NASA Facts Proving the Space Transportation System the Orbital Flight Test Program

8/7/2019 NASA Facts Proving the Space Transportation System the Orbital Flight Test Program

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PRJVING THE S ACEORBITAL FLIGHT

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Mission Crew Launch/LandingCommander 4/12181John W. Kennedy Space

STS-1 Young CenterPilot 4/14/81Robert L. Dry lakebed,Crippen Edwards AFB

Commander 11 /12181Joe H. Engle Kennedy SpaceCenterSTS-2 Pilot 11 /14/81Richard H. Dry lakebed,Truly Edwards AFB

Commander 3/22/82Jack R. Kennedy SpaceLousma CenterSTS-3 3/30/82Pilot Northrup StripC. GordonFullerton White Sands,New Mexico

Commander 6/27/82Thomas K. Kennedy SpaceMattingly CenterSTS-4 Pilot 7/4/82Henry W. Runway 22 ,Hartsfield , Jr. Edwards AFB

1981 and landed on a dry lakebed atEdwards Air Force Base in Californiaon April 14. Stresses on the vehiclewere kept to a minimum for this firstflight , and the only cargo weightswere the Data Flight Instrumentation(OFI) and the AerodynamicCoefficient Identification Package(ACIP). ACIP was a group ofaccelerometers and gyros includedon all test flights to gatheraerodynamic data during theShuttle 's atmospheric flight. STS-1successfully demonstrated two vitalspacecraft systems: the payload bay

Orbital Total WeightAltitude/ inInclination Payload Bay Payloads and Onboard Experiments

237 kilometers148 nautical 4870 Data Flight Instrumentation (DF I); Pass ive Opticalmiles (n .mi.) kilograms Sample Assembly ; Aerodynamic Coefficient(10 ,823 Ibs.) Identification P a c k a g ~ (ACIP )40

DFI ; ACIP ; Induced Environment ContaminationMonitor (IECM) Tile Gap Heating Experiment ; (Tile)Catalytic Surface Experiment ; Dynamic, Acoustic andThermal Experiment (DATE);222 x 230 km . 05TA-1 Payload (for Office of Space & Te rrestrial(139 x 144 8900 kg . Applications) Shuttle Imaging Radar-An.mi .) (19 ,778Ibs.) Shuttle Multispectral Infrared Radiometer38 Feature Identification & Location Experiment Measurement of Air Pollution From Satell ites Ocean Color Experiment Night/Day Optical Survey of Lightn ing Heflex Bioengineering Test

DFI; ACIP ; IECM ; Tile Gap Heating; Catalytic Surface;DATE ; Getaway Special Canister ; Monodisperse LatexReactor; Electrophoresis Test ; Heflex BioengineeringTest ; Shuttle Student Involvement Pro ject (Insects inFlight) ;055-1 Payload (for Office of Space Science)208 km . Contamination Monitor(130 n.mi.) 10 ,220 kg . Microabrasion Foil Experiment(22 ,710 Ibs.)38 Vehicle Charging & Potential Experi ment Shuttle-Spacelab Induced Atmosphere Solar Flare X-Ray Polarimeter Solar Ultraviolet Spectral Irrad iance Monitor Plant Growth Unit Thermal Canister Experiment

Plasma Diagnostics PackageDFI ; ACIP ; IECM ; Tile Gap Heating Experiment;Catalytic Surface Experiment ; DATE ; Getaway Special258 km. 11 ,021 kg. (9 experiments) ; Shuttle Student Involvement Project(161 n.mi .) (24 ,492 Ibs .) (2 experiments) ; Monodisperse Latex Reactor ;28S Continuous Flow Electrophoresis System; Night/DayOptical Survey of Lightning; Department of DefensePayload DOD-82-1

doors with their attached heatradiators and the Reaction ControlSystem thrusters used for attitudecontrol in orbit.

first tests of the Remote ManipulatorSystem's 15-meter (50 foot) arm andthe successful operation of Earthviewing instruments in the cargo bay.Most importantly, STS-2 proved theShuttle 's re-usabili ty.Originally scheduled for five days,the STS-2 mission had to be cut

short because one of Columbia 'sthree electricity-generating fuel cellsfailed shortly after the vehiclereached orbit. Commander Joe Engleand Pilot Richard Truly still managedto achieve most of their flightobjectives during the 54-hour missionfrom November 12 to November 14,1981 . Milestones for STS-2 were the

The third mission was the longestof the test series. Commander JackLousma and Pilot Gordon Fullertonwere launched on March 22, 1982and landed on March 30 at the WhiteSands Missile Range's Northrup Stripin New Mexico, a backup site chosenafter rains flooded the normally drylakebed at the pr ime landing site in

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California. High winds at WhiteSands also caused a delay inlanding, extending the week-longmission to eight days.Just as STS-2 had featured theShuttle 's first Earth-viewing payload,STS-3 launched the first spaceviewing instruments, a collection ofastronomical and space-environmentsensors designated OSS-1 (after theirsponsor, NASA's Office of SpaceScience). STS-3 continued withtesting of the Remote ManipulatorSystem arm, carried the first studentdeveloped experiment (a study ofinsect flight in weightlessness) in theOrbiter's mid-deck cabin , and beganan important series of thermal testsof the spacecraft.The fourth Shuttle mission,commanded by T. K. Mattingly withHenry Hartsfield, Jr. as Pilot,completed the OFT program. STS-4was launched on June 27 , 1982 andlanded on July 4. Among theaccomplishments of this last testflight were: continued thermaltesting, va lidation of the RemoteManipulator System, the transport ofShuttle's first Department of Defensecargo, the first privately fundedGetaway Special , and the firstlanding on a hard surface runway.Getting Into Orbit:The Rockets

The sequence of events for aShuttle launch begins with a startcommand to the Orbiter'S three mainliquid-fueled engines, followed byseveral seconds of thrust buildupbefore the twin Solid RocketBoosters ignite, release from theirhold-down mechanisms, and lift theentire Shuttle assembly from the pad .

