Presented by:
Dr. Bobby G. Williams and James K. Miller,
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Abstract
The Near Earth Asteroid Rendezvous Shoemaker (NEAR) mission posed several new and difficult challenges for spacecraft navigation. Many of these resulted from the fact that NEAR was the first mission to send a spacecraft to rendezvous with, orbit about, and finally land on an asteroid, the asteroid 433 Eros. The navigation for the cruise phase of the mission, even with its stringent requirements, was routine by comparison to the orbit and landing phases of the mission. The navigation challenge for the orbit phase was to adapt the orbit plan while adjusting for the crudely known asteroid physical parameters. Improvements in the estimates of Eros' physical parameters such as spin state, shape and the gravity potential of Eros, as the spacecraft approached and inserted into orbit about the asteroid, was crucial to mission success. Unlike a planetary orbiter, the very low gravity of the asteroid meant that the spacecraft could easily escape or crash into the surface of Eros with small changes in velocity. This placed additional demand on navigation accuracy while also imposing a generally shorter response time than that usual for planetary orbit missions. New challenges arose late in the mission as the navigation team designed and executed several close flybys of the surface (as close as 2.7 km) and finished with the soft landing on Eros, which was a historic first in space exploration. This presentation details the methods developed and implemented by the NEAR navigation team to successfully deal with this very unique mission.
The Speakers
Dr. Bobby G.
Williams
Dr. Williams holds degrees in Aerospace Engineering from the University of
Texas (B.S. and M.S.) and the University of Southern California (PhD). He
participated in and eventually headed the orbit determination teams at JPL
for the Viking missions to Mars, the Pioneer Venus Orbiter mission to
Venus, and the Earth oceanographic mission TOPEX/Poseidon. He participated
in gravity field determination for both Mars and Venus by analyzing orbiter
tracking data and was a member of the Phobos Experiment Team that first
determined the mass of the Martian moon, Phobos, from spacecraft tracking
data. Currently, he is the technical group supervisor of the outer planet
navigation group in the Navigation and Mission Design section at JPL while
also serving as the navigation team chief for NASA's Near Earth Asteroid
Rendezvous (NEAR) mission.
James K. Miller
James K. Miller graduated from Carnegie Mellon University with the degree
of B.S. in Electrical Engineering. He is currently the lead technical
engineer for Near Earth Asteroid Rendezvous (NEAR) navigation. His previous
experience with JPL includes guidance and control analyst on the Mariner
Mars 1969 mission, assistant flight team chief for the Viking mission and
navigation analyst for the Galileo mission. He also provided navigation
support for the Comet Rendezvous Asteroid Flyby mission that included
development of software used for NEAR navigation.