NASA Space Shuttle News Reference 1981

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Space ShuttleNews Reference

N/ ANational Aeronautics andSpace Administration


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Foreword


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CONTENTS

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34

56

89

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ABC

INTRODUCTION ....................... 1-1SPACE TRANSPORTATION SYSTEMPROPULSION .......................... 2-1Space Shuttle Main Engines ............ 2-3Solid Rocket Boosters ................. 2-17External Tank ......................... 2-33ORBITER STRUCTURE ................. 3-1ORBITER SYSTEMS ................... 4-1Propulsion ............................ 4-3Power Generation ..................... 4-9Environmental Control and Life SupportSystem ............................... 4-17Thermal Protection .................... 4-25Purge, Vent, and Drain System .......... 4-33Avionics .............................. 4-37ORBITER CREW ACCOMMODATIONSAND EQUIPMENT ...................... 5-1MISSION OPERATIONS ANDSUPPORT ............................. 6-1Launch and Landing Facilities andOperations ............................ 6-3Tracking and Communications Network.. 6-43Flight Operations and MissionControl ............................... 6-49FLIGHTCREW COMPLEMENT ANDCREW TRAINING ...................... 7-1TESTING ............................. 8-1MANAGEMENT ........................ 9-1CONTRACTORS ....................... 10-1APPENDIXESAcronyms and Abbreviations ............ A-1Glossary ............................. B-1Unit Conversion Table ................. C-1

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1. INTRODUCTION


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1. INTRODUCTION

Development History ...................... . 1-5A Versatile Vehicle ........................ 1-6Space Shuttle Components ................. 1-7Typical Shuttle Mission ..................... 1-9Crew .................................... 1-10

I

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Briefly...The primary function of the Space Shuttle is to deliver payloads to Earth orbit. On a standardmission, the Orbiter will remain in orbit for 7 days, return to the Earth with the flightcrew andthe payloads, land like an airplane, and be readied for another flight in1 4 days.

I

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1 INTRODUCTION reuse. The Shuttle can be used to carry outmissions inwhich scientists and techniciansconduct experiments inEarth orbit or serviceautomated satellites already orbiting.

The Space Shuttle is the prime element of the U.S.Space Transportation System (STS) (fig. 1-1 ) forspace research and applications in futuredecades.Satellites of all types will be deployed andrecovered by the Shuttle. Carrying payloadsweighing up to 29 500 kilograms (65 000pounds), the Space Shuttle will replace most ofthe expendable launch vehicles currently usedand will be capable of launching deep-spacemissions into their initial low Earth orbit. It willalso provide the first system capable of returningpayloads from orbit on a routine basis.Shuttle crews will be able to retrieve satellitesfrom Earth orbit and repair and redeploy themorbring them back to Earth for refurbishment and

Development HistoryIn September 1969, a few months after the firstmanned lunar landing, a Space Task Groupappointed by the President of the United States tostudy the future course of U.S. space researchand exploration made the recommendation that"... the United States accept the basic goal of abalanced manned and unmanned space program.To achieve this goal, the United States should ...develop new systems of technology for spaceoperation.., through a program directed initiallytoward development of a new spacetransportation capability .... "Inearly 1970, NASA initiated extensiveengineering, design, and cost studies of a SpaceShuttle. These studies covered a wide variety ofconcepts ranging from a fully reusable mannedbooster and orbiter to dual strap-on solidpropellant rocket motors and an expendableliquid propellant tank. In-depth studies of eachconcept evaluated development risks and costsin relation to the operational suitability and theoverall economics of the entire system.

SSUS-A SPINNING SOLID UPPER

IUS INERTIAL UPPER STAGEMMS MULTIMISSION MODULAR

SPACECRAFTLDEF LONG-DURATION

EXPOSURE FACILITYTDRS TRACKING DATA RELAY

SATELLITE

Figure 1-1 .BThe SpaceTransportation System.

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OnJanuary5, 1972,PresidentRichardM.NtxonannouncedhatNASAwouldproceedwiththedevelopmentfareusableow-costSpaceShuttlesystem.NASAandits aerospacendustrycontractorscontinuedengineeringtudiesthroughJanuarynd February of 1972; finally, onMarch 15, 1972, NASA announced that the Shuttlewould use two solid-propellant rocket motors.The decision was based on informationdeveloped by studies which showed that thesolid rocket system offered lower developmentcost and lower technical risk.

A Vorsatllo VohioleThe Space Shuttle (fig. 1-2) is a true aerospacevehicle: it takes off like a rocket, maneuvers inEarth orbit like a spacecraft, and lands like anairplane. The Space Shuttle is designed to carryheavy loads into Earth orbit. Other launchvehicles have done this; however, unlike thosevehicles which could be used just once, eachSpace Shuttle Orbiter may be reused more than1O0 times.The Shuttle permits the checkout and repair ofunmanned satellites in orbit or their return toEarth for repairs that cannot be done inspace.Thus, the Shuttle makes possible considerablesavings inspacecraft cost. The types ofsatellitesthat the Shuttle can orbit and maintain includethose involved in environmental protection,energy, weather forecasting, navigation, fishlng,farming, mapping, oceanography, and many otherfields useful to man.Interplanetary spacecraft can be placed in Earthorbit by the Shuttle together with a rocket stagecalled the Inertial Upper Stage (IUS), which isbeing developed by the Department of Defense.After the IUS and the spacecraft are checked out,the IUS is ignited to accelerate the spacecraftinto deep space. The IUS also will be used toboost satellites to higher Earth orbits than theShuttle's maximum altitude, which isapproximately 1000 kilometers (600 miles).Unmanned satellites such as the SpaceTelescope, which can multiply man's view of theuniverse, and the Long-Duration ExposureFacility, which can demonstrate the effects onmaterials of long exposure to the spaceenvironment, can be placed in orbit, erected, andreturned to Earth by the Space Shuttle. Shuttle

Figure 1-2.--The Space Shuttle vehicle.

crews also can perform such services asreplacing the filmpacks and lenses on the SpaceTelescope.The Shuttle Orbiter is a manned spacecraft, but,unlike manned spacecraft ofthe past, it touchesdown on a landing strip. The Shuttle thuseliminates the expensive recovery at sea thatwas necessary for the Mercury, Gemini, Apollo,and Skylab spacecraft.The reusable Shuttle also has a short turnaroundtime. It can be refurbished and ready for anotherjourney into space within weeks after landing.The Shuttle can quickly provide a vantage point inspace for observation of interesting but transientastronomical events or of sudden weather,agricultural, or environmental crises on Earth.Information fromShuttle observations wouldcontribute to sound decisions for dealing withsuch urgent matters.The Shuttle will also be used to transport acomplete scientific laboratory called Spacelabinto space. Developed by the European SpaceAgency, Spacelab is adapted to operate in zerogravity (weightlessness). Spacelab providesfacilities for as many as four laboratoryspecialists to conduct experiments insuch fieldsas medicine, manufacturing, astronomy, andpharmaceuticals. Spacelab remains attached tothe Shuttle Orbiter throughout its mission. Uponreturn to Earth, it is removed from the Orbiter andoutfitted for its next assignment. The Spacelabcan be reused about 50 times.

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TheSpaceShuttlewill bringwithinreachprojectsthatmanyconsideredmpracticalnottoo longago.TheShuttlecouldcarryintoorbitthe"building blocks" for constructing large solarpower stations that would convert the unlimitedsolar heat and sunlight of space into electricityfor an energy-hungry world. The componentswould be assembled by specialists transportedto and supported in space by the Shuttle. TheShuttle could also carry into Earth orbit themodular units for self-sustaining settlements. Theinhabitants of the settlements could be employedinbuilding andmaintaining solar power stationsand inmanufacturing drugs, metals, electronicscrystals, and glass for lenses. Manufacturing inweightless space can, among other things,reduce the cost of certain drugs, create newalloys, produce drugs and lenses of unusualpurity, and enable crystals to grow very large.

Space Shuttle ComponentsThe Space Shuttle has three main units: theOrbiter, the External Tank (ET), and two SolidRocket Boosters (SRB's) (fig. 1-3). Each boosterrocket has a sea level thrust of 11 600kilonewtons (2 600 000 pounds).

The Orbiter is the crew- and payload-carryingunit of the Shuttle system. It is 37 meters (121feet) long, has a wingspan of 24 meters (79 feet),and weighs approximately 68 000 kilograms(150 000 pounds) without fuel. It is about the sizeand weight of a DC-9 commercial air transport.The Orbiter can transport a payload of 29 500kilograms (65 000 pounds) into orbit. It carries itscargo in a cavernous payload bay 18.3 meters(60 feet) long and 4.6 meters (15 feet) indiameter. The bay is flexible enough to provideaccommodations for unmanned spacecraft inavariety of shapes and for fully equipped scientificlaboratories.The Orbiter's three main liquid rocket engineseach have a thrust of 21 O0 kilonewtons (470 000pounds). They are fed propellants from theExternal Tank, which is 47 meters (154 feet) longand 8.7 meters (28.6 feet) in diameter. At lift-off,the tank holds 703 000 kilograms (1 550 000pounds) of propellants, consisting of liquidhydrogen (fuel) and liquid oxygen (oxidizer). Thehydrogen and oxygen are inseparate pressurizedcompartments of the tank. The External Tank isthe only part of the Shuttle system that is notreusable.

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FRONT VIEW

TOP VIEW REAR VIEW BOTTOM VIEW

PAYLOAD ORBITAL MANEUVERING SYSTEM/BAY DOORS REACTION CONTROL

FORWARD REACTION _YSTEMCONTROL SYSTEM

O" " Stateso

RUDDER/SPEED BRAKEAFT REACTIONCONTROLSYSTEM

MAIN ENGINES

-- BODY FLAP

ELEVONS

NOSE LANDING GEAR SIDE HATCH MAIN LANDING GEAR

DIMENSIONS AND WEIGHTWING SPAN .................. 23.79 mLENGTH ..................... 37.24 rnHEIGHT ..................... 17.25 mTREAD WIDTH ................ 6.91 mGROSS TAKEOFF WEIGHT .......GROSS LANDING WEIGHT ........INERT WEIGHT (APPROX) ........MINIMUM GROUND CLEARANCESBODY FLAP (AFT END) .......... 3.68 mMAIN GEAR (DOOR) ............ 0.87 rnNOSE GEAR (DOOR) ............ 0.90 mWINGTIP .................... 3.63 m

Figure 1-3.--The Space Shuttle Orbiter.

