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Orbiter Systems

The Space Shuttle Orbiter remains the most complex flying machine ever built, and is made up of operational systems which include:

1. The Thermal Protection System, which consists of various materials that are applied to the Orbiter external skin to help maintain the skin at acceptable temperatures during flight. Additional thermal protection is provided by insulation installed inside the Orbiter.

Thermal protection materials protect the Orbiter from all temperatures above 350 degrees Fahrenheit experienced during ascent and re-entry. These materials also protect the Orbiter in a range of temperatures from minus 250 degrees Fahrenheit to 3,000 degrees Fahrenheit experienced while in orbit.

A number of different materials are used in the Thermal Protection System, including reinforced carbon-carbon, black high-temperature reusable surface insulation tiles, black fibrous refractory composite insulation tiles, white low-temperature reusable surface insulation tiles, quilted insulation blankets and more specialized materials.

2. The Main Propulsion System, which is made up of the three Space Shuttle Main Engines and all of their related hardware. These include the Orbiter Main Propulsion System Helium Subsystem, Main Propulsion System Propellant Management Subsystem, External Tank interfaces and Pogo Suppression System.

In addition, the Main Propulsion System includes Space Shuttle Main Engine controllers, malfunction detection systems, hydraulic systems, thrust vector control systems and helium, oxidizer and fuel flow sequence systems.

3. The Orbiter/External Tank Separation System, which contains all of the hardware and control systems necessary to support safe separation of the External Tank from the Orbiter. This is made up of two 17-inch disconnects, an External Tank separation system and two Orbiter umbilical doors.

4. The Orbital Maneuvering System, which is made up of two Orbital Maneuvering System engines and all of their related hardware. One Orbital Maneuvering System engine is housed in each of two Orbital Maneuvering System (OMS)/Reaction Control System (RCS) pods attached to the top aft end of the Orbiter.

Each OMS engine burns a combination of monomethyl hydrazine and nitrogen tetroxide liquid fuel, and can produce a thrust of 6,000 pounds. Each OMS engine can be gimbaled to provide pitch and yaw control for the Orbiter as it maneuvers toward its intended mission orbit.

5. The Reaction Control System, which is made up of thrusters fired to help the Orbiter achieve a precise orbital path or perform changes in its position, and all of their related hardware. Thrusters are located at the forward end of the Orbiter and in each of the two aft Orbital Maneuvering System (OMS)/Reaction Control System (RCS) pods.

The RCS contains a total of 38 primary thrusters and 6 vernier thrusters. The forward RCS array contains 14 primary thrusters and two vernier thrusters. A total of 12 primary thrusters and two vernier thrusters are housed in each of the two OMS/RCS pods.

Each RCS thruster burns a combination of monomethyl hydrazine and nitrogen tetroxide liquid fuel. Each primary thruster can produce a thrust of 870 pounds, while each vernier thruster can produce a thrust of 24 pounds. The RCS thrusters can be fired in a plethora of combinations depending on the specific mission requirements.

6. The Electrical Power System, which provides the Orbiter with electricity. The Electrical Power System is made up of the Power Reactant Storage and Distribution Subsystem, the Fuel Cell Power Plants and the Electrical Power Distribution and Control Subsystem.

The Power Reactant Storage and Distribution Subsystem stores and delivers liquid oxygen and liquid hydrogen fuel to three Fuel Cell Power Plants. In burning the liquid oxygen and liquid hydrogen, the Fuel Cell Power Plants are each capable of producing 21,000 watts of continuous output, plus 15-minute peaks of up to 36,000 watts.

Electrical power produced by the Fuel Cell Power Plants is distributed and regulated by the Electrical Power Distribution and Control Subsystem. Prior to launch, Orbiter electricity is provided by ground systems and the Fuel Cell Power Plants. The Fuel Cell Power Plants assume full control of Orbiter power at launch minus 3.5 minutes.

7. The Environmental Control and Life Support System, which controls and regulates the astronaut life support functions of the Orbiter. Life support functions include crew compartment pressure, cabin air revitalization, water cooling, temperature control, water supply, waste collection, airlock support and crew altitude protection.

8. The Auxiliary Power Unit System, which is a storable liquid hydrazine-fueled, turbine-driven power unit that generates mechanical shaft power to drive a hydraulic pump that produces hydraulic pressure for the Orbiter hydraulic system.

The Auxiliary Power Unit System is vital to the Orbiter, since it controls hydraulic devices that gimbal the Space Shuttle Main Engines, operate various propellant valves in the Space Shuttle Main Engines and move the Orbiter elevons, body flap and rudder speed brake.

In addition, the Auxiliary Power Unit System controls devices that retract the External Tank/Orbiter 17-inch disconnects, deploy and retract the landing gear and support the braking and steering of the Orbiter at landing.

The Auxiliary Power Unit System is made up of three Auxiliary Power Units (APU) located in the aft fuselage. Each APU is identical, but each is operated independently of the others. All three APU's are started five minutes before launch, and are turned off shortly before the Orbiter reaches orbit.

One APU is started shortly before the Orbiter makes its de-orbit burn, with the remaining two APU's started just after the de-orbit burn is completed. All three APU's run until the Orbiter completes its landing and rollout.

9. The Water Spray Boiler System, which cools the Auxiliary Power Unit (APU) lubrication oil and hydraulic fluid. Three independent Water Spray Boilers each serve a corresponding APU. The Water Spray Boiler System sprays water onto the APU lubrication oil and hydraulic fluid lines, thus cooling the fluids within them.

