or assists in controlling, most of the shuttle systems. - The vehiclerelies on computerized control and monitoring for successful performance. software is divided into two major groups: system softwareand applications software. identical computers aboard the orbiter control vehicle systems. functions for all mission phases requires about 400,000 wordsof computer memory. CRT Display Systemon the flight deck allow onboard monitoring of systems, softwareprocessing and manual control for crew data and software manipulation. GPC complex requires an accurate time source because its softwareuses GMT to schedule processing. Data Bus Networkis divided into specific groups that perform specific functions. MDMs convert and format serial digital GPC commands into separatecommands for various vehicle system hardware. signalls to arm and safe pyrotechnics during SRB/ET separation. Bus Isolation Amplifiersdevices for the GSE/LPS and SRB MDMs. fifth GPC, loaded with different software, provides backupin case primary GPCs fail. Navigation and Control- GNC softwarecommands effect vehicle control and provide sensor data neededto compute these commands. Control System Hardwareto one of eight flight-critical MDMs. IMUS, tacan units, air data probe assemblies, and more.of an all-attitude, four-gimbal, inertially stabilized platform. star tracker units are part of the navigation system. Optical Alignment Sightif IMU alignment is in error more than 1.4 degrees. slant range and magnetic bearing to ground station. information on the movement of the orbiter in the air mass. Scan Beam Landing Systemduring landing phase to determine slant range, azimuth andelevation to landing runway. absolute altitude from the orbiter to nearest terrain withinbeamwidth of orbiter's antennas. vehicle acceleration along lateral and vertical axes. Rate Gyro Assembliesby flight control system to sense roll, pitch and yaw ratesduring ascent and entry. Rocket Booster Rate Gyro Assembliesas feedback to find rate errors from liftoff to SRB separation.by flight crew to gimbal engines and OMS/RCS systems. for manual control of translation along the longitudinal,lateral, and vertical axes to control RCS. Stick Steering Push Button Light Indicatorscontrol stick mode. orbiter rotation about the yaw axis by positioning the rudderduring atmospheric flight. during ascent to vary thrust level of main engines; used duringentry to control aerodynamic drag. manual control for positioning body flap during entry.signals to GPCs, prohibiting execution of related softwarecommands while RHC is active. to move the aerosurfaces in roll, pitch and yaw. commands during atmospheric flight, causing aerosurface deflections.of several software modules that interpret maneuver commandsand generate commands for the appropriate effectors. thrusting periods can be used to correct or modify the orbitboxes are situated in several locations around the orbiter. the flight crew with data required to fly the vehicle manuallyor to monitor automatic FCS performance. attitude data, including attitude rates and errors. a pictorial view of the vehicle's position. vehicle angle of attack.vertical acceleration, vertical velocity, barometric altitudeand radar altitude.actual and commanded positions of elevons, body flap, rudder,aileron and speed brake. Control System Push Button Indicatorsmoding requests to digital autopilot. RCS jet comands by axis and direction. - Senses linearacceleration along the Z axis of the vehicle. miniprocessor that cues the commander during final landing approach.