All of the spacecraft'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 some personal
computers and videogame systems. With 128 megabytes
of random access memory and three megabytes of non-volatile
memory, which allows the system to maintain data even
without power, the subsystem runs Genesis' flight software
and controls the spacecraft through interface electronics.
Interface electronics are used to communicate with external
peripherals. They allow the use of redundant, identical
sets of computer and interface electronics, so that
if one fails the spacecraft can switch to the other.
Communication with Genesis' sensors that measure the
spacecraft's 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 Genesis'
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 entire command and data handling subsystem weighs
11.9 kilograms (26.2 pounds).
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