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<title>AAS 98-207</title><body BGCOLOR="ffffff"> <h2>AAS 98-207</h2> <h2>COMPRESSION EPHEMERIDES IN ATTITUDE DYNAMICS</h2> <h4>R. Barrio, A. Elipe - Universidad de Zaragoza, Spain; M. Vallejo - Real Observatorio de la Armada, Spain</h4> <h2> Abstract </h2> In describing the attitude dynamics of rigid bodies with three different moments of inertia, elliptic functions play an essential role Most of asteroids have a clear non spherical shape. For instance, the asteroid Eros (target of the NEAR mission) is a tri-axial body with estimated dimensions of 40.5 by 14.5 by 14.1 kilometers. Hence, for computing the ephemerides of the rotation of such a body, the evaluation of elliptic functions at the desired instants is necessary, which computationally speaking, is very expensive. In order to save computing time and to have a fast transmission of data, we propose to compress the ephemerides. In the present communication, the compression technique is based on the use of Chebyshev polynomials of the first kind. These polynomials have special features that make them suitable for the approximation of functions. The optimization process is performed in the norm L-infinity or the Chebyshev norm in order to have a near minimax approximation and a uniform behavior of the compression error. By using this method, we are able to compress the attitude elements corresponding to the several revolutions, by using only 80 coefficients to reach a precision of more than 10 digits. Finally, we make several tests for an Eros-like body to show the behavior of the compressed ephemerides. <P><A HREF="http://www.space-flight.org/AAS_meetings/1998_winter/sessions.html">Back</A>