An early and very significantfinding of the test program was thatthe water deluge system designed tosuppress the powerful acousticpressures of liftoff would need to berevised , after the shock from thebooster rockets was seen to be muchlarger than anticipated for STS-1 . Inthe seconds before and after liftoff, a"rainbird " deluge system had poured4

LiquidOxygenTank

Intertank

Liqu idHydrogenTank

SolidRocket __ _Motor .....~ I - ~ AFTSkirtNozzle __ _

tens of thousands of gallons of wateronto the launch platform and intoflame trenches beneath the rocketsto absorb sound energy that mightotherwise damage the Orbiter or itssensitive cargo. Strain gages andmicrophones were used to measurethe acoustic shock, and they showedup to four times the predicted valuesin parts of the vehicle closest to thelaunch pad.Although Columbia suffered nocritical damage, the soundsuppression system had to bemodified before the launch of STS-2.Rather than dumping into the bottom

Height56 .14 Meters184 .2 Feet

of the flame trenches, water was nowinjected directly into the exhaustplumes of the booster rockets at apoint just below the exhaust nozzlesat the time of ignition . In addition,energy-absorbing water troughs wereplaced over the exhaust openings.The changes were enough to reduceacoustic pressures to 20-30%of STS-1 levels for the secondlaunch , and they remained atacceptable levels for all subsequentmissions.STS-1 was the first opportunity toobserve the Shuttle's array of solidand liquid rockets as a combined


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Space Shuttle Orbiter, External Tank and Solid Rocket Booster

ObservationWindows -=::::::::::::;;;......>111"".. & i " ~ ' " " \

-:::::ystem

StarTrackerDoorsCrewSideHatch

propulsion system. On all OrbitalFlight Test flights, slow motioncameras mounted on the launch paddocumented main engine and solidrocket firing as well as the Shuttle'sascent from the pad. Engineperformance was assessed byexamining the ascent trajectories forall four flights, reviewing vehicle dataand by post-flight inspections.Main Propulsion SystemAt the end of Orbital Flight Tests,Columbia's main engines had beendemonstrated successfully up to100% of thei r rated power level(upgraded engines will throttle to

Rudder/speed BrakeFi xedRadiatorPanels

Orbital-- ,1-__ Maneuvering

~ SystemEngines(2)

AFTReSThrusters

Body Flap

RemoteManipulatorSystemPay loadBay Door

MainLandingGear

ArmOrbiter Length37 .24 Meters122.2 FeetWingspan23.79 Meters78.06 Feet

109% of this level on later flights) anddown to 65%. Designed to provide1.67 million Newtons (375 ,000pounds) of thrust each at sea levelfor an estimated 55 missions, theengines were on target to meet theseguidelines at the end of the testprogram. They met all requirementsfor start and cutoff timing , thrustdirection control and the flow ofpropellants. As engineers learnedmore about the system 's fuelefficiency, and as ground crewsimproved propellant loadingtechniques, extra fuel margins werealso reduced.

The Shuttle was tested in itslaunch phase by planningincreasingly more demanding ascentconditions for each test flight, andthen by comparing predicted flightcharacteristics with data returnedfrom ACIP and DF I instruments andground tracking . Columbia liftedslightly heavier payloads into spaceon each mission. The altitudes andspeeds at which the solid rocketsand external tank separated werevaried, as was the steepness of thevehicle 's climb and main enginethrottling times. Al l of these changescorresponded to a gradual increasing

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over the course of the test programin the maximum dynamic pressure,or peak aerodynamic stress, inflictedon the vehicle. Maximum dynamicpressu re for the STS -1 ascent was607 pounds per square foot (psf).This was raised to 640 psf for STS-2 ,650 psf for STS-3 and finally to 703psf for STS-4. The Shuttle'soperational limit is 819 psf. At notime did Columbia experience anysignificant problems with theaerodynamic or heat stresses ofascent.A major milestone in the testprogram was the shift (after STS-2)from using wind tunnel data forcomputing Columbia's ascent path tousing aerodynamic data derived fromthe first two flights. On STS 1 and 2the Shuttle showed a slight loft ingabout 3000 meters (10 ,000 feet) atmain engine cutoff-above itsplanned trajectory. This was due tothe inability of wind-tunnel models tosimulate the afterburning of hotexhaust gasses in the real6

atmosphere. Beginning with the thirdflight, the thrust of the boosterrockets was re-oriented slightly toreduce this lofting.On STS 3 and 4, however, thetrajectory was seen to be too shallow,in part due to a slower thanpredicted burn rate for the solidboosters that had also been observedon the first two flights. Engineerscontinued tc use OFT data afterSTS-4 to refine their predictions ofthis solid propellant burn rate so thatascent trajectories could be plannedas accuratel)1 as possible on futuremissions. In all cases the combinedpropulsion of main engines, solidboosters and Orbital ManeuveringSystem engines delivered the Shuttleto its desired orbit.STS-4 w a the first mission to orbitat a 28.5 inclination to the equator.The first flights flew more steeplyinclined orbits (38-40) that tookthem over more ground trackingstations. ThE! more equatorial STS-4inclination is favored because it gives

Twin solid rockets separate from theExternal Tank, then parachute downto the Atlantic Ocean for recovery.Because there were problems withseparation of the parachutes duringthe test flights, they were leftattached to the rockets after waterimpact on STS-S.the vehicle a greater boost from therotating Earth at launch. The first twoflights also verified that the vehiclehas enough energy to press on to anemergency landing in Spain orSenegal , as abort options, shouldtwo main engines fail during ascent.After STS-5 the crew ejection seatswere removed from Columbia,eliminating the option to eject, andending the need for astronauts towear pressure suits during launch.Solid Rocket BoostersOn each test flight, the twin SolidRocket Boosters, the largest everflown and the first designed for reuse, provided evenly matched thrust,shut off at the same times and


