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yATLAS-CENTAUR FLIGHT AC-4 I1COAST-PHASE PROPELLANT

C'ievelund Vhzo

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O N . ASHINGTON: D . c . . E C E M B E R 1 9 6 5


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NASA TM X-1189 I

ATLAS- CENTAUR FLIGHT AC-4 COAST-PHASEPROPELLANT AND VEHICLE BEHAVIOR

By Steven V. Szabo, J r., William A. Groesbeck, Kenneth W. Baud,Andrew J . Stofan, Theodore W . Porada, and Frederi ck C. YehLewis Research CenterCleveland, Ohio

MIear intervals;C LASS1F IE D DOCUMENT-T I T L E UNCLASSIF IED NOTICET hi s material contoins informotion affecting the T his document should not be returtied after it hasnational defense of the United States within the satisfi ed your requirements. It may be disposedmeaning of the espionage laws, T it le 18, U.S.C., of in accordance wi th your local security regula-Secs. 793 and 794, the transmission or revelation tio nr or the appropriate provis ions of the Industrialof which in any manner to an unauthorized person Security Manual for Safe-G uarding C lass ifi edi s prohibited by Icw. Informotion.

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION


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ATLAS-CEN'I'ATJR FLIGHT AC-4 COAST-PHASE PROPELLANT AND VMICLE BEHAVIORby Steven V. Szabo, J r . , W i l l i a m A. Groesbeck, Kenneth W. Baud,Andrew J . Stofan, Theodore W. Porada, and Frederi ck C. Yeh

Lewis Research Center

SUMMARYThe Atlas-Centaur f l i ght AC-4 was the fourth i n a seri es of research and

A coast-phase experiment wasdevelopment fl i ghts.jection i nto a 90 nautical-mile ci rcul ar orbit.planned t o evaluate control led venting of the hydrogen tank, a second enginestart at the end of the coast period, and a turnaround and retromaneuver t o sim-ul ate separation from the spacecraft.

The fl i ght sequence included a 25-minute coast af ter i n-

Parts of the coast-phase experiment were not accomplished primari ly becauseof an uncontrol led propel lant behavior exci ted by vehicle disturbances at thef irst Centaur main engine cutoff. The combined ef fects of engine shutdowntransi ents, vehicl e dynamics, and other energy inputs to the propel lants, i n-duced a forward displacement and ci rcul ation of the l i qui d residuals wi thin thetank. V iscous damping of the l i quid hydrogen was insufficient to dissipate thepropell ant ki neti c energy, and the propell ant settl i ng motor thrust, producingan ar ti f i c i al gravi ty level of about 3~10' ~, was inadequate to prevent l i q-ui d motion (due to ki neti c energy) from covering the vent opening at the "for-ward" end of the hydrogen tank. Failure to settle the l i qui d hydrogen at thet i m e of venting resul ted i n venting of mixed-phase or l i qui d flow, which, on ex-panding from the vent exi ts, produced high impingement forces i n excess of theatti tude control system capabi l i ty, and the vehicle tumbled out of control .Continued tumbling centri f iged the l i qui d hydrogen to the forward end of thetank. Subsequent venting of the l i quid hydrogen to maintain tank pressuresdepleted the resi dual and prevented accomplishment of the remaining coast-phaseexperiments.

INTRODUCTIONThe advent of cryogenic propel lants f or upper stage space vehicl es withmissions requi ri ng extended periods of coast and multiple engine restarts i n anear-zero-gravity environment has brought to the forefront the important problemof coast-phase propel lant management. This poses a pzrticularly acute pr obl emwith cryogenics because of the need to vent and rel ieve tank pressures period-ically.to prevent entrainment of l i qui d i n the vent f l ows arises.I n turn, the problem of maintaining propellants away from vent outletsEntrainment of l i q-


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uid i n vent flows, or l i quid venting, depletes avai lable propell ants for missionrequirements and produces complexi ties i n the design of true nonpropulsive andbalanced vent systems.Much work has been done to date on the behavior of cryogenic and other pro-pell ants i n near-zero-gravity conditions produced for short periods i n droptowers and scale-model f l i ght tests (e.g., refs. 1 o 5). This work has pro-

duced much valuable data on fundamental l a ws and scal ing parameters for modelwork. This ef fort, however, has not shown the i nteracti on between forces, en-ergies, and transients peculiar t o a given confi guration of operating hardwarei n a full-scale space vehicle.The A tlas-Centaur vehicle AC-4 launched from Cape Kennedy on December 11,1964, provided data givi ng much insi ght to the near-zero-gravity behavior of acryogenic i n a ful l -scale space vehicl e. For the f irst time, the Centaur en-gines were planned to be restarted f or a short duration burn.

DISCUSSION AND ANALYSIS OF FLIGHT DATAA correlation of the post-MECO (main engine cutof f ) coast-phase events arepresented i n the fol lowing chronological sequence:(1) i rst MECO (T + 572.8 sec) to start of hydrogen venting ( T + 840 sec)(where T + 0 = l ift-off of vehicle)( 2 ) First-phase hydrogen venting ( T + 840 sec) to loss of telemetry( T + ll.00 sec)(3) A cquisition of data ( T + 1225 sec) to complete hydrogen venting( T + 2006 sec)(4) Second main-engine prestart ( T + 2006 sec) through retromaneuver( T + 3000 sec)The liquid-hydrogen tank on AC-4 was extensively instrumented (see f ig . 1)The majori ty of the fol lowing discus-i th skin temperature measuring devices.sion, which defines the behavior and interacti ons of the l i qui d hydrogen wi ththe vehicle, i s based primari ly on these temperature data and vehi cl e dynamicsdata received from downrange telemetry.First MECO (T + 572.8 sec) to S tart of Hydrogen Venting ( T +840 sec)The vehi cl e at MECO was holding a f l i ght-path angle of approximately -0.02

degree i n pi tch and was rol l ed counterclockwise approximately 15 degrees. (Seef ig. 2 for vehicl e coordinate system and att i tude engine locati ons.) Rates ofrotati on imparted to the vehicle fol lowing the MECO transient were approximately-1.0 degree per second i n pi tch, 0. 2 degree per second i n yaw, and -0.5 degreeper second i n r ol l , as shown i n f i gure 3. Coincident with MECO, the atti tudecontrol engines were enabled to function and the propellant settl i ng engineswere igni ted producing approximately 3x10'4 g. A tti tude control engines A- 2and A- 4 (shown i n f i g. 2) were acti vated immediately and burned f or 1.6 seconds2 3 b