74 844 kg

(78.06 FT)(122.17 FT)(56.58 FT)(22.67 FT)

VARIABLEVARIABLE

(165 000 L8)

(12.07 FT)(2.85 FT)(2.95 FT)(11.92 FT)

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EXTERNAL TANK

SEPARATION (__

STAGING

,_,2RBIT INSERTION%

\

LAUNCH

BOOSTERSPLASHDOWN

RETURN TO

UNCH SITE

ORBITAL OPERATIONS

DEORBIT

EXTERNAL TANKIMPACT

ENTRY

TERMINALPHASE

KENNEDYSPACECENTER

PRELAUNCHFigurel_._A SpaceShuttletypicalmissionprofile.

HORIZONTALLANDING

Typical Shuttle MissionIn a typical Shuttle mission (fig. 1-4), which couldlast from 7 to 30 days, the Orbiter's main enginesand the boosters ignite simultaneously to rocketthe Shuttle from the launch pad. The Shuttle islaunched from the NASA John F. Kennedy SpaceCenter in Florida for east-west orbits or fromVandenberg Air Force Base in California fornorth-south orbits.At a predetermined point, the two Solid RocketBoosters separate from the Orbiter and parachuteto the sea where they are recovered for reuse.The Orbiter continues into space and jettisonsthe external propellant tank just before orbiting.The External Tank enters the atmosphere andbreaks up over a remote ocean area.In orbit, the Orbiter uses its orbital maneuveringsystem (OMS) to adjust its path; to conductrendezvous operations; and, at the end of themission, to slow down for the return to Earth. The

OMS propellants, which ignite on contact, aremonomethyl hydrazine as the fuel and nitrogentetroxide as the oxidizer.The Orbiter does not follow a ballistic path to theground as did earlier manned spacecraft. It canmaneuver to the right or left.of its entry path asmuch as 2034 kilometers (1264 miles).A special insulation that sheds heat so readilythat one side is cool enough to hold in bare handswhile the other side is red hot serves as theOrbiter heat shield. The insulation survivestemperatures up to 1533 K (1260"C or 2300" F)for 100 flights with little or no refurbishment.Previous manned spacecraft used heat shieldsthat charred to carry heat away during the fieryentry into the Earth's atmosphere,The Orbiter touches down like an airplane on arunway at Kennedy Space Center or VandenbergAir Force Base. The landing speed isapproximately 335 km/hr (208 mph).

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Figure 1-5.--A Space Shuttle flightcrew.

Crew

The Shuttle crew (fig. 1-5) can include as many asseven people: the commander; the pilot; themission specialist, who is responsible formanagement of Shuttle equipment and resourcessupporting payloads during the flight; and one tofour payload specialists, who are in charge ofspecificpayload equipment. The commander,pilot, and mission specialist are NASA astronautsand are assigned by NASA. Payload specialistsconduct the experiments and may or may not beastronauts. They are nominated by the payloadsponsor and certified for flight by NASA.

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2. SPACE TRANSPORTATION SYSTEMPROPULSION


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F'._A

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%

Space Shuttle Main Engines

OPERATION OF THE SPACE SHUTTLEMAIN ENGINES ........................... 2-5COMBUSTION DEVICES .................... 2-8Ignition System ........................... 2-8Preburners ............................... 2-8Main Injector ............................. 2-9Main Combustion Chamber ................. 2-9Nozzle Assembly .......................... 2-10ENGINE SYSTEMS ......................... 2-10Hot-Gas Manifold ......................... 2-10Heat Exchanger ........................... 2-11Thrust Vectoring .......................... 2-11Pneumatic Subsystem ...................... 2-11TURBOPUMPS ............................ 2-12Propellant Feed System Summary ........... 2-12Fuel Turbopumps .......................... 2-1 2Oxidizer Turbopumps ...................... 2-12MAIN VALVES ............................ 2-13Main Oxidizer Valve ....................... 2-13Main Fuel Valve ........................... 2-13Oxidizer Preburner Oxidizer Valve ............ 2-13Fuel Preburner Oxidizer Valve ............... 2-13Chamber Coolant Valve .................... 2-13HYDRAULIC SUBSYSTEM ................... 2-14CONTROLLER ............................ 2-14Controller Functional Organization ........... 2-15Controller Software ........................ 2-15

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Briefly...The three main engines of the Space Shuttle, inconjunction with the Solid Rocket Boosters,provide the thrust to lift the Orbiter off the ground for the initial ascent. The main enginesoperate for approximately the first 8.5 minutes of flight.

THRUSTSea level: 1670 kilonewtons (375 000 pounds)Vacuum: 2100 kilonewtons (470 000 pounds)(Note: Thrust given at rated or 100-percent powerlevel.)THROTTLING ABILITY65 to 109 percent of rated power levelSPECIFIC IMPULSESea level: 356.2 N/._.ss363.2 Ibf/s_kg \ I-_/Vacuum: 4464 N/s (455.2 Ibf/s'_kg(Given in newtons per second to kilograms ofpropellant and pounds-force per second to pounds-mass of propellant)CHAMBER PRESSURE20 480 kN/m 2 (2970 psia)MIXTURE RATIO6 parts liquid oxygen to 1 part liquid hydrogen (byweight)AREA RATIONozzle exit to throat area 77.5 to 1WEIGHTApproximately 3000 kilograms (6700 pounds)LIFE7.5 hours, 55 starts

\t

4.3 METERS(14 FEET)

L

_._ 2.3 METERS7.5 FEET)

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2. SPACE TRANSPORTATIONSYSTEMPROPULSION

Space Shuttle Main EnginesA cluster of three Space Shuttle Main Engines(SSME's) (figs. 2-1 and 2-2) provides the mainpropulsion for the Orbiter vehicle. The liquidhydrogen/liquid oxygen engine isa reusablehigh-performance rocket engine capable ofvarious thrust levels. Ignited on the ground priorto launch, the cluster of three main enginesoperates inparallel with the Solid RocketBoosters (SRB's) during the initial ascent. Afterthe boosters separate, the mainengines continueto operate. The nominal operating time isapproximately 8.5 minutes.

The main engines develop thrust by using high-energy propellants ina staged combustion cycle(fig. 2-3). The propellants are partially combustedindual preburners to produce high-pressure hotgas to drive the turbopumps. Combustion iscompleted in the maincombustion chamber. Thecycle ensures maximum performance because iteliminates parasitic losses.Each Space Shuttle Main Engine operates at aliquid oxygen/liquid hydrogen mixture ratio of 6to 1 to produce a sea level thrust of 1668kilonewtons (375 000 pounds) and a vacuumthrust of 2091 kilonewtons (470 000 pounds).The engines can be throttled over a thrust rangeof 65 to 109 percent, which provides for a highthrust level during lift-off and the initial ascentphase but allows thrust to be reduced to limitacceleration to 3g's during the final ascent phase.The engines are gimbaled to provide pitch, yaw,and roll control during the Orbiter boost phase.Modified airline maintenance procedures will beused to service the engine without removing itfrom the vehicle between flights. Most enginecomponents can be replaced inthe field as linereplacement units without extensive enginerecalibration orhot-fire testing. Theseprocedures result inan economical and efficientturnaround method.

OPERATION OF THE SPACE SHUTTLEMAIN ENGINESThe flow of liquid hydrogen and liquid oxygenfrom the External Tank (ET) is restrained fromentering the engine by prevalves located intheOrbiter above the low-pressure turbopumps (fig.2-3, nos. 1 and 11). Before firing, the prevalvesare opened to allow propellants to flow throughthe low-pressure turbopumps (1 and 11) and thehigh-pressure turbopumps (2 and 12) and thentothe main propellant valves (3 and 13). On theliquid oxygen side, the system also fills topreburner valves (7 and 14). The cryogenicpropellants are held in the ducts for sufficienttime to chill the engine and attain liquidconditions inthe respective propellant systems.The chill process is aided by bleedlines (notshown) that allow circulation of the propellants.

Figure 2-1 .----Space Shuttle Main Engines (MSFC 002382).

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Inthestart sequence, the hydrogen and oxygensides operate almost simultaneously. On thehydrogen (fuel) side, the ignition command fromthe Orbiter opens the main fuel valve (3). Thispermits hydrogen to flow into the coolant loop,through the nozzle tubes (5), and throughchannels in the maincombustion chamber (6).Part of this coolant loop flow is diverted by thecoolant control valve (4) to the preburners (8 and15). Some of the hydrogen used in the coolantloop iswarmed inthe process to virtually ambientconditions and is tapped offat the maincombustion chamber (6) and routed back to thelow-pressure turbopump (1) to drive the turbinefor that pump. This flow passes through theturbine and is returned to the walls of the twopreburners (8 and 15) where it cools thepreburners, the hot-gas manifold (9), and the maininjector (10).On the oxygen (or oxidizer) side, the ignitioncommand opens the main oxidizer valve (13). Theliquid oxygen flows through the two turbopumps(11 and 12) to the main injector (1O)and also

(through valves 7 and 14) to the two prebumers(8 and 15). Oxygen, tapped off downstream of thehigh-pressure oxidizer turbopump (12), is routedto the low-pressure turbopump (11) to drive theliquid turbine for that pump. This flow continuesthrough the low-pressure oxidizer turbopump(11), thus reentering the circuit.

Spark igniters located in the dome of bothpreburners (8 and 15) and the main chamber (10)initiate combustion. The two prebumers areoperated at mixture ratios of less than one partoxygen to one part hydrogen to produce hot gas(or hydrogen-rich steam). The hot gas or steam isused to drive the turbines of the two high-pressure turbopumps (2 and 12) before enteringthe hot-gas manifold (9), This hydrogen-richsteam is transferred by the hot-gas manifold (9)from the turbines to the main injector (10) where itismixed with additional liquid oxygen from thehigh-pressure oxidizer turbopump (12) forcombustion. This combustion process iscompleted at a mixture ratio of six parts oxygento one part hydrogen.

LOW-PRESSUREFUEL TURBOPUMP

FUELPREBURNER

HOT-GASMANIFOLD

HIGH-PRESSUREFUEL TURBOPUMP

CONTROLLER

GIMBALBEARING

rlNJECTOR Figure 2-2..--SSME majorcomponents.

