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Near Earth Asteroid Rendezvous (NEAR) Revised Eros Orbit Phase Trajectory DesignTrajectory design of the orbit phase of the NEAR mission involves a new process that departs significantly from those procedures used in previous missions. In most cases, a precise spacecraft ephemeris is designed well in advance of arrival at the target body. For NEAR, the uncertainty in the dynamic environment around Eros does not allow the luxury of a precise spacecraft trajectory to be defined in advance. The principal cause of this uncertainty is the limited knowledge oi' the gravity field a,-id rotational state of Eros. As a result, the concept for the NEAR trajectory design is to define a number of rules for satisfying spacecraft, mission, and science constraints, and then apply these rules to various assumptions for the model of Eros. Nominal, high, and low Eros mass models are used for testing the trajectory design strategy and to bracket the ranges of parameter variations that are expected upon arrival at the asteroid. The final design is completed after arrival at Eros and determination of the actual gravity field and rotational state. As a result of the unplanned termination of the deep space rendezvous maneuver on December 20, 1998, the NEAR spacecraft passed within 3830 km of Eros on December 23, 1998. This flyby provided a brief glimpse of Eros, and allowed for a more accurate model of the rotational parameters and gravity field uncertainty. Furthermore, after the termination of the deep space rendezvous burn, contact with the spacecraft was lost and the NEAR spacecraft lost attitude control. During the subsequent gyrations of the spacecraft, hydrazine thruster firings were used to regain attitude control. This unplanned thruster activity used Much of the fuel margin allocated for the orbit phase. Consequently, minimizing fuel consumption is now even more important.
Document ID
20000057504
Acquisition Source
Jet Propulsion Laboratory
Document Type
Other
Authors
Helfrich, J (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Miller, J. K. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Antreasian, P. G. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Carranza, E. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Williams, B. G. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Dunham, D. W. (Johns Hopkins Univ. Laurel, MD United States)
Farquhar, R. W. (Johns Hopkins Univ. Laurel, MD United States)
McAdams, J. V. (Johns Hopkins Univ. Laurel, MD United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 1999
Subject Category
Astrophysics
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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