Centaur for Thte 80's

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CENTAUR FOR THE 1980s

JOHN E. NIESLEYAdvanced Systems Project EngineerAdvanced Centaur ProgramsGeneral Dynamics Convair Division

San Diego, California

ABSTRACTCentaur is currently the world's only operational high-energy upper stage, and is the United States primaryupper stage for launching solar system probes, large

< geosynchronous communication satellites, and obser-J vatories to study the farthest limits of space. Centaur isIIurrently launched on Atlas, but has also flown with. the larger Titan booster. NASA recently decided to in-, tegrate Centaur with the Space Shuttle for future solarsystem exploration missions.Current status of the Centaur program is discuss-ed including: vehicle characteristics, planned perfor-. mance improvements, and launch schedules. Modifica-tions required to integrate Centaur with Shuttle andthe resulting capabilities are discussed.INTRODUCTIONCentaur development began in 1958 when GeneralDynamics/Convair was awarded a contract to developthe first space vehicle to use liquid hydrogen fuel.Because NASA's Lewis Research Center (LeRC) didmuch of the pioneering work in liquid hydrogen tech-nology, LeRC was later assigned technical manage-ment of Centaur and contributed to the first successfullaunch in 1963. This successful working relationshipcontinues today. After completing the developmentphase in 1966, the resulting operational vehicle, calledCentaur 0, was launched 21 times on Atlas.

In the early 1970s, Centaur electronics and guid-ance systems were completely modernized. A newhigh-speed digital computer was added that permits ex-tensive use O f software to perform functions previouslyrequiring hardware, thus simplifying new missionadaptation. Computer controlled launch set (CCLS)was added to provide rapid automatic checkout of theCentaur and diagnostic capabilities for anomalies.This new version of Centaur, designated 0-1, was in-tegrated with both the Atlas vehicle and the morepowerful Titan booster, and has flown 32 operationalmissions.

Currently, Centaur is undergoing additional per-formance improvements for Intelsat, which willenhance its capabilities for the 1980s. NASA has alsorecently decided to integrate Centaur with the SpaceShuttle for solar exploration missions, large futuregeosynchronous commercial satellites, and potentialDepartment of Defense (000) missions. These appli-cations will ensure continued use of Centaur throughthe remainder of the 1980s.CENTAUR RECORDA little over two decades ago, Centaur was conceivedas the upper stage for United States' solar system ex-ploration and geosynchronous communications sat-ellites. Today that dream has truly been fulfilled by theaccomplishments of this vehicle. Centaur has launched22 solar system exploration missions includingVoyager, Viking, Helios, Mariner, .Surveyor andPioneer. Its selection by NASA for launching theGalileo and International Solar Polar missions from'Space Shuttle means continuation of this enviablerecord. In addition, 24 geosynchronous communica-tion satellites have been launched as well as 6 spaceobservatories (Figure 1). Centaur has flown 55 timeswith Atlas and 7 times on Titan for a total of 62 flightsand is now ready for integration with the SpaceShuttle.

During the past fifteen years of operationalflights, Centaur has established itself as a reliable up-per stage. 96070of all operational flights were suc-cessful, with 100070or 36 consecutive successes since1971. The Pratt and Whitney RL-I0 engines have aperfect flight success record and the current Centaur0-1 guidance and navigation system has also perform-ed 100% successfully on all countdowns and launchesas indicated in Figure 2.ATLAS dHARACTERISTICSThe Atla~ vehicle that boosts Centaur is a stage-and-a-half configuration in which all engines are ignited on

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Missions Solar system exploration (22)

- Voyager, Viking, Helios- Mariner, Pioneer, Surveyor

Communications(25)- Intelsat, Fltsatcom, Comstar Astronomy (6)- HEAD, DAD

Launch platforms Atlas Titan

Figure 1. Centaur enabled the United States to achieve many dramatic firsts in space and provided a valuable capability forgeosynchronous missions.