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separated as planned from theexternal tank, then parachuted downto their designated recovery area inthe Atlantic Ocean for towing back tothe mainland and re-Ioading withsolid propellant. Each booster hasthree main parachutes that inflatefully about twenty seconds beforewater impact. Prior to the test flights,these parachutes were designed toseparate automatically from theboosters by means of explosive boltswhen the rockets hit the water, sinceit was thought that recovery would beeasier if the chutes were not stillattached .On the first and third flights,however, some parachutes sankbefore recovery. Then, on STS-4, theseparation bolts fired prematurelydue to strong vibrations, theparachutes detached from therockets before water impact, and therockets hit the water at too great aspeed and sank. They were notrecovered . As a result of theseproblems, the recovery hardware and

procedures were altered beginningwith STS-5 . Instead of separatingautomatically with explosives, theparachutes remained attached to theboosters through water impact, andwere detached once the recoveryteam arrived. There were alsosections of the boostersstrengthened as a result of waterimpact damage seen on the testflights.External TankThe Shuttle'S huge external fueltank at 47 meters (154 feet) high, istaller than many office buildings. Thetank met all performance standardsfor OFT. Heat sensors have shownascent temperatures to be moderateenough to allow planned reductionsin the thickness and weight of thetank's insulation . Beginning withSTS-3, white paint on the outside ofthe tank was left off to save another243 kilograms (540 pounds) ofweight, leaving the tank the browncolor of its spray-on foam inSUlation.Onboard cameras showed flawless

separation of the tank from theOrbiter after the main engines cut offon each fl ight , and Shuttle crewsreport that th is separation is sosmooth that they cannot feel ithappening. To assist its breakup inthe atmosphere, the tank has apyrotechnic device that sets ittumbling after separation rather thanskipping along the atmosphere like astone. This tumble device failed onSTS-1 , but worked perfectly on allsubsequent missions. On all the testflights radar tracking of the tankdebris showed it to fa ll well w ithinthe planned impact area in the IndianOcean.Orbital Maneuvering SystemShortly after it separates from thefuel tank, the Orbiter fires its two aftmounted Orbital ManeuveringSystem engines for additional booststo higher and more circularizedorbits. At the end of orbitaloperations, these engines are calledon again to decelerate the vehicleand begin its fall to Earth. The

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engines performed these basicfunctions during OFT with normallevels of fuel consumption andengine wear. Further testing includedstartups after long periods ofidleness in vacuum and low gravity(STS 1 and 2), exposure to cold(STS-3) and exposure to the Sun(STS-4). Different methods ofdistributing the system 's propellantswere also demonstrated. Fuel fromthe left tank was fed to the right tankand vice versa, and from the OrbitalManeuvering System tanks to thesmaller Reaction Control Systemthrusters (they both use the samecombination of hydrazine andnitrogen tetroxide). On STS-2 theengine cross-feed was performed inthe middle of an engine burn tosimulate the engine's failure.Orbital Operations:The Spacecraft

Once in space, an early priority forany Shuttle mission is to open thetwo large payload bay doors withtheir attached heat radiators. If thedoors do not open in orbit, theShuttle is not able to deploypayloads or shed its waste heat. Ifthey fail to close at mission's end, reentry through the atmosphere isimpossible.The STS-1 crew ran an importantseries of payload bay door testsduring Columbia 's first few hours inspace. The doors were first unlatchedfrom the bulkheads and from eachother. One at a time they wereopened in the manual drive mode,while TV cameras and the crewrecorded their motion. Themovement of the doors was slightlymore jerky and hesitant in spacethan in Earth-gravity simulations, butthis was expected, and did not affecttheir successful opening and closing.The doors were closed and reopened again one day into the STS-1mission as a further test, then closedfor good before re-entry. The crewverified normal alignment andlatching of the doors as did theSTS-2 crew during their door cycling8

tests, including one series in theautomatic mode.Door cycling was also tested afterprolonged exposure to heat and cold .The doors are made of a graphiteepoxy composite material , while theOrbiter itself is made of aluminum. Itwas therefore important tounderstand how they would fittogether after the aluminumexpanded or contracted in thetemperature extremes of space. Atthe beginn ing of STS-3 orbitaloperations the doors were opened asusual. The payload bay was thenexposed to cold shadow for a periodof 23 hours. When the port-side doorwas closed at the end of this"coldsoak" it failed to latch properly,

Orbital Maneuvering Systemengines fire to place vehicle in orbit,to change orbits, and to break outof orbits at end of mission.as it did after a similar cold exposureon the STS-4 mission. Apparently theOrbiter warps very slightly into a"banana" shape with nose and tailbent upward toward each other,accounting in part for the doors'inability to clear the aft bulkhead .The solution on both flights wasthe same, and has become standardprocedure for closing the doorsfollowing a long cold exposure : theOrbiter holds a top-to-Sun positionfor 15 minutes to warm the cargobay, then undergoes a short


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STS-1 tested payload bay doors anddeployment of radiator panels (left).Photo also shows blanketed "box "of Data Flight Instrumentation (OFI)in the rear of cargo bay, andmissing white tiles on aft enginepod (upper r i g h t ~ "barbecue roll " to even out vehicletemperatures, allowing the doors toclose and latch normally. In addition ,there have been hardware changes tothe doors and to the aft bulkheaddesigned to improve their clearance.Thermal Tests

