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Thermal Protection System
Various materials applied to the outer structure protect the orbiter from excessive heat.
Overview
Seven different materials, chosen for their weight efficiency and stability at high temperatures, are used.
Reinforced Carbon-Carbon
RCC protects areas where temperatures exceed 2,300 degrees F during entry.
High-Temperature Reusable Surface Insulation Tiles
Black tiles are applied on areas where temperatures do not exceed 2,300 degrees F.
Fibrous Refractory Composite Insulation Tiles
Black tiles developed later in the program replace some HRCI tiles.
Low-Temperature Reusable Surface Insulation Tiles
White tiles are used in areas where temperatures do not exceed 1,200 degrees F.
Advanced Flexible Reusable Surface Insulation Blankets
Quilted composite fabric replaced most of the LRSI tiles.
Felt Reusable Surface Insulation
Nomex felt blankets are used on the payload bay doors and other areas where temperatures do not exceed 700 degrees F.
Thermal Barriers
Various materials are used to fill in gaps.
Tile Identification
Each tile has a unique ID code.
Flags and Letters
Flags and letters are painted on.
Rewaterproofing
After each flight the orbiter is rewaterproofed.
Contractors
List of contractors for the thermal protection system.

Main Propulsion System
Along with SRBs, provides velocity increment necessary to reach orbit.
Overview
The main propulsion system includes three main engines, controllers and supporting equipment.
Orbiter Main Propulsion System Helium Subsystem
Helium is used to purge tanks and actuate valves.
Main Propulsion System Propellant Management Subsystem
Liquid hydrogen and liquid oxygen are fuels used by the system.
External Tank
The external tank feeds fuel to the main propulsion system.
Space Shuttle Main Engines
The main engines are reusable, high-performance, liquid-propellant rocket engines with variable thrust.
Pogo Suppression System
A pogo suppression system prevents engine thrust oscillation.
Space Shuttle Main Engine Controllers
Each controller operates in conjunction with other components to provide a self-contained system for engine control, checkout and monitoring.
Malfunction Detection
There are three separate means of detecting malfunctions within the main propulsion system.
Orbiter Hydraulic Systems
Three hydraulic systems supply pressure to the main propulsion system, providing thrust vector control and actuating engine valves on each SSME.
Thrust Vector Control
Ascent thrust vector control directs thrust of the main engines and SRBs to control attitude and trajectory from liftoff through second-stage ascent.
Helium, Oxidizer and Fuel Flow Sequence
The complete sequence begins several hours before launch and ends after main engine cutoff.
Main Propulsion System Contractors
List of contractors.

Orbiter/External Tank Separation System
Includes system components on both sides of the separation.
Overview
When the external tank separates from the orbiter, several components act at once for a clean disconnect.
17-inch Disconnect
Mated pairs of disconnects contain valves that allow propellant to flow until time for ET separation.
External Tank Separation System
The external tank is separated from the orbiter at three structural attach points.
Orbiter Umbilical Doors
After external tank jettison, doors close the umbilical cavities.

Orbital Maneuvering System
The orbital maneuvering system provides the thrust for orbit insertion, circularization, orbit transfer, rendezvous, and deorbit.
Overview
The OMS is housed in two independent pods located on each side of the orbiter's aft fuselage.
Helium Pressurization
The OMS system uses helium to pressurize fuel tanks.
Propellant Storage and Distribution
OMS propellant tanks enable the orbiter to reach a 1,000-foot-per-second velocity change.
Engine Bipropellant Valve Assembly
Each OMS engine receives pressure-fed propellants at its bipropellant valve assembly.
Engine Thrust Chamber Assembly
The thrust chamber is where the fuel and oxydizer react in the injector.
OMS Thrusting Sequence
The OMS thrusting sequence commands the OMS engines on or off and commands the engine purge function.
Engine Thrust Vector Control System
The engine TVC system consists of a gimbal ring assembly, two gimbal actuator assemblies, and two gimbal actuator controllers.
Thermal Control
OMS thermal control is achieved by insulation in the OMS pods and strip heaters.
OMS-RCS Interconnect
OMS propellant can be used to operate the Reaction Control System.
OMS-to-RCS Gauging Sequence
The OMS-to-aft-RCS propellant quantities are calculated by burn time integration.
Abort Control Sequences
The abort control sequence software manages OMS and RCS configuration and thrusting periods during ascent aborts.
OMS Engine Fault Detection and Identification
The OMS engine FDI function detects and identifies off-nominal performance of the OMS engine.
OMS Gimbal Actuator FDI
The OMS gimbal actuator FDI detects and identifies off-nominal performance of the pitch and yaw gimbal actuators of the OMS engines.