Vehicle operational successes- 96% overall- 100% since 1971

(36 consecutive successes)P&W RL-10 engine

100% successful flight record(66,000 sec in space)

Guidance & Navigation - 0-1(Honeywell IRU & Teledyne DCU)100% flight & countdown success(33 missions with 450 operationalhours)

Figure 2. Centaur's success record proves its reliabilty as a high-energy upper stage.the ground and share common propellant tanks. Thebooster engines are jettisoned at approximately 140seconds into the flight when vehicle accelerationreaches 5.5 g. The sustainer engine continues to burnuntil propellant .depletion occurs about 110 secondslater. Two small vernier engines burn throughout thebooster phase and provide all roll control during thesustainer phase. All engines use liquid oxygen (L02)and RP-l fuel, which is similar to kerosene. Vehiclecharacteristics are shown in Figure 3.The Atlas vehicle is 10 ft in diameter and approx-imately 70 ft in length, not including the interstageadapter. Tanks are made of thin-walled stainless steelbands which are welded together and pressure stabi-lized for structural strength. A helium pressurizationsystem maintains tank pressure for structural integrityand turbopump pressure head during flight. Vehicle

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control is accomplished by gimbaling the Atlas enginaduring flight under direction of the Centaur guidancaand navigation system.CENTAUR CHARACTERISTICSCentaur is a high energy upper stage powered by twOPratt & Whitney RL-1O engines developing 33.~ IDtotal vacuum thrust at a rated Isp of 446 seconds (Figure 4). The stage burns 30,000 lb of liquid hydro.-(LH2) and liquid oxygen (L02) propellants. Tanu alemade of thin-walled type 301 stainless steel '.construction that is pressure stabilized. The yseparated by a double-wall vacuum-insulated mediate common bulkhead and pressurized ..eous helium. Until now, tank-mounted booJlhave been used to provide the required eo,mtpressures. The boost pumps are driven by [


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RP-1Vernierengine (2)Sustainerengine

Boosterengine (2)

01100698-8

Oxidizerboiloff valve

Length:Diameter:Jett wt:Booster 7,916 IbSustainer 8,035 IbPropellants: 28~,OOOIbPropulsion Rocketdyne MA-5Rated thrust (SL)Booster 370,000 IbSustainer 60,000 IbVernier 2,000 Ib

70 ft10ft

Figure 3. The Atlas booster vehicle is a state-and-a-half configuration with a sustainer engine that continues to burn 90~ seconds after the initial booster engines are jettisoned.

'~ Aft bulkhead

RL-10 engines

Length:Diameter:Dry weight:Guidance:Propulsion:Rated Thrust:Rated lsp (vac):Propellants:

Figure 4. Centaur characteristics.

30 ft10ft3,8501bInertialP&W RL-1 OA-3-316,500 Ib per engine446 secL02/LH2; 30,750 Ib

020306989A

powered by hydrogen peroxide, the same monopropel-lant used in the -reaction control system. Beginningwith vehicle AC-62, minor tank and engine changeshave allowed the elimination of boost pumps. Reducedcost and improved reliability and performance willresult. Associated changes are gaseous hydrogen

engine bleed for LH2 tank pressurization duringengine operation, and hydrazine monopropellant forthe reaction control system.

The Centaur integrated astrionics system is illus-trated in Figure 5. The heart of this system is the Tele-dyne Digital Computer Unit (DCU) which has 16,000

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'.

PGM DOWNLINKroundCheckoutMonitor & GGLS/ DGU UPLINKCommands

ABBREVIATIONSDigital Computer UnitInertial Reference UnitSystem Electronics UnitSequence Control UnitServo Inverter UnitRemote Multiplex UnitsPropellant UtilizationComputer Controlled Launch SetPyrotechnic Control UnitComputer Controlled Vent andPressurtzatlori System

DCUIRUSEUSCUSIURMUPUCeLSpyeCCVAPSInstrumentationSignals


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Payload systemweight capability(Ib)

Performance -Ib (kg)

5,500 r--------------------.

5,000

4,500

4,000

16

1984 capability(80 in. Atlas stretch)- ,

1983 capability(Intelsatimprovements)

50 Ib propellant launchvehicle contingency

225 Ib propellant flightperformance reserve

90 nmi perigee Not constrained byascension trackerelevation

18 20 22 24 26 28Transfer orbit inclination (deg)

Figure 6. Atlas/Centaur synchronous transfer performance .

StretchedAtlas (80 in.)