To understand the Shuttle'sreaction to the thermal extremes ofspace was a key objective of the OFTprogram, and thermal testsaccounted for hundreds of hours ofmission time. The temperatures ofspacecraft structures can changedramatically in space depending ontheir exposure to the Sun.Temperatures on the surface ofpayload bay insulation, for example,went from a low of - 96 C(140F) toa peak of 12rC (260F) on the sameSTS -3 mission. The Space Shuttlekeeps its components within theirdesigned temperature limits throughits active thermal control system,

which includes two coolant loopsthat transport waste heat fromOrbiter and payload electronics tothe door-mounted radiator panels fordumping into space, and by the useof in sulation and heaters.The OFT program tested thisability to keep cool and keep warmunder conditions much moreextreme than the average mission 's.STS 3 and 4 featured extendedthermal "soaks," where parts of theOrbiter were deliberately heated upor cooled down by holding certainattitudes relative to the Sun. OnSTS-3 the Orbiter was first held withits tail to the Sun for 25 hours,heating its aft engines but coolingthe nose and payload bay. Followingthat it held nose-to-Sun for 80 hours,cooling down those same OrbitalManeuvering System engines andreaction control jets. Finally, thepayload bay was heated by holdingthe Orbiter'S top tothe Sun for 28hours. These long thermal soakswere separated by shorter periods of"barbecue roll " for even heating. OnSTS -4 the thermal soak testscontinued with long tail-to-Sun andbottom-to-Sun exposures.Overall , these hot and cold soak

tests showed that the Shuttle has abetter than predicted thermalstability. STS-3 readings showed thatthe Orbiter's skin kept considerablywarmer during coldsoaks than hadbeen expected and that many criticalsystems like the orbital maneuveringengines were also warmer. Mostvehicle structures also tend to heatup or cool down at slower rates thanexpected .The Active Thermal ControlSystem, with its coolant loops andspace radiators, proved capable ofhandl ing Shuttle heat loads in orbiteven under extreme conditions. Thisis important to know for futuremissions where instrument pointingrequirements may demand longperiods of Sun or shadow on partsof the vehicle. On a mission withmoderate heating and cooling suchas STS-1 the total heat load on theAct ive Thermal Control System wasfound to be 15% lower thanexpected .The space radiators were testedwith all eight panels deployed, andthey proved capable of sheddingmost heat loads with only half thepanels deployed. These radiators arebut one part of the thermal controlsubsystem. During ascent theShuttle's flash evaporators transferheat from circulating coolant towater, beginning about two minutesinto the ascent when the vehicle firstrequires active cooling. These flashevaporators normally work until thespace radiators are opened in orbit.Then , at the end of the mission theflash evaporators are reac tivated andused down to an altitude ofapprox im ately 36 ,000 meters (120 ,000feet) during re-entry. From thataltitude down to the ground the heatis shed by boiling ammonia ratherthan water.During OFT these differentmethods of cooling down weresuccessfully tested as backups toeach other. The flash evaporatorsproved capable of handling heatloads in space for a short whilewithout help from the radiators, and

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OFT Thermal Tests

PASSIVE THERMAL CONTROL(Barbecue Mode)(j)/ EarthPAYLOAD TO SUN

~ I

~ I Earth/

--__ Sun---

--__ Sun---

TP,IL TO SUN(Payload Bay to Space)

/ct '/

BOTTOM TO SUN

/I

~ / Earth

I1

--__ Sun---

--__ Sun---

Thermal testing of Orbiter was accomplishl:!d by holdingdifferent attitudes relative to the Sun for I,ong periods.

the (stowed) radiators were allowedto absorb some of the vehicle'sinternal heat loads during re-entry,bypassing the ammonia boilers .SubsystemsAll four of the two-man crews forthe test flight program were keptbusy every minute they were in orbit,testing and re-testing the Shutt le 'smain subsystems under varyingconditions, like new car ownerschecking out their options. On thefour OFT flights virtually everyone ofthese systems-hydraulic , electrical,navigation and guidance,communications and environmentalcontrol-performed up to designstandards or better.

The hydrau lic subsystem thatcontrols movement of the Shuttle'sengine nozzles, its airplane-likecontrol flaps and its landing gearfunctioned well during OFT launchesand re-entries. Normally idle whenthe Shuttle is in orbit, the hydraulicsystem must keep its fluids warmand ready for action. The hydraulicsystem was tested successfully onSTS-2 by cycling the eleven controlsurfaces while in orbit. On STS-4 thehydraulics were evaluated after a longcoldsoak, when it was found thatcirculation pumps need only operateat minimal levels to keep thehydraulic fluids above criticaltemperatures. These minimal dutycycles for circulation pumps will saveon electrical power.Although an oil filter clog in thehydraulic system's Auxiliary PowerUnits delayed the launch of STS-2 bymore than a week, the problem didnot recur during the test program.The solution was to use tighter sealsto prevent the oil from beingcontam inated by the units' hydrazinefuel.The same STS-2 mission was cutshort due to a failure of one of thethree Shuttle fuel cells that convertsupercold (cryogen ic) hydrogen andoxygen to electricity. A clog in thecell 's water flow lines (water for thecrew is produced as a by-product ofthe fuel cell 's generation of


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electricity) was the cause of thefailure, and this problem wasremedied during OFT by addingfilters to the pipes. An uplanned-forbenefit from this failure , though, wasa test of the vehicle using only twofuel cells instead of three, whichwere enough to handle all electricalneeds. One concern before OFT wasthat uneven mixing of the cryogenichydrogen and oxygen in theirstorage tanks would hinder their flowto the fuel cells in low gravity. Aftertwo tests for this effect with the tanksnearly full and nearly empty, it didnot appear to be a significantproblem. Partly as a result of theShuttle's thermal stability, electricityconsumption by the Orbiter provedto be lower than expected , rangingfrom 14 to 17 kilowatts per hour inorbit as opposed to the pred icted 15to 20 ki lowatts.The ability of the Shuttle 'scomputers to control virtually everyphase of each mission from finalcountdown sequencing to re-entrywas successfully demonstrated on allflights, with only minor programmingchanges being necessary during thetest program. The on-orbit navigationand guidance aids were checked outthoroughly. The Orbiter "senses" itsposition in space by means of threeInertial Measurement Units (IMU 's)whose accuracy is checked andperiodically updated by a star trackerlocated on the same navigation basein the cockpit-like flight deck. Thisvital star tracker/lMU alignment wastested extensively on the first Shuttlemission, including once when thevehicle was rolling , and on all flightstheir agreement was good. The startracker was able to find its guidestars both in darkness and indaylight. Its accuracy is better thanexpected , and the entire navigationinstrument base showed its stabilityunder extreme thermal conditions.Crew optical alignments of the IMU 'swere also demonstrated as a backup.Radio and TV communication weresuccessfully carried out on all fourflights with only minimal hardware

