Dr. Bobby G. Williams
Navigation and Mission Design Section
The Near Earth Asteroid Rendezvous (NEAR) Mission began its record setting exploration of the asteroid 433 Eros by inserting the NEAR spacecraft into orbit about Eros on February 14, 2000. The NEAR mission has overcome a failed insertion burn attempt on December 20, 1998, an event that would have ended most planetary missions, to return to the same target and successfully begin its science mapping a little more than a year later.
NEAR will gather science data at EROS until February 14, 2001, which is the nominal end of mission. The NEAR mission is managed by the Johns Hopkins University, Applied Physics Laboratory in Laurel, Maryland. Since the beginning mission concept in 1992, the JPL Navigation and Mission Design Section (312) has led the design and implementation of the NEAR navigation system. This presentation will show some of the unique features of navigation and mission design related to orbiting an asteroid, and to designing a robust navigation system for the NEAR spacecraft. The problem of navigating a spacecraft about an asteroid is made difficult by the relative uncertainty in the asteroid physical properties which perturb the orbit; i.e., the mass, gravity field, and spin state. To help solve this problem, the navigation system for NEAR uses traditional DSN radio metric Doppler and range tracking, along with new technology tracking types of optical landmark tracking and laser ranging to the asteroid surface. The experience to date for each of these data types in the navigation solutions will be presented. Future plans for the NEAR mission will be presented, which include low orbits (down to 35 km radius circular orbits), and close flybys that may pass within 1 km of the surface. In addition, possible hovering and landing scenarios that are being considered for the end of mission, pending approval by NASA, will be discussed.