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t o nul l r ol l rate below the threshold of the control system of 0.2 degree persecond. No other atti tude control engine acti vi ty was observed unt i l T + 577.8seconds, 5 seconds af ter MECO, when a programed change i n the guidance steeringequati ons commanded a pitch error of -8 degrees (command nose down) and a yawerror of -1degree (command nose left) . This maneuver was designed to give thevehicle an atti tude paral l el with the l ocal horizontal and i n the plane of thetrajectory.commands immediately, and the desi red atti tude was achieved wi thin 16 seconds.A tti tude control j ets P-2, A- 3, and A-4 responded to guidance

Throughout the remainder of the control led coast ( to start of hydrogenventing at T + 840 sec) sporadic correcti ons were observed i n pi tch and r o l l ,and a nearl y-constant duty cycle was observed i n yaw (see f i g. 4) .control operation was more frequent than expected and was probably a result ofA tti tude(1)Unpredicted propellant behavior(2) Ullage engine exhaust impinging on main engine bel l s and other compo-nents i n the thrust section(3) Misalinement of the propellant settl i ng engine thrust vectorThe 30-percent duty cycle observed from the yaw rate gyro (f i g. 3), i s ampli f i ed i n f igure 5.The disturbance accelerations, defined as the slope of the curve where theatti tude control engines are off, are an indication of the distrubing torquesacting on the vehicle. During the control led coast period, the disturbance ac-celerations averaged 0.012 degree per second, with resul ti ng disturbing torquesof 100 t o 113 inch-pounds depending on the chosen vehicle mass moment of iner-tia. Ullage motor misalinement to maximum design tol erances and cal cul ated i m-

pingement forces can account for only 60 inch-pounds of torque. A center-of-gravi ty shi f t attri butable to propel lant location i s not stable, and there wereno indications of hardware movement. Therefore, motor misalinement beyond de-sign tolerances and atti tude control engine thrusts below nominal thrusts couldaccount f or the rotati onal rate responses observed.Immediately on entering the coast phase, the propel lant behavior was char-acteri zed by a predominantly forward movement of l i qui d hydrogen i n the tank.Within 14 seconds following W O , al l temperature instruments on the l i qui d hy-drogen tank surface (see f i g. 6) indicated the presence of l i qui d hydrogen.Forward bulkhead ski n temperatures and the l iquid-hydrogen ul lage gas temper-ature dropped abruptl y t o l i qui d hydrogen temperatures within 4.5 seconds, as

shown i n f igure 7. This behavior of the l iqui d hydrogen can be attributed tothe following disturbances as illustrated i n figure 8:(1)Fuel-boost-pump volute-bleed spray toward the forward end of the tankduring boost-pump coastdown(2) Hydrogen-duct reci rculation- l ine spray enteri ng the tank at stati on 350on the posi ti ve x-axis during boost-pump coastdown; thi s spray i s di -rected across the tank

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(3) Resi dual sl osh ener gy i n t he f l ui d at MECO(4) Spr i ngback of t he i nt er medi at e bul khead and l ower cyl i ndr i cal sect i onof t he t ank by t hr ust t er m nat i on at MECO(5) Backf l ow of m xed- phase hydr ogen t hr ough t he pr opel l ant duct i ng andboost - pump i nl et at MECO , caused by a combi nat i on wat er - hammer ef f ect

f r omr api d val ve cl osi ng, pr essur e sur ges f r om t he mai n engi ne pr i ort o engi ne i nl et val ve cl osi ng and expansi on back t o t ank pr essure andt emper at ur e of t he hi gh- ener gy l i qui d hydr ogen t r apped bet ween t heboost - pump and engi ne i nl et val ve(6) Ener gy associ at ed wi t h convect i ve t her mal cur r ent s i n t he f l ui d bound-ar y l ayer set up dur i ng t he boost and powered phases of f l i ghtThe f uel - boost - pump vol ut e- bl eed- l i ne f l ow was est i mat ed t o be i ni t i al l yabout 340 gal l ons per m nut e. Dur i ng pump coast down, approxi mat el y 23 poundsof l i qui d hydr ogen was r et ur ned t o t he t ank. Si m l ar l y, t he hydr ogen- duct -r eci r cul at i on- l i ne r et ur n f l ow was est i mat ed i ni t i al l y at about 40 gal l ons perm nut e maxi mumwi t h 2. 56 pounds of l i qui d hydr ogen r et ur ned t o t he t ank dur i ngpump coast down. ( See appendi x A f or boost - pump and f l ow- syst emdescr i pt i ons.The possi bl e ener gy i nput s t o t he l i qui d hydr ogen r esi dual f r om t hese si xdi st ur bi ng sour ces have been est i mated f or t he AC-4 f l i ght as shown i n t abl e I .