OXIDIZERPREBURNER

HIGH-PRESSUREOXIDIZER TURBOPUMP

COMBUSTION CHAMBER

LOW-PRESSUREOXIDIZER TURBOPUMP

NOZZLE

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Twoadditionalcomponentsf theengineshouldalsobementioned.Thepogo suppressor (16) isprovided to absorb any closed-loop longitudinaldynamic oscillations that might be generatedbetween the vehicle structural dynamics and theengine combustion process. A suppressor is notrequired onthe hydrogen side of the enginebecause the low density of that fluid has beenshown to be insufficient to transmit anyappreciable dynamic oscillations.Another major component of the engine, notshown in figure 2-3, is the controller, whichoperates all engine controls. Mounted on the

engine, the controller includes a computer tointegrate commands received from the Orbiterwith data input from sensors located on theengine. The controller monitors the engine beforeignition, controls purges before and duringoperation of the engine, manages the engine'sredundancy features, receives and transmits clarato the Orbiter for either storage or transmission tothe ground, and operates the engine controlvalves. The five control valves numbered 3, 4, 7,13, and 14 in figure 2-3 effectively control theentire engine operation.

ORBITERPREVALVEII

LIQUID HYDROGEN

HOT GAS

Figure 2-3._SME propellant flow schematic.

ORBITERPREVALVEII

LIQUID OXYGEN

@HOT GAS I

1 -- LOW-PRESSURE FUEL TURBOPUMP2 - HIGH-PRESSURE FUEL TURBOPUMP3- MAIN FUEL VALVE4 - COOLANT CONTROL VALVE5- NOZZLE TUBE6- MAIN COMBUSTION CHAMBER7 - FUEL PREBURNER VALVE8-- FUEL PREBURNER9 -- HOT-GAS MANIFOLD10- MAIN INJECTOR11 - LOW-PRESSURE OXIDIZER TURBOPUMP12 - HIGH-PRESSURE OXIDIZER TURBOPUMP13- MAIN OXIDIZER VALVE14 - OXIDIZER PREBURNER VALVE15- OXIDIZER PREBURNER16 - POGO SUPPRESSOR

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COMBUSTIONDEVICESCombustionevicesarelocatedinthosepartsoftheenginewherecontrolledcombustion,rbuming,oftheliquidoxygenand liquid hydrogenoccurs. The five major components in this groupare the ignition system, the prebumers, the maininjector, the main combustion chamber, and thenozzle assembly (fig. 2-4).

Ignition SystemThe ignition system starts the combustionprocess in the main engine. There are threeignition units, one for the mainchamber injectorand one for each of the two prebumer injectors.Each ignition unit, located inthe center of itsrespective injector, includes a small combustionchamber, two spark igniters (similar to sparkplugs), and propellant supply lines. At enginestart, all six spark igniters are activated, ignitingthe propellants as they enter the ignitercombustion chamber and thusproviding an

ignition source for propellants entering theprebumers and the maincombustion chamber.The ignition unit remains active for the duration ofengine operation, but the spark igniters areturned off after ignition is complete.

PreburnerlEach main engine has fuel and oxidizerprebumers that provide hydrogen-rich hot gasesat approximately 1030 K (760" C or 1400" F).These gases drive the fuel and oxidizer high-pressure turbopumps. The preburner gases passthrough turbines and are directed through a hot-gas manifold to the main injector where they areinjected into the main combustion chambertogether with liquid oxygen and burn atapproximately 3590 K (3315" C or 6000" F).

FUELPREBURNER

INJECTOR OXIDIZERPREBURNER

r jSSURE

HYDROGENTURBOPUMP

MAIN COMBUSTION CHAMBERNOZZLE ASSEMBLYt

Figure 2-4._SME powerhead component arrangement.

HIGH-PRESSUR EOXIDIZERTURBOPUMP

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Thedesignof thetwoprebumera is similar. Eachconsists of fuel and oxidizer supply manifolds, aninjector, stability devices, a cylindricalcombustion zone, and an ignition unit. The supplymanifolds ensure uniform propellant distributionso that each injector element receives thecorrect amount of oxygen and hydrogen. Theprebumer injectors consist of many individualinjection elements that introduce the propellantsinconcentric streams. Each oxygen stream issurrounded by its companion hydrogen stream.The injector contains baffles to help maintainstable combustion inthe prebumera and thussuppress disturbances that might occur Inthecombustion process. Gaseous hydrogen flowsthrough passages ineach baffle for cooling and isthen discharged into the combustion chamber.The cylindrical combustion zone consists of astructural shell and a thln inner liner. The liner iscooled by passing gaseous hydrogen between itand the structural wall.

Main InjectorThe main injector performs the vital function offinally mixing all the liquid oxygen and liquidhydrogen together as thoroughly and uniformly aspossible to produce efficient combustion.An intricately fabricated component, the maininjector consists of a thrust cone, an oxidizersupply manifold, two fuel cavities, 600 injectionelements, and an ignition unit. The thrust conetransmits the total thrust of the engine through thegimbal bearing to the Orbiter vehicle. Theoxidizer supply manifold receives oxygen fromthe high-pressure turbopump and distributes itevenly to the 600 injection elements. One of thetwo fuel cavities supplies the fuel-rich hot gasesthat originate in the prebumers and are used torun the high-pressure turbines. The other fuelcavity supplies gaseous hydrogen from the hot-gas manifold cooling circuit.The 600 main injector elements have the samebasic design as the prebumer injection elements;i.e., an outer fuel shroud that surrounds a centraloxidizer stream. The propellants are thoroughlymixed as they are introduced into the maincombustion zone for burning at approximately3590 K (3315" C or6000" F).

Seventy-five of the injection elements also formbaffles that divide the injector into sixcompartments. The baffles are designed tosuppress any pressure disturbances that mightoccur during the combustion process.Main Combustion ChamberThe main combustion chamber is a double-walledcylinder between the hot-gas manifold and thenozzle assembly. Its primary function is to receivethe mixed propellants from the main injector,accelerate the hot combusted gases to sonicvelocity through the throat, and expand themsupersonically through the nozzle. The mainchamber operating pressure at rated power levelisapproximately 20 700 kN/m 2 (3000 psi). Themain combustion chamber consists of a coolantliner, a high-strength structural jacket, coolantinlet and outlet manifolds, and actuator struts.

The intemal contour of the coolant liner forms thetypical contraction-throat-expansion shapecommon to conventional rocket enginecombustion chambers. The contraction area ratio(the ratio ofthe area at the injector face to thethroat area) is 2.96 to 1. The expansion area ratio(the ratio of the area at the aft end of thecombustion chamber to the throat area) Is 5 to 1.The contraction contour is shaped tominimize thetransfer of heat from the combustion gases to thecoolant liner. The expansion contour acceleratesthe combustion gases to the 5-to-1 expansionratio with minimum energy loss.The coolant liner passes hydrogen coolant (fuel)through 390 channels. Approximately 25 percentof the total hydrogen flow is used to cool theliner. The chamber jacket goes around theoutslde of the llner to provlde structural strength.Inlet and outlet coolant manifolds are welded tothe jacket and to the liner. Two actuator struts arebolted to the chamber and are used, inconjunctlon with hydraulic actuators, to gimba!the engine during flight when it is necessary tochange the direction of the thrust.

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NozzleAssemblyToprovidemaximumossiblethrustefficiency,thenozzleassemblyfig.2-5)allowscontinuedexpansionof thecombustiongasescomingromthe maincombustion chamber. It isdesigned for a77.5-to-1 thrust chamber expansion ratio forthrust efficiency at highaltitudes. The nozzleassembly i8 the largest component on the engine,measuring approximately 3 meters (10 feet) inlength and 2.4 meters ( 8 feet) in diameter at thebase. The nozzle assembly consists of a forwardmanifold subassembly and a stacked tube nozzlesubassembly.The forward manifold subassembly provides theattachment to the main combustion chamber. Italso distributes hydrogen to the mainchamberand nozzle cooling circuits and to both the fueland oxidizer prebumers.

The stacked tube nozzle subassembly contains1080 tubes brazed together to form the desiredcontour. They are connected at the aft end to 8coolant inlet manifold and at the forward end to acoolant outlet manifold. Hydrogen passesthrough the tubes and again provides a coolingfunction, The nozzle tubes are enclosed in areinforced structural jacket, The jacketreinforcements (hatband8) are insulated forprotection against the extreme heat encounteredduring launch and reentry.

ENGINE SYSTEMS

Hot-Gas ManifoldThe hot-gas manifold (see fig. 2-2) is a double-walled, hydrogen-gas-cooled structural supportand fluid manifold. It is the structural backbone ofthe engine and Interconnects and supports theprebumers, high-pressure turbopumps, maincombustion chamber, and main injector.

TO OXIDIZER ANDFUEL PREBURNERS

MIXERCHAMBERCOOLAN"

COOLANT OUTLETMANIFOLD "_"_HEAT SHIELDSUPPORT RING

DRAIN LINE

TO MAIN COMBUSTION CHAMBERCOOLANT INLET MANIFOLD

"_"4"- FROM MAINFUEL VALVE

DIFFUSER

TRANSFERDUCTS

DS

COOLANTINLETMANIFOLD

Figure 2-5,_SME nozzleassembly.

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Thehot-gasmanifoldconductshotgas(hydrogen-richteam)romtheturbinesothemainchambernjector.Theareabetweenhewallandthe linerprovidesacoolantflow path for thehydrogen gas that is exhausted from the low-pressure fuel turbopump turbine. This protectsthe outer wall and liner against the temperatureeffects of the hot gas from the preburners. Aftercooling the manifold, the hydrogen also serves ascoolant for the primary faceplate, the secondaryfaceplate, and the main combustion chamberacoustic cavities. The high-pressure turbopumpsare stud-mounted to the canted flanges oneachside of the hot-gas manifold. The preburners arewelded to the upper end of each side of the hot-gas manifold above the high-pressureturbopumps.

Thrust VectoringThe gimbal bearing assembly is a spherical low-friction universal joint that has ball and socketbearing surfaces. The bearing assembly providesthe mechanical interface with the vehicle fortransmitting thrust loads and permits angulationof the actual thrust vector (force) about each oftwo vector control axes. The gimbal bearing isattached to the engine main injector by bolts thatallow lateral positioning of the bearing. Thegimbal bearing position is established by opticalalinement during engine buildup to ensure that theactual thrust vector is within 30 minutes of arc tothe engine centerline and 1.5 centimeters (0.6inch) of the gimbal center. Cycle life is obtainedby low-friction antigalling bearing surfaces thatoperate under high loads.

