How Space Shuttles Work

To lift the 4.5 million pound (2.05 million kg) shuttle from the pad to orbit (115 to 400 miles/185 to 643 km) above the Earth, the shuttle uses the following components:

Let's look at these components closely.

Solid Rocket Boosters

The SRBs are solid rockets that provide most of the main force or thrust (71 percent) needed to lift the space shuttle off the launch pad. In addition, the SRBs support the entire weight of the space shuttle orbiter and fuel tank on the launch pad. Each SRB has the following parts:

Because the SRBs are solid rocket engines, once they are ignited, they cannot be shut down. Therefore, they are the last component to light at launch.

Main Engines

The orbiter has three main engines located in the aft (back) fuselage (body of the spacecraft). Each engine is 14 feet (4.3 m) long, 7.5 feet (2. 3 m) in diameter at its widest point (the nozzle) and weighs about 6,700 lb (3039 kg).

The main engines provide the remainder of the thrust (29 percent) to lift the shuttle off the pad and into orbit.

The engines burn liquid hydrogen and liquid oxygen, which are stored in the external fuel tank (ET), at a ratio of 6:1. They draw liquid hydrogen and oxygen from the ET at an amazing rate, equivalent to emptying a family swimming pool every 10 seconds! The fuel is partially burned in a pre-chamber to produce high pressure, hot gases that drive the turbo-pumps (fuel pumps). The fuel is then fully burned in the main combustion chamber and the exhaust gases (water vapor) leave the nozzle at approximately 6,000 mph (10,000 km/h). Each engine can generate between 375,000 and 470,000 lb (1,668,083 to 2,090,664 N) of thrust; the rate of thrust can be controlled from 65 percent to 109 percent maximum thrust. The engines are mounted on gimbals (round bearings) that control the direction of the exhaust, which controls the forward direction of the rocket

External Fuel Tank­

As mentioned above, the fuel for the main engines is stored in the ET. The ET is 158 ft (48 m) long and has a diameter of 27.6 ft (8.4 m). When empty, the ET weighs 78,000 lb (35,455 kg). It holds about 1.6 million lb (719,000 kg) of propellant with a total volume of about 526,000 gallons (2 million liters).

The ET is made of aluminum and aluminum composite materials. It has two separate tanks inside, the forward tank for oxygen and the aft tank for hydrogen, separated by an intertank region. Each tank has baffles to dampen the motion of fluid inside. Fluid flows from each tank through a 17-inch (43 cm) diameter feed line out of the ET through an umbilical line into the shuttle's main engines. Through these lines, oxygen can flow at a maximum rate of 17,600 gallons/min (66,600 l/min) and hydrogen can flow at a maximum rate of 47,400 gallons/min (179,000 l/min).

The ET is covered with a 1-inch (2.5 cm) thick layer of spray-on, polyisocyanurate foam insulation. The insulation keeps the fuels cold, protects the fuel from heat that builds up on the ET skin in flight, and minimizes ice formation. When Columbia launched in 2003, pieces of the insulating foam broke off the ET and damaged the left wing of the orbiter, which ultimately caused Columbia to break up upon re-entry.

Next, we'll look at the orbital maneuvering system and liftoff.

­The two orbital maneuvering systems' (OMS) engines are located in pods o­n the aft section of the orbiter, one on either side of the tail. These engines place the shuttle into final orbit, change the shuttle's position from one orbit to another, and slow the shuttle down for re-entry.

The OMS engines burn monomethyl hydrazine fuel (CH₃NHNH₂) and nitrogen tetroxide oxidizer (N₂O₄). Interestingly, when these two substances come in contact, they ignite and burn automatically (i.e., no spark required) in the absence of oxygen. The fuel and oxidizer are kept in separate tanks, each pressurized by helium. The helium pushes the fluids through the fuel lines (i.e., no mechanical pump required). In each fuel line, there are two spring-loaded solenoid valves that close the lines. Pressurized nitrogen gas, from a small tank located near the engine, opens the valves and allows the fuel and oxidizer to flow into the combustion chamber of the engine. When the engines shut off, the nitrogen goes from the valves into the fuel lines momentarily to flush the lines of any remaining fuel and oxidizer; this purge of the line prevents any unwanted explosions. During a single flight, there is enough nitrogen to open the valves and purge the lines 10 times!

Either one or both of the OMS engines can fire, depending upon the orbital maneuver. Each OMS engine can produce 6,000 lb (26,400 N) of thrust. The OMS engines together can accelerate the shuttle by 2 ft/s² (0.6 m/s²). This acceleration can change the shuttle's velocity by as much as 1,000 ft/s (305 m/s). To place into orbit or to de-orbit takes about 100-500 ft/s (31-153 m/s) change in velocity. Orbital adjustments take about 2 ft/s (0.61 m/s) change in velocity. The engines can start and stop 1,000 times and have a total of 15 h burn time.