Reaction Control System
The RCS units provide the thrust for pitch, yaw and roll maneuvers and for small velocity changes along the orbiter axis.
Overview
The forward and aft RCS systems consist of helium storage tanks, pressure systems, propellant systems, and thermal control.
Pressurization System
Gaseous helium supplies pressure to the fuel and oxidizer tanks.
Propellant System
A system of tanks, lines and valves distributes propellant to the RCS thrusters.
RCS Quantity Monitor
Onboard computers calculate the usable percent of fuel and oxidizer in each RCS module.
Engine Propellant Feed
Isolation valves control the amount of propellant being fed to each RCS module.
RCS Engines
Each RCS engine contains a fuel and oxidizer valve, injector head assembly, combustion chamber, nozzle and electrical junction box.
Heaters
Heaters maintain propellant and pod temperatures within safe operating ranges.
RCS Jet Selection
Based on crew commands, the onboard computers direct RCS burns.

Electrical Power System
EPS subsystems work together to provide electrical power to the vehicle during all mission phases.
Overview
The EPS consists of three subsystems: power reactant storage and distribution, fuel cell power plants, and electrical power distribution and control.
Power Reactant Storage and Distribution
Cryogenic hydrogen and oxygen are stored in specially-equipped tanks.
Fuel Cell Power Plants
The fuel cells are located under the payload bay area and in the forward portion of the orbiter's midfuselage.
Electrical Power Distribution and Control
The EPDC subsystem distributes 28-volt dc electrical power and generates and distributes 115-volt, three-phase, 400-hertz ac electrical power to all of the space shuttle systems' electrical equipment throughout all mission phases.

Environmental Control and Life Support System
ECLSS systems interact to provide a habitable environment for the flight crew and cooling or heating for various orbiter systems and components.
Overview
The ECLSS consists of atmosphere and water treatment and thermal systems.
Crew Compartment Cabin Pressurization
The cabin is pressurized to 14.7 psia and maintained at an average 80-percent nitrogen and 20-percent oxygen mixture by the air revitalization system.
Cabin Air Revitalization
There are five independent air loops in the cabin.
Water Coolant Loop System
The WCLS provides thermal conditioning of the crew cabin by collecting heat at a heat exchanger and transferring it to the water coolant loops.
Active Thermal Control System
The ATCS consists of Freon interchangers, radiators and heat exchangers to control thermal conditions.
Supply and Waste Water
The supply and waste water systems provide water for the flash evaporator, crew consumption and hygiene.
Waste Collection System
The waste collection system is an integrated, multifunctional system used primarily to collect and process biological wastes from crew members in a zero-gravity environment.
Waste Water Tank
A single waste water tank receives waste water from the ARS humidity separator and the waste collection system.
Airlock Support
The airlock and airlock hatches permit EVA flight crew members to transfer from the middeck crew compartment into the payload bay in EMUs without depressurizing the orbiter crew cabin.
Extravehicular Activity Mobility Units
EMU space suits provide the necessities for life support during space walks.
Crew Altitude Protection System
The crew altitude protection system is worn by the flight crew members during launch and entry.
Radioisotope Thermoelectric Generator Cooling and Gaseous Nitrogen Purge for Payloads
A cooling and purge system is installed in Discovery and Atlantis to support those payloads with RTGs or gaseous nitrogen purging requirements.

Auxiliary Power Units
The orbiter has three APUs, hydrazine-fueled, turbine driven power units produce pressure for the vehicle's hydraulic systems.

Water Spray Boilers
The water spray boiler system consists of three identical independent water spray boilers, one per corresponding auxiliary power unit and hydraulic system.

Hydraulic System
The hydraulic system consists of three independent systems, each providing mechanical shaft power to drive a hydraulic pump.

Landing Gear System
Each landing gear includes a shock strut with two wheel and tire assemblies.
Overview
The landing gear system on the orbiter is a conventional aircraft tricycle configuration consisting of a nose landing gear and a left and right main landing gear.
Main Landing Gear Brakes
Each of the orbiter's four main landing gear wheels has electrohydraulic disc brakes and an anti-skid system.
Nose Wheel Steering
The orbiter nose wheel is steerable after nose wheel touchdown at landing.

Caution and Warning System
Designed to provide the crew with both visual and aural cues when a system exceeds predefined operating limits.
Orbiter Lighting System
The orbiter lighting system provides both interior and exterior lighting.
Smoke Detection and Fire Suppression
Smoke detection and fire suppression capabilities are provided in the crew cabin avionics bays, the crew cabin and the Spacelab pressurized module.
Payload Deployment and Retrieval System
The payload deployment and retrieval system includes the electromechanical arm that maneuvers a payload from the payload bay of the space shuttle orbiter to its deployment position and then releases it.
Payload Retention Mechanisms
Non-deployable payloads are retained by passive retention devices, and deployable payloads are secured by motor-driven, active retention devices.