Strap-onsolids (4)Current(baseline)

4,900 (2,220) 5,300 (2,400)Figure 7. Atlas/Centaur can provide additional performance growth.

643

2,500

(Kg)

2,000

3025031069811S

6,400 (2,900)250310698 198


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Existing, nose fairing Boron-aluminum strutsSeparation fitting (10) ~

spnt + Split fairmq b I(mod) arreSpacecraft ASpacecraft BCentaur tandem adapterMission peculiar adapterTotal

Capability - strap on solids

Weight (Ib)2,8002,80056065

6,2256,400

Figure 8. Dual spacecraft can be flown with Atlas/Centaur capability.

LAUNCH SCHEDULEThe current firm Atlas/Centaur launches are shown inFigure 9. Three Intelsat V launches, one COMST ARand one Fleetsatcom launch are scheduled in 1981.COMST AR 4 was successfully launched on 21February 1981 with the second Intelsat V as the nextscheduled launch in May.

Currently, Intelsat is considering accelerating theproduction schedule for the three Intelsat V-A vehiclesin order to be able to launch them starting in mid-1983,

25031069825A

and replacing these vehicles with additional Atlas/Cen-taurs for launch in 1984.SHUTI'LE/CENTAURGeneral Dynamics Convair Division, under a numberof separate contracts and company funded activities,has been studying the integration of the Centaur stageinto the Space Shuttle since 1971. This activity culmi-nated with a 1979 Centaur-in-Shuttle integration studywhich defined in detail the modifications to Centaurrequired for interface compatibility and mission safety.

YFirm Calendar YearVPotential 1980 1981 1982 1983 1984 1985IFltsatcomj I t ComstarComplex 36A " ./ Fltsatcom

Complex 368 Intelsat V Intelsat VA" ' - - - Intelsat V .\ I ,~ , -7 'f"y"t'"y ,- . 't '"7C"v .v v "

Figure 9..Atlas/Centaur launches are planned through (he mid 19805.

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Shuttle modifications were defined by Rockwell Inter-national under the direction of NASA-Johnson SpaceCenter (JSC). The ability to safely integrate Centaur-in-Shuttle was determined by JSC and Kennedy SpaceFlight (KSC) center personnel during Phase 1 safetyreviews. All of these activities concluded that Centauris ready for Space Shuttle integration (Figure 10).

During the last two months of 1980, NASA con-ducted a concentrated study of Shuttle upper stages joperform the Galileo and International Solar Polar(lSPM) missions. The conclusion of that analysis wasthe FY 1981 and 1982 budgeted resources would allowNASA to begin modification of Centaur for integra-tion with the Shuttle so this powerful combinationwould be available for first launch in 1985. Shuttle/Centaur would satisfy the NASA planetary mission re-quirements and also be available for future commercialand national security missions. In January 1981, Dr.Frosch made the decision to recommend to Congressand the administration that NASA pursue this courseof action.CENTAUR MODIFICATIONS FOR SHUTILEThe Centaur stage modifications required for Shuttlecompatibility can be separated into two distinct areas:(1) interface compatibility and mission requirementsand (2) safety considerations. For interface com-patibility, the structural adapters must be modified;fill, drain, and vent systems are changed; a new LH2tank insulation blanket is added; and zero-g ventdevices are required. Mission requirements dictate aTDRS compatible transponder and may require a startracker for guidance update to meet mission accuraciesif a number of Shuttle orbits are required prior to Cen-taur deployment.

Safety considerations required additional reddant valves and tank pressure transducers for ppellant control, a new propellant dump system, recfiguring of the helium purge system, and a new racommand link to inhibit engine firing after separatifrom the orbiter should a problem arise. Thmodifications still leave 950/0 of Centaur stage coponents unchanged.WIDE BODY CENTAURThe 1979 Centaur-in-Shuttle studies were based oning the current Centaur stage, which is 30 ft in lenand 10 ft in diameter, and integrating it directlythe Shuttle. Performance requirements for the 1Galileo and ISPM missions dictated a significantcrease in propellant weight that would be requiredaccomplish the missions. Since stretching the currCentaur in length only would result in inefficient usethe cargo bay, it was decided to stretch the LH2 tank170 inches in diameter, thus utilizing the full orbibay available and increasing the length availablespacecraft as shown in Figure 1 1 . The L02 tadiameter was held constant while a 30-inch cylindrisection was added. Centaur's propulsion system ischanged; however, the forward equipment module aadapter diameter was increased to match the hydrogtank diameter.PERFORMANCE CAP ABILITIESShuttle/Centaur performance capability significantexpands NASA's capability to perform solar explortion missions. Galileo can be launched in 1985 ascombined orbiter/probe using either a modified Typtrajectory (broken plane) or a Type II trajectory wharrives somewhat later. This is one of the most difficu

