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CDS collection process and operations methods

CDS information is currently sent down in what is known as Time Division Multiplexed telemetry where every piece of information has a fixed time slot assigned to it. This will be completely changed after the spacecraft reaches Jupiter. After Jupiter arrival, the CDS software will be modified to use a packet telemetry system that uses asynchronous variable length packets (i.e.- packets are only as large as they need to be and are only sent when there is data to send).

The CDS has six RCA COSMAC 1802 8-bit microprocessors. The CDS, in the current software design, consists of two completely independent strings of hardware, either of which can completely perform the functions that the CDS must perform. Each of these strings contains three of the 1802 microprocessors as well as some other hardware. Both strings of the CDS are normally operating, but only one is controlling the spacecraft at any moment. This will completely change once the spacecraft arrives at Jupiter in that after that time only spacecraft health and safety functions will remain redundant, while all other CDS science processing and telemetry functions will use all six 1802 microprocessors as a single multiprocessor computer.

Each of the 1802 microprocessors in the CDS has its own memory and executes its own independent software. Each CDS processor communicates with the other CDS processors (and the AACS and science instruments, for that matter) via the two CDS communication busses. Traffic is controlled on these busses by one processor in each string.

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