TABLE I . - POSSI BLE: ENERGY INF'UTSSource Ener gy l evel ,f - 1b

Fuel - boost - pump vol ut e bl eedHydr ogen- duct - r eci r cul at i on l i neSl oshBul khead spr i ngbackBackf l ow f r ompr opel l ant duct sEnergy of boundary l ayer due t oconvect i ve cur r ent s

1023500. 12351. 07

Fur t her di scussi on and anal ysi s of t hese di st ur bances i s pr esent ed i n appendi x B.The i ni t i al di spl acement of t he l i qui d hydr ogen i n t he t ank by t hese di st ur -bances appe. ar ed t o be a wave movi ng f or war d al ong t he posi t i ve x- axi s and neg-at i ve y- axi s as shown i n f i gur e 6. Thi s wet t i ng sequence i s at t r i but ed t o spr ayf r omt he vol ut e bl eed al ong t he posi t i ve x- axi s and spr ay f r om t he r eci r cul at i onl i ne hi t t i ng the negat i ve x- axi s, di sper si ng l at er al l y, and wet t i ng t he negat i vey- axi s i n t he f orward di r ect i on. The wave mot i on t hen cont i nued over t he f orwardbul khead.A l l t emperat ur e sensors i ndi cated l i qui d hydr ogen f r o mMECO unt i l appr oxi -mat el y 50 seconds pr i or t o vent i ng. The pr opel l ant behavi or at t hi s t i me was

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uncertain, but there was some evidence of drying toward the forward end of thetank, as sensors on the posi ti ve y-axis began drying from the top ( f i g. 6) . I tmay be conj ectured that ei ther the propell ant settl i ng engines were beginningto sett l e the propel lants, or some l ocal skin drying was occurring due to heat-transfer effects.

Pitch0.4500

22%

Star t of L iquid-Hydrogen Venting (T -I-840 see)

Y aw Roll33 24500 240

228 180

to Loss of Telemetry (T + 1100 see)The liquid-hydrogen vent valve was programed i n the rel i ef mode ( i .e. , theThe fuelalve would open at or above cracking pressure) at T + 614.4 seconds.tank pressure at thi s time was w e l l below the valve cracking pressure, but byT + 840 seconds it had reached the valve cracking pressure. The first indica-ti ons of hydrogen venting were noted at thi s time. (See appendix A for vent-system descripti on.)The presence of l i qui d hydrogen at the forward end of the tank, however,resulted i n mixed-phase or l i qui d flow through the vent system.rates were high, and Venturi flow temperature dropped abruptly to liquid-hydrogen l evel s.

I ndicated flow

Simultaneous with venting, as shown i n f i gure 9, was the occurrence of ayaw torque input, which exceeded the capabi l i ti es of the atti tude control sys-tem and produced an increasing yaw rate and vehicle spin-up.A comparison of the predicted vehi cle torques due to normal gaseous hydro-gen venting wi th the actual measured resul ts i s shown i n table 11.

TABLE 11. - COMPARISON OF PREDICTED VEHICLE TORQUES WTHACTUAL MEASURED RESULTS

~

Condition

Inputs due to normal gaseous hydrogen ventingEstimated torque inputs f romAC-4 f l i ght data(maximum measured during coast)Predicted control torques f rom atti tude con-trol system (based on center of gravity atstati on 343)%aximum torque noted at T + 915 see was not a sustained torque.The uncontrol lable yaw torque experienced during venting was credi ted tol arge l ateral impingement forces on the forward bulkhead due to venting of l i q -uid of mixed-phase hydrogen. L ateral forces of 2 to 10 pounds i n the forwardbulkhead area would have produced the yaw torques noted. The predicted force

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for pure gaseous venting was only 0.2 pound.and the liquid-hydrogen ul lage temperature i ndi cated liquid-hydrogen tempera-tures pri or to and during venting.known quantity of l i qui d hydrogen was l ocated i n the forward end of the tank i nspi te of the fact that an ul lage settl i ng gravi ty of approximately 3x10'4 ghad been applied to the vehicl e for about 267 seconds.ti on of uncontrolled vehicle rates with vent periods i s evident i n fi gure 10.

Forward bulkhead skin temperaturesThus, the theory was supported that an un-

Also, excell ent correla-

By T + 905 seconds, vehicl e r ol l had increased to 0.2 degree per second,and the yaw rate had increased t o -0.5 degree per second, as shown i n f igure 9.A t T + 915 seconds, a torquing transient i n pi tch and r ol l coupled the yawsteering error i nto the pi tch channel causing the rol l and pitch rates t o re-verse.-0.6 degree per second i n pi tch, and about -0.5 degree per second i n r o l l .By T +l o30 seconds, vehicle rates were -2.4 degrees per second i n yaw,Hydrogen tank pressure from T + 840 to about T +1055 seconds was unsteadybut remained within the vent-valve operating range.fuel-tank pressure began a steady rise, indicating a vent flow of increasingl i quid quali ty that was no longer of suf f i ci ent volume to rel i eve tank pressure.

The centri fugal f orce due to the increased tumbling rates was settl i ng some ofthe l i quid hydrogen i n the forward end of the tank, and pure l i qui d was beingvented.

A t T + 1055 seconds, the

Acquisition of Data (T + 1225 sec) to CompleteHydrogen Venting (T + 2006 sec)

Reaquisition of data at T + 1225 seconds, as shown i n fi gures 11and 12,indicated that the liquid-hydrogen tank pressure, vent flow rates, and vehi cl eyaw rates were up sharply and increasing steadi l y.comparison of vent flow rates i f pure l i quid or pure gas flow i s assumed.Again the i nabi l i ty of the tank pressure to rel i eve under high indicated flowrates w as further evidence of l i qui d vent flow, which, i n turn, produced anexcessive yaw torque on the vehicle.

