J. K. Miller

Recovery of near's mission to eros

Abstract On December 20, 1998, the main bipropellant thruster on the Near Earth Asteroid Rendezvous (NEAR) spacecraft was commanded to start a 15-minute burn. It was the first and largest of four planned maneuvers that would cancel NEARs velocity relative to (433) Eros to allow capture into orbit about the asteroid in January 1999. But the burn aborted and the spacecraft tumbled, causing loss of communication. The spacecraft corrected the problem, but used 29 kg of fuel in the process. A day later, NEAR was reacquired with just enough time to upload a sequence of commands to image Eros extensively as the spacecraft hurtled past the asteroid on December 23. The NEAR team designed a large bipropellant maneuver that successfully cancelled most of NEARs velocity relative to Eros on January 3, 1999. But then NEAR was almost 1 million kilometers from Eros, so a long “U-turn” journey was begun to return to the asteroid on February 14, 2000. The spacecraft remains healthy and enough fuel remains to enter orbit about Eros to complete all of the mission goals. This will be the first time that an interplanetary spacecraft has failed an orbital capture burn and returned to accomplish its objectives. This is possible because NEAR had a generous fuel supply and a robust contingency plan.

Application of Tisserand's criterion to the design of gravity assist trajectories

In this paper, a procedure is described for finding these encounter times using Lamberts theorem and a new criterion based on Tisserands criterion to identify pairs of transfer orbits between the launch planet and intermediate planet and between the intermediate planet and target planet.

Orbit determination of the Comet Rendezvous/Asteroid Flyby mission - Post-rendezvous phases

Orbit determination during the post-rendezvous phases of the Comet Rendezvous/Asteroid Flyby mission is described. The orbit determination process is discussed, with emphasis placed on optical imaging of landmarks and Doppler tracking. Rotational dynamics are introduced for the cometary nucleus. State estimation errors are given for spacecraft trajectory prediction and cometary nucleus attitude prediction. Estimation errors are also given for parameters that describe the cometary nucleus such as moments of inertia and gravity harmonics. The orbit determination performance in support of science observations while in orbit about the nucleus is described.