The Ariane 5 Structure for Auxiliary Payloads (ASAP5) platform provides a low-cost means of launching interplanetary missions using the Ariane 5 launch vehicle. However, use of the ASAP5 platform presents several key constraints on the spacecraft system design. In particualr, the ASAP5 places a tight constraint on spacecraft mass which, coupled with the need to carry a large amount of fuel for interplanetary propulsive maneuvers, leaves very little flexibility for subsystem design. Orbital Sciences Corporation has conceived a spacecraft bus that accommodates a variety of interplanetary mission payloads such as probes, remote sensing instruments, and communication transponders. The attitude control system is comprised of heritage components and software to provide high performance with low mass, power, and cost. This single-string platform provides arcminute-level pointing accuracy, in either inertial or nadir-pointing orientations, using a star tracker, a fiber-optic gyro, and six coarse sun sensors. Furthermore, the attitude control system manages spacecraft attitude during trajectory correction maneuvers as well as dynamic events such as probe deployment using a monorpopellant-based reaction control system. This paper quantitatively discusses the difficult tradeoff decisions made in the design of this control system. In addition, performance, nad possible applications of this powerful new spacecraft bus are presented.
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