Command and Data Handling

Command and Data Handling

All of Odyssey's computing functions are performed by the command and data handling subsystem. The heart of this subsystem is a RAD6000 computer, a radiation-hardened version of the PowerPC chip used on most models of Macintosh computers. With 128 megabytes of random access memory (RAM) and three megabytes of non-volatile memory, which allows the system to maintain data even without power, the subsystem runs Odyssey's flight software and controls the spacecraft through interface electronics.

Interface electronics make use of computer cards to communicate with external peripherals. These cards slip into slots in the computer's main board, giving the system specific functions it would not have otherwise. For redundancy purposes, there are two identical strings of these computer and interface electronics, so that if one fails the spacecraft can switch to the other.

Communication with Odyssey's sensors that measure the spacecraft' orientation in space, or "attitude," and its science instruments is done via another interface card. A master input/output card collects signals from around the spacecraft and also sends commands to the electrical power subsystem. The interface to Odyssey's telecommunications subsystems is done through another card called the uplink/downlink card.

There are two other boards in the command and data handling subsystem, both internally redundant. The module interface card controls when the spacecraft switches to backup hardware and provides the spacecraft time. A converter card takes power from the electrical power subsystem and converts it into the proper voltages for the rest of the command and data handling subsystem components.

The last interface card is a single, non-redundant, one-gigabyte mass memory card that is used to store imaging data.

The entire command and data handling subsystem weighs 11.1 kilograms (24.5 pounds).