Autonomous optical navigation for interplanetary missions

The automation of interplanetary spacecraft is becoming increasingly desirable to meet various mission requirements. A prototype autonomous spacecraft which will flyby an asteroid and comet is slated for flight in mid-1998 as part of NASA's New Millennium Program. This spacecraft will navigate by using optical data taken by the onboard camera to determine its orbit, and use this information to predict its future trajectory and make necessary course corrections. The basic navigation data available from the camera are star-relative astrometric observations of solar system bodies which can be used to determine line-of-sight vectors to those objects. The directional sightings are obtained by determining the precise centers of the object and stars in the image. During interplanetary cruise, centerfinding is performed by using two pattern matching techniques inherited from the Galileo mission. Near-encounter images are processed with a separate algorithm employing image modeling and brightness centroiding. This paper describes the image processing algorithms, and the results of a ground-based test of the algorithms using real data.