10. The Hydraulic System, which distributes the hydraulic pressure produced by the Auxiliary Power Unit (APU) System. The Hydraulic System is made up of three independent hydraulic systems, each of which is mated to a corresponding APU.

11. The Landing Gear System, which is a conventional aircraft tricycle configuration landing gear consisting of a single forward nose landing gear and a left and right main landing gear. Each landing gear includes a shock strut with two tire and wheel assemblies.

Each main landing gear wheel is equipped with a brake assembly with anti-skid protection. The nose landing gear is steerable. The landing gear are retracted and deployed by hydraulic mechanism, and are locked in position within a wheel well and protected by landing gear doors when not in use.

12. The Caution and Warning System, which is designed to warn the crew of any conditions that may adversely affect the performance of the Orbiter. The Caution and Warning System primarily consists of a set of visual and aural alarms that alert the crew when any system has exceeded or strayed from its operational limits.

13. The Orbiter Lighting System, which provides both interior and exterior lighting for the Orbiter. Interior lighting is used primarily to support crew operations. Exterior lighting is used primarily to illuminate the payload bay area in order to aid visibility during payload operations and spacewalks.

14. The Smoke Detection and Fire Suppression System, which is designed to warn the crew of any fires, as well as protect the Orbiter from any fires that might develop. The system is made up of smoke detectors, portable fire extinguishers and automatic fire extinguishers.

15. The Payload Deployment and Retrieval System, which includes an electromechanical arm that maneuvers a payload from the payload bay and back again, plus all of its related hardware. This is more commonly known as the Remote Manipulator System (RMS), and is operated by the crew from inside the Orbiter.

The RMS can remove payloads from the payload bay for deployment. It can also grapple free-flying payloads and berth them back in the payload bay. It has been used to grapple satellites and the Hubble Space Telescope for repair and redeployment.

The RMS has also acted as an aid to astronauts participating in spacewalks. It has been used as a mobile extension ladder, work station and foot restraint for astronauts working in the payload bay during spacewalks. Cameras attached to the RMS have also been used to aid astronauts in visual inspections of the payload bay area.

16. The Payload Retention System, which is made up of a wide variety of hardware used to keep payloads secure within the payload bay. The Payload Retention System is designed to provide three-axis support for up to five separate payloads per mission.

17. The Communications System, which consists of all the equipment necessary to support the flow of voice and data transmissions to and from the Orbiter. Primary communications to and from the Orbiter flow through the NASA Space Flight Tracking and Data Network and the Tracking and Data Relay Satellite System.

The Communications System incorporates a huge and complex network of communications equipment and instrumentation. In addition to allowing both visual and aural communication with the crew, the Communications System supports a constant flow of data regarding the performance of the Orbiter, its systems and its position.

18. The Avionics System, which controls or assists in the control of most Orbiter systems. Primary functions of the Avionics System include automatic determination of Space Shuttle operational readiness, plus sequencing and control of the Solid Rocket Boosters and External Tank during launch and ascent.

The Avionics System also monitors the performance of the Orbiter, supports digital data processing, communications and tracking, payload and system management, guidance, navigation and control, as well as the electrical power distribution for the Orbiter, External Tank and Solid Rocket Boosters.

The Avionics System is made up of more than 300 computer black boxes located at various positions in the Orbiter, connected by about 300 miles of electrical wiring. A number of redundant hardware and software back-ups are incorporated within the Avionics System due to its critical nature.

Remarkably, the Avionics System is so complex that it can support fully automatic flight of the Space Shuttle from launch through landing. Although the Space Shuttle is typically guided to the runway manually during landing, the Avionics System can perform all flight functions automatically, with the exception of on-orbit rendezvous.

19. The Purge, Vent and Drain System, which is designed to produce gas purges that help regulate Orbiter temperature, prevent the accumulation of hazardous gases, vent unpressurized compartments during ascent and re-entry, drain any excess trapped fluids and keep window cavities clear.

The Purge, Vent and Drain System is made up of three separate sets of distribution plumbing located throughout the Orbiter. Purge gas consists of cool, dry air and gaseous nitrogen. Using a number of purge ports and vents, the system maintains constant humidity and temperature and assures that contaminants can not enter the Orbiter.

20. The Orbiter Flight Crew Escape System, which is a system designed to allow the crew to escape the Orbiter under a variety of flight situations. The system consists of an Inflight Crew Escape System, Emergency Egress Slide and Secondary Emergency Egress hardware.

The Inflight Crew Escape System, introduced after the Challenger accident, allows the crew to bail out of the Orbiter during flight. It will not, however, allow the crew to escape under circumstances similar to the Challenger accident. To use this system, the Orbiter must be on a level glide path.

The specific scenario under which astronauts might benefit from the Inflight Crew Escape System would be if the Orbiter could for some reason not reach a runway. Since astronauts might not survive either a water or land ditching of the Orbiter, the Inflight Crew Escape System does provide significant advantages.

Using the Inflight Crew Escape System, the astronauts would first blow the side hatch door. They would then deploy an escape pole, which extends from the inside to the outside of the Orbiter. The astronauts would then each use hardware attached to their space suits to slide along the escape pole, then parachute to safety.

Should the astronauts need to escape the Orbiter after performing a landing, an Emergency Egress Slide can be deployed out the side hatch after the hatch is blown or opened manually. Secondary Emergency Egress is provided by blowing the left overhead window, after which hardware allows astronauts to be safely lowered to the ground.

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