Figure l l al so shows a

These rates continued unti l about T + 1366 seconds when the tank pressure,which had reached 24.2 pounds per square inch absolute, suddenly star ted t o de-crease. There was al so evidence (see f i g. ll) of l i qui d depletion at the for-ward end of the tank; that i s, the Venturi flow rate began a decreasing trend.Ullage and Venturi gas flow temperature data, shown i n f i gure 11, show a dis-ti nc t warming and l iquid-to-vapor transi ti on i n the character of the vent flow.The tank pressure decreased t o the operating range of the number 1vent valveby T + 1455 seconds.Vehicle motion during thi s time, obtained from the resolver-chain outputdata, indicated that the vehicl e was tumbling predominantly i n the yaw planewith a sl i ght nose-high atti tude.a maximum of about 21 rpm at T +1550 seconds, as shown i n f i gure 12.r ol l rates during thi s time, as shown i n f igure 13 varied i n a random fashion.This random nature of the pi tch and r ol l rates i s believed t o be caused by thebuildup and breakaway of sol i d hydrogen deposi ts at the vent exi t ports.

The yaw rate increased from about 8.5 rpm toPi tch and

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l i shed data by General Dynamics/Convair has indicated that sol i d deposits canbuild up at vent exi ts when a l iquid or a liquid-vapor mixture i s vented i nto avacuum.The dynamic response of the vehicl e to apparent vent f l ui d qual i ty was verypronounced. T ransi tion from venting of l iquid to venting of gas was coincident

with a decreased r i se i n yaw rate. Signi f i cantly, however, the vent impingementforces continued to spin-up the vehicl e from about T + 1450 to T + 1550 seconds(about 100 sec af ter the Venturi flow indicated nominal coast-phase gas flowrate). This l ag was attri buted to the purging of residual l i qui d hydrogen i nthe vent system downstream of the Venturi and sublimation of possibl e i ce de-posi ts bui l t up on the forward bulkhead.During the total coast-vent period, from T + 840 to T + 2006 seconds, itwas estimated that 960 pounds of hydrogen were vented overboard and that about120 pounds of l i qui d remained i n the tank at T + 2006 seconds.sors indicated, as shown i n f igure 6, that the forward end of the tank was dry;however, tank-skin temperature sensors below stati on 344 on the posi ti ve x-axis

and the boost-pump i nl et temperatures remained at l i quid levels, indicating somesl i ght residual at the bottom of the tank and i n the sump.

Temperature sen-

Second Engine Prestart (T + 2006 sec) to Endof Retromaneuver (T +3000 see)

The prestar t sequence for the second Centaur main engine start (MES) beganat approximately T + 2006 seconds with the vent-valve lockup and i ni ti ati on oftank burp. A t thi s time, however, as shown i n f i gure 14, the l i qui d hydrogenul lage temperature dropped from approximately -380' to -420' F. Apparently, as m a l l quanti ty of l i qui d hydrogen remained i n the forward end of the tank andwas entrained wi th the helium pressuri zi ng gas as it blew across the forwardbulkhead.

The liquid-hydrogen boost-pump start, as shown i n figure 15, began at aboutT + 2010 seconds.for the f i rst 7 seconds of pump operation. Coincident with a drop i n pump-inletpressure and liquid-hydrogen ul lage pressure, the pump headrise became errati c,indicating the occurrence of cavi tation or vapor pullthrough. By T + 2025 sec-onds boost-pump headrise had peaked-out at about 25 pounds per square inch di f -f erenti al , and ul lage pressure had dropped t o approximately 14 pounds per squareinch absolute. Within 5 seconds, headrise dropped to 2 pounds per square inchdi f f erenti al and boost-pump over-speed trip-out occurred, i ndi cati ng an absenceof liquid at the pump inl et.

Boost-pump headrise ( AP) appeared normal ( l i qui d being pumped)

The l i qui d hydrogen remaining i n the tank by T + 2010 seconds had been re-The decay of theuced drasti cal l y as a result of l i qui d venting during coast.liquid-hydrogen ul l age pressure at boost-pump start can probably be attri butedto the cooling of the large ul lage by the liquid-hydrogen boost-pump volutebleed spray.l i qui d hydrogen i s extracted from the ul lage gas and (2) the i ni ti al ull age tem-If it i s assumed that (1)al l the heat required to vaporize the

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perature i s 60' to 65' R, then vaporizing approximately 15 to 17 pounds of thesprayed l iqui d hydrogen would produce the pressure drop noted. Calculationsal so indicated that the boost pwnp sprayed approximately 30 pounds of l i qui dhydrogen back i nto the tank during thi s t i m e .The command for the second MES occurred at T + 2049.7 seconds. I nsuff i -ci ent l i qui d hydrogen, as previously discussed, was avai l able to sustain boost-

pump operation and the normal engine start did not occur.Even though the l i qui d hydrogen vent valve was locked up at burp, theliquid-hydrogen tank pressures remained low throughout the planned second en-gine burn period.began t o increase at about 2.8 pounds per square inch per minute. Heat-transfercalculations show that thi s pressure-ri se r ate would be associated wi th a f u l ltank of hydrogen gas. A t T + 2385 seconds, the hydrogen tank pressure reachedthe cracking pressure of the secondary vent valve and it rel i eved momentarily;2 seconds l ater , the retrothrust signal was commanded, and the engine inletvalves were opened. This allowed the l i qui d oxygen and l i qui d hydrogen tanks toblow down and should have produced an axial thrust of approximately 30 pounds.Propel lant tank pressures with l i qui d remaining i n the tanks should have re-mained fai rl y steady, being sustained by boi l of f gases. The absence of resi d-ual l i quid hydrogen, however, resul ted i n the hydrogen tank pressure droppingoff rather rapidly, as shown i n f igure 16, to 3 pounds per square inch absoluteat T + 3000 seconds. L iquid oxygen tank pressure, though, remained f ai r l y con-stant indicating that a quantity of l i qui d oxygen s t i l l remained i n the tank andthat the boi loff was suf f i ci ent to maintain tank pressure. Actual thrust l evelsproduced by the engine blowdown, however, could not be assessed because the datawere obscured by the vehi cl e spinning motion.