Heat Exchanger

The heat exchanger is a single-pass coil packinstalled in the oxidizer side of the hot-gasmanifold. It converts liquid oxygen to gaseousoxygen for vehicle oxygen tank and pogo-systemaccumulator pressurization. The heat exchangerconsists of a helically wound small tubeapproximately 0.8 meter (2.6 feet) long, inserieswith two parallel larger tubes, eachapproximately 7.9 meters (25.8 feet) long. Thetubes are attached to supports welded to theinner wall of the hot-gas manifold coolant jacket.The hot turbine exhaust gases from the high-pressure oxidizer turbopump heat the liquidoxygen to a gas. Liquid oxygen, tapped off thedischarge side of the high-pressure oxidizerturbopump, is supplied to the inlet of the heatexchanger through an antiflood valve.The oxygen is heated to a gas inthe small tube(first stage) and to the final outlet temperature inthe two larger tubes (second stage). Anorificedbypass line around the heat exchanger injects anunheated portion (approximately 30 percent) ofthe total oxygen flow into the outlet of the heatexchanger for control of temperature and flow-rate operating characteristics. Orifices intheheat exchanger bypass line and in the vehiclecontrol heat exchanger flow rate.

Pneumatic SubsystemThe pneumatic control assembly provides (1)control of ground-supplied gaseous nitrogenused for engine prestart purges and of vehicle-supplied helium for the operational purge, (2)control of the oxidizer and fuel bleed valves, and(3) emergency shutdown control of the mainpropellant valves in the event of electrical powerloss to the engine. The pneumatic controlassembly consists of a ported manifold to whichsolenoid valves and pressure-actuated valvesare attached.

The oxidizer and fuel bleed valves are opened bypneumatic pressure from the pneumatic controlassembly during engine-start preparation toprovide a recirculation flow for propellantsthrough the engine to ensure that the propellantsare at the required temperatures for engine start.At engine start, the valves are closed by ventingthe actuation pressure.The pneumatic control system purge checkvalves are spring-loaded normally closed poppetvalves that isolate propellants from the pneumaticsystems. The check valves are opened bypressure actuation.

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TURBOPUMPSPropellantFeed System SummaryThe propellant feed system includes fourturbopumps, two of which are low pressure andtwo high pressure. There is one of each for theliquid hydrogen fuel and liquid oxygen oxidizer.All four are line replaceable units for maintenancepurposes.

Fuel TurbopumpsThe low-pressure fuel turbopump is an axial-flow(inline) pump driven by a two-stage turbine. Itraises the pressure of the fluid being applied tothe high-pressure fuel pump to prevent cavitation,the formation of partial vacuums in a flowing liq-uid. The rotor assembly is supported onthree ballbearings, which are cooled internally by liquidhydrogen. The low-pressure fuel turbopumpnominally operates at a speed of 14 700 rpm,develops 1790 kilowatts (2400 brake horse-power) of power, and increases the pumppressure from 207 to 1600 kN/m 2 (30 to 232psia) at a flow rate of 67 kg/s (147 Ib/s). Theturbine is driven by gaseous hydrogen at anominal inlet pressure of 29 434 kN/m 2 (4269psia).The high-pressure fuel turbopump is a three-stage centrifugal pump driven directly by a two-stage turbine. The latter, in turn, is driven by hotgas supplied by the fuel preburner. Fuel flows inseries through the three impellers from the pumpinlet to the pumpoutlet and the flow is redirectedbetween impellers by interstage diffusers. Twodouble sets of ball bearings support the rotatingassembly. A thrust bearing at the pump end of therotating assembly provides axial rotor thrustcontrol during startup and shutdown, while adynamic self-compensating balance systembalances axial forces during mainstageoperation. The bearings are cooled internallywith liquid hydrogen. Two dynamic seals are usedto prevent turbine-to-pump leakage.The high-pressure fuel pump is a high-speedhigh-power turbopump that operates at a nominalspeed of 35 000 rpm and develops 46 435 kilo-watts (62 270 brake horsepower) of power. Itincreases the pump pressure from 1213 to42 817 kN/m 2 (176 to 6210 psia) at a flow rate of2-1 2

67 kg/s (147 Ib/s). The nominal turbine inletpressure and temperature are 35 605 kN/m 2(5164 psia) and 961 K (688 C or 1271 F),respectively.

Oxidizer TurbopumpsThe low-pressure oxidizer turbopump is an axial-flow pump that isdriven by a six-stage turbineand powered by oxidizer propellant. Because thepump and turbine propellants are both liquidoxygen, the requirements for dynamic seals,purges, and drains have been eliminated. Theprimary function of the low-pressure oxidizerpump is to maintain sufficient inlet pressure to thehigh-pressure oxidizer pump to preventcavitation. The rotor assembly issupported bytwo ball bearings, which are cooled internallywith oxidizer. Turbine-drive fluid at 30 944 kN/m 2(4488 psia) is provided from the high-pressureoxidizer pump discharge. The low-pressureoxidizer pump nominally operates at a speed of5150 rpm, develops 1096 kilowatts (1470 brakehorsepower), and increases the pump pressurefrom 690 to 2861 kN/m 2 (1O0 to 415 psia) at aflow rate of 401 kg/s (883 Ib/s).The high-pressure oxidizer turbopump consistsof a main pump, which provides liquid oxygen tothe main injector, and a boost pump, whichsupplies liquid oxygen to the preburners. Themain pump has a single inlet and flow is split to adouble-entry impeller with a common discharge.Two double sets of ball bearings support therotor assembly and are cooled internally withliquid oxygen. Dynamic seals within theturbopump prevent the mixing of liquid oxygenand turbine gases. The turbopump rotor axialthrust is balanced by a self-compensatingbalance piston.The high-pressure oxidizer turbine is powered byhot gas generated by the oxidizer prebumer. Thisgas passes through the turbine blades andnozzles and discharges into the hot-gas manifold.The turbine housing is cooled by gaseoushydrogen supplied by the oxidizer preburnercoolant jacket.


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Thehigh-pressurexidizerturbopumpsahigh-speedhigh-powerurbopumphatoperatesatanominalspeedof29 057 rpm with a turbine inletpressure and temperature of 36 046 kN/m 2 (5228psia) and 817 K (544" C or 1011 F),respectively. The main oxidizer pump develops15 643 kilowatts (20 977 brake horsepower) ofpower with a pump pressure increase from 2482to 31 937 kN/m 2 (360 to 4632 psia) at a flow rateof 484 kg/s (1066 Ib/s). The preburner pumppressure increases from 30 592 to 52 642 kN/m 2(4437 to 7635 psia) at a flow rate of 39 kg/s (86Ib/s) with 1098 kilowatts (1472 brakehorsepower) of power.

MAIN VALVESThe main propellant valves consist of the mainoxidizer valve, the main fuel valve, the oxidizerpreburner oxidizer valve, the fuel preburneroxidizer valve, and the chamber coolant valve. Allexcept the chamber coolant valve are ball-typevalves and have two major moving components,the integral ball-shaft cams and the ball-sealretracting mechanism. The ball inlet seal isamachined plastic, bellows-loaded, closed seal.Redundant shaft seals, with an overboard draincavity between them, prevent leakage along theshaft (actuator end) during engine operation. Inletand outlet sleeves aline the flow to minimizeturbulence and the resultant pressure loss. Ballseal wear is minimized by cams and a cam-follower assembly that moves the seal away fromthe ball when the valve is being opened.All valves are operated by a hydraulicservoactuator mounted to the valve housing andreceive electrical control signals from the enginecontroller.

Main Oxidizer Valvei

The main oxidizer valve has a 6.4-centimeter(2.5-inch) propellant flow passage and is flange-mounted between the mainchamber oxidizerdome and the high-pressure oxidizer duct. Thevalve controls oxidizer flow to the mainchamberliquid oxygen dome and the main chamberaugmented spark igniter.

Main Fuel ValveThe main fuel valve has a 6.4-centimeter (2.5-inch) propellant flow passage and is flange-mounted between the high-pressure fuel duct andthe coolant inlet dis_J_butionmanifold on thethrust chamber nozzle. It controls the flow of fuelto the thrust chamber coolant circuits, the low-pressure fuel turbopump turbine, the hot-gas-manifold coolant circuit, the oxidizer preburner,the fuel preburner, and the three augmented sparkigniters.

Oxidizer Preburner Oxidizer ValveThe oxidizer preburner oxidizer valve has a 2.8-by 0.724-centimeter (1.1 - by 0.285-inch)propellant flow slot. It is flange-mounted betweenthe oxidizer supply line to the oxidizer prebumerand the oxidizer prebumer oxidizer inlet. Thisvalve controls the flow of oxidizer to the oxidizerprebumer and the oxidizer prebumer augmentedspark igniter. During mainstage operation, thevalve is modulated to control engine thrust be-tween minimum and full power levels.

Fuel Preburner Oxidizer ValveThe fuel preburner oxidizer valve has a 2.8-centimeter (1.1 -inch) propellant flow passage. Itis flange-mounted between the oxidizer supplyline to the fuel prebumer and the fuel prebumeroxidizer inlet. This valve controls the flow ofoxidizer to the fuel preburner and the fuelpreburner augmented spark igniter. Duringmainstage operation, the valve ismodulated tomaintain the desired engine mixture ratio.

Chamber Coolant ValveThe chamber coolant valve is a gate-type valvethat serves as a throttling control to maintainproper fuel flow through the main combustionchamber and nozzle coolant circuits. It is installedin the chamber coolant valve duct, which is anintegral component of the nozzle forward manifoldassembly and provides housing for the valve.

ORIGINAL PAGE ISOF POOR QUAIJ'I'Y

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Thegatehasa 4.1 -centimeter (1.6-inch) flowpassage. The chamber coolant valve does nothave a gate seal since it is located downstreamfrom the main fuel valve and is not required to be apositive shutoff valve. Redundant shaft seals, withan overboard drain cavity between them, preventleakage along the shaft (actuator end) duringengine operation.

