Using Rayleigh Scattering To Measure Spacecraft Attitude

Two reports describe a Rayleigh-scattering attitude sensor (RSAS) - an optoelectronic instrument for determining the orientation of a spacecraft. An RSAS comprises a telescope/video-camera/image-digitizer combination that is mounted on the spacecraft and that captures images of the limb of the Earth in 355-nm-wavelength sunlight that has been Rayleigh-scattered from the atmosphere. (At 355 nm, the atmosphere scatters strongly but does not absorb significantly.) A computational model of the 355-nm radiance of the atmosphere as a function of altitude, lighting conditions, and viewing angle is then used to extract, from the image data, an estimate of the angle between the line of sight of the RSAS and the nadir.