A t second MECO, the liquid-hydrogen tank pressure rapidly

A t the end of the engine blowdown, the engine i nl et valves were closed andthe tank pressure recovered gradually on subsequent orbi ts, being influenced bysolar heating and vehicle posi ti on i n and out of the Earth's shadow. The ve-hi cl e impacted i n the South Paci f i c Ocean af ter completing 10 orbi ts.

CONCLIDING REMARKSThe Atlas-Centaur AC-4 f l i ght revealed some problems of cryogenic propel -l ant management associ ated wi th attempts to obtai n multiple engine starts. Fromthe f l i ght data, the following observations were made:1. A si gni f i cant amount of kineti c energy was imparted to the propel lants

by the engine shutdown transi ents. This, i n turn, caused motion of the fuel i nthe tank. Viscous damping was i nsuf f i ci ent to di ssipate the energy imparted tothe fuel , and the propel lant settl i ng thrust was inadequate to settl e the pro-pel l ants.2. The presence of l i quid propel lant near the vent port resul ted i n l i qui dor mixed-phase flow through the vent system.pinged on the forward bulkhead, which produced a yaw torque far beyond the re-covery capabi l i ty of the atti tude control system, and caused the vehi cl e to

The greatly increased flow i m-

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t umbl e i n yaw. The f or mat i on of sol i ds i n the pr ocess of vent i ng l i qui d orm xed- phase f l ow may have occur r ed, whi ch t ended t o bl ock t he vent pass age un-evenl y and f ur t her cont r i but e t o vehi cl e i nst abi l i t y. The dat a cor r el at i on be-t ween vehi cl e mot i on and vent i ng per i ods was excel l ent .3. The command f or t he mai n- engi ne prest art sequence and second mai n- engi nest ar t was pr oper l y gi ven by t he pr ogr amer .mand, but oper at ed er r at i cal l y as a resul t of cavi t at i on. The absence of l i qui df uel i n t he f eed l i nes pr ecl uded a successf ul second engi ne st ar t .

The f uel boost pump st ar t ed on com

The AC- 4 f l i ght demonst r at ed t hat f or ces ot her t han mol ecul ar f or ces pl ayedt he dom nant r ol e i n det er m ni ng pr opel l ant behavi or even t hough an ul l age set -t l i ng f or ce suf f i ci ent t o over come t he mol ecul ar f or ces was pr ovi ded.t he work t o dat e i n pr edi ct i ng l ow- gr avi t y pr opel l ant behavi or has been concen-t r at ed on mol ecul ar f or ces. I t appear s t hat a r ef ocusi ng of at t ent i on t o t heef f ect s of i nduced t r ansi ent f or ces woul d yi el d gr eat er i nsi ght and under st and-i ng i n t he ar ea of propel l ant management .

Most of

The AC- 4 f l i ght has r eveal ed many ar eas i n need of at t ent i on. Among t hesear e1. At t enuat i on of t r ansi ent di st ur bances dur i ng engi ne shut down and r e-s t a r t2. Eval uat i on of t he ef f ect i veness of ener gy- di ssi pat i on devi ces3. Det er m nat i on of t he pr opel l ant set t l i ng t hr ust l evel r equi r ed i n r el a-t i on t o t he magni t ude of t he expect ed di st ur bances4. Devel opment of means of gaseous vent i ng when vent i ng i s r equi r ed, i n a

t r ue nonpr opul si ve mode t o ensur e vehi cl e st abi l i t ySt udi es and opt i m zat i ons i n t hese ar eas woul d be hel pf ul i n t he desi gn off ut ur e space vehi cl e ut i l i z i ng cr yogeni c pr opel l ant s and capabl e of mul t i pl eengi ne st ar t s.

Lewi s Resear ch Cent er ,Nat i onal Aer onaut i cs and Space Adm ni st r at i on,Cl evel and, Ohi o, August 13, 1965.

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APPENDIX A

VMICLE AND SYSTEM DESCRIPTIONSGeneral V ehicle Description

The Atlas-Centaur vehicle, as shown i n f igure 1 7 i s essentially a two andone-half stage vehi cl e whose operational purpose i s to place a Surveyor space-craf t on a lunar intercept.The f i r s t stage i s an A t l a s intercontinental bal l i sti c missile whose ta-pered nose secti on has been modified to a constant 10-foot diameter.eight 500-pound-thrust retrorockets have been added to the af t section to in-crease the rate of separation from Centaur.stainless-steel structure maintaining i ts i ntegri ty through i nternal pressur-i zation. The f i rst stage, which weighs about 262 500 pounds at l i f t-of f , con-sists of a j etti sonable booster section, the sustainer and propellant-tank sec-ti on, and the interstage adapter. I ts propul sion system includes two boosterengines, a sustai ner engine, and two s m a l l verni er engines.thrust of the f i ve engines i s approximately 389 000 pounds, wi th al l enginescapable of gimball ing for di recti onal control .

Al so,The tank i s a f ul l y monocoque

Total l i f t - of f

The Centaur stage i s the nation's f i rst hydrogen-fueled space booster. Thetank structure, l i ke the A t l as , i s a thin-walled 301 stai nl ess- steel , monocoquecyl indrical -section structure, pressure-stabil i zed to maintain i ts shape. Thecyli ndrical portion i s capped on each end by an el l i pt i cal l y shaped stai nl ess-steel bulkhead. A double-walled el l i psoidal inner bulkhead separates the l i q-ui d oxygen and l i qui d hydrogen tanks. Vehicle thrust i s provided by two 15 000-pound-thrust turbopump-fed regenerati vely cooled engines, that use l i qui d oxygenand l iqui d hydrogen as propel lants. Proper net posi ti ve sucti on head (NPSH) f orthe engine turbopumps i s provided by boost pumps from each propel lant tank.