HYDRAULIC SUBSYSTEMHydraulic power is provided by the Orbiter for theoperation of five valves in the propellant feedsystem: the oxidizer preburner oxidizer, fuelpreburner oxidizer, main oxidizer, main fuel, andchamber coolant valves. Servoactuators mountedto the propellant valves convert vehicle-suppliedhydraulic fluid pressure to the rotary motion of theactuator shaft by electrical input command.Two servovalves, which are integral with eachservoactuator, convert the electrical commandsignal from the engine controller to hydraulic flowthat positions the valve actuator. The dualservovalves provide redundancy that permits onesarvovalve to fail and still produce no change inactuator performance. A fail-operate servoswltchis used to automatically select the redundantsarvovalve upon failure of a single sarvovalve. Ifboth sarvovalves fail, a fail-safe servoswitchhydraulically locks the sarvoactuator.

All actuators, except for the chamber coolantvalve, have an emergency shutdown system topneumatically close the propellant valves.Sequence valves in the oxidizer prebumeroxidizer valve, the fuel prebumer oxidizer valve,and the chamber coolant valve actuators closethe five propellant valves inproper order during apneumatic shutdown.

CONTROLLERThe checkout, start, in-flight operation, andshutdown of the Space Shuttle Main Engines aremanaged by dual redundant 16-bit digitalcomputers and their input and output electronics.This electronics package is called a controller(fig. 2-6) and ismounted onthe engine.

The controller interfaces with the hydraulicactuators and their position feedbackmechanisms, spark igniters, solenoids, andsensors to provide closad-loop control of thethrust and propellant mixture ratio, whilemonitoring the performance of criticalcomponents on the engine and providing thenecessary redundancy management to ensure thehighest probability ofproper and continuedengine performance. These monitoring andcontrol tasks are repeated every 20 milliseconds(50 times per second). Critical engine operationparameters (temperature, pressure, and speed)are monitored for exceeding predeterminedvalues, which indicates impending enginemalfunction. Exceeding any of these parameterswill result in the controller performing a safeengine shutdown. Status information isreportedto the vehicle for proper action and postflightevaluation.

AFT

COMPUTER CONTROL OF ENGINE WEIGHT

97 kg (213 LB) SIZE

36.8 BY 46.4 BY 58.7 m (14.5 BY 18.25 BY 23.5 IN.)Figure 2-6._SSME controller assembly.

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The controller receives commands from thevehicle's guidance and navigation computers forthe checkout, start, thrust-level requirements(throttling), and shutdown. The controller, in turn,performs the necessary functions to start, changefrom one thrust level to another within 1-percentaccuracy, and shut down as defined by thecommands from the vehicle.In addition to controlling the engine, thecontroller performs self-tests and switches to thebackup computer channel and its associatedelectronics in the event of a failure. Similar testsare performed on the components interfacing withthe controller and the necessary actions aretaken to remove faulty components from theactive control loop. One failure in any of theelectronic components can be tolerated andnormal engine operation will continue. Somesecond failures can be tolerated if the only resultis degraded performance of the engine; however,in all cases, the controller will effect an engineshutdown when all methods for engine electricalmonitoring and control are exhausted.The controller is packaged in a sealed,pressurized chassis, with cooling provided byconvection heat transfer (transfer of heat from itssource to that of a lower temperature) through pinfins as part of the main chassis.

The output electronics subsystem converts thecomputer digital control commands into voltagessuitable for powering the engine spark igniters,the solenoids, and the propellant valve actuators.The computer interface electronics subsystemcontrols the flow of data within the controller, theinput data to the computer, and the computeroutput commands to the output electronics. Italso provides the controller interface with thevehicle for receiving engine commands (tripleredundant channels) from the vehicle and fortransmission of engine status and data (dualredundant channels) to the vehicle.The digital computer subsystem is an internallystored general-purpose digital computer thatprovides the computational capability necessaryfor all engine control and monitoring functions.The computer memory has a program storagecapacity of 16 384 words. Typical computerinstruction times are 2 microseconds to add and9 microseconds to multiply.The power supply electronics subsystemconverts the 115-volt, three-phase, 400-hertzvehicle power to the individual voltages requiredto operate the computers, input and outputelectronics, computer interface electronics, andother engine electrical components.

Controller Functional OrganizationThe controller is functionally divided into fivesubsystems: input electronics, outputelectronics, computer interface electronics,digital computer, and power supply electronics.Each of the five subsystems is duplicated toprovide dual redundant capability.The input electronics subsystem receives datafrom the engine sensors, conditions the signals,and converts them to digital form for computeruse. The sensors for engine control and criticalparameter monitoring (redlines) are dualredundant. The sensors for data only arenonredundant.

Controller SoftwareThe software is an online, real-time, processcontrol program. The program will process inputsfrom engine sensors; control the operation ofactuators, solenoids, and spark igniters; acceptand process vehicle commands; provide andtransmit data to the vehicle; and providetest/checkout and monitoring capabilities.

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H

0

Solid Rocket Boosters

SOLID ROCKET MOTOR .................... 2-19Motor Case ............................... 2-19Insulation and Liner ........................ 2-20Propellant ................................ 2-20Ignition System ........................... 2-21Nozzle ................................... 2-22Refurbishment ............................ 2-23STRUCTURES ............................. 2-23Forward Assembly ......................... 2-23Aft Skirt ................................. 2-24SRB/ET Attach Points and Separation ......... 2-24Systems Tunnel ........................... 2-25THRUST VECTOR CONTROL ................ 2-25PARACHUTE RECOVERY SYSTEM ........... 2-27ELECTRICAL SYSTEM ANDINSTRUMENTATION ....................... 2-29ORDNANCE .............................. 2-30BOOSTER SEPARATION MOTORS ........... 2-30THERMAL PROTECTION SYSTEM ............ 2-31

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Briefly...The Solid Rocket Boosters operate inparallel with the main engines for the first 2 minutes offlight to provide the additional thrust needed for the Orbiter to escape the gravitational pull ofthe Earth. At an altitude of approximately 45 kilometers (24 nautical miles), the SRB's separatefrom the Orbiter/External Tank, descend on parachutes, and land in the Atlantic Ocean. Theyare recovered by ships, returned to land, and refurbished for reuse.

STATISTICS FOR EACH BOOSTERTHRUST AT LIFT-OFF11 790 kilonewtons (2 650 000 pounds)PROPELLANTAtomized aluminum powder(fuel), 16 percentAmmonium perchlorate(oxidizer), 69.83 percentIron oxide powder(catalyst), 0.17 percent (varies)Polybutadiene acryl ic acidacrylonitrile (binder), 12 percentEpoxy curing agent, 2 percentWEIGHTEmpty: 87 550 kilograms

(193 000 pounds)Propellant: 502 125 kilograms

(1 107 000 pounds)Gross: 589 670 kilograms

(1 300 000 pounds)THRUST OF BOTH BOOSTERSAT LIFT- OFF23 575 kilonewtons (5 300 000 pounds)GROSS WEIGHT OF BOTH BOOSTERSAT LIFT-OFF1 179 340 kilograms (2 600 000 pounds)

NOSE CAPRING

FRUSTUM FORWARDATTACH POINT

FORWARD SKIRT

FORWARDSEGMENT

FORWARDCENTERSEGMENT

AFTCENTERSEGMENT

AFTATTACHRING

AFT SEGMENTWITH NOZZLE

AFT SKIRT

-i

45.46 METERS(149.16 FEET)

3.8 METERS12.38 FEET)

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Solid Rocket BoostersTwo Solid Rocket Boosters (SRB's) operate inparallel to augment the thrust of the SpaceShuttle Main Engines (SSME's) from the launchpad through the first 2 minutes of powered flight.The boosters also assist in guiding the entirevehicle during the initial ascent; followingseparation (fig. 2-7), they are recovered,refurbished, and reused. Each SRB containsseveral subsystems inaddition to its basiccomponent, the solid rocket motor (SRM). Theseare the structural, thrust vector control,separation, recovery, and electrical andinstrumentation subsystems.

SOLID ROCKET MOTORThe heart of the booster is the solid rocket motor(fig. 2-8). It is the largest solid propellant motorever developed for space flight and the first built

to be used on amanned craft. Larger solid motorshave been test-fired but have never been carriedthrough complete development to the flight cycle.The huge solid rocket motor is composed of asegmented motor case loaded with solidpropellants, an ignition system, amovable nozzle,and the necessary instrumentation andintegration hardware.Motor CaseEach motor case is made of 11 individual weld-free steel segments. Averaging approximately1.27 centimeters (0.5 inch) thick, the steel is highstrength. Each segment is heat-treated, hardened,and machined to the exact dimensions required.The 11 segments are held together by 177 high-strength steel pins at each case segment joint.The clevis-type joints are wrapped withreinforced fiberglass tape and sealed with arubber seal band that is bonded to the case withadhesives.

Figure 2-7._eparation of Space Shuttle Solid RocketBoosters (MSFC 003382).

FORWARDSEGMENT

FORWARDCENTERSEGMENT

AFTCENTER

. SEGMENT

AFTSEGMENT

:;,.,. i{ I r )Figure 2-8._pace Shuttle solid rocket motor.

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The propellant is poured under vacuum into thesegments around the mandrels. After the pouring,the vacuum is released and a cover is placedover the casting pit. The segments are then curedfor 4 days at a temperature of 330 K (57 C or135 F). Following this, the mandrel is removed,creating the burning cavity of the motor.

The high thrust level during lift-off of the Shuttleresults from an 11 -point-star propellantconfiguration in the forward segment. After l ift-off,thrust is reduced by the total burnout of the starpoints (at 62 seconds into the flight) to constrainflight dynamic pressure. Thrust then graduallyincreases because of the design of the burningcavity. When the flame surface of the burningpropellant reaches the liner surface, the thrustagain starts to decay and continues to decay untilburnout (about 10 seconds later).

Ignition SystemThe ignition system (fig. 2-10) is located in theforward dome segment. The ignition sequence isfast-moving and begins when two devices knownas NASA standard initiators (NSI's) are fired,igniting a booster charge of boron potassiumnitrate (BKNO3) pellets. The pellets start a smallrocket motor, called a pyrogen igniter, which is amotor within a motor. The first motor is the igniterinitiator. It is approximately 18 centimeters (7inches) long and 13 centimeters (5 inches) indiameter. The second motor is the main igniter. Itis approximately 91 centimeters (36 inches) longand 53 centimeters (21 inches) in diameter. Theigniter motor flame reaches 31 72 K (2899 C or5250 F) to start SRM propellant burning. Oncethe SRM propellant begins to burn, flame-spreading occurs in approximately 0.15 secondand the motor reaches full operating pressure inless than 0.5 second.

