Rayleigh scattering attitude sensor

A new instrument has been developed to measure spacecraft attitude which utilizes ultraviolet radiation scattered in the Earth's limb. The sensor consists of a very stable UV bandpass filter with a center wavelength at 355 nm, imaging optics, and a linear diode array detector. The radiance of the limb at this wavelength is dominated by Rayleigh scattering and typically decreases by 15% per kilometer above 20 lan The theoretical resolution at the limb of this device is 0.39 lan per pixel for a nominal orbital altitude of 306 ion (similar or equal to 0.012 degrees) and represents a significant improvement over typical infrared-based attitude sensors which have an accuracy of similar or equal to 0.1 degrees. This system was integrated with the Shuttle Solar Backscatter Ultraviolet (SSBUV) experiment and flown on STS-72 in January of 1996. The calibration and optical characterization of the device will be presented. Results from the first flight of this instrument showing an agreement with available shuttle pointing data of +/-0.05 degrees, will also be discussed.