AC-4 Nonpropulsive Vent SystemThe AC- 4 nonpropulsive vent system, as shown i n f i gure 18, consi sts of a

Gaseous hydrogen f low from the tank through thestandpipe, V enturi flowmeter, two vent valves, and a plenum, wi th opposing exi tsi n the vehicle pi tch plane.standpipe was measured by the calibrated Venturi.regulated by the number 1vent valve (19.5 t o 20.5 psia) during f l i ght, wi th thenumber 2 valve (24.8 to 26.8 psia) acting only i n the safety rel i ef mode. Thenumber l val ve was capable of being placed i n a locked or relief mode t o sched-ul e periods of vent and desired tank pressure l evel s. During boost, vent flowwas directed through a vent stack located on the nose fai ri ng as shown. A t nosefai ri ng j ettison, the ducting from the plenum t o the vent stack and a cap on theopposing vent ex i t were disconnected, allowing venting i n the nonpropulsive modethrough the plenum exi ts. With gaseous hydrogen flow, torques imparted to thevehicl e during vent periods were predicted at:inch-pounds i n yaw, and 2 . 0 inch-pounds i n rol l .

Hydrogen tank pressure was

0.4 inch-pound i n pi tch, 33.0

10


13/42

Propellant Feed SystemThe Centaur vehicle propel lant feed system i s composed of three main itemsof hardware: propel lant ducting, boost pumps, and reci rculati on l i nes. Thefuel system only i s described herein si nce the primary problem concerns the con-tro l of l i qui d hydrogen during the coast phase. A schematic diagram of the fuel

supply system conf iguration on Atlas-Centaur ( AC- 4) i s shown i n figure 19. Thef uel boost pump i s mounted to an elbow sump on the side of the f uel tank.main fuel supply l i ne i s a Y conf iguration with the common l i ne mating with theboost-pump discharge f lange, and branch l i nes to each engine inl et. A recircu-l ati on l i ne attaches to each branch l i ne just above the engine i nl et t o bleedoff trapped gases i n the ducting and thereby permit l i qui d at the engine i nl etpr ior to l i f t -of f .

The

The boost-pump uni t consi sts of a centri fugal pump that i s driven by a hy-drogen peroxide turbine constant power (18 hp) dri ve.requires a NPSH of approximately 0.1 pound per square inch to be provided t oprevent cavi tation. The dri ve has a speed l imiting system that controls theturbine speed by opening and closing a valve in the peroxide feed l i ne. I n theevent that the drive speed reaches a predetermined upper l i m i t , the peroxidesupply valve i s automatically closed, thereby cutti ng of f al l power to the tur-bine. The supply valve remains cl osed as the turbine coasts down to a predeter-mined speed, at which time the valve i s automatically opened again and peroxideflow i s resumed. This cycling w i l l continue indefi ni tely unti l normal operationi s obtained, or unti l the uni t i s intentional ly shut down by command.

The pump speci f i cati on

The fuel pump i s provided with a volute bleed l i ne that bypasses l i qui d hy-drogen around the impel ler and permits the pump to operate without cavi tationduring "deadhead" operation (no flow to the main engines). This bleed flow i saccomplished by slotted openings cast i nto the impel ler housing on the dischargeend. The impeller housing i s enclosed by a col lector manifold provided with a1-inch outl et l i ne that has a 13/16-inch ori f i ce to meter the bypass flow. Whenthe pump i s i nstal l ed i nto the elbow sump the 1-i nch outl et l i ne protrudes i ntoa 2-inch sump-mounted bypass l i ne that di rects the bleed flow away from pump i n-l et and back i nto the hydrogen tank.

The primary purpose of the boost pump i s to supply l i quid hydrogen to theRL10-A3 engines wi th the required NPSH for al l phases of engine operation. Toguarantee adequate NPSH to support the engine start transient, the boost pumpi s star ted several seconds in advance of the in- f l ight chilldown (prestart) andMES. I n the period between boost-pump start(BPS) and prestart, the engine i nl etvalves remain closed, and the boost pump accelerates t o normal speed, where i toperates i n a "deadhead1' mode w i t h only the small flow through the recirculationl i ne passing through the pump discharge. This flow has been estimated at 40 t o50 gallons per minute during the time j ust pri or to prestart. Although the pumpdischarge flow i s only 40 gallons per minute, an addi ti onal 340 gallons of l iq -ui d hydrogen per minute i s returned to the tank by the vol ute bypass l i ne duringthe"deadhead" period.valves open allowing an additional 375 gallons per minute to f low overboard fori n- f l i ght chilldown of the main engine pumps. A t MES, the cooldown valves close,the main fuel shut-off valves open and engine start occurs. For steady-state

A t prestart, the main engine inl et valves and cooldown

11


14/42

engi ne oper at i on, t he boost pump del i ver s 1210 gal l ons per m nut e t o t he engi nes,appr oxi mat el y 50 gal l ons per m nut e i s r et ur ned t o t he t ank by t he r eci r cul at i onl i ne, and appr oxi mat el y 240 gal l ons per m nut e i s ret ur ned to t he t ank by t hevol ut e bypass l i ne. At MECO, t he engi ne i nl et val ves cl ose, and t he boost pm1passumes t he deadhead mode of oper at i on. Si mul t aneous wi t h MFCO, t he boost pumpi s shut down.t he boost pump t o cont i nue r ot at i ng f or sever al seconds ( coast down t i me vari es,dependi ng on whet her or not l i qui d i s r et ai ned at t he pump i nl et dur i ng t hecoast peri od) .

The i nert i a of t he r ot at i ng t ur bi ne and pump at shut down causes

The per i od of boost - pump oper at i on, whi ch i s of pr i mar y i nt erest as f ar aspr opel l ant behavi or i s concer ned, i s t he coast down per i od f ol l owi ng MECO. Dur-i ng t hi s per i od t he pump cont i nues t o del i ver l i qui d hydr ogen back i nt o thet ank by the vol ut e and r eci r cul at i on l i nes at f l ow r at es t hat decrease wi t h t ur -bi ne speed. Thi s r et ur n f l ow cont r i but es si gni f i cant l y t o t he di st ur bances i nt he l i qui d hydr ogen t hat must be di ssi pat ed pr i or t o vent i ng of t he t ank.