Communications
Ground-based, orbiter and satellite systems are employed to keep the crew in touch with Mission Control.
Space Flight Tracking and Data Network
Provides tracking, data acquisition and associated support.
Tracking and Data Relay Satellite System
Provides continuous global coverage of Earth-orbiting satellites at altitudes from 750 miles to about 3,100 miles.
Orbiter Communications
Transfers telemetry information, commands, documentation and voice communications.
Overview
Information is transferred through hardline and radio frequency links.
S-Band System
Operates in the S-band portion of the RF spectrum of 1,700 to 2,300 MHz.
Ku-Band System
Used only when the orbiter is on orbit.
Ku-Band Rendezvous Radar
Ku-Band system includes a rendezvous radar that skin-tracks satellites and other rendezvous targets.
Payload Communication System
Used to transfer information between orbiter and its payloads.
Ultrahigh Frequency System
Used as a backup fro S-Band PM and Ku-Band voice communications, primarily for EVAs.
Audio System
Interfaces with caution/warning system, UHF, S-Band, Ku-Band, and tacan systems.
Instrumentation
Several camera systems are used by the flight crew to document activities during the mission.
Overview
Used to collect, route and process information throughout the orbiter and its payloads.
Pulse Code Modulation Master Unit
Receives data from MDMs and formats them for transmission to the ground.
Network Signal Processor
Responsible for processing and routing commands, telemetry and voice between the orbiter and the ground.
Ground Command Interface Logic
Also referred to as the ground command interface logic controller.
General-Purpose Computer and Communication Interface
Computers process communication controls and provide a command path between the ground and orbiter subsystems.
Master Timing Unit
A stable crystal-controlled timing source for the orbiter.
Operational Recorders
Used for serial recording and dumping of digital voice and PCM data.
Payload Recorder
Records and dumps payload data through S-Band or Ku-Band transmitter.
Teleprinter
Interim system designed tro transmit written data from the ground to the crew.
Text and Graphics System
Fax scanner on the ground that sends text and graphics to hard copier in orbiter.
Close-Circuit Television System
Used to support on-orbit activities that require visual feedback to the crew.
Operational Recorders
Used for serial recording and dumping of digital voice and PCM data.
Orbiter Experiments Support Systems for OV-102 (Columbia)
Records data obtained through OEX sensors.
Shuttle Infrared Leeside Temperature Sensing
Obtains high-resolution infrared imagery of orbiter surfaces during atmospheric entry.
Shuttle Entry Air Data System
takes measurements required for precise determination of air data during launch and landing phases.
Shuttle Upper Atmosphere Mass Spectrometer
Obtains measurements of free-stream density during atmospheric entry.
Aerodynamic Coefficient Identification Package
A group of sensors palced on the orbiter to obtain experiment measurements unavailable through the baseline system.
High-Resolution Accelerometer Package
Measures low-level aerodynamic accelerations along the orbiter's principal axed during re-entry.
Modular Auxiliary Data System
Measures and records selected pressure, temperature, strain, vibration and event data.

Avionics Systems
      Controls, or assists in controlling, most of the shuttle systems.
Overview
Controls, or assists in controlling, most of the shuttle systems.
Data Processing System
The vehicle relies on computerized control and monitoring for successful performance.
Software
DPS software is divided into two major groups: system software and applications software.
General-Purpose Computers
Five identical computers aboard the orbiter control vehicle systems.
Mass Memory Units
Computing functions for all mission phases requires about 400,000 words of computer memory.
Multifunction CRT Display System
Displays on the flight deck allow onboard monitoring of systems, software processing and manual control for crew data and software manipulation.
Master Timing Unit
The GPC complex requires an accurate time source because its software uses GMT to schedule processing.
Computer Data Bus Network
Network is divided into specific groups that perform specific functions.
Multiplexers/Demultiplexers
DPS MDMs convert and format serial digital GPC commands into separate commands for various vehicle system hardware.
Master Events Controllers
Send signals to arm and safe pyrotechnics during SRB/ET separation.
Data Bus Isolation Amplifiers
Interfacing devices for the GSE/LPS and SRB MDMs.
Backup Flight Control
The fifth GPC, loaded with different software, provides backup in case primary GPCs fail.
Guidance, Navigation and Control
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 Switches
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.
Dedicated Display Systems
Provide the flight crew with data required to fly the vehicle manually or to monitor automatic FCS performance.
Attitude Director Indicator
Provide attitude data, including attitude rates and errors.
Horizontal Situation Indicator
Displays a pictorial view of the vehicle's position.
Alpha Mach Indicator
Display vehicle angle of attack.
Altitude/Vertical Velocity Indicator
Display vertical acceleration, vertical velocity, barometric altitude and radar altitude.
Surface Position Indicator
Displays actual and commanded positions of elevons, body flap, rudder, aileron and speed brake.
Flight Control System Push Button Indicators
Transmit moding requests to digital autopilot.
RCS Command Lights
Indicate RCS jet comands by axis and direction.
G-Meter
Senses linear acceleration along the Z axis of the vehicle.
Head-up Display
Optical miniprocessor that cues the commander during final landing approach.


Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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