Preliminary collimating measurement experiment for a large-scale antenna using image processing

Abstract

Previous efforts to assemble and deploy structures in space have opened up the possibility of constructing in space such large structures as large space platforms and space stations. In some cases, extremely precise fabrication is essential when performing construction in space. One example in which this accurate fabrication is required is in the assembly or deployment of large-scale antennas. When constructing these antennas, it is essential that they are collimated with high precision. In order to collimate large ground-based antennas, a theodolite is popularly used as a surveying instrument. However, because of the very limited resources available for measurement, conventional collimation systems are too heavy for use in space. Hence, we must develop a lighter surveying instrument. We propose a shape measurement system for a large-scale antenna. This measurement system is composed of several marks and mirrors located on the back side of the antenna, a camera that captures the mark images in one view, and an image processing computer that calculates the movement of the mark images and determines the antenna's shape. We applied a collimation method that uses the cross-correlation of images to mark-patterns mounted on an antenna dish to detect slight displacements. By calculating a cross-correlation function between the target and reference mark-patterns, and by interpolating this calculated function, we can measure the displacement of the target mark-pattern in sub-pixel precision.