Engi ne Syst emA schemat i c drawi ng of t he engi ne sys t empl umbi ng i s shown i n f i gur e 20.The maj or component s of i nt erest ar e t he f ol l owi ng val ves:(1) Fuel pump i nl et shut of f val ve(2) Fuel pump i nt er st age cool down and bl eed val ve(3) Fuel pump di schar ge cool down and bl eed val ve(4) Mai n f uel shut of f val veThese val ves ar e of pr i mar y i nt er est because of t he sequenci ng at engi neshut down, whi ch i s i l l ust r at ed i n f i gur e 21. Note t hat t he f uel pump i nl etshut of f val ve r emai ns open af t er t he mai n f uel shut of f val ve i s cl osed, whi chper m t s a shor t - dur at i on hi gh- pr essur e sur ge of hydr ogen t o backf l ow t hr ought he i nl et val ve and subsequent l y back t o t he t ank by t he f uel suppl y duct i ngand boost pump. The cool down and bl eed val ves ar e opened bef or e t he mai n f uelshut of f val ve i s f ul l y cl osed t o pr event excessi ve pr essur e bui l dup i n t he sys-t em Si m l ar l y, t he i nl et val ve r emai ns f ul l y open f or appr oxi mat el y 0.1 secondaf t er t he mai n shut of f val ve i s ful l y cl osed. The i nl et val ve has a cl osi ngt i me of appr oxi mat el y 389 m l l i seconds ( r ef . 6).

12


15/42

APPENDIX B

CAL CUTI ON OF ENERGY LEVELSFuel - Boost - Pump Vol ut e Bl eed Fl ow at F i r st E O

The f l ow r at e as a f unct i on of t i me f or t he vol ut e bl eed f l ow may be cal -cul at ed f r om t he boost - pump headr i se dat a ( f i g. 22) i f i t i s assumed t hat t hepr essur e dr op across t he bl eed- l i ne or i f i ce i s di r ectl y pr opor t i onal t o pumpheadr i se. The f l ow equat i on i s t henQQ =K-Er-* - K

wher eQ f l ow rat e, gal / m nK const ant of pr opor t i onal i t yAP pump headr i se, psiThe f l ow r at e was det er m ned f r omgr ound tests t o he appr oxi mzt el y 340 gal l emper m nut e at a corr espondi ng headr i se of 28 pounds per square i nch.known i ni t i al condi t i ons , t he f l ow r at e f or any ot her gi ven headr i se can be de-t er m ned f r om

W t h t hese

wher esubscri pt 1 i ni t i al known condi t i onssubscri pt 2 any ot her condi t i onsThe i nst ant aneous wei ght f l ow r at e( B2) wi t h t he appr opr i at e conver si on f act or s.densi t y of 4. 32 pounds per cubi c f oot i s assumed,

$ ( l b/ sec) may be cal cul at ed f r omequat i onI f a const ant l i qui d- hydr ogen

= 0. 613 033)The t ot al wei ght of l i qui d hydr ogenl i ne dur i ng t he post - MECO coast down i sW ( pounds mass) t hrough t he vol ut e bl eed

13


16/42

which represents the area under the curve shown i n f i gure 23.from the 2-inch-diameter volute bleed l i ne at any time i s The exi t veloci ty

Wve = - = 10.61PAwhereV, exi t velocity, f t/sec

instantaneous weight flow rate, lb/sec3p l i qui d density, l b/f t

A exit area of l i ne, f t2The incremental kineti c energy associated wi th a given amount of l i qui d pumpedi n a f i ni te time period i s

( f t- lb)6W f26KE = --2 g avwhere6W incremental weight of f l ui d pumped, l b massVav average exi t veloci ty of f l ui d within f i ni te time span of i nterestSince the outlet vel oci ty and, therefore, ki neti c energy, varies over a largerange during the coastdown, a numerical integration was performed by usings m a l l increments of time to cal culate the total ki netic energy input to the tank

The headrise curve of f i gure 22 and the formulas given i n equations (Bl )to (B6) were used to cal cul ate the total l i qui d hydrogen returned t o the tankand the kineti c energy. Results show that 22.7 pounds of l i qui d hydrogen werereturned i n the 20-second coastdown period with a to tal ki netic energy of102 f O O t-pounds.Fuel-Recirculation-L ine Flow at F i rs t MECO

The reci rculation- l ine-f low has been estimated between 40 and 50 gallonsper minute at a corresponding headri se across the boost pump of 28 pounds persquare inch differential. For the purpose of the fol lowing calculations, thelower f igure of 40 gal lons per minute was used. The reci rcul ation l i ne out-si de diameter as it enters the tank at stati on 350 i s 0. 625 inch with a w a l lthickness of 0.035 inch, which represents a flow area of 0.2415 square inch.The same method and equations developed f or the volute-bleed-flow cal cula-tions of the previous section may be uti l i zed for the reci rculation- l ine-f low

14


17/42

calculations.tions: Changing the necessary constants resul ts i n the fol lowing equa-

The weight f low rate as a function of t i m e i s plotted i n f i gure 24. C a l -culated results that use thi s data indicate a total of 2.56 pounds of l i qui d hy-drogen returned to the tank during the 20-second coastdown period, wi th a totalki neti c energy of 35 foot-pounds.Backflow Through Boost-Pump Inlet

A rigorous theoreti cal analysis of the actual ki netic energy level of thef l ui d backflow i nto the tank i s vi rtual l y impossible because of the many vari -ables and unknowns involved.fi lms taken during low-l iquid-level engine shutdowns of stati c tests. A camerawas l ocated at the top of the tank so that a view of the boost-pump i nl et areawas obtained. Films from three stati c tests were analyzed to establ i sh an av-erage veloci ty of the backflow wave at. shutdom of 31. 74 f eet per secenc?.

However, an estimate was obtained by uti l i zi ng

I t was assumed that the worst condition exi sted i n which al l the liquidThe total volume of the ducts i s approximately 0.5235trapped i n the fuel duct between the engine inl et valves and the boost-pump wasreturned to the tank.cubic foot. Therefore, the mass returned t o the tank i s

Volume) (Density) - (0.5235 f t3) (4.32 lb/f t3) = o. 0703 sl ug2ass = ( - 32.2 ft/secravityThe kineti c energy associ ated wi th the mass of liquid i s

2(0.0703) (31.74) = 35.15 f t - l b2K E = - W = -2 2

Bulkhead SpringbackThe energy associated wi th the intermediate bulkhead springback at MECO wascalculated as follows:engine cutoff i s transmitted i nto ki netic energy of the fl ui d. ThenA ssume al l str ai n energy i n the bulkhead j ust pri or to

15


18/42

wherePE potenti al energy or strai n energy of bulkheadKE ki netic energy of f l ui dK intermediate bulkhead spring constant, 2. O6X1O6 lb/in. (cal culated from

ref. 7)X defl ection of intermediate bulkhead due to axi al f orce, i n.The axi al force on the bulkhead at E O s equal to the mass of l i quid hydrogentimes the acceleration:

Axial force = F = 1084 l b mass LH2 X 2.25 g's = 2450 l bThe axi al force i s also

F=K Xor

x = F/Ktherefore,

- = 1.455 in.- l b = 0.122 f t- l b6X1064. 12XlObPropellant Sloshing

Although a careful analysi s of rate gyro data from AC-4 revealed that pro-pel lant sloshing was i nsigni f i cant pri or to main engine cutoff , i t should not beignored as a potenti al source of disturbance. For the AC-4 Configuration, thenatural frequency of the l i quid hydrogen would be 4.6 radians per second wi th awave velocity, up the w a l l , as high as 2.5 feet per second for a 10-degree s l oshangle.Propellant sl oshi ng may have been a problem during the low-thrust coastphase of AC-4. The natural frequency i n the l i qui d hydrogen tank under 4 poundsof thrust would be 0.053 radian per second, wi th a period of approximately120 seconds. Sloshing during the coast phase could not be detected because ofthe l arge number of energy inputs to the tank and the resul ti ng disturbances(refs. 8 and 9) .

16


19/42

Thermal Boundary Layer EnergyDuring ground hold and powered f l i ght, thermal convective currents are es-tabl ished i n the boundary layer due to environmental heating. When the vehi cl eacceleration i s suddenly reduced at MECO, i t i s believed that the boundary l ayerwould continue to move forward against a weak acceleration fi el d. To establ i shthe upper l i m i t of the ki neti c energy content the fol lowing equations from ref -erence 10 were uti l i zed.Centaur fuel tank would be equivalent t o that of a f l a t plate:I t was assumed that the boundary l ayer wi thin the

= 5.7826 (K)pqw 5/14 ($-)/ 21 (2. 2442+ Pr 2/3)-5/14

whereU

UY6XgPqWC

pB

l ocal velocity i n boundary layer, ft/secequivalent f ree stream veloci ty, f t/sechori zontal distance from tank w a l l , f tboundary-layer thickness, f tverti cal distance i n tank, f tacceleration, ft/sec2volumetric coef f i ci ent of thermal expansion, 1Ru n i t area heat f l ux at tank w a l l , Btu/(ft )(see)specific heat, Btu/( l b) (%)f lu id mass density at bulk f l ui d condition, lb/ft3

2

17


20/42

Pr Pr andt l numberv ki nemat i c vi s cos y, f 2/ s ecFi gur es 25 and 26 were pl ot t ed by usi ng t he pr ecedi ng equat i ons f or t he condi -t i ons exi sti ng i n t he Cent aur f uel t ank at MECO.i n est abl i shi ng t hese cur ves:gj3 = 0.0106/0Rqw = 0. 029 Btu/ ( sec) (ft')C = 1. 5 Btu/ ( l b) ( 9)

The f ol l owi ng val ues were used

= 2. 25 X 32. 2 f t / sec2 = 72. 5 f t / sec 2

= 4. 3 l b mass/ f t 3PBPr = assumed uni t yv = 1. 93X10- 6 f t 2/ sec

Ut i l i zi ng t hese t wo cur ves and a l i qui d dept h at MECO of 5. 5 f eet r esul t si n a boundar y- l ayer t hi ckness of 1. 9 i nches at t he l i qui d- vapor i nt er f ace and acor r espondi ng boundar y- l ayer vel oci t y of 0. 92 f eet per second.boundar y- l ayer t hi ckness i s 1. 34 i nches. Usi ng t he average boundar y- l ayert hi ckness and t he maxi mum boundary l ayer vel oci t y r esul t s i nThe aver age

Mass i n boundary l ayer :

Dens t y) ( Vol ume)Mass = ( Gr avi t y- ( 4. 3 l b/ f t 3) ( 0. 112 ft )(5. 5 f t ) (31. 4 f t )32. 2= 2. 58 sl ugs

Ki net i c ener gy:

18

KE = - (Mass)(Vel oci ty) '2= 1 ( 2. 58) (0. 92) 22= 1- 07 t - l b


21/42

REFERENCES1. Petrash, Donald A .; Zappa, Robert F.; and Otto, Edward W. : ExperimentalStudy of the Effects of Weightlessness on the Configuration of Mercuryand Alcohol i n Spherical Tanks. NASA TN D-1197, 1962.

2. Petrash, Donald A .; