How Space Shuttles Work (II)

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“Man always wanted to explore and in his lust for exploring new worlds, has developed one of the most complicated and beautiful machines of all time, to unlock the secrets of the universe”

How Space shuttles work

A project by: Ankit Bahuguna

Class XII-A



How Space Shuttles workAnkit Bahuguna (XII-A)

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How Space Shuttles Work

In its 25-year history, the space shuttle program has seen exhilarating highsand devastating lows. The fleet has taken astronauts on dozens of

successful missions, resulting in immeasurable scientific gains. But thissuccess has had a serious cost. In 1986, the Challenger exploded duringlaunch. In 2003, the Columbia broke up during re-entry over Texas. Since theColumbia accident, the shuttles have been grounded pending redesigns toimprove their safety. The 2005 shuttle Discovery was supposed to initiate thereturn to flight, but a large piece of insulating foam broke free from its externalfuel tank, leaving scientists to solve the mystery and the program grounded oncemore.

In this article, we examine the monumental technology behind America's shuttle

program, the mission it was designed to carry out, and the extraordinary effortsthat NASA has done to return the shuttle to flight.

Liftoff of the space shuttle {Photo courtesy: NASA}




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The End of the Space Shuttle Program? The future of the space shuttle program rides on the success ofthe Discovery's launch on July 1, 2006. If it has a problem-free

liftoff and mission, NASA plans two more flights in 2006 with thegoal of finishing the International Space Station and fixing the

Hubble Telescope. But if it's damaged at launch, NASA chiefMichael Griffin says, "I would be moving to shut the programdown [...] I think, at that point, we're done". If the program shutsdown, the next trip to space may not take place for another five

years.

The Basics Let's look at the parts of the space shuttle and a typical mission.

The space shuttle consists of the following major components:

two solid rocket boosters (SRB) - critical for the launchexternal fuel tank (ET) - carries fuel for the launchorbiter - carries astronauts and payload

A typical shuttle mission is as follows:

getting into orbit launch - the shuttle lifts off the launching padascentorbital maneuvering burn

orbit - life in spacere-entry landing

A typical shuttle mission lasts seven to eight days, but can extend to asmuch as 14 days depending upon the objectives of the mission.

Getting Into Orbit

To lift the 4.5 million pound (2.05 million kg) shuttle from the pad to orbit (115 to400 miles/185 to 643 km) above the Earth, the shuttle uses the followingcomponents:

two solid rocket boosters (SRB)three main engines of the orbiterthe external fuel tank (ET)orbital maneuvering system (OMS) on the orbiter

Let's look at these components closely.




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Solid Rocket Boosters

The SRBs are solid rockets that provide most of themain force or thrust (71 percent) needed to lift the

space shuttle off the launch pad. In addition, theSRBs support the entire weight of the space shuttleorbiter and fuel tank on the launch pad. Each SRBhas the following dimensions, parameters and parts:

solid rocket motor - case, propellant, igniter,nozzlesolid propellant

fuel - atomized aluminum (16 percent)oxidizers - ammonium perchlorate (70percent)

catalyst - iron oxide powder (0.2 percent)binder - polybutadiene acrylic acid acrylonite (12 percent)curing agent - epoxy resin (2 percent)

jointed structure synthetic rubber o-rings between joints flight instruments recovery systems

parachutes (drogue, main)floatation devicessignaling devices

explosive charges for separating from the external tank

thrust control systems self-destruct mechanism

Because the SRBs are solid rocket engines, once they are ignited, they cannotbe shut down. Therefore, they are the last component to light at launch.

The Trouble with O-rings During the January, 1986 launch of Challenger, the temperature wasbelow zero. The cold shrank the rubber o-rings and they did not sealthe joints properly. During ascent, hot gases escaped through one ofthe joints of the SRB. Like a blowtorch, the gases cut through the thin

skin of the ET and ignited the liquid hydrogen fuel. Challenger broke upand the crew was lost. NASA re-designed the SRB joints, implementednew rules regarding launches in cold weather, and built a new system

for the crew to escape from the shuttle during ascent.

