Abstract: An earth horizon sensor on board an orbiting spacecraft is designed to produce four (4) scans across the earth at geosynchronous altitudes using only two non-visible wavelength (infrared) detectors. The four scans are essentially parallel and permit the earth center to be offset from the null axis of the earth sensor permitting the offset pointing of high gain communication. By providing four scans using only two detectors, components are minimized and reliability is improved. The four scans are generated with only two detectors by using both the front and rear surfaces of a rotating scanning mirror.

Abstract: The disclosure is of apparatus including a duct-like light guide having an inlet end and an outlet end, light source means at the inlet end, a document at the outlet end, an optical reading system for receiving light reflected from the document, and electronic circuit means for converting the reflected light to electrical signals. Typically, the optical reading system has non-uniform light transmission characteristics, and, with one type of lens system, there is fall-off in intensity at the ends of the system. To compensate for this fall-off, the light source means is designed and positioned to provide a corresponding non-uniform light distribution so that the net effect is a uniform light distribution at the output of the lens system.

Abstract: A folded retro-reflective optical scanner using common major optics for both scanning and reading and achieving a long scan line (8.25 inches) with a short throw distance and little bow. Astigmatic effects in the reading beam are minimized by utilizing only the center portion of the return beam for reading.