and signal acquisition problems atground stations. Specific testschecked different transmissionmodes, radio voice through theShuttle's rocket exhaust duringascent, and UHF transmission as abackup to the primary radio linkduring launch and operations inspace. All were successful. On STS-4there was also an evaluation of howdifferent Orbiter attitudes affect radioreception in space, important forplanning future missions.The closed-circuit television systeminside the Orbiter and out in thecargo bay gave high-quality videoimages of operations in orbit. InSunlight and in artificial floodlightingof the payload bay they showed thenecessary sensitivity, range of vision ,remote control and video-recordingcapabilities.Attitude ControlWhen in orbit, the Shuttle uses itsReaction Control System of 38primary and 6 smaller vernierthrusters to control its position(attitude) and to make small scale"translations," or movements, inspace. These jets are located in theOrbiter'S nose area and on the aftpods near the other larger engines ,and they fire in differentcombinations to move the Shuttle tonearly any desired position. "Wehaven 't taught it to dance yet ," says aShuttle official , "but it can do justabout anything else." This importantsubsystem was the object ofextensive testing beginning withSTS-1 .The jets were evaluated in ageneral way by seeing how theOrbiter responded during a series ofattitude maneuvers in space-vehiclerolls around all three axe&-roll , pitchand yaw-and translations up-anddown, sideways, and forward-andbackward . Both primary and vernierthrusters were tested in thesevalidation runs. Automatic and crewcommanded manual reaction controlwas demonstrated at differentvelocities. Under automatic controlsColumbia successfully changed and

held its position to support missionrequirements, such as star tracking .The .thrusting power and propellantusage of both types of jets were asexpected , with the smaller verniersmore fuel-efficient than expected.Two of the four vernier jets inColumbia's tail area were seen tohave a problem with the downwarddirection of their thrust. The exhausthits the aft body flap and erodessome of its protective tiles , whichalso cuts down on the power of thejets. One solution being consideredafter OFT was to re-orient these jetsslightly on future Orbiters. In themeantime, a protective coating wasapplied to the tiles on the body flap.

The Orbiter's ab ility to come to res tafter a maneuver was alsodemonstrated. At faster rates itproved nearly impossible to stop thevehicle 's motion withoutovershooting , then coming back tothe required "stop" position ,particularly with the large primaryengines. Both types of thrusters wereused to keep the Orbiter steady in"attitude hold " postures. The smalljets were particularly successful andfuel-efficient at this, holding thevehicle steady down to % of a degreeof drift at normal rates of fuel use ,which is three times their requiredsensitivity.There was some concern after thetest program about the lifetime of thevernier engines. When it wasdiscovered that a protective enginecoating had eroded substantially ontwo of these engines they were allreplaced with new ones after STS-4,even though they had been designedto last 37 missions before beingreplaced. While testing continued todetermine why the coating eroded,mission planners attempted toschedule more efficient use of thesmall jet&-they were fired twice asoften as planned during the testprogram, partly as a result of theirneed to compensate for"overshooting" and the need to holdvery steady attitudes for long periodsof time.

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Further tests of the ReactionControl System assessed how wellColumbia could hold steady withoutfir ing its jets, when differential forcesof gravity tend to tug the 37 meter(122 foot)-Iong veh ide out ofposition. The results of these testslooked promising for the use of"passive gravity gradient" attitudesfor future missions where steadinessfor short periods of time is requiredwithout jet firings.Remote Manipulator SystemOne of the most important as wellas most time-consuming of all OFTtest series involved the 15 meter (50foot) mechanical arm of the RemoteManipulator System. This Canadianbuilt device, jointed like a humanarm at shoulder, elbow and wrist, is12

attached to the Orbiter at variouscradle points running the length ofthe inside of the cargo bay. It is anoptional piece of equipment usedonly on missions where it is neededto move objects into or out of thecargo bay. In place of a hand the armhas a cylindrical "end effector" thatgrapples a payload and holds it rigidwith wire snares. The arm iscontrolled by the crew from insidethe Orbiter and can be moved freelyaround the v,ehide in a number ofmodes, with or without help from theShuttle computers.All of the manual and automaticdrive modes were tested during OFT,as was the al'm 's ability to grab apayload firm ly, remove it from astowed posit ion, then re-berth it

STS-3 test instruments andpayloads. Note Canadian-builtRemote Manipulator System arm atrigh t.precisely and securely. Lighting andtelevision cameras also needed to beverified-the crew relies on sensitiveelbow and wrist cameras as well ascameras mounted in the payload bayto monitor day and night operations .For the test program there were alsospecial Data Acquisition Cameras inthe cargo bay for documenting armmotion.The first mission to carry the armwas STS-2, an d the crew of thisshortened flight ran an extensiveseries of arm movements to test itsmobility in space. Ground simulators


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c. Gordon Fullerton, STS-3 pilot,with flight data and teleprinter copyat pilot's station.are not able to practice threedimensional maneuvers because thearm is too fragile to support its ownweight in Earth gravity. The crewbegan by releasing the arm, thenrelatching it to the Orbiter, both inthe joint-by-joint computer assistedmode (the preferred method) and inthe direct wiring contingency modethat bypasses the computer. Oncethis ability to deploy and re-stow thearm was verified it was moved aroundColumbia in validation runs to test alljoints in all drive modes at differentrates of speed. Fully automatic runswere documented by videotape andby analyzing the motor rates for eachjoint. They agreed well with pre-flightpredictions, and the crew watched asthe arm accurately "flew" from onepre-programmed spot to the next.Braking of the arm was normal andsmooth in both automatic andmanual drive.Although the STS-2 crew did notpick up a payload with the arm, bothastronauts 'performed manualapproaches to a grapple fixture inthe cargo bay, and they found thearm to control smoothly, very muchlike ground simlJlators. The second

crew also began tests to see howmovement of the arm interacts withOrbiter motions. Problems with TVcameras reduced the documentationof these tests, but the crew reportedthat firings of the small vernierthrusters did not influence armposition , nor did arm motions triggerattitude adjustment firings by theOrbiter.The prime objective of STS-3 armtests was to test it " loaded" with apayload. First, though, the crew hadto finish tests left over from theshortened STS-2 mission , particularlya verification of the computer's abilityto automatically stop an arm jointfrom rotating past the limit of itsmobility. The third crew completed 48hours of arm tests, including oneunplanned demonstration of theelbow camera's ability to photograph

