The surface configuration of a high-gain radio-frequency transmitting and/or receiving antenna (e.g., a large unfurlable antenna for deployment from a satellite or spacecraft in extraterrestrial space) ordinarily must conform to a precisely specified configuration, typically a parabolic configuration, in order to achieve diffraction-limited performance. However, the requirements of light-weight construction and thermal stability imposed by the constraints of typical applications in extraterrestrial space often preclude such an antenna from having the rigidity necessary to ensure that the actual surface configuration remains continuously in conformity with the specified surface configuration during an extended period of antenna operation.
Engineers involved in antenna technology customarily refer to the surface configuration of an antenna as the antenna's "figure". A system for monitoring the actual surface configuration (i.e., the figure) of an antenna, and for generating correction signals to change the actual surface configuration as required to maintain conformity with a specified surface configuration, is called a figure control system.
Proposals for figure control systems for use with large space-based unfurlable antennas have been described in the following documents:
1) C. C. Huang et al., "Structure Alignment Sensor Feasibility Demonstration", Lockheed Missiles & Space Company, Inc., Report No. D644951, 1978.
2) R. S. Neiswander, "Conceptual Design of a Surface Measurement System for Large Deployable Space Antennas", Proceedings: Large Space Systems Technology Conference, NASA Langley Research Center, 1981.
3) P. W. Collyer et al., "Electro-Optical System for Remote Position Measurement in Real Time", Proceedings: Large Space Systems Technology Conference, NASA Langley Research Center, 1981.
4) M. Berdahl, "Surface Measurement System Development", Proceedings: Large Space Systems Technology Conference, NASA Langley Research Center, 1981.
5) J. M. McLauchlan, "Spatial High-Accuracy Position-Encoding Sensor (SHAPES) for Large Space System Control Applications", Proceedings: Large Space Systems Technology Conference, NASA Langley Research Center, 1981.
Applications presently contemplated for large space-based unfurlable antennas require that the figure of the antenna be accurate to within 1/50 of the wavelength of the signal being transmitted and/or received, where the signal would have a frequency as high as 100 GHz. Such applications would require a measurement accuracy of about 0.06 mm in mapping the figure of the antenna at a measurement data rate of about 50 Hz. In contrast with such requirements, the measurement accuracies achievable with the antenna figure control systems previously proposed are from about 0.5 mm to about 0.15 mm (depending upon the particular system) at a measurement data rate of only about 10 Hz.