Centaur integration & modificationsdefined by General Dynamics &NASA LeRC

Shuttle modifications defined byRockwell & NASA JSC

Safe integration determined by NAJohnson Space Center & KennedySpace Flight Center

. Figure 10. Centaur is ready for Shuttle integration.25031088

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10ft

~-- -- .. .i '\

Increaseddiameterforward Uses 15ft diameterstructure available inorbiter payload bay..Increase LH2 Increases Centaurtank diameter 14.2 ft propellant loadingto 170 in.

30 ft Increases lengthavailable forAdd 30-in. spacecraftL02 tankcylindrical Maintains L02 tanksection diameter & propulsionsystem unchanged

Current I ShuttleFigure 11. The wide body Centaur is a minimum modification to the current Centaur.

launch years for Galileo and could not be accom-plished with any other upper stage, even by launchingthe orbiter and probe separately (Figure 12).International Solar Polar can also be launched in1985 with a single launch for both spacecraft and dur-ing the same launch opportunity as Galileo; however, a

Star 48 upper stage is required. Future solar explora-

25

Injectedmass 20(103Ib)

15

10

09021088 18A

tion missions such as Venus Orbiting Imaging Radar(VOIR), Saturn Orbiter Probe, Uranus Orbiter Probeand Solar Probe will benefit from this improvedcapability.Shuttle/Centaur will have a geosynchronouscapability of 14,000 lb in orbit with the standard widebody configuration. This is nearly three times the pro-

Solar system exploration

VOIR Spacecraft 14mass(103Ib)

Galileo

140

Figure 1 2. Centaur dramatically enhances Shuttle capability.

16Geosynchronous

6

. . . . ~'.. . . . . . . . . .

. ' .'.' .5 IUS ( t w i n s t : : : ; ~ . : . : : : : : : . . . . . . . . . . . . . . z : . polar

IUS (twin + spin)! ..O~ __~ __~~ __~ ~~~ __~~ __~o 20 40 60 80 100 120C3 (KM2 per sec2)

12108

421-OL-~L- __~ ~

IUS Shuttle/ Shu ttJe lCentaurCenlllllow r t w u t t


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jected capability of Shuttle/IUS. For spacecraft withlarge deployed structures, Centaur engines can beoperated in a low thrust mode (83,000 see test time),which will allow the structures to be deployed andchecked out prior to synchronous transfer. Thegeosynchronous capability for this type of mission ex-ceeds 12,000 lb on orbit.P OT EN TIA L M IS SIO N SSome of the potential missions that Shuttle/Centaurcould launch during the latter part of the 1980s includeNASA's solar exploration missions Galileo, ISPM,VOIR, Solar Probe, and either an asteroid mission orcomet mission. A geostationary platform demonstra-. tion flight, planned for 1987, could use Centaurcapability in the low thrust mode. Large commercialcommunication satellites could also be launched eitherin single or tandem mode.

SUMMARYAtlas/Centaur is a flight proven, reliable launch vehi-cle currently being uprated to deliver 5,300 lb togeosynchronous transfer orbit. Potential uprates in-clude strap-on solid motors that could further increasethis capability to 6,400 lb. This would allow launch ofdual full-size Delta class spacecraft. Launches forAtlas/Centaur extend into the mid-1980s.

Shuttle/Centaur is ready for integration and nowplanned for a 1985 launch. Vehicle modifications re-quired are minimal, and the stage has been determinedsafe by NASA. Geosynchronous orbit capability forthis vehicle is 14,000 lb with a potential capability of12,000 Ib for a low thrust mission. 'Centaur willenhance NASA's solar system exploration capabilitywith missions for this powerful combination extendingthrough 1989 and beyond.

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Centaur for Thte 80's

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