SRB Dimensions

1. height - approximately 150ft (46 m)

2. diameter - 12 ft (3.7 m)3. weight:

empty - 192,000 lbs (87,090kg)full - 1,300,000 lbs (589,670kg)

4. thrust - 2.65 million lb (11.7million N)




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

Photo courtesy NASA One of the space shuttle's main engines

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

The engines burn liquid hydrogen and liquid oxygen, whichare stored in the external fuel tank (ET), at a ratio of 6:1.They draw liquid hydrogen and oxygen from the ET at anamazing rate, equivalent to emptying a family swimming

pool every 10 seconds! The fuel is partially burned in apre-chamber to produce high pressure, hot gases thatdrive the turbo-pumps (fuel pumps). The fuel is then fullyburned in the main combustion chamber and the exhaustgases (water vapor) leave the nozzle at approximately

6,000 mph (10,000 km/h). Each engine can generate between 375,000 and470,000 lb (1,668,083 to 2,090,664 N) of thrust; the rate of thrust can becontrolled from 65 percent to 109 percent maximum thrust. The engines are




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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 is158 ft (48 m) long and has a diameter of 27.6 ft (8.4 m). When empty, the ETweighs 78,000 lb (35,455 kg). It holds about 1.6 million lb (719,000 kg) ofpropellant with a total volume of about 526,000 gallons (2 million liters).

The ET is made of aluminum and aluminum composite materials. It has twoseparate tanks inside, the forward tank for oxygen and the aft tank forhydrogen, separated by an intertank region. Each tank has baffles to dampenthe 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 mainengines. 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 47,400gallons/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, protectsthe fuel from heat that builds up on the ET skin in flight, and minimizes iceformation. When Columbia launched in 2003, pieces of the insulating foam brokeoff the ET and damaged the left wing of the orbiter, which ultimately causedColumbia to break up upon re-entry.

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




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Orbiter and Life in Space

The two orbital maneuvering systems' (OMS) engines are located in pods onthe aft section of the orbiter, one on either side of the tail. These engines placethe 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 incontact, they ignite and burn automatically (i.e., no spark required) in theabsence of oxygen. The fuel and oxidizer are kept in separate tanks, eachpressurized 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-loadedsolenoid valves that close the lines. Pressurized nitrogen gas, from a small tanklocated near the engine, opens the valves and allows the fuel and oxidizer to flowinto the combustion chamber of the engine. When the engines shut off, thenitrogen goes from the valves into the fuel lines momentarily to flush the lines ofany remaining fuel and oxidizer; this purge of the line prevents any unwantedexplosions. 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 orbitalmaneuver. Each OMS engine can produce 6,000 lb (26,400 N) of thrust. TheOMS engines together can accelerate the shuttle by 2 ft/s2 (0.6 m/s2). Thisacceleration 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 invelocity. Orbital adjustments take about 2 ft/s (0.61 m/s) change in velocity. Theengines can start and stop 1,000 times and have a total of 15 h burn time.




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

The Lift off of a space shuttle: minute by minute

As the shuttle rests on the pad fully fueled, it weighs about

4.5 million pounds or 2 million kg. The shuttle rests on theSRBs as pre-launch and final launch preparations are goingon through T minus 31 seconds:

1. T minus 31 s - the on-board computers take over thelaunch sequence.

2. T minus 6.6 s - the shuttle's main engines ignite oneat a time (0.12 s apart). The engines build up to more than 90 percent oftheir maximum thrust.

3. T minus 3 s - shuttle main engines are in lift-off position.4. T minus 0 s -the SRBs are ignited and the shuttle lifts off the pad.

5. T plus 20 s - the shuttle rolls right (180 degree roll, 78 degree pitch).6. T plus 60 s - shuttle engines are at maximum throttle.7. T plus 2 min - SRBs separate from the orbiter and fuel tank at an altitude

of 28 miles (45 km). Main engines continue firing.

