Thruster-Imaging Analysis for Control of a Solar Concentrator
Abstract
A major requirement for using a solar propulsion system is the proper placement of the focal spot on the thruster absorber plane. Without proper placement of the focal spot, solar energy is not transferred to the propellant gas, or in the worst case, a significantly smaller proportion of the incident energy is transferred to the gas. Previous work has determined that alignment accuracy needs to be 0.1 degree for angular and 0.1 inch for translation. Human-in-the-loop fine focus image processing can handle the focal spot positioning, but human-in-the-loop sensors and algorithms need to be replaced with a space flight-oriented solution. The problem of positioning the solar focal spot on the thruster absorber is due to the visual complexity of the absorber, which is compounded by specular reflection from the secondary concentrator. A charge-coupled device camera, the SBIG ST-6, was chosen as the fine focus device for this study. An SRS 1x2 meter elliptical concentrator was used to form images on the thruster. Thruster images were taken at 1-inch intervals in both vertical and horizontal locations using the 1m x 2m concentrator and a simulated light source. A scissors jack on block was used to vary the position of the light source. A Sony notebook computer was used to take the images, and Matlab was used for image enhancement and analysis. Histogram equalization of the images was necessary before final processing. Results show that averaging filtering was the most useful filtering for using the STFT for determining focal spot location. Laplacian and Gaussian filtering was not useful for STFT, but may be useful for locating specular reflections using other methods. The study shows that images should be taken using a variety of exposures to ensure that the image histograms are more reasonably populated. (10 figures)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 23, 2003
- Accession Number
- ADA417134
Entities
People
- Joseph N. Beasley
Organizations
- Air Force Research Laboratory