SRMCHAMBERPRESSURETRANSDUCE R

SAFE ANDARM DEV

ADAPTE R

rlON

CHAMBERPROPELLANT

GRAIN(40 POINT STAR)

BKNO3PELLETCHARGE BASKET

112cm (441N.)INITIATORPROPELLANT(30 POINT STAR)

3ZZLEINSERT

Figure 2-10.---Solid rocket motor igniter.

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A built-in safety mechanism, the safe-and-armdevice, prevents the propellant from ignitingprematurely even if the NSI initiators areinadvertently fired. The entire ignition system,including the safe-and-arm device, is 112centimeters (44 inches) long and weighs almost318 kilograms (700 pounds), of which nearly 64kilograms (140 pounds) is igniter propellant.

NozzleThe huge nozzle (fig. 2-11 ) is 4.19 meters (13.75feet) long and weighs more than 9950 kilograms(22 000 pounds). The nozzle throat is 137centimeters (54 inches) indiameter and the exitcone is376 centimeters (148 inches) in diameter.To survive a temperature of 3474 K (3204 C or5800 F) for 2 minutes, materials that restrict andablate rather than absorb heat are used to make aliner that is attached to the metal shell of thenozzle.

As the propellant bums, huge quantities of hotgases are formed and forced through the nozzle.The nozzle restricts the flow of these gases,providing the pressure and producing thrust. Thegaseous products accelerate quickly as theyexpand past the narrow part of the nozzle, whichcauses the gases to speed up to approximately9700 km/h (6000 mph) by the time they leave theexit cone.Aflexible bearing allows the nozzle to move, orgimbal, to control the direction of the rapidlymoving gases. During the recovery sequence, alinear-shaped charge separates most of thenozzle exit cone, which is not recovered. This isdone to prevent excessive loads inthe boostersat the time of water impact.

FLEXIBLE

KICKRING 137 m(54 IN.)DIAMETER AFT SKIRT

135.m (53-1N. ) ACTUATOR16.3-cm (6.4-1N. ) STROKE

EXITCONEPLANE_2

I

LINEARSHAPEDCHARGE

L='_ 376 cm (148 IN.) DIAMETER"--_"_ II528 cm (208 IN.) DIAMETER

Figure 2-11 .--Solid rocket motor nozzle.

.t

RING

HEAT SHIELD

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RefurbishmentTheusedsolid rocketmotorsareretumedo themanufacturinglantthesamewaytheyweredelivered;.e.,separatedntofour castingsegments. The first stop for the segments afterarrival at the plant isa washout facility where theinsulation and any remaining propellant arewashed out. To do this, the casting segment ispositioned on a tilt table and raised to a 30"angle. Streams of water at pressures up to 41 370kN/m 2 (6000 psi) are used to remove thepropellant and insulation. The casting segmentsare then disassembled into the original 11 smallercase segments and sent through a degreasingand grit-blasting process. The segments thenundergo magnetic particle inspection todetermine whether any cracks or defects exist.Next, the case segments are filled with oil andhydroproof tested, during which the oil pressureis raised to 7612 kN/m 2 (1104 psig). A secondmagnetic inspection is performed to see if thehydroproof test resulted inany damage. Therefurbished case segments are then reassembledinto casting segments, repainted, and preparedagain for flight.

STRUCTURESThe structural subsystem (fig. 2-12) providesstructural support for the Shuttle vehicle on thelaunch pad; transfers thrust loads to theET/Orbiter combination; and provides thehousing, structural support, and bracketryneeded for the recovery system, the electricalcomponents, the separation motors, and thethrust vector control system.

Forward AssemblyThe Solid Rocket Booster forward assemblyconsists of the nose cap, the frustum, theordnance ring, and the forward skirt.

Nose cap.--The nose cap, bearing theaerodynamic load, is made of lightweightstiffened aluminum. The 145-kilogram (320-pound) cap is 190.5 centimeters (75 inches) inoverall length and has a base diameter of 172.11centimeters (67.76 inches). The nose cap housesthe pilot and drogue parachutes.

Frusturn.m The frustum is a truncated cone 320centimeters (126 inches) long, 370.8 centimeters(146 inches) in diameter at the base (identical tothe SRB diameter), and 172.11 centimeters(67.76 inches) at the top where it joins the nosecap. Mounted on top are six alinement pins, 10centimeters (4 inches) long and 1.90 centimeters(0.75 inch) in diameter, to position the nose cap.

NOSE CAP

FLOTATION

FRUSTUMORDNANCE RINGCABLE TIEDOWNFORWARD SRB DOMEDATA CAPSULESYSTEMTOWING PENDANTASSEMBLYALTITUDE SENSORASSEMBLYFORWARD SKIRT

SYSTEMS TUNNEL

AFT RING

ROCKETMOTOR

ETISRB STRUTS

AFT SKIRT

BOOST ERSEPARATIONMOTORS SUPPORTASSEMBLY

Figure 2-12.--SRB structural system (MSFC 776268A).

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The1606-kilogram3540-pound)rustumhousesthethreemainparachutes of the recovery system,the altitude switch and frustum location aids, andthe flotation devices. The frustum also providesstructural support for a cluster of four boosterseparalion motors.Ordnance ring.-- The ordnance ring connectsthe frustumwith the forward skirt and contains alinear-shaped pyrotechnic charge that cuts thefrustum and forward skirt apart. The 145-kilogram(320-pound) ring is 15.2 centimeters (6 inches)wide and 5.1 centimeters (2 inches) thick with adiameter of 370.8 centimeters (146 inches).Forward skirt.--The forward skirt is 317.5centimeters (125 inches) long and 370.8centimeters (146 inches) indiameter and weighs2919 kilograms (6435 pounds). The structure is av_elded cylinder of individual aluminum skinpanels, varying in thickness from approximately1.3 to 5 centimeters (0.5 to 2 inches), andcontains a welded aluminum thrust post thatabsorbs axial thrust loads from the External Tank.The forward skirt houses flight avionics, rate gyroassemblies, range safety system panels, andsystems tunnel components. The structure alsocontains a towing pendant assembly that isdeployed from a parachute riser aftersplashdown. A forward bulkhead seals the skirtfrom seawater intrusion and provides additionalbuoyancy.

Aft SkirtThe aft skirt is a truncated cone 229.9centimeters (90.5 inches) long, 370.8centimeters (146 inches) indiameter at the top(identical to the SRB diameter), and 538.5centimeters (212 inches) at the base.The skirt, which weighs 5443 kilograms (12 000pounds), is manufactured of high-strength 1.3- to5-centimeter (0.5- to 2-inch) thick aluminumstiffened with integrally machined aluminumIongerons. The skin sections are rolled to theskirt's contour and welded together to providethe structural capability of supporting the entire2 041 200-kilogram (4 500 O00-pound) weight ofthe Space Shuttle onthe mobile launch platformuntil launch, and ofabsorbing and transferringside loads during SRM nozzle gimbaling during

flight. The SRM nozzle gimbals a nominal 4.7" inall directions and up to 6.65" under certainconditions.The aft skirt provides mounting provisions for thethrust vector control system and providesstructural support for the aft cluster of fourbooster separation motors.The weight of the entire Space Shuttle is bome byholddown post assemblies that provide rigidphysical links between the mobile launch platformand the two aft skirts. The uppermost componentsof the holddown post assemblies are four forgedaluminum posts welded to the skirt's exterior.Each post has a rectangular base 50.8 by 30.5centimeters (20 by 12 inches) and tapers into thecontour of the aft skirt. Each is designed towithstand compression loads in a 344 700- to413 700- kN/m 2 (50 000- to 60 O00-psi) range tosupport 255 150 kilograms (562 500 pounds), orone-eighth of the weight of the flight-ready SpaceShuttle. The posts rest on aft skirt shoes, whichprovide the interface between the post and thelaunch platform.At lift-off, an electrical signal is sent to 16detonators, 2 in each of the 8 frangible nutsholding the Solid Rocket Boosters to the launchpedestal. The detonation cracks open the nuts,releasing their grip onthe holddown posts andpermitting lift-off.

SRB/ET Attach Points and SeparationThe External Tank is attached to each SolidRocket Booster in two locations: the thrust postof the forward skirt at the forward end and threeaft attach struts mounted to the ET attach ring atthe aft end.A single pyrotechnic separation bolt joins thethrust post ofthe forward skirt and the ET attachfitting. The bolt, 66.98 centimeters (26.37 inches)long and 8.76 centimeters (3.45 inches) in shankdiameter, ismade of high-grade steel (similar incomposition and design to the separation bolt ofthe Viking Mars orbiter/lander). It is designed tocarry the 899-kilonewton (202 O00-pound)tension load that occurs after SRM thrust hasdecayed to zero.

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Thethreeaftattachstrutsaredesignedo reactto lateralloadsinducedbySRB/ETmovements,bothonthemobilelaunchplatform because ofcryogenic loading and after lift-off because ofdynamic loads associated with ascent. The strutsalso provide the separation joint for SRB/ETseparation, Each strut is 90.8 centimeters (35.75inches) long and 19 centimeters (7.5 inches) indiameter and ismade of a high-strengthcorrosion-resistant steel alloy designed to carrya maximum 1753-kilonewton (394 O00-pound)tension or compression load.Embedded in each strut is a single pyrotechnicbolt 29.85 centimeters (11.75 inches) long and12.07 centimeters (4.75 inches) in shankdiameter. The struts are attached to the SolidRocket Booster and the External Tank by pinjoints. Spherical bearings ineach strut's clevisends permit rotation to avoid bending loads. (Aclevis end is a U-shaped piece of metal with abolt or pin passing through holes at both ends toallow rotation of the fastened components.)The upper strut differs from the two lower struts inthat an external flange is incorporated on eachside of the separation plane to provide amounting ring for pullaway connectors. One of thetwo lower struts is positioned diagonally forrotation stability.The ET attach ring, located at the top of the aftmotor casting segment, provides the structure onwhich the three aft attach struts are mounted.At thrust tail-off, when pressure transducerssense a pressure drop, SRB separation from theET is electrically initiated. The single forwardseparation bolt is broken when pressurecartridges force tandem pistons to function,causing the bolt housing to fail in tension. Thesame technique is used to break the separationbolts inthe three aft attach struts.