Parachutes deploy from the SRBs.SRBs will land in the ocean about 140 miles (225 km) off the coast ofFlorida.Ships will recover the SRBs and tow them back to Cape Canaveral forprocessing and re-use.

8. T plus 7.7 min - main engines throttled down to keep acceleration below3g's so that the shuttle does not break apart.9. T plus 8.5 min - main engines shut down.10.T plus 9 min - ET separates from the orbiter. The ET will burn up upon re-

entry.11.T plus 10.5 min - OMS engines fire to place you in a low orbit.12.T plus 45 min - OMS engines fire again to place you in a higher, circular

orbit (about 250 miles/400 km).

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

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




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

do is to open the cargo bay doors to cool the orbiter.




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The orbiter consists of the following parts:

crew compartment - where you will live and workforward fuselage (upper, lower parts) - contains support equipment(fuel cells, gas tanks) for crew compartment

forward reaction control system (RCS) module - contains forwardrocket jets for turning the orbiter in various directionsmovable airlock - used for spacewalks and can be placed inside the crewcompartment or inside the cargo baymid-fuselage

contains essential parts (gas tanks, wiring, etc.) to connect the crewcompartment with the aft enginesforms the floor of the cargo bay

cargo bay doors - roof of the cargo bay and essential for cooling theorbiterremote manipulator arm - located in the cargo bay

moves large pieces of equipment in and out of the cargo bayplatform for spacewalking astronautsaft fuselage - contains the main enginesOMS/RCS pods (2) - contain the orbital maneuvering engines and the aftRCS module; turn the orbiter and change orbitsairplane parts of the orbiter - fly the shuttle upon landing

wingstailbody flap




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

The crew compartment has three decks:

flight deck - uppermost deckforward deck - contains all of the controls and warning systems for thespace shuttle (also known as the cockpit)seats - commander, pilot, specialist seats (two)aft deck - contains controls for orbital operations

maneuvering the orbiter while in orbit (rendezvous, docking)deploying payloadsworking the remote manipulator arm

mid-deck living quarters (galley, sleeping bunks, toilet)stowage compartments (personal gear, mission-essential equipment,experiments)exercise equipmentairlock - on some flightsentry hatch

lower deck (equipment bay) - contains life support equipment, electricalsystems, etc.




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Now that you have seen the parts of the orbiter, let's look closely at how theorbiter lets you live in space.

Life in Space The shuttle orbiter provides an environment where you can live and work in

space.

Photo courtesy NASA Space shuttle Endeavour (STS113) in orbit as seen from the International Space Station.

It must be able to do the following:

provide life support - everything the Earth does for usatmosphere control, supply and recyclingwatertemperature controllightfood supplywaste removalfire protection

change position and change orbits let you talk with ground-based flight controllers (communications andtracking)find its way around (navigation)

make electrical power coordinate and handle information (computers)enable you to do useful work

launch/retrieve satellitesconstruction - such as building the International Space Station conduct experiments

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




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Life Support

The orbiter must provide you with an environment similar to Earth. You musthave air, food, water, and a comfortable temperature. The orbiter must also takeaway 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 lifesupport system.

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

atmosphere similar to Earthcarbon dioxide removedcontaminating or trace gases removednormal humid environment

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 andout. The space shuttle must provide a similar atmosphere. To do this, the orbitercarries 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 offour tanks). The cabin pressurization system combines the gases in the correctmixture at normal atmospheric pressure. While in orbit, only one oxygen-nitrogensystem is used to pressurize the orbiter. During launch and landing, bothsystems of each gas are used.

Five loops of fans circulate the atmosphere. The circulated air picks up carbondioxide, heat and moisture:

Chemical carbon dioxide canisters remove carbon dioxide by reacting itwith lithium hydroxide. These canisters are located in the lower deck of thecrew compartment and changed every 12 hours.Filters and charcoal canisters remove trace odors, dust and volatilechemicals from leaks, spills and outgassing.A cabin heat exchanger in the lower deck cools the air and condensesthe moisture, which collects in a slurper. Water from the slurper is movedwith air to a fan separator, which uses centrifugal force to separate waterfrom air. The air is recirculated and the water goes to a wastewater tank.