Now let's put these pieces together to lift off!

Profile of shuttle launch and ascent into orbit

As the shuttle rests on the pad fully fueled, it weighs about 4.5 million pounds or 2 million kg. The shuttle rests on the SRBs as pre-launch and final launch preparations are going on through T minus 31 seconds:

You are now in outer space and ready to continue your mission.

Now, let's look at where and how you will be living while you are in space.

Orbiter

Once in space, the shuttle orbiter is your home for seven to 14 days. The orbiter can be oriented so that the cargo bay doors face toward the Earth or away from the Earth depending upon the mission objectives; in fact, the orientation can be changed throughout the mission. One of the first things that the commander will do is to open the cargo bay doors to cool the orbiter.

The orbiter consists of the following parts:

You will live in the crew compartment, which is located in the forward fuselage. The crew compartment has 2,325 cu.ft of space with the airlock inside or 2,625 cu.ft with the airlock outside.

The crew compartment has three decks:

flight deck - uppermost deck

mid-deck

lower deck (equipment bay) - contains life support equipment, electrical systems, etc. Now that you have seen the parts of the orbiter, let's look closely at how the orbiter lets you live in space.

Living Environment

The shuttle orbiter provides an environment where you can live and work in space.

It must be able to do the following:

Now let's look at the orbiter's systems and how it achieves these functions.

­Th­e­ orbiter must provide you with an environm­ent similar to Earth. You must have air, food, water, and a comfortable temperature. The orbiter must also take away the wastes that your body produces (carbon dioxide, urine, feces) and protect you from fire. Let's look at these various aspects of the orbiter's life support system.

On board the space shuttle, you need to have the following:

­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:

Besides air, water is the most important quantity aboard the orbiter. Water is made from liquid oxygen and hydrogen in the space shuttle's fuel cells (the fuel cells can make 25 lb (11 kg) of water per hour). The water passes through a hydrogen separator to eliminate any trapped hydrogen gas (excess hydrogen gas is dumped overboard). The water is then stored in four water storage tanks located in the lower deck. Each tank can hold 165 lb (75 kg). The water tanks are pressurized by nitrogen so that water can flow to the mid-deck for use by the crew. Drinkable water is then filtered to remove microbes and can be warmed or chilled through various heat exchangers depending upon the use (food preparation, consumption, personal hygiene). Excess water produced by the fuel cells gets routed to a wastewater tank and subsequently dumped overboard.

Outer space is an extremely cold environment and temperatures will vary drastically in different parts of the orbiter. You might think that heating the orbiter would be a problem. However, the electronic equipment generates more than enough heat for the ship. The problem is getting rid of the excess heat. So the temperature control system has to carry out two major functions:

To do this, the shuttle has two methods to handle temperature control:

­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:

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:

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.

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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.

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:

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 space suit.

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:

­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.

Now let's look at the kind of work you'll be doing during your shuttle mission.

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).

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.

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.

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:

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:

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).

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).

Shuttle flight path for landing

When the orbiter is 2,000 ft (610 m) above the ground, the commander pulls up the nose to slow the rate of descent. The pilot deploys the landing gear and the orbiter touches down. The commander brakes the orbiter and the speed brake on the vertical tail opens up. A parachute is deployed from the back to help stop the orbiter. The parachute and the speed brake on the tail increase the drag on the orbiter. The orbiter stops about midway to three-quarters of the way down the runway.

After landing, the crew goes through the shutdown procedures to power down the spacecraft. This process takes about 20 minutes. During this time, the orbiter is cooling and noxious gases, which were made during the heat of re-entry, blow away. Once the orbiter is powered down, the crew exits the vehicle. Ground crews are on-hand to begin servicing the orbiter.

The shuttle's technology is constantly being updated. Next, we'll look at future improvements to the shuttle.

­As ­mentioned previously, falling debris (foam insulation) from the ET damaged the shuttle orbiter, leading to Columbia's break up upon re-entry. To bring the shuttles back to flight status, NASA has focused on three major areas:

Let's take a closer look at each of these.

ET Redesign

The ET holds cold liquefied gases as fuel (oxygen, hydrogen). Because the temperatures are so cold, water from the atmosphere condenses and freezes on the surfaces of the ET and the fuel lines leading in to the orbiter. Ice can fall off the ET itself or cause the ET foam insulation to crack and fall off. In addition to ice, if any of the liquid gas were to leak and get under the foam, it would expand and cause the foam insulation to crack. So much of the ET redesign has focused on eliminating places where condensation can occur.

First, the bipod fitting is the forward point where the ET attaches to the underside of the orbiter. Engineers and technicians discovered that this point is especially susceptible to icing. In the past, ramps of foam insulation over this part prevented ice buildup; however, this insulation fell off frequently, thereby presenting a danger to the orbiter.

In the redesign, the insulation has been removed and the fitting now mounts across the top of a copper plate, which contains electric heaters. The heater can warm the fitting and prevent ice buildup.

Second, liquid nitrogen is used to purge the intertank connection of any potentially explosive hydrogen gas. However, liquid nitrogen can freeze around the bolts in that area and cause foam insulation to break off. The bolts in that area have been redesigned to prevent leaks of liquid nitrogen.

Third, five liquid oxygen feedline bellows lie along the umbilicus that connects the liquid oxygen tank with the main engines and are attached to the liquid hydrogen tank. The bellows compensate for expansions and contractions that occur when the liquid hydrogen tank is filled and emptied. The bellows prevent stresses on the feedline. Previously, the foam insulation overlying the bellows was angled. This angle allowed water vapor to condense, run between the foam insulation, and freeze, thereby breaking the foam. To correct this problem, the foam skirt of this joint has been extended over the insulation below and squared off so that water cannot run between the foam.

­Expl­osive bolts separate the SRBs from the external tank when the SRBs burn out in flight. Engineers assessed that fragments of the bolts could also damage the shuttle. They designed a bolt catcher to prevent the bolts from damaging the ET or hitting the orbiter.

To detect falling debris and possible damage to the shuttle, NASA has done the following:

Finally, engineers and technicians have installed 66 tiny accelerometers and 22 temperature sensors in the leading edge of both wings on the orbiter. The devices will detect the impact of any debris hitting the orbiter's wings.

The entire purpose of the imaging and wing sensors is to detect possible damage from falling debris. Engineers and administrators can analyze these images and make recommendations to the crew during the mission.

NASA also formulated ideas on how to repair damaged shuttles while in flight, including:

These ideas were tested aboard the shuttle Discovery in June 2005.

­Near the end of the Apollo space program, NASA officials were looking at the future of the American space program. They were using one-shot, disposable rockets. What they needed was a reliable, less expensive rocket, perhaps one that was reusable. The idea of a reusable "space shuttle" that could launch like a rocket but land like an airplane was appealing and would be a great technical achievement.

NASA began design, cost and engineering studies on a space shuttle and many aerospace companies also explored the concepts. In 1972, President Nixon announced that NASA would develop a reusable space shuttle or space transportation system (STS). NASA decided that the shuttle would consist of an orbiter attached to solid rocket boosters and an external fuel tank and awarded the prime contract to Rockwell International.

At that time, spacecraft used ablative heat shields that would burn away as the spacecraft re-entered the Earth's atmosphere. However, to be reusable, a different strategy would have to be used. The designers of the space shuttle came up with an idea to cover the space shuttle with many insulating ceramic tiles that could absorb the heat of re-entry without harming the astronauts.

Remember that the shuttle was to fly like a plane, more like a glider, when it landed. A working orbiter was built to test the aerodynamic design, but not to go into outer space. The orbiter was called the Enterprise after the "Star Trek" starship. The Enterprise flew numerous flight and landing tests, where it was launched from a Boeing 747 and glided to a landing at Edwards Air Force Base in California.

Finally, after many years of construction and testing (i.e. orbiter, main engines, external fuel tank, solid rocket boosters), the shuttle was ready to fly. Four shuttles were made (Columbia, Discovery, Atlantis, Challenger). The first flight was in 1981 with the space shuttle Columbia, piloted by astronauts John Young and Robert Crippen. Columbia performed well and the other shuttles soon made several successful flights.

In 1986, the shuttle Challenger exploded in flight and the entire crew was lost. NASA suspended the shuttle program for several years, while the reasons for the disaster were investigated and corrected. After several years, the space shuttle flew again and a new shuttle, Endeavour, was built to replace Challenger in the shuttle fleet.

In 2003, while re-entering the Earth's atmosphere, the shuttle Columbia broke up over the United States. NASA grounded the space shuttle program after the accident and worked feverishly to make changes and return the shuttles to flight. In 2006, the shuttle Discovery lost foam from its external fuel tank. Once again, the program was grounded and scientists struggled to solve the problem. The Discovery launched twice in 2006, once in July and again in December. According to NASA, the July 2006 launch was the most photographed shuttle mission in history. The Atlantis launched in September 2006, after delays due to weather, a problem with the fuel cell and a faulty sensor reading.

While the space shuttles are a great technological advance, they are limited as to how much payload they can take into orbit. The shuttles are not the heavy lift vehicles like the Saturn V or the Delta rockets. The shuttle cannot go to high altitude orbits or escape the Earth's gravitational field to travel to the Moon or Mars. NASA is currently exploring new concepts for launch vehicles that are capable of going to the Moon and Mars.

For more information on space shuttles and related topics, check out the links on the following page.