Galileo system design for orbital operations

In April 1991, Galileo´s X-band high gain antenna failed to deploy. An alternate approach which utilizes the spacecraft´s S-band low gain antenna was conceived and is in development. This approach will enable the accomplishment of at least 70 percent of Galileo´s original scientific objectives. The short development period dictates that the spacecraft system design, the ground data system design, and the operational system scenarios and procedures necessary to conduct the mission be developed concurrently, and places a premium on validating the system designs as early as possible. This paper presents an overview of the Galileo mission, briefly describes the changes required to implement the orbital phase of the Galileo mission, and describes the functional model of the end to end system which was developed to support the systems design effort