NADIR SEEKER ORIENTATION OF A SPACE VEHICLE IN RELATION TO THE PLANET BEING ORBITED

摘要

A space vehicle orientation system, for sensing the space vehicles orientation relative to the Z axis or vertical axis in the nadir direction, which uses a pulsed doppler radar to trace the nadir. The antenna of the radar is directed at the plantes surface. Operating in the beam limited condition, a coherent pulse is transmitted and when the center of the beam is pointed exactly at nadir the illuminated patch on the earth is essentially circular or symmetrically illuminated and the returned signal is symmetrical in doppler frequency shift and in pulse shape. Any deviation from the nadir will result in a change in either or both the doppler shift or the pulse width. By sensing these changes the radar beam may be redirected toward the spot directly below the space vehicle, the nadir.