Our atmosphere is a mixture of gases (78 percent nitrogen, 21 percent oxygen, 1 percent other gases) at a pressure of 14 lbs/in2 (1 atm) that we breathe in and out. The space shuttle must provide a similar atmosphere. To do this, the orbiter carries liquid oxygen and liquid nitrogen in two systems of pressurized tanks, which are located in the mid-fuselage (each system has two tanks for a total of four tanks). The cabin pressurization system combines the gases in the correct mixture at normal atmospheric pressure. While in orbit, only one oxygen-nitrogen system is used to pressurize the orbiter. During launch and landing, both systems of each gas are used.
Five loops of fans circulate the atmosphere. The circulated air picks up carbon dioxide, heat and moisture:
The cabin heat exchanger also controls the cabin temperature. It circulates cool water to remove excess heat (cabin air is also used to cool electronic equipment) and transfers this heat to a Freon exchanger. The Freon then transfers the heat to other orbiter systems (e.g., cryogenic gas tanks, hydraulic systems) and radiates excess heat to outer space.
The orbiter has internal fluorescent floodlights that illuminate the crew compartment. The orbiter has external floodlights to illuminate the cargo bay. Finally, the control panels are lighted internally for easy viewing.
Food is stored on the mid-deck of the crew compartment. Food comes in several forms (dehydrated, low moisture, heat-stabilized, irradiated, natural and fresh). The orbiter has a galley-style kitchen module along the wall next to the entry hatch, which is equipped with the following:
food storage compartments
food warmers
a food preparation area with warm and cold water outlets
metal trays so the food packages and utensils do not float away
Like any home, the orbiter must be kept clean, especially in space when floating dirt and debris could present a hazard. Wastes are made from cleaning, eating, work and personal hygiene. For general housecleaning, various wipes (wet, dry, fabric, detergent and disinfectant), detergents, and wet/dry vacuum cleaners are used to clean surfaces, filters and the astronauts. Trash is separated into wet trash bags and dry trash bags, and the wet trash is placed in an evaporator that will remove the water. All trash bags are stowed in the lower deck to be returned to Earth for disposal. Solid waste from the
toilet is compacted, dried and stored in bags where it is returned to Earth for disposal (burning). Liquid waste from the toilet goes to the wastewater tank where it is dumped overboard.
Fire is one of the most dangerous hazards in space. The orbiter has a
Fire Detection and Suppression Subsystem that consists of the following:
smoke detectors in each rack of electrical equipment
alarms and warning lights in each module
personal breathing apparatus - mask and oxygen bottle for each crew member
After a fire is extinguished, the atmosphere control system will filter the air to remove particulates and toxic substances.
Next, we'll look at the technologies that help the space shuttle navigate, change direction and communicate from space.
Space Shuttle Positioning, Communication and Navigation
To change the direction that the orbiter is pointed (
attitude), you must use the
reaction control system (RCS) located on the nose and OMS pods of the aft fuselage.

Photo courtesy NASA
OMS firing
The RCS has 14 jets that can move the orbiter along each axis of rotation (pitch, roll, yaw). The RCS thrusters burn monomethyl hydrazine fuel and nitrogen tetroxide oxidizer just like the OMS engines described previously. Attitude changes are required for deploying satellites or for pointing (mapping instruments, telescopes) at the Earth or stars.
To change orbits (e.g., rendezvous, docking maneuvers), you must fire the OMS engines. As described above, these engines change the velocity of the orbiter to place it in a higher or lower orbit (see
How Satellites Work for details on orbits).
Tracking and Communication
You must be able to talk with flight controllers on the ground daily for the routine operation of the mission. In addition, you must be able to communicate with each other inside the orbiter or its payload modules and when conducting spacewalks outside.
NASA's Mission Control in Houston will send signals to a 60 ft radio antenna at White Sands Test Facility in New Mexico. White Sands will relay the signals to a pair of Tracking and Data Relay
satellites in orbit 22,300 miles above the Earth. The satellites will relay the signals to the space shuttle. The system works in reverse as well.
The orbiter has two systems for communicating with the ground:
S-band - voice, commands, telemetry and data files
Ku-band (high bandwidth) - video and transferring two-way data files
The orbiter has several intercom plug-in audio terminal units located throughout the crew compartment. You will wear a personal communications control with a headset. The communications control is
battery-powered and can be switched from intercom to transmit functions. You can either push to talk and release to listen or have a continuously open communication line. To talk with spacewalkers, the system uses a
UHF frequency, which is picked up in the astronaut's
spacesuit.
The orbiter also has a series of internal and external
video cameras to see inside and outside.
Navigation, Power and Computers
The orbiter must be able to know precisely where it is in space, where other objects are and how to change orbit. To know where it is and how fast it is moving, the orbiter uses
global positioning systems (GPS). To know which way it is pointing (attitude), the orbiter has several
gyroscopes. All of this information is fed into the flight computers for rendezvous and docking maneuvers, which are controlled in the aft station of the flight deck.
All of the on-board systems of the orbiter require electrical power. Three
fuel cells make electricity; they are located in the mid fuselage under the payload bay. These fuel cells combine oxygen and hydrogen from pressurized tanks in the mid fuselage to make electricity and water. Like a
power grid on Earth, the orbiter has a distribution system to supply electrical power to various instrument bays and areas of the ship. The water is used by the crew and for cooling.
