| Guidance,
Navigation and Control
Overview
GNC software commands effect vehicle control and provide sensor
data needed to compute these commands.
Flight
Control System Hardware
Hard-wired to one of eight flight-critical MDMs.
Navigational
Aids
Include IMUS, tacan units, air data probe assemblies, and more.
Inertial
Measurement Units
Consist of an all-attitude, four-gimbal, inertially stabilized platform.
Star
Trackers
Two star tracker units are part of the navigation system.
Crewman
Optical Alignment Sight
Used if IMU alignment is in error more than 1.4 degrees.
TACAN
Determine slant range and magnetic bearing to ground station.
Air
Data System
Provides information on the movement of the orbiter in the air mass.
Microwave
Scan Beam Landing System
Used during landing phase to determine slant range, azimuth and
elevation to landing runway.
Radar
Altimeter
Measure absolute altitude from the orbiter to nearest terrain within
beamwidth of orbiter's antennas.
Accelerometer
Assemblies
Sense vehicle acceleration along lateral and vertical axes.
Orbiter
Rate Gyro Assemblies
Used by flight control system to sense roll, pitch and yaw rates
during ascent and entry.
Solid
Rocket Booster Rate Gyro Assemblies
Used as feedback to find rate errors from liftoff to SRB separation.
Rotational
Hand Controller
Used by flight crew to gimbal engines and OMS/RCS systems.
Translational
Hand Controller
Used for manual control of translation along the longitudinal, lateral,
and vertical axes to control RCS.
Control
Stick Steering Push Button Light Indicators
Indicate control stick mode.
Rudder
Pedals
Command orbiter rotation about the yaw axis by positioning the rudder
during atmospheric flight.
Speed
Brake/Thrust Controller
Used during ascent to vary thrust level of main engines; used during entry to
control aerodynamic drag.
Body
Flap Switch
Provide manual control for positioning body flap during entry.
RHC/Panel
Enable/Inhibit
Provide signals to GPCs, prohibiting execution of related software
commands while RHC is active.
Trim
Switches
Used to move the aerosurfaces in roll, pitch and yaw.
Aerosurface
Servoamplifiers
Receive commands during atmospheric flight, causing aerosurface
deflections.
Digital
Autopilot
Composed of several software modules that interpret maneuver commands
and generate commands for the appropriate effectors.
Rendezvous
Thrusting Maneuvers
OMS/RCS thrusting periods can be used to correct or modify the orbit
as required.
Component
Locations
Black boxes are situated in several locations around the orbiter.
| 