Besides air, water is the most important quantity aboard the orbiter. Water ismade from liquid oxygen and hydrogen in the space shuttle's fuel cells (the fuelcells can make 25 lb (11 kg) of water per hour). The water passes through ahydrogen separator to eliminate any trapped hydrogen gas (excess hydrogengas is dumped overboard). The water is then stored in four water storage tankslocated in the lower deck. Each tank can hold 165 lb (75 kg). The water tanks arepressurized by nitrogen so that water can flow to the mid-deck for use by thecrew. Drinkable water is then filtered to remove microbes and can be warmed orchilled through various heat exchangers depending upon the use (food




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preparation, consumption, personal hygiene). Excess water produced by the fuelcells gets routed to a wastewater tank and subsequently dumped overboard.

Outer space is an extremely cold environment and temperatures will varydrastically in different parts of the orbiter. You might think that heating the orbiter

would be a problem. However, the electronic equipment generates more thanenough heat for the ship. The problem is getting rid of the excess heat. So thetemperature control system has to carry out two major functions:

Distribute heat where it is needed on the orbiter (mid-fuselage and aftsections) so that vital systems do not freeze in the cold of space.Get rid of the excess heat.

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

Passive methods - generally simple, handle small heat loads and require

little maintenanceInsulating materials (blankets), surface coatings, paints - reduceheat loss through the walls of the various components just like yourhome insulation.Electrical heaters - use electrically-heated wires like a toaster to heatvarious areas.

Active methods - more complex, use fluid to handle large heat loads,require maintenance

Cold plates - metal plates that collect heat by direct contact withequipment or conduction Heat exchangers - collect heat from equipment using fluid. The

equipment radiates heat to a fluid (water, ammonia) which in turnpasses heat on to freon. Both fluids are pumped and recirculated toremove heat.Pumps, lines, valves - transport the collected heat from one area toanother.Radiators - located on the inside surfaces of the cargo bay doors thatradiate the collected heat to outer spaceFlash evaporator/ammonia boilers - these devices are located in theaft fuselage and transfer heat from Freon coolant loops overboardwhen cargo bay doors are closed or when cargo bay radiators areoverloaded.

Flash evaporator

1. Freon coolant loops wrap around an inner core.2. The evaporator sprays water on the heated core.3. The water evaporates removing heat.4. The water vapor is vented overboard.

Ammonia boiler




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5. Freon coolant loops pass through a tank ofpressurized ammonia.

6. Heat released from the freon causes the ammonia toboil.

7. Ammonia vapor is dumped overboard.

The cabin heat exchanger also controls the cabin temperature. It circulates coolwater 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 heatto other orbiter systems (e.g., cryogenic gas tanks, hydraulic systems) andradiates excess heat to outer space.

The orbiter has internal fluorescent floodlights that illuminate the crewcompartment. 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 severalforms (dehydrated, low moisture, heat-stabilized, irradiated, natural and fresh).The orbiter has a galley-style kitchen module along the wall next to the entryhatch, which is equipped with the following:

food storage compartmentsfood warmersa food preparation area with warm and cold water outletsmetal 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 areused to clean surfaces, filters and the astronauts. Trash is separated into wettrash bags and dry trash bags, and the wet trash is placed in an evaporator thatwill remove the water. All trash bags are stowed in the lower deck to be returnedto Earth for disposal. Solid waste from the toilet is compacted, dried and storedin bags where it is returned to Earth for disposal (burning). Liquid waste from thetoilet 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:

area smoke detectors on each decksmoke detectors in each rack of electrical equipmentalarms and warning lights in each modulenon-toxic portable fire extinguishers (carbon dioxide-based)personal breathing apparatus - mask and oxygen bottle for each crewmember




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After a fire is extinguished, the atmosphere control system will filter the air toremove particulates and toxic substances.

