93-128
COMET NAVIGATION AND RENDEZVOUS A FLIGHT SOFTWARE DESIGN STUDY
Christopher C. Varner* and Wallace T. Fowler**
Abstract
Spacecraft flight software for the approach phase of a comet rendezvous mission is designed and analyzed. The proposed code is evaluated against a simulated rendezvous with the comet Churyumov-Gerasimenko near aphelion in the year 2005. The software incorporates an Extended Kalman filter. This navigation filter is developed lo improve the estimate of the rendezvous approach trajectory During the approach, the filter is capable of reducing the trajectory uncertainties by three orders of magnitude. The observations, which consist of measurements of the comet's right ascension and declination, allow the filter to determine the relative position of the comet to an accuracy better than 35 kilometers (km). A maneuver schedule which positions the spacecraft on the sun-comet line, 5,000 km from the comet, is also generated by the navigation filter. The calculated maneuvers are determined autonomously, and are not specific to the Churyumov-Gerasimenko mission. several flight difficulties are examined. The comet's large positional uncertainties highlight the need for an on-board wide angle camera. Manuevering required to complete the rendezvous degrades solution accuracies. Adequate separation between maneuvers is required to prevent navigation failuers.
*Senior Staff Engineer Eagle Engineering, Incorporated, 16915 El Camino Real, Suite 200, Houston, Texas 77058. Member of AIM
**Professor of Aerospace Engineering, University of Texas, Austin, Texas 78712. Associate Fellow AIM.