Systems TunnelEach Solid Rocket Booster has a systems tunnelthat provides protection and mechanical supportfor the cables associated with the electrical andinstrumentation subsystem and the linear-shapedexplosive charge of the range safety system. Thetunnel extends along almost the entire length ofthe booster.The 457-kilogram (1008-pound) tunnel isapproximately 41 meters (133 feet) long, 25centimeters (10 inches) wide, and 13 centimeters(5 inches) thick. It is constructed of an aluminumalloy slightly thicker than a filing cabinet wall.

THRUSTVECTORCONTROLThe thrust vector control (TVC) system, locatedin the aft skirt, is the assembly that gimbals theSRM nozzle and thus helps to steer the entireShuttle vehicle. Rate gyros continuously measurethe rate of SRB attitude deviation, and the Orbitercomputer signals the TVC electromechanicalservoactuators to impart to the nozzle the forceto create yaw, pitch, and roll vehicle movements.The normal gimbal range is 4.7" in all directionsand upto a maximum of 6.65".The thrust vector control system in each SolidRocket Booster is composed of two powermodules or hydraulic power units (HPU's) and twoservoactuators. Each power unit normallyprovides the power to drive a single actuator;however, both units are interconnected to bothactuators, enabling either to drive both actuators(at a slightly reduced response rate). Eachhydraulic power unit has an auxiliary power unit(APU) (similar to a motor but fueled by liquidhydrazine), a fuel supply module, a fuel isolationvalve, a hydraulic fluid reservoir, a hydraulicpump, and a hydraulic manifold.

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A servoactuator isthe heart of the self-adjustingmechanism that continually compares desiredperformance with actual performance and makesthe necessary corrections. The TVCservoactuators extend or retract a dual-actionpiston inresponse to hydraulic pressure. Thepistons' extended rods exert mechanicalpressure on the nozzle, causing it to gimbalaround a pivot. For identification purposes, oneactuator in each TVC system is designated"rock" and the other "tilt." The joint actionproduces yaw, pitch, and roll movements inthebooster and thereby attitude control in alldirections. Each actuator measuresapproximately 135 centimeters (53 inches) inlength and has a 16.3-centimeter (6.4-inch)stroke. Inoperation, the stroke isconsiderablyshorter and is capable of making minute SRBattitude corrections.Early in the countdown, the hydraulic power unitsare leak-tested with helium and pressurized withgaseous nitrogen, and the fuel supply module isloaded with liquid hydrazine. At T- 20 seconds,signals originating inthe launch processingsystem are sent to the TVC system through amultiplexer-demultiplexer in the SRB aftintegrated electronics assembly (lEA).Thereafter, the TVC system is on internalcommand.

The fuel flows over the APU catalyst bed,decomposes, and becomes a gas that drives theturbine. The turbine is linked to both the fuel pumpand the hydraulic pump by a fixed-ratio gearbox.As the turbine speed increases, the fuel pumppressure output rises. Anelectronic controlassembly monitors and controls the fuel flow,closing and reopening valves to maintain anominal turbine speed of 72 000 rpm. Thevariable-delivery hydraulic pump, driven throughthe gearbox at a nominal 3600 rpm, provideshydraulic fluid from the hydraulic reservoir to themanifold, which collects and distributes the fluidto the servoactuators.A heat shield (thermal curtain) insulates the TVCsystem and its servoactuators from high heatrates due to radiated heat from gases escapingfrom the SRM nozzle and the Orbiter's liquidengines. Not only must the TVC components beprotected during flight and preserved forsubsequent reuse, but the liquid hydrazine storedin the TVC system must also be kept cool enoughto prevent autoignition. (Liquid hydrazine canbum above 394 K (121" C or 250" F).)The nozzle gimbaling requires a heat shield that"gives" with the movements; therefore, it is not arigid structure but a flexible "curtain" (similar tothose used on other launch vehicles). It isattached inboard to the SRM nozzle's compliancering and outboard to the aft ring of the aft skirt.

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PARACHUTERECOVERYSYSTEMAfterseparation,heSolidRocketBoosterscoastupward then fall toward Earth in a ballistictrajectory for almost 4 minutes (fig. 2-13). Theboosters attain a maximum speed ofapproximately 4650 km/h (2890 mph) during thetrajectory before being slowed by atmosphericdrag.The parachutes of the recovery system havecanopies of concentric nylon ribbons, spacedlike a venetian blind. The ribbon constructionadds tensile strength for high-velocitydeployment.

The pilot parachute, stored in the nose cap (fig.2-14), is 3.5 meters (11.5 feet) indiameter and isdesigned for a maximum load of 6584 kilograms(14 515 pounds) during drogue parachutedeployment. To begin deployment at an altitudeof 4694 meters (15 400 feet), a barometricswitch actuates three thrusters on the frustumthat eject the nose cap. As the nose cap movesaway from the vehicle, the pilot parachute isdeployed. As soon as the pilot parachute inflates,cutters release the drogue parachute pack.The drogue parachute, 16.5 meters (54 feet) indiameter and designed to sustain a maximum loadof 122 470 kilograms (270 000 pounds), initially

IZ PILOT PARACHUTE (1)NOSE CAP

":

Figure 2-13._SRB parachute deployment.

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ELECTRICALSYSTEMANDINSTRUMENTATIONTheelectricalsystem(fig.2-15) distributespower to, from, and within the Solid RocketBoosters for operation during ascent and descentand range safety. It uses two power sources, theOrbiter fuel cells and the SRB batteries. Rangesafety has an independent, redundant electricalcircuitry activated during the final countdownhourand powered down at SRB/ET separation.Power from the fuel cells and from the recoverybattery (one for each booster) is routed throughtwo integrated electronics assemblies. Duringascent, each Solid Rocket Booster is controlledby commands from the Orbiter processed throughthe electronics assemblies. This system alsoprovides for data acquisition.

ALTITUDEFRuSTuMSWITCH

LOCATION AIDS

SAFETY SUBSYSTEM -_

RATE GYRO ASSEMBLY

SYSTEMS TUNNEL

(INTERCONNECTING _ABLES)

INTEGRATEDELECTRONICS _ASSEMBLY (AFT)

J

J SOLID_ROCKETMOTOR

SEPARATION MOTORS _(_

Figure 2-15.--SRB electrical system,

All commands are automatic and, for all criticalfunctions, are routed by redundant solid-statecomponents through redundant buses overredundant channels. In addition, the astronautscan initiate SRB/ET separation whether or not theautomatic separation cue is received.All information relating tomission safetynignition of solid rocket motors, performance ofthe TVC system, and separation--is conveyedover redundant hard lines. All other commandsand interrogations are routed through the tworedundant multiplexer-demultiplexers of theintegrated electronics assemblies. Thesedevices receive and send coded messages overa single pair of wires and therefore saveconsiderable weight.The operational system includes the forward andaft electr()nics assemblies, rate gyro assemblies,SRB location aids, frustum location aids, therecovery battery, altitude switches, and somesensors. The lEA distributor contains thepyrotechnic initiator controllers that are essentialfor functional reliability of the pyrotechnics.These controllers are integrated logic circuitsthat are the Space Shuttle version of automotivespark plugs. Each pyrotechnic initiator controlleris a capacitor energy storage and dischargedevice that requires three separate signals inproper sequence and timing to initiate an action.Each Solid Rocket Booster has three rate gyroassemblies. Analtitude switch assembly in thefrustum initiates component separation atspecific altitudes.The SRB location aids consist of aradiofrequency beacon (radio transmitter) with a17-kilometer (9-nautical-mile) range and aflashing white strobe light with a 9-kilometer (5-nautical-mile) range, pulsating at 500 wattsintensity (similar inoutput to an aircraft beacon).The radio's 30.5-centimeter (12-inch) antennaand the strobe light are mounted on the apex ofthe dome of the forward skirt. These aids areactuated by the altitude switch and powered fromthe recovery battery.

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The frustum location aids consist of aradiofrequency beacon and a strobe light of thesame range, output, and configuration as the SRBlocation aids. These aids are powered by internalbatteries and are activated by the closing of a"saltwater switch" inwhich saltwater acts as theconductor between two metal pins.

ORDNANCEAll major Solid Rocket Booster functions exceptsteering--from launch pad release throughSRB/ET separation to recovery of SRBsegments--depend on electrically initiatedpyrotechnics. The boosters use the following fivetypes of explosive-actuated devices.1. NASA standard initiator cartridges thatcontain compressed explosives2. Frangible nuts with built-in weak points thatbreak open fromshock imparted by the cartridges3. Thrusters with pressure-producingpyrotechnic charges that impart velocity to areleased component to achieve distance4. Separation bolts that incorporate tandempistons exerting pressure onone another,causing the outer housing to stretch (fail intension) and break at a weakened separationgroove5. Linear-shaped charges that compressexplosive powder into rigid, chevron-shapedchannels and, upon detonation, cut apart largestructures by essentially the same technique asthat used by the steel industry to cut bridgegirdersAll but the frangible nutsand separation bolts useso-called ordnance trains. Such a "train"consists of a NASA standard detonator (NSD)connected to a metal-sheathed fiberglass-wrapped fuse, called a confined detonating fuse,through a fuse manifold. The pencil-lead-thin fusediffers from industrial mild detonating fuses, suchas those used in the mining industry, only bybeing "confined" in fiberglass. All SRBpyrotechnics are triggered by electrical signalsfrom the pyrotechnic initiator controllers.

BOOSTER SEPARATION MOTORSSmall solid-fueled booster separation motors"translate" or move the Solid Rocket Boostersaway from the Orbiter's still-thrusting mainengines and External Tank. Four boosterseparation motors are clustered in each SRB'sfrustum; another cluster of four is mounted oneach SRB's aft skirt. Both clusters are mounted onthe SRB sides closest to the External Tank. Thethrust of the clusters moves the SRB's away fromthe Orbiter.Each of the 16 booster separation motors on thetwo Solid Rocket Boosters is 79 centimeters(31.1 inches) long and 32.64 centimeters (12.85inches) indiameter and weighs 69 kilograms(152 pounds). Each has a specific impulse of 250at vacuum and develops a nominal 97 860newtons (22 000 pounds) of thrust. The nozzlesof the booster separation motors are protectedagainst autoignition from aerodynamic andradiated SSME plume heating. The aft clustershave 19-centimeter (7.5-inch) diameter aluminumnozzle covers. The ignition blast fractures thecovers at predetermined notches and the exhaustplumes carry them away from the Orbiter/ET. Theforward separation motor clusters, located withinthe frustum except for the protruding nozzles, areclose enough to the Orbiter that blow-awaycovers might strike the vehicle. Therefore, thesenozzle exits are protected by 19-centimeter (7.5-inch) diameter stainless steel covers that aremerely blown open like doors when the boosterseparation motors are fired and thus remainattached to the motors. Detonators ignite themotors, which burna nominal 0.66 second(maximum 1.05 seconds) to push the boostersaway from the Orbiter/ET. At thrust termination,the distance vector between the noses of theSRB's and the Orbiter is a nominal 318centimeters (125 inches).