The orbiter has five on-board computers that handle data processing and control critical flight systems. The computers monitor equipment and talk to each other and vote to settle arguments. Computers control critical adjustments especially during launch and landing:
operations of the orbiter (housekeeping functions, payload operations, rendezvous/docking)
interface with the crew
caution and warning systems
data acquisition and processing from experiments
flight maneuvers
Pilots essentially fly the computers, which fly the shuttle. To make this easier, the shuttles have a Multifunctional Electronic Display Subsystem (MEDS), which is a new, full color, flat, 11-panel display system. The MEDS, also known as the "glass cockpit", provides graphic portrayals of key light indicators (attitude, altitude, speed). The MEDS panels are easy to read and make it easier for shuttle pilots to interact with the orbiter.
Photo courtesy NASA
The glass cockpit
Now let's look at the kind of work you'll be doing during your shuttle mission.
Work Aboard the Shuttle
The shuttle was designed to deploy and retrieve satellites as well as deliver payloads to
Earth orbit. To do this, the shuttle uses the Remote Manipulator System (RMS). The RMS was built by Canada and is a long arm with an elbow and wrist joint. You can control the RMS from the aft flight deck. The RMS can grab payloads (satellites) from the cargo bay and deploy them, or grab on to payloads and place them into the bay.
In the past, the shuttle was used for delivering satellites and conducting experiments in space. Within the mid-deck, there are racks of experiments to be conducted during each mission. When more space was needed, the mission used the Spacelab module, which was built by the
European Space Agency (ESA). It fit into the cargo bay and was accessed by a tunnel from the mid-deck of the crew compartment. It provided a "shirt-sleeve" environment in which you could work. The Spacelab was lost along with Columbia in 2003. Now, most experiments will be conducted aboard the International Space Station (ESA is building a new science module called Columbus for the ISS).
Photo courtesy NASA
Astronaut Michael E. Lopez-Alegria uses a laser ranging device as Endeavour (STS113) approaches the International Space Station.
The shuttle's major role is building and resupplying the International Space Station. The shuttle delivers components built on Earth. Astronauts use the RMS to remove components from the cargo bay and to help attach them to existing modules in space station.
Photo courtesy NASA
Astronauts install a truss, which was delivered to the space station by Endeavour (STS113).
You will spend most of your time on the shuttle doing work to accomplish the mission objectives. Besides work, you must exercise frequently on the treadmill to counteract the loss of bone and muscle mass associated with weightlessness. You will also eat at the galley and sleep in your bunk-style sleeping quarters. You will have a toilet and personal hygiene facilities for use. You may have to perform spacewalks to accomplish the mission objectives. This will involve getting into a
space suit and going through depressurization procedures in the airlock.
When your mission objectives have been accomplished, it will be time to return to Earth. Let's look at this process in the next section.
The Shuttle's Return to Earth
For a successful return to
Earth and landing, dozens of things have to go just right.
First, the orbiter must be maneuvered into the proper position. This is crucial to a safe landing.
When a mission is finished and the shuttle is halfway around the world from the landing site (Kennedy Space Center, Edwards Air Force Base), mission control gives the command to come home, which prompts the crew to:
Close the cargo bay doors. In most cases, they have been flying nose-first and upside down, so they then fire the RCS thrusters to turn the orbiter tail first.
Once the orbiter is tail first, the crew fires the OMS engines to slow the orbiter down and fall back to Earth; it will take about 25 minutes before the shuttle reaches the upper atmosphere.
During that time, the crew fires the RCS thrusters to pitch the orbiter over so that the bottom of the orbiter faces the atmosphere (about 40 degrees) and they are moving nose first again.
Finally, they burn leftover fuel from the forward RCS as a safety precaution because this area encounters the highest heat of re-entry.
Columbia's AccidentOn the morning of February 1st, 2003, the space shuttle Columbia broke up during re-entry, more than 200,000 feet above Texas. The subsequent investigation revealed the cause of the accident. During lift-off, pieces of foam insulation fell off the ET and struck the left wing. The insulation damaged the heat protection tiles on the wing. When Columbia re-entered the atmosphere, hot gases entered the wing through the damaged area and melted the airframe. The shuttle lost control and broke up.
Because it is moving at about 17,000 mph (28,000 km/h), the orbiter hits air molecules and builds up heat from friction (approximately 3000 degrees F, or 1650 degrees C). The orbiter is covered with ceramic insulating materials designed to protect it from this heat. The materials include:
Reinforced carbon-carbon (RCC) on the wing surfaces and underside
High-temperature black surface insulation tiles on the upper forward fuselage and around the windows
White Nomex blankets on the upper payload bay doors, portions of the upper wing and mid/aft fuselage
Low-temperature white surface tiles on the remaining areas
Maneuvering of the orbiter for re-entry
These materials are designed to absorb large quantities of heat without increasing their temperature very much. In other words, they have a high heat capacity. During re-entry, the aft steering jets help to keep the orbiter at its 40 degree attitude. The hot ionized gases of the atmosphere that surround the orbiter prevent radio communication with the ground for about 12 minutes (i.e., ionization blackout).
Photo courtesy NASA
Artist's concept of a shuttle re-entry
When re-entry is successful, the orbiter encounters the main air of the atmosphere and is able to fly like an
airplane. The orbiter is designed from a lifting body design with swept back "delta" wings. With this design, the orbiter can generate lift with a small wing area. At this point, flight computers fly the orbiter. The orbiter makes a series of S-shaped, banking turns to slow its descent speed as it begins its final approach to the runway. The commander picks up a
radio beacon from the runway (Tactical Air Navigation System) when the orbiter is about 140 miles (225 km) away from the landing site and 150,000 feet (45,700 m) high. At 25 miles (40 km) out, the shuttle's landing computers give up control to the commander. The commander flies the shuttle around an imaginary cylinder (18,000 feet or 5,500 m in diameter) to line the orbiter up with the runway and drop the altitude. During the final approach, the commander steepens the angle of descent to minus 20 degrees (almost seven times steeper than the descent of a commercial airliner).
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