The Importance of Hardware-In-The-Loop Testing to the Cassini Mission to Saturn

The Cassini-Huygens Program is a joint effort between European Space Agency (ESA), which delivered the Huygens probe, and the National Aeronautics and Space Administration (NASA), which delivered the Cassini spacecraft. The Jet Propulsion Laboratory (JPL) manages the Cassini spacecraft for NASA. Cassini's primary mission is to survey the complex Saturnian system and release the ESA-Huygens probe at Titan. The Cassini Integrated Test Lab (ITL) at JPL is a high-fidelity hardware-in-the-loop testbed. It uses Attitude and Articulation Control Subsystem (AACS) and Command and Data Subsystem (CDS) flight hardware (H/W), as well as high-fidelity simulations of the other spacecraft subsystems and signals. The ITL's primary objective is to validate and verify sequences, Flight Software, and mission critical events, and it serves other purposes such as training the flight crew. This paper examines some of the AACS and CDS H/W and their peripheral devices used in the ITL. It examines the unique advantages gained by using H/W in the Cassini ITL, as well as the tradeoffs of using H/W versus simulations of these devices. Of late, consideration has been given in developing test plans for future flight projects to using purely software simulation testbeds: this paper offers evidence of the value of hardware-in-the-loop testbeds, demonstrating that hardware-in-the-loop testbeds should continue to have an important role in assuring the success of flight projects.