The pointing control functions of the Cassini spacecraft attitude and articulation control subsystem have been designed to enhance operability by establishing a behavioral model at the command interface that raises pointing operations to a more intuitive level. The control system tracks this model to closely achieve the commanded behavior. Versatility is achieved by composing the behavioral model of independently commandable, interacting modules. Each directs activities directly related to a particular pointing issue, such as observation goals, instrument characteristics, attitude constraints, and navigation. A key feature of this design is the use of propagated vectors that precisely describe the motion of targets. Our design has enabled a new, more streamlined approach to mission operations whereby the many science and engineering activities sharing this system can be given direct control over pointing activities. This is possible because the behavioral model is easy to replicate in distributed ground software, it includes enforcement of constraints, and the maintenance of its components can be performed independently.
|