Columbia 's nose area during an onorbit search for missing tiles.A Shuttle .payload, the 186kilogram (413 pound) PlasmaDiagnostics Package, was grappledby the end effector, removedmanually from its berth in the cargobay, and maneuvered automaticallyaround the Orbiter in support of OFTspace environment studies.Gordon Fullerton deployed and reberthed the package a total of threetimes, and was impressed with the

arm's ease and responsiveness.Before one such deployment the armautomatically found its way to within3.8 centimeters (1.5 inches) of thegrapple point, in accord with preflight predictions.TV cameras provided excellentvision of arm operations in bothsunshine and darkness, and theSTS-4 crew reported that nighttime

operations, although marginal , werestill possible after three of the sixpayload bay cameras failed. The thirdand fourth crews continuedevaluation of vehicle interactions witharm motion by performing rollmaneuvers as the arm held payloadsstraight up from the cargo bay. Thiswas done with the PlasmaDiagnostics Package on STS-3 andwith the twice-as-heavy InducedEnvironment Contaminat ion Monitoron STS-4. In both cases the crewnoted a slight swaying of the armwhen the vehicle stopped, which wasexpected.Further tests of these dynamicresponses will be done on latermissions. The Remote ManipulatorSystem is designed to move apayload of 29 ,250 kilograms (65,000pounds), but was tested only withmasses under 450 kilograms (1000pounds) during OFT. Future arm testswill graduate to heavier payloads,

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some with grapple points fixed tosimulate the inertias of even moremassive objects.The Shuttle EnvironmentIn addition to these hardwarecheck-outs, another objective of thetest program was to assess theenvironment the Shuttle travelsthrough and creates around itself inspace. This is important for planningmissions that will carry instrumentssensitive to noise, vibration, radiationor contamination . During OFT,Columbia carried two sensorpackages for examining the cargobay environment. The Dynamic,Acoustic and Thermal Environment(DATE) experiment-a group ofaccelerometers, microphones andheat and strain gages-stablishedthat noise and stress levels inside thebay were generally lower thanpredicted. The Induced EnvironmentContamination Monitor (IECM),normally secured in the cargo bay,was also moved around by themanipulator arm to perform anenvironmental survey outside theOrbiter on STS-4. The IECM lookedfor deposits on payload bay surfacesand had sensors for detectinghumidity and trace gasses. Noengine exhaust pollutants were foundin the cargo bay during launch or reentry. The IECM showed low levels of"outgassing" by payload bay surfacesand no sign of heavy moleculedeposits. The particles that wereobserved, probably originating on theground, were in the microscopicrange (1-5 microns), and thesedeteriorated after a period of 15--17hours in space. The monitor showedwater to be the Shuttle's principalcontaminant, and this was well withinacceptable levels.The IECM's survey of pollutingparticles and gasses was backed upby two other STS-3 instruments, theContamination Monitor and theWorking in the Shuttle, AstronautHenry Hartsfield, Jr. gathers printouts from Columbia's tele-printer,located in mid-deck area.

Shuttle-Spacelab InducedAtmosphere Experiment, and bypost-landing inspections of the cargobay. These inspections also revealedminor deposits and somediscoloration of films and paintedsurfaces in the bay, which were stillbeing studied after OFT. A newpayload bay lining was added afterSTS-4.For measuring energy fieldsaround the Orbiter STS-3 carried thePlasma Diagnostics Package (PDP).The PDP was positioned at variouslocations around Columbia and usedin conjunction with the VehicleCharging and Potential Experimentto map the distribution of chargedparticles around the spacecraft.These readings showed a vehicle thatis relatively "quiet" electrically-itmoves through the Earth 's energyfields with interference levels muchlower than acceptable limits. AnotherSTS-3 highlight was the discovery ofa soft glow around some of theShuttle's surfaces that appeared inseveral nighttime photographs.An experiment added to STS-4to identify the glow's spectrumsupported a tentative explanation ofthe phenomenon as due to aninteraction with atomic oxygen in thethin upper atmosphere. Positiveidentification of the cause awaitedfurther experiments after OFT.The flight test program will allowprecise contamination data to bedistributed to those designingsensitive Shuttle experiments. Thesuitability of the cargo bay formounting both Earth- and spaceviewing instruments was alsodemonstrated. A prototype of theSpacelab pallet gave adequateheating and power to its payload onboth STS-2 and STS-3.Inside the Shuttle, the cabin andmid-deck areas have proventhemselves to be livable and practicalworking environments for a newgeneration of astronauts. The testflight crews monitored cabin airquality, pressure, temperature,radiation and noise levels and took

films of their chores and activities inspace, all to document the Shuttle's"habitability. " Noise levels at certainlocations inside the vehicle werehigher than desirable, and continuedtesting was planned after OFT. Someitems new to the Shuttle programalso required minor adjustments, ashappens often with a test program.New food packages generated largeamounts of trash that requiredadditional storage space ; theShuttle's toilet (Waste CollectionSystem) needed several hardwareadjustments before working correctly ;and the STS-2 crew switched towireless radio headsets after wiresproved to be a nu isance to the crewof STS-1. On the posit ive side, thecrews reported thtat their mobilityinside Columbia was excellent, andthey found that anchoring themselvesin low gravity was easier thanexpected. There was almost no needto use special foot restra ints, andcrew members were able toimprovise with ordinary duct tapeattached to their shoes to holdthemselves in place. Further redesign of low-gravity shoescontinues.In general , the eight astronauts ofthe test program found Columbia tobe a. comfortable place in which tolive, work and perform experiments.Return to Earth:The Airplane

At the conclusion of its business inorbit the Shuttle's pay load bay doorsare closed, the vehicle assumes atail-first, upside-down posture andretro-fires its Orbital ManeuveringSystem engines to drop out of orbit.It then flips to a nose-up attitude andbegins its descent through theatmosphere back to Earth.

