Determination of the minimal reflecting surface points number required for assessment of large-size transformable antenna pattern deviation

Construction of communication spacecraft with large-size transformable antennas developed tendencies to increase the operational band frequencies, to reduce specific mass and to increase the overall dimensions of the structures. The improvement of technical performance of communication spacecraft with large-size antennas cannot be achieved with- out ensuring the required accuracy of antenna pattern and of the antenna gain coefficient at its maximum. Factors affecting the final quality of large-size structures for space application (of antennas in particular), keep influencing the products through all their service life - from design and production to tests and actual operation. The “direct” elimination of the negative factors affecting the final output is often unprofitable considering the present de- velopment of technological support in hi-tech industries. In this respect, control of the ultimate operational characteris- tics of large-size spacecraft antennas in conditions of real performance, and compensation, if necessary, of deviations from the required values, is optimal with respect to the output/cost ratio. This approach is practical in determining the onboard antenna pattern and compensating its operational distortions in the process of specified spacecraft performance. There are two methods of measuring the antenna pattern at the orbit. The first method is based on measurements of radio engineering characteristics obtained from ground space vehicles’ service stations. This method is sufficiently accurate, but it has several drawbacks. For example, this method increases the number of requirements to ground stations - their number, location and characteristics of the equipment in use. The second method bases on obtaining radio engi- neering characteristics from the configuration and orientation of antenna reflector. The reflector is imaged as a cloud of checkpoints reflecting the deviations of the construction’s configuration and orientation from the specified values. To obtain the antenna pattern measurements using the second method, an antenna configuration control system (ACCS) must be worked out for measuring the coordinates of the reflector surface points. To perform its specific func- tion, the system should have the following configuration: measuring equipment mounted on the spacecraft casing, and control elements fixed on the construction components. This configuration allows to present the antenna construction components in the form of checkpoint cloud. In the process of the system development the constructional analysis of the possibility of using the antenna configu- ration measurements for the its pattern calculation and for further assessment of its deviation from the specified values was made. This article presents the assessment of the required number of monitored checkpoints on the reflector sur- face. For this purpose, Ku-band of frequencies was chosen as one of the most common frequency bands used by telecommunication spacecraft. Several sets of points were considered, among them the sets belonging both to the deformed reflector profile and to the one without deformation. For each set the antenna pattern calculation was made. Visual representations of the focal beam and the directive antenna gain were compared. The analysis of the obtained data allowed to determine the necessary minimum of checkpoints for antenna pattern calculation with the required accuracy. The obtained data were taken into account in formulating the requirements for the system of orbital control of antenna configuration.