Positioning, Communication and Navigation

To change the direction that the orbiter is pointed (attitude), you must use thereaction control system (RCS) located on the nose and OMS pods of the aftfuselage.

Veiw of the front of the orbitor:

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 nitrogentetroxide oxidizer just like the OMS engines described previously. Attitude




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changes are required for deploying satellites or for pointing (mappinginstruments, telescopes) at the Earth or stars

To change orbits (e.g., rendezvous, docking maneuvers), you must fire the OMSengines. 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 You must be able to talk with flight controllers on the ground daily for the routineoperation of the mission. In addition, you must be able to communicate with eachother inside the orbiter or its payload modules and when conducting spacewalksoutside.

NASA's Mission Control in Houston will send signals to a 60 ft radio antenna atWhite Sands Test Facility in New Mexico. White Sands will relay the signals to apair of Tracking and Data Relay satellites in orbit 22,300 miles above the Earth.

The satellites will relay the signals to the the space shuttle. The system works inreverse as well.

The orbiter has two systems for communicating with the ground:

S-band - voice, commands, telemetry and data filesKu-band (high bandwidth) - video and transferring two-way data files

The orbiter has several intercom plug-in audio terminal units located throughoutthe crew compartment. You will wear a personal communications control with aheadset. The communications control is battery-powered and can be switched

from intercom to transmit functions. You can either push to talk and release tolisten or have a continuously open communication line. To talk withspacewalkers, the system uses a UHF frequency, which is picked up in theastronaut's spacesuit.

The orbiter also has a series of internal and external video cameras to see insideand outside.

Navigation, Power and Computers The orbiter must be able to know precisely where it is in space, where otherobjects 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 itis pointing (attitude), the orbiter has several gyroscopes. All of this information isfed into the flight computers for rendezvous and docking maneuvers, which arecontrolled in the aft station of the flight deck.

All of the on-board systems of the orbiter require electrical power. Three fuelcells 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 midfuselage to make electricity and water. Like a power grid on Earth, the orbiter




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has a distribution system to supply electrical power to various instrument baysand 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 controlcritical flight systems. The computers monitor equipment and talk to each other

and vote to settle arguments. Computers control critical adjustments especiallyduring launch and landing:

operations of the orbiter (housekeeping functions, payload operations,rendezvous/docking)interface with the crew (IBM Thinkpads with microprocessors andWindows operating systems)caution and warning systemsdata acquisition and processing from experimentsflight maneuvers

Pilots essentially fly the computers, which fly the shuttle. To make this easier, theshuttles have a Multifunctional Electronic Display Subsystem (MEDS), which is anew, 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 forshuttle pilots to interact with the orbiter

The glass cockpit




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Useful Work

The Shuttle was designed to deploy and retrieve satellites as well as deliverpayloads 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 elbowand wrist joint. You can control the RMS from the aft flight deck. The RMS cangrab payloads (satellites) from the cargo bay and deploy them, or grab on topayloads and place them into the bay.

In the past, the shuttle was used for delivering satellites and conductingexperiments in space. Within the mid-deck, there are racks of experiments to beconducted during each mission. When more space was needed, the missionused 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-deckof the crew compartment. It provided a "shirt-sleeve" environment in which you

could work. The Spacelab was lost along with Columbia in 2003. Now, mostexperiments will be conducted aboard the International Space Station (ESA isbuilding 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 will be building the International Space Station. Theshuttle will deliver components built on Earth. Astronauts will use the RMS toremove components from the cargo bay and to help attach them to existingmodules in space station.




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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 themission 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. Youwill have a toilet and personal hygiene facilities for use. You may have to performspacewalks to accomplish the mission objectives. This will involve getting into aspace suit and going through depressurization procedures in the airlock.