In the early 1970 's, the challenge ofdesigning a re-usable spacecraftcreated the need for a spec ial kind ofinsulation system that couldwithstand the burning friction of reentry. Whereas earlier spacecraftused one-time-only shields thatburned away, the Shuttle requires15


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insulation that will survive intact to flyon the next mission .Columbia's aluminum surface wascovered with several different types ofinsulation during the test program,with their distribution based onpredicted heating patterns. These

included more than 30 ,000 rigid silicatiles of two types (black for hightemperatures , white for lower) thataccount for over 70% of the Orbiter'ssurface area. Since these tiles were acritical new technology for the SpaceShuttle, their performance was amajor concern of the test program.As soon as Columbia opened itspayload bay doors in orbit on thefirst mission, TV cameras clearlyrevealed that several tiles were16

missing from the aft engine pods,having been shaken loose during thevehicle 's ascent. These tiles had notbeen densified-a process thatstrengthens the bond between tileand Orb iter- -as had all the tiles incritical areas and every tile installedafter Octobe r, 1979. None of thedensified tiles were lost during thetest f lights.

On each flight there was somedamage to ti le surfaces during bothlaunch and entry. Hundreds of pitsand gouges were discovered duringvehicle inspections after STS -1 , thenagain after STS-2. While the damagewas not critica l, many tiles needed tobe replaced. Crew reports, launchpad c a m e r a ~ and cockpit films

STS-3 environmental survey usingPlasma Diagnostics Package alsotested arm motion in preprogrammed stops.rec orded chunks of ice and/orinsulation falling from the externaltank during ascent as well as launchpad debris flying up and hitting theOrbiter, and these impacts wereblamed for most of the tile damage.Over the course of the testprogram various solutions to thisproblem we re implemented. Ageneral Clean-up of the pad beforelaunch and the removal of aparticular insu lation that had keptcoming loose from the boosterrockets cut down significant ly on pad


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~ . ! ; : 3 ! ! . . ~ l Reinforced Carbon-Carbon. h ~ ~ : ~ (Above 1260C)(:::::::::::::::::::::::::::1 High-Temperature Reusable Surfacef ':-:':':':':':':';':':':':'J Insulation (Black Tiles) (648-1260)V/ / / / / / J Low-Temperature Reusable SurfaceV// IJ 1/1 Insu lation (White Tiles) (371-648C)I Flexible Reusable SurfaceL - - _ ~ . Insulation (Below 371 C) ~ ~ I Meta l or Glass

debris. On the external tank, ce rtainpieces of ice -forming ha rd wa re wereremoved. As a resul t, impact damageto the tiles was greatly reduced .Wh ile some 300 ti les ne eded to bereplaced after STS -1, fewer than 40were replaced after STS-4.Weather also inflicted its sh are oftile damage during the test program.Factory waterproofing of new tilesdoes not survive the heat of a reentry, and so Co lumbia had to besprayed with a commercialwaterproofing agent after eachmission so as not to absorb rainwateron the pad. The wa terproofing agentwas found to loosen tile bonds whereit formed pu ddles, though, andSTS-3 lost some ti les as a result.

Then, while STS-4 sat on the padawai t ing launch, a heavy hail andrainstorm allowed an estimated 540kilograms (1200 pounds) of rainwater to be absorbed into the poroustiles through pits made by hailstones.This water added unwanted weightduring ascent and later causedmotion disturbances to the veh iclewhen it evaporated into space.Shuttle engineers now plan to use aninjection procedure that willwaterp roof the interior of the tilesbetween future missions.As a whole, the Thermal ProtectionSystem kept the Orbiter's skin withinrequired limits du ri ng the OFT fl ights,even during the hottest periods of reentry. For the test program 's last

Columbia was covered with severaltypes of insulation during the testprogram, all with different heatload capac ities. Reinforced carboncarbon was used where temperatures exceeded 1260C (2300 F),whereas a flexible insulation wasade quate for the cooler enginepods.three flights the crews performedshort-duration "push-over/pull-up"maneuvers-changes in the vehicle 'spitch angle--designed in part to testthe effects of different attitudes onheating . Heating on the controlsurfaces was increased in stages overthe four flights, and on STS 3 and 4the angle of entry into the

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atmosphere was flown steeper tocollect data under even moredemanding conditions. On eachflight hundreds of heat sensorsplaced around the vehicle, next to itsskin and at various depths in theinsulation contributed data on reentry heating. In most areas thesesensors reported temperaturesconsistent with pre-flight predictions.Notable exceptions were the aftengine pods, where some lowtemperature flexible insulation wasreplaced with high-temperature blacktiles after STS-1 showed hightemperatures and scorching.Data collected during the OFTprogram will allow engineers tocontinue with planned weightreductions and changes in insulation,including the replacement of thewhite tiles with an advanced flexibleinsulation.Aerodynamic TestsAt the same time as Shuttleheating was being evaluatedColumbia was also being tested asthe world 's most advanced gliderduring its return to Earth at the endof each mission. The major objectiveof aerodynamic testing was to verifycontrolled fl ight over a wide range ofaltitudes (beginning at 120 ,000meters (400 ,000 feet) where the air isvery thin) and velocities, fromhyperson ic to subsonic. In bothmanual and automatic control modesthe vehicle flew very reliably and inagreement with wind tunnelpredictions.The OFT tests required largeamounts of data from theAerodynamic CoefficientIdentification Package (ACIP) as wellas ground tracking data and pilotreports on vehicle handling. Dataanalysis will continue many flightsinto the operational era as engineersrefine their models.In the early, computer-controlledphase of re-entry the Shuttle keepsits nose up at a steady "angle ofattack" as it descended. This anglewas 40for the test flights, but it willoften be shallower later in the Shuttle18

