Magellan attitude control mission operations

From the Martin Marietta Astronautics Group base in Denver, Colorado, spacecraft engineers have been operating the Magellan spacecraft for the past three and one half years, along with the Jet Propulsion Laboratory, for NASA. The spacecraft team in Denver is responsible for the health of the vehicle, from command generation to evaluation of engineering telemetry. Operation of the spacecraft's Attitude and Articulation Control Subsystem (AACS) has specifically posed several in-flight challenges. This system must provide accurate pointing of the spacecraft throughout each 3.2 hour orbit which typically consists of 5 - 9 discrete maneuvers. Preparation of bi-weekly command sequences, monitoring execution, and trending of subsystem performance is of paramount importance, but in-flight anomalies have also demanded the attention of AACS engineers. Anomalies are often very interesting and challenging aspects of a project, and the Magellan mission was no exception. From the first unsuccessful attempts to perform a starscan, to spacecraft safing events, much has been experienced to add to the `lessons learned' from this mission. Many of Magellan's in-flight experiences, anomalies, and their resolutions are highlighted in this paper.