When your mission objectives have been accomplished, it will be time to return toEarth. Let's look at this process in the next section.

Return to Earth and Return to Flight 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 asafe landing.

When a mission is finished and the shuttle is halfway around the world from thelanding site (Kennedy Space Center, Edwards Air Force Base), mission controlgives the command to come home, which prompts the crew to:




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1. Close the cargo bay doors. In most cases, they have been flying nose-firstand upside down, so they then fire the RCS thrusters to turn the orbiter tailfirst.

2. Once the orbiter is tail first, the crew fires the OMS engines to slow theorbiter down and fall back to Earth; it will take about 25 minutes before the

shuttle reaches the upper atmosphere.3. During that time, the crew fires the RCS thrusters to pitch the orbiter overso that the bottom of the orbiter faces the atmosphere (about 40 degrees)and they are moving nose first again.

4. Finally, they burn leftover fuel from the forward RCS as a safetyprecaution because this area encounters the highest heat of re-entry.

Columbia's Accident On the morning of February 1st, 2003, the space shuttle

Columbia broke up during re-entry, more than 200,000 feetabove 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. Theinsulation damaged the heat protection tiles on the wing.

When Columbia re-entered the atmosphere, hot gasesentered 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 airmolecules and builds up heat from friction (approximately 3000 degrees F, or1650 degrees C). The orbiter is covered with ceramic insulating materialsdesigned to protect it from this heat. The materials include:

Reinforced carbon-carbon (RCC) on the wing surfaces and undersideHigh-temperature black surface insulation tiles on the upper forwardfuselage and around the windowsWhite Nomex blankets on the upper payload bay doors, portions of theupper wing and mid/aft fuselageLow-temperature white surface tiles on the remaining areas

These materials are designed to absorb large quantities of heat withoutincreasing their temperature very much (i.e., high heat capacity). During re-entry,the aft steering jets help to keep the orbiter at its 40 degree attitude. The hotionized gases of the atmosphere that surround the orbiter prevent radiocommunication with the ground for about 12 minutes (i.e., ionization blackout).




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Photo courtesy NASA Artist's concept of a shuttle re-entry

When re-entry is successful, the orbiter encounters the main air of theatmosphere and is able to fly like an airplane. The orbiter is designed from alifting body design with swept back "delta" wings. With this design, the orbiter cangenerate 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 isabout 140 miles (225 km) away from the landing site and 150,000 feet (45,700m) high. At 25 miles (40 km) out, the shuttle's landing computers give up controlto 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 anddrop the altitude. During the final approach, the commander steepens the angleof descent to minus 20 degrees (almost seven times steeper than the descent ofa commercial airliner).

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 theorbiter touches down. The commander brakes the orbiter and the speed brake onthe vertical tail opens up. A parachute is deployed from the back to help stop theorbiter. The parachute and the speed brake on the tail increase the drag on theorbiter. The orbiter stops about midway to three-quarters of the way down therunway.




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Photo courtesy NASA Space shuttle orbiter touching down

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

Photo courtesy NASA Parachute deployed to help stop the orbiter on landing




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Photo courtesy NASA Orbiter being serviced just after landing

Undoubtedly, the space shuttle computers will be overhauled as computertechnology improves. Space shuttles may also have touch screen controls in thefuture.

Return to Flight

As mentioned previously, falling debris (foaminsulation) 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 hasfocused on three major areas:

Redesign the ET to prevent insulation fromdamaging the shuttle orbiterImprove inspection of the shuttle to detectdamageFind ways to repair possible damage to the orbiter while in orbitFormulate contingency plans for the crew of a damaged shuttle to stay atthe ISS until rescue

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

Photo courtesy NASA




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ET Redesign

The ET holds cold liquefied gases as fuel (oxygen, hydrogen). Because thetemperatures are so cold, water from the atmosphere condenses and freezes onthe 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 toice, if any of the liquid gas were to leak and get under the foam, it would expandand cause the foam insulation to crack. So much of the ET redesign has focusedon eliminating places where condensation can occur.

Photo courtesy NASA

ET redesign

First, the bipod fitting is the forward point where the ET attaches to the undersideof the orbiter. Engineers and technicians discovered that this point is especiallysusceptible to icing. In the past, ramps of foam insulation over this part preventedice buildup; however, this insulation fell off frequently, thereby presenting adanger to the orbiter.




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Photo courtesy NASA. Photo credit: Lockheed martin/NASA Michoud The foam ramps that protected ET bipod fittings from ice build up(above) have been replaced with a new joint that is electrically heated (below).

Photo courtesy NASA. Photo credit: Lockheed martin/NASA Michoud

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 canwarm the fitting and prevent ice buildup.

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




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Photo courtesy NASA. Photo credit: Lockheed martin/NASA Michoud The foam ramps that protected the liquid oxygen feedline bellow

were angled and could permit ice build up (above). They havebeen replaced with a design called a drip-lip that prevents ice

build up (below).

Photo courtesy NASA. Photo credit: Lockheed martin/NASA Michoud

Third, five liquid oxygen feedline bellows lie along the umbilicus that connects theliquid oxygen tank with the main engines and are attached to the liquid hydrogentank. The bellows compensate for expansions and contractions that occur when




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the liquid hydrogen tank is filled and emptied. The bellows prevent stresses onthe 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 his problem, the foam skirt ofthis joint has been extended over the insulation below and squared off so that

water cannot run between the foam.

SRB Modification and Improved Imaging

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

Photo courtesy NASA A bolt catcher (above) was designed to prevent the explosive bolts on the

SRBs (below) from damaging the ET or the orbiter




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Photo courtesy NASA

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

One hundred and seven cameras (Infrared, High Speed Digital Video,HDTV, 35 mm, 16 mm) have been placed on and around the launch padto film the shuttle during liftoff.Ten sites within 40 miles of the launch pad have been equipped withcameras to film the shuttle during ascent.On days of heavier cloud cover when ground cameras will be obscured,two WB-57 aircraft will film the shuttle from high altitude as it ascends.Three radar tracking facilities (one with C-band and two with Dopplerradar) will monitor the shuttle to detect debris.New digital video cameras have been installed on the ET to monitor theunderside of the orbiter and relay the data to the ground through antennaeinstalled in the ET.Cameras have been installed on the SRB noses to monitor the ET.The shuttle crew has new handheld digital cameras to photograph the ETafter separation. The images will be downloaded to laptops on the orbiterand then transmitted to the ground.A digital spacewalk camera will be used for astronauts to inspect theorbiter while in orbit.Canada made a 50-foot long extension, called the Remote ManipulatorSystem/Orbiter Booster Sensor System (RMS/OBSS), that can beattached to the robotic arm. This extension will allow the RMS to reach theunderside of the orbiter. Cameras mounted on this extension willphotograph the underside for damage.




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Photo courtesy NASA The RMS/OBSS will allow astronauts to inspect the underside andleading edge of the wings for damage.

Finally, engineers and technicians have installed 66 tiny accelerometers and 22temperature sensors in the leading edge of both wings on the orbiter. Thedevices 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 damagefrom falling debris. Engineers and administrators can analyze these images andmake recommendations to the crew during the mission.

Repair Damage In-Flight

NASA is currently formulating ideas on how to repair damaged shuttles while inflight. These ideas include:

Applying pre-ceramic polymers to small cracksUsing small mechanical plugs made of carbon-silicone carbides to repairdamage up to 6 inches in diameter

How the orbiter is repaired will depend upon where it is in flight. If it is docked

with the ISS, astronauts could make repairs using the station's robotic arm as aplatform for repair spacewalks. If the shuttle is alone in orbit, the RMS/IBSSmight be used as a platform for spacewalkers. These ideas will be tested on theupcoming return to flight mission of Discovery .

