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<title>AAS 98-184</title><body BGCOLOR="ffffff"> <h2>AAS 98-184</h2> <h2>MISSION DESIGN AND NAVIGATION OF NEAR'S ENCOUNTER WITH ASTEROID 253 MATHILDE</h2> <h4>D. J. Scheeres - Iowa State University; D. W. Dunham, R. W. Farquhar - Applied Physics Laboratory; C. E. Helfrich - Jet Propulsion Laboratory; J. V. McAdams - APL; W. M. Owen, Jr., S. P. Synnott, B. G. Williams, P. J. Wolff, D. K. Yeomans - JPL</h4> <h2> Abstract </h2> On June 27, 1997 the NEAR spacecraft had a successful close encounter with minor planet 253 Mathilde, flying by the asteroid at a distance of 1225 km and a speed of 9.93 km/s. The flyby was a complete success: all the planned science images were captured, the mass of Mathilde was determined and the spacecraft was delivered to its target point well within the predicted 1-sigma delivery accuracy in the B-plane and in time-of-flight. This paper reviews the mission design and navigation plans and operations leading up to the flyby and analyzes their performance in light of the post-flyby analysis. Topics covered in this paper are: trajectory design and characteristics; pre-flyby radio metric orbit determination of NEAR; pre-flyby ephemeris estimation of Mathilde using ground-based observations; optical navigation detection and reduction prior to the flyby; combining radio metric, ground-based ephemeris and spacecraft-based optical data into a joint solution for the spacecraft and for Mathilde; post-flyby optical navigation images, reconstruction of the actual flyby conditions and estimation of the Mathilde mass. <P><A HREF="http://www.space-flight.org/AAS_meetings/1998_winter/sessions.html">Back</A>