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THERMALPROTECTIONSYSTEMTheexteriorsurfacesoftheSolidRocketBooster,exposedtothermalheatloads,areinsulatedbyablativematerialsowithstandfriction-induced heat.Heating rates vary between SRB lift-off and SRBinert splashdown. Broadly, maximumtemperatures of approximately 1533 K (1260 =Cor 2300 F) are encountered at the time ofSRB/ET separation, when the boosters are

exposed to the plumes of the three Space ShuttleMain Engines. Maximum reentry temperatures arein the range of 578 to 589 K (304" to 31 5C or580" to 600 F). Splashdown temperatures arelimited to 344 K (71C or 160 =F).Various types of insulation, each with specialcharacteristics, are used inthermally protectingthe boosters. Cork and a sprayable ablativematerial are the primary insulating materials.Molded fiberglass is also used inthe high-heatprotuberance areas.

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f %

External Tank

STRUCTURES ............................. 2-35Liquid Oxygen Tank ....................... 2-35Liquid Hydrogen Tank ...................... 2-37Intertank ................................. 2-38PROPULSION SYSTEM ..................... 2-39Liquid Oxygen Feed Subsystem ............. 2-39Liquid Hydrogen Feed Subsystem ............ 2-40Pressurization, Vent Relief, and TumblingSubsystem ............................... 2-40Environmental Conditioning ................. 2-41ELECTRICAL SYSTEM ...................... 2-41Instrumentation ........................... 2-41Cabling .................................. 2-41Lightning Protection .. ..................... 2=41THERMAL PROTECTION SYSTEM ............ 2-41INTERFACE HARDWARE ................... 2-42External Tank/Solid Rocket BoosterInterfaces ................................ 2-42External Tank/Orbiter Interfaces ............. 2-42External Tank/Facilities Interfaces ............ 2-43

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Briefly...The External Tank is the "gas tank" for the Orbiter; it contains the propellants used by the mainengines. Approximately 8.5 minutes into the flight with most of its propellant used, the ET isjettisoned and splashes down in the Indian Ocean. It is the only major part of the Space Shuttlesystem that is not reused.

TOTAL WEIGHTEmpty:Gross:

NOSE CAP

Liquid hydrogen:Total:

35 425 kilograms(78 100 pounds)756 441 kilograms LIQUID(1 667 677 pounds) OXYGEN

TANKPROPELLANT WEIGHTLiquid oxygen: 616 493 kilograms

(1 359 142 pounds)102 618 kilograms(226 237 pounds)719 11 2 kilograms(1 585 379 pounds)

PROPELLANT VOLUMELiquid oxygen tank: 541 482 litersLiquid hydrogentank:

(143 060 gallons)1 449 905 liters(383 066 gallons)1 991 387 liters(526 126 gallons)

Total:

(Propellant densi ties of 1138 and 70.8 kg/m 3(71.07 and 4.42 Ib/ft 3) used for liquid oxygenand liquid hydrogen, respectively)DIMENSIONSLiquid oxygen tank: 16.3 meters (53.5 feet)Liquid hydrogentank: 29.6 meters (97 feet)Intertank: 6.9 meters (22.5 feet)

INTERTANK

LIQUIDHYDROGENTANK

/\/47.0 METERS(154.2 FEET)

|

|11...8.4 METERS(2"/_ FEET)

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External TankThe External Tank (ET) contains the propellantsfor the three Space Shuttle Main Engines(SSME's) and forms the structural backbone ofthe Shuttle system in the launch configuration. Atlift-off, the External Tank absorbs the total28 580-kilonewton (6 425 O00-pound) thrustloads of the three main engines and the two solidrocket motors. When the Solid Rocket Boosters(SRB's) separate at an altitude of approximately44 kilometers (27 miles), the Orbiter, with themain engines still burning, carries the ExternalTank piggyback to near orbital velocity,approximately 113 kilometers (70 miles) abovethe Earth. There, 8.5 minutes into the mission, thenow nearly empty tank separates (fig. 2-16) andfalls in a preplanned trajectory into the IndianOcean. The External Tank is the only majorexpendable element of the Space Shuttle.The three main components of the External Tank(fig. 2-17) are an oxygen tank, located in theforward position, an aft-positioned hydrogentank, and a collar-like intertank, which connectsthe two propellant tanks, houses instrumentationand processing equipment, and provides theattachment structure for the forward end of theSolid Rocket Boosters.

f_

Figure 2-16.--Separation of Space Shuttle External Tank(MSFC 00308).

The hydrogen tank is 2.5 times larger than theoxygen tank but weighs only one-third as muchwhen filled to capacity. The reason for thedifference inweight isthat liquid oxygen is 16times heavier than liquid hydrogen.The skin of the External Tank is covered with athermal protection system that is a nominal 2.54-centimeter (1-inch) thick coating of spray-onpolyisocyanurate foam. The purpose of thethermal protection system isto maintain thepropellants at an acceptable temperature, toprotect the skin surface from aerodynamic heat,and to minimize ice formation.The Extemal Tank includes a propellant feedsystem to duct the propellants to the Orbiterengines, a pressurization and vent system toregulate the tank pressure, an environmentalconditioning system to regulate the temperatureand render the atmosphere in the intertank areainert, and an electrical system to distribute powerand instrumentation signals and provide lightningprotection. Most of the fluid control components(except for the vent valves) are located in theOrbiter to minimize throwaway costs.

STRUCTURESThe tank structure is designed to accommodatecomplex load effects and pressures from thepropellants as well as those from the two SolidRocket Boosters and the Orbiter. Primarilyconstructed of aluminum alloys, the tank contains917.6 meters (3010.5 linear feet) of weld. Thebasic structure ismade of 2024, 2219, and 7075aluminum alloys and the thickness ranges from0.175 to 5.23 centimeters (0.069 to 2.06 inches).

Liquid Oxygen TankThe liquid oxygen tank (fig. 2-18) contains541 482 liters (143 060 gallons) of oxidizer at 90K (-183 C or -297" F). It is 16.3 meters (53.5feet) long and 8.4 meters (27.5 feet) indiameter.The weight, when empty, is 5695 kilograms(12 555 pounds); loaded, it weighs 622 188kilograms (1 371 697 pounds).

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PROPELLANT FEED.PRESSURIZATIONLINES _1

ET/ORBITER /IAFTATTACH_ / l

I"" ETIORBITER _lg

E,,SRBORWARD,TAC.--\ _cmuID OXYGENSLOSH _.,r=s=F-_ \ _ _m-.'_.a zLIQUID BAFFLES _ ___ _ _ | _oxY,_EN ___h"'_ _..----'_ -_.=_=,_-._FAIRING._

_ _ / HYDROGEN..\ _-_ . _ TANK"_ _Mrm_mmNw"- /'_"_', INTERTANK

LIQUID/ OXYGEN INTERTANK

TANK UMBI LICALPLATEFigure 2-17.---Space Shuttle External Tank.

LIQUID OXYGEN TANK

AFT DOMEASSEMBLY

AFT SLOSH OGIVEBAFF LE FORWARDASSEMBLY OGIVE

Figure 2-18.--ET liquid oxygen tank structural assembly.

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The liquid oxygen tank is an assembly ofpreformed fusion-welded aluminum alloysegments that are machined or chemically milled.It is composed of gores, panels, machinedfittings, and ring chords. Because the oxygen tankis the forwardmost component of the ExternalTank and also of the Space Shuttle vehicle, itsnose section curves to an ogive, or pointed archshape, to reduce aerodynamic drag. A shortcylindrical section joins the ogive-shapedsection to the aft ellipsoidal dome section. A ringframe at the juncture of the dome and cylindricalsection contains an integral f lange for joining theliquid oxygen tank to the intertank.The major assemblies comprising the liquidoxygen tank are the nose cap and cover plate, theogive nose section, the cylindrical barrel section,the slosh baffles, and the aft dome.The conical nose cap that forms the tip of theliquid oxygen tank is removable and serves as anaerodynamic fairing for the propulsion andelectrical system components. The cap containsa cast aluminum lightning rod that providesprotection for the Shuttle launch vehicle. Thecover plate serves as a removable pressurebulkhead and provides a mounting location forpropulsion system components.The ogive nose section isfusion-welded andconsists of a forward ring, 8 forward gores, and12 aft gores. It connects to the cylindrical barrelsection, which isfabricated from four chemicallymilled panels.Slosh baffles are installed horizontally in theliquid oxygen tank to prevent the sloshing ofoxidizer. The baffles, which minimize liquidresiduals and provide damping of fluid motion,consist of eight rings tied together withlongitudinal stringers and tension straps. Sloshbaffles are required only inthe liquid oxygen tankbecause liquid oxygen, which is 12 percentheavier than water (1137 kg/m 3 (71 Ib/ft 3)compared to 1025 kg/m 3 (64 Ib/ft3)), could sloshand throw the vehicle out of control. The densityof liquid hydrogen is low enough that baffles arenot required.Antivortex baffles are installed inboth propellanttanks to prevent gas from entering the engines.Without them, the propellants would create a

vortex similar to a whirlpool in a bathtub drain.The baffles minimize the rotating action as thepropellants flow out the bottom of the tanks. Theslosh baffles form a circular cage assembly; theantivortex baffles look more like fan blades.The dome section of the liquid oxygen tankconsists of a ring frame, 12 identical goresegments, and a dome end cap 355.6 centimeters(140 inches) in diameter. The end cap contains apropellant feed outlet, an electrical connector,and a 91 A-centlmeter (36-inch) manhole f

Documents

NASA Space Shuttle News Reference 1981