Discovery's return to flight mission objectives will be as follows:

Test and evaluate new safety proceduresDemonstrate shuttle repair techniques during a spacewalkReplace a failed gyroscope on the ISS




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Install the External Stowage Platform, a large shelf for storing parts, on theISSTransfer the Raffaello module to the ISS (Like a moving van, Raffaello isused for transporting supplies to the station.)

A Brief History and the FutureNear the end of the Apollo space program, NASA officials were looking at thefuture of the American space program. They were using one-shot, disposablerockets. What they needed was a reliable, less expensive rocket, perhaps onethat was reusable. The idea of a reusable "space shuttle" that could launch like arocket but land like an airplane was appealing and would be a great technicalachievement.

NASA began design, cost and engineering studies on a space shuttle and manyaerospace companies also explored the concepts. In 1972, President Nixon

announced that NASA would develop a reusable space shuttle or spacetransportation system (STS). NASA decided that the shuttle would consist of anorbiter attached to solid rocket boosters and an external fuel tank and awardedthe prime contract to Rockwell International.

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

Photo courtesy NASA The Enterprise separates from a Boeing 747 to begin one of its flight and landing

tests

Remember that the shuttle was to fly like a plane, more like a glider, when itlanded. A working orbiter was built to test the aerodynamic design, but not to go




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into outer space. The orbiter was called the Enterprise after the "Star Trek"starship. The Enterprise flew numerous flight and landing tests, where it waslaunched from a Boeing 747 and glided to a landing at Edwards Air Force Basein California.

Finally, after many years of construction and testing(i.e. orbiter, main engines, external fuel tank, solidrocket boosters), the shuttle was ready to fly. Fourshuttles were made (Columbia, Discovery, Atlantis,Challenger). The first flight was in 1981 with thespace shuttle Columbia, piloted by astronauts JohnYoung and Robert Crippen. Columbia performed welland 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 shuttleflew again and a new shuttle, Endeavour, was built to replace Challenger in theshuttle fleet.

In 2003, while re-entering the Earth's atmosphere, the shuttle Columbia broke upover the United States. NASA grounded the space shuttle program after theaccident 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. Thefuture of the space shuttle program now rides on the July 2006 launch of theDiscovery.

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

Enterprise Enterprise is now on displayat the National Air & SpaceMuseum's Steven F. Udvar-Hazy Center near DullesInternational Airport inWashington, DC.



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Bibliography

The Great Shuttle Debate The Space Shuttle Reference Manual Space Shuttle Operational Data Book

Shuttle Press Kit STS-97: Space-Shuttle Orbiter Systems Manual Space Shuttle Operational Data Book: Statistics Space Shuttle News Reference Manual (1988) Space Shuttle Basics The Space Transportation System The Space Shuttle Virtual Tour United Space Alliance: The Space Shuttle Space.com: Interactive Space Shuttle Discovery School Online: The Space Shuttle Lesson Plan

Books

The Space Shuttle Operators Manual by Kerry Mark Joels, Gregory P.Kennedy (Contributor), David Larkin (Contributor)To Rise from Earth: An Easy-To-Understand Guide to Space Flight byWayne LeeEngineering Ethics: Balancing Cost, Schedule and Risk : Lessons Learnedfrom the Space Shuttle by Rosa Lynn B. Pinkus (Editor), Larry J. Shuman,Norman P. HummonColumbia: First Flight of the Space Shuttle (Countdown to Space) byMichael D. ColeChallenger: America's Space Tragedy (Countdown to Space) by Michael D.ColeFlying Without Wings: Nasa Lifting Bodies and the Birth of the SpaceShuttle by Milton O. Thompson, Curtis PeeblesJohn Glenn Returns to Orbit: Life on the Space Shuttle (Countdown toSpace) by Carmen Bredeson - ages 9-12Space Shuttle (Fast Forward Series) by Mark Bergin, David Salariya - ages9-12

On the Shuttle: Eight Days in Space by Barbara Bondar, Roberta Bondar(Contributor) - ages 9-12

How Space Shuttles Work (II)

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