[Image] XTE ------------------------------------------------------------------------ FY94 analysis for the X-ray Timing Experiment (XTE) included a number of attitude and orbit studies in support of mission operations definition and preparation. Filter/Smoother Specification XTE mission operations will be very involved with up to 20 attitude maneuvers expected each day. With such a large number of attitude maneuvers, the need to accurately calibrate the spacecraft gyros and compensate for errors becomes essential. Existing FDD Batch Least Squares methods were not expected to handle this mission scenario very well because of limitations in the ability of such algorithms to model changing gyro biases over a batch segment. As a result, the FDSB chose to look to filter/smoother algorithms to provide the dynamic gyro modeling necessary to support the tight XTE attitude accuracy requirements. In FY94, specifications for a filter/smoother were defined and analysis was performed to demonstrate the advantages of this approach. Attitude Error Analysis In response to a project request, the FDSB has analyzed XTE Charged Couple Device (CCD) star tracker design characteristics in order to assess expected limitations in the field of view (FOV) calibration accuracy and the corresponding effect on XTE attitude determination uncertainties. A report detailing the results of this study was delivered to the XTE project. Star Catalog Validation The FDD has played a significant role in the quality assurance of the XTE onboard star catalog. The FDSB helped define star selection criteria, devise methods for handling multiple stars, and validate candidate stars in support of a Code-700 effort to define a baseline catalog. The FDF will assume control of the catalog and enhance it using new and more accurate source information in the coming months in preparation for launch. Orbit Analysis The FDSB provided analysis support to the XTE project in order to identify the number of tracking data passes required per day to achieve orbit determination accuracy requirements. The FDSB also assessed ground station coverage for spacecraft separation and for extended mission life operations using portable antennae located in Puerto Rico, American Samoa, Hawaii, and Miami. [Technical Contact: Richard Harman/553.1] Project information is available at the XTE Project Homepage.