Technicians reposition and level the Cassini orbiter.

Before discussing the flight operations of the mission, an important element in the preparation of the spacecraft is the development phase. In this phase, development refers to the process of designing the spacecraft all the way from its conception through its final implementation.

After approval of the NASA proposal for Cassini by Congress several years ago, designers began the daunting task of devising plans and obtaining international cooperation for the Cassini orbiter and Huygens probe. Upon completion of the final design, engineers began to build the spacecraft. As fabrication progressed, it became necessary to test the newly completed assemblies.

The Cassini spacecraft's central computers, called the Command and Data Subsystem (CDS) and the Attitude and Articulation Control Subsystem (AACS) came to "life" early on within their development. Their jobs were to replicate telemetry and command with the spacecraft through communication with the scientists, so that proper commands could be administered throughout Cassini's operation. This was accomplished in the form of the Test Telemetry and Command Subsystem (TTCS), a portable version of the ground system.

To accurately monitor and control the spacecraft while it remains in operation, scientists designed and assembled Cassini while simultaneously developing what is known as its ground system. The ground system, officially called Cassini Mission and Science Operations, is the collection of people, computers, software and procedures linking directly to the spacecraft.

Time Lapse Movie

This development phase will never really be complete, since new command sequences are continually being created throughout Cassini's operation. New flight software will also be developed and loaded aboard the spacecraft periodically, to run in the Command Data Subsystem, Attitude and Articulation Control Subsystem, as well as in the physical science instruments onboard. The Spacecraft section contains detailed information about the subsystems and instruments. Flight software, as well as command sequences can be tested using duplicates of the Flight Command and Data Subsystem and Attitude and Articulation Control Subsystem within the Cassini Program's Integration and Test Laboratory.

Rudimentary concepts outlined in Basics of Space Flight, an online reference, apply directly to the Cassini Huygens mission. Cassini Flight Operations ultimately means keeping track of the spacecraft as it seems to coast for years through the solar system. In reality, this means that engineers in Cassini Flight Operations are constantly busy-- regularly telling the spacecraft what to do, measuring its course and speed, making sure it's going where it's supposed to, as well as identifying and repairing any occasional glitches in the spacecraft or in the worldwide ground data system that keeps the spacecraft in touch with Earth.