The MISI Optical System

The overall optical system with the various focal planes is shown in the figure. The 6-inch clear aperture scan mirror will spin at up to 40 revolutions per second and folds the image onto a second fold mirror which reflects the image into the Dall-Kirkham Cassegrainian-style telescope. The converging image is split onto four slightly off-axis (less than 2 degrees) focal planes by a four-sided pyramid mirror. The on-axis rays pass through a hole in the center of the pyramid mirror and are used to sample the visible/near-infrared EM region. Of the four off-axis focal planes, two are in the along-track scan direction (one fore and one aft of the primary optical axis) and two are in the cross-track direction (one leading, one lagging the primary optical axis). Presently, only the on-axis (VIS/NIR) and cross-track (long-wave infrared) focal planes are utilized. The along-track focal planes are intended for additional detector modules. The modular nature of the focal planes allow for easy addition of new detectors arrays or modification of the existing ones. The total field-of-view is 90 degrees (plus/minus 45 degrees) with calibration standards being viewed within every full rotation.
Line-Scanner Optical Schematic Showing Complete Radiation Path From Ground