The space shuttle
avionics system controls, or assists in controlling, most of the
shuttle systems. Its functions include automatic determination of
the vehicle's status and operational readiness; implementation sequencing
and control for the solid rocket boosters and external tank during
launch and ascent; performance monitoring; digital data processing;
communications and tracking; payload and system management; guidance,
navigation and control; and electrical power distribution for the
orbiter, external tank and solid rocket boosters.
flight control can be used for every phase of the mission except
docking, which is a manual operation performed by the flight crew.
Manual control-referred to as the control stick steering mode-also
is available at all times as a flight crew option.
equipment is arranged to facilitate checkout, access and replacement
with minimal disturbance to other systems. Almost all electrical
and electronic equipment is installed in three areas of the orbiter:
the flight deck, the three avionics equipment bays in the middeck
of the orbiter crew compartment and the three avionics equipment
bays in the orbiter aft fuselage. The flight deck of the orbiter
crew compartment is the center of avionics activity, both in flight
and on the ground. Before launch, the orbiter avionics system is
linked to ground support equipment through umbilical connections.
The space shuttle
avionics system consists of more than 300 major electronic black
boxes located throughout the vehicle, connected by more than 300
miles of electrical wiring. There are approximately 120,400 wire
segments and 6,491 connectors in the vehicle. The wiring and connectors
weigh approximately 7,000 pounds, wiring alone weighing approximately
4,600 pounds. Total weight of the black boxes, wiring and connectors
is approximately 17,116 pounds.
The black boxes
are connected to a set of five general-purpose computers through
common party lines called data buses. The black boxes offer dual
or triple redundancy for every function.
are designed to withstand multiple failures through redundant hardware
and software (computer programs) managed by the complex of five
computers; this arrangement is called a fail-operational/fail-safe
capability. Fail-operational performance means that, after one failure
in a system, redundancy management allows the vehicle to continue
on its mission. Fail-safe means that after a second failure, the
vehicle still is capable of returning to a landing site safely.