Post-Iandingl inspection of tiles onlower surface of body flap revealsdamage callsed by impacts andscorching 011 tile fillers.program. During this time the vehiclealso executes several ro lling S-turnsdesigned to reduce lift and veloci ty.These were successfully tested asboth manual and automaticmaneuvers.There were also a number ofspecial test maneuvers- up to 23 onSTS-2-performed on each fl ighteither as prog rammed inputs by theguidance computer or as controlstick commands by the crew, wherethe vehicle's fl aps and rudder werepositioned to stimulate more

demanding fl ight conditions or to filldata gaps where wind tunnel testingwas not adequate.They included the "push-over/pullup" changes in pitch angle thatmomentarily simUlate a differentvehicle center of gravity so thatengineers can predict theaerodynamics with different payloadsin the cargo bay. There were alsostress tests on the rudder andcontrol flaps at various speeds andpressures, and exercises where the"autopilot" wa s called on to correctthe Shuttle's attitude after the crewdeliberately induced other motions.These corrections were executedperfectly. On the first flight Columbiaeven made an unplanned-for


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correction in the angle of its aft bodyflap. While engineers had predictedan angel of 8 to 9for the flap athigh altitudes, the actual anglerequired to maintain the properattitude was 14. The computersmade this adjustment automatically.

In the thin upper atmosphere theShuttle uses its reaction controlthrusters to help maintain its attitude.Over the four test f lights thesethrusters showed a greater-thanexpected influence on the vehicle'smotion in the atmosphere. This mayallow engineers, as they Jearn moreabout Shuttle flight, to reduce thereliance on these thrusters orperhaps even phase out their usealtogether during re-entry. This wouldsave on reaction control fuel.The Orbiter's navigation andguidance equipment also served wellduring re-entry. Probes that monitorair speeds were successfullydeployed at speeds belowapproximately Mach 3 (three timesthe speed of sound), and navigationalaids by which the Orbiter checks itsposition relative to the groundworked well with only minoradjustments.Unlike returning Apollo capsules,the Space Shuttle has somecrossrange capability-it can deviatefrom a purely ballistic path by glidingright or left of its aim point and so ,even though it has no powered thrustduring final approach it does have adegree of control over where it lands.The largest crossrange demonstratedduring the test program was 930kilometers (580 miles) on STS-4 , andthis will be increased on later flights.OFT astronauts flying the Shuttle incalm ai r reported that Columbiashowed tighter control than had theirShuttle training aircraft, and called ita "fantastic flying machine."The Space Shuttle has thecapability to return to Earth with fullcomputer control from atmosphericentry to the runway. During the testprogram, however, Columbia was notlanded automatically. The STS-1approach and lanc;:ling was fully

manual. On STS-2 the auto-landcontrol was engaged at 1500 meters(5000 feet) altitude, and the crewtook over at 90 meters (300 feet).Similarly, STS-3 flew on auto-landfrom 3000 meters (10,000 feet) downto 39 meters (130 feet) before thecommander took stick control. It wasdecided after an error in noseattitude during the STS-3 landingthat the crew should not take controlof the vehicle so short a time beforetouchdown. The STS-4 crewtherefore took control from the autoland as Columbia moved into its finalshallow glide slope at 600 meters(2000 feet). Full auto-land capabilityremained to be demonstrated afterSTS-5, as did a landing with arunway crosswind.Stress gages on the landing gearand crew reports indicate that aShuttle landing is very smoothsmoother than most commercialairplanes. Roll-out on the runwayafter touchdown was well within the4500 meter (15,000 foot) design limiton each landing, but the actualtouchdown points were allconsiderably beyond the plannedtouchdown points. This is becausethe Shuttle has a higher ratio of liftto drag near the ground than wasexpected , and "floats " farther downthe runway.Ground Work

Most of the work of the SpaceTransportation System is actuallydone on the ground , most of it at theKennedy Space Center in Florida.The OFT program verified thousandsof ground procedures from matingthe veh icle before launch torefurbishing the Solid RocketBoosters and ferrying the Orbiterform landing site to launch pad.As the test program progressedmany ground operations werechanged or streamlined as engineerslearned more about the vehicle 'scapabil ities. Certain tasks that hadbeen necessary for an untried vehiclebefore STS-1 could be eliminatedaltogether. As a result of this learning

the "turnaround" time betweenmissions was shorteneddramatically-fror:n 188 days forSTS-2 to 75 days between STS-4 andSTS-5.Major timesaving steps included : Leaving cryogen ic fuels intheir onboard storage tanksbetween flights rather thanremoving them after landing Alternating the use of primaryand backup systems on eachflight rather than checking outboth sets of redundanthardware on the ground beforeeach launch Reducing the number of testsof critical systems as theyproved flight-worthy frommission to missionBy the end of the test program, theSpace Transportation System haddemonstrated ontime launch andlanding (STS-4). The next mission(STS -5) delivered a commercialpayload into orbit and soinaugurated the operational Shuttleera. Many tests we re still to be done.The Shuttle will gradually progress toheavier payloads. But, not until the

third Orbiter Discovery, is a Shuttlescheduled to have full 29 ,250kilogram (65 ,000 pound) capability,due to a combination of weightreductions and engine upgrading .Manned aspects of the program suchas spacewalks and seven-personcrews had not yet been verified, norhad the Tracking and Data RelaySatell ite Sys tem (TDRSS) for on-orbitcommunication, or the first Spacelab.Satell ite servicing, launches fromCalifornia, and landings in Floridahad not been tried.But the Orbital Flight Test programdid verify that the SpaceTransportation System is sound andready for the scientific , commercialand defense appl ications of the1980's. Engineers will continue usingdata from the test program toupgrade the current fleet of Shuttlesand to begin designing the spacevehicles of the next century.

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Documents

NASA Facts Proving the Space Transportation System the Orbital Flight Test Program