UVIS is controlled by a microprocessor that operates the instrument, executes various operating modes for data handling and compression, and buffers the instrument’s observation data for pickup by the Cassini Orbiter’s Command and Data Subsystem (CDS).
The Cassini spacecraft points the UVIS telescopes to the desired target (including stars, the Sun, atmospheric features, and the limbs of Saturn and its moons). The spacecraft attitude control allows for slews, steps, or drifts across the target. Generally, these spacecraft motions are executed by commands issued from the spacecraft CDS. Synchronization of the instrument activities with the spacecraft motion is achieved by having the CDS send trigger commands to the UVIS at the correct time. These trigger commands instruct the UVIS to execute actions that have been pre-loaded in the UVIS memory.
The data from the observation are buffered for pickup by the CDS. Two pickup rates are allowed: 32 kbps (for occultations) and 5 kbps (for spectral imaging, FPSCAN, and all others). UVIS team members generate command sequences for each observation, which are loaded in the UVIS memory using a set of tools known as the Uplink Product Generation System (UPGS). The sequence of internal commands is then submitted to the sequencing team at JPL via the UVIS SOPC (Science Operations and Planning Computer). Using the SOPC and the UVIS GSE (Ground Support Equipment), the UVIS team can also monitor the health of the instrument in near real-time. In addition, the SOPC is used to access the data played back by the spacecraft and stored in the JPL Telemetry Data Server (TDS). These data are processed and achieved at LASP.