carried out: Theories of computer vision are firstly well studied and similarites between theodolites and cameras used in computer vision are fully considered. And then calibration and measurement algorithms used in vision measurement system are now applied to theodolite system for calibration and special triangulation. Perspective projecting model is then built up for theodolite. Special 3D coordinate measurement models are devoped for 2 or more theodolites when used in free state. The measurement uncertainty of the sytem is then analized theoretically and simulation experiments are performed at the same time. The simulation result shows that the free state theodolite measurement model does not need to level theodolites, thus the measurement accuracy is not only garanteed, but measurement efficiency of the system is improved.Calibration methods of free state theodolites are developed based on the theory of perspective projecting model, mainly including calibration methods using linear calibration rig, 2D calibration rig and 3D calibraitn rig. Performance analyses for 3 kind of calibration methods are carried out, and the most useful calibration method is then conformed.For the techniques in spacecraft antenna assembly, measurement and setting up methods are firstly developed, which mainly include the transitional cube coordinate frame, spacecraft designing coordinate frame and final coordinate transforming method. Vectod multiplication method is proposed to establish the cube frame. Theoretical research shows that the setting up result has nothing to do with the orthogonality of two adjacent surface of the cube. A new type of target with 5 aiming points is designed to measure spacecraft antenna. A tangent plane will be constructed with the 5 pointed measured directly, and normal direction will be obtained to compensate the thickness of targets and then the coordinates of points right on the antenna surface are obtained. A general fitting method of antenna is proposed to calculate the geometric parameters of antenna surface. The algorithm is proved to have good performance by theoretical analysis and simulation testing.Finally, the calibration and measurement algorithms, proposed in the paper, for free state theodolite system are proved to be correct by experiments. A standard scale bar is adopted to test the repeatability of theodolite system. Comparing with the traditional method, the current algorithm can be found having certain repeatitive accuracy and at the same time it can improve measurement efficiency. Methods of setting up cube coordinate reference frame and spacecraft total coordinate reference frame, generally used in the process of spacecraft antenna assembly are proved to be correct by measuring experiments. Traditional targets and new type of targets are respectively used to measure a spacecraft antenna, and new type of targets are proved to be faster to compensate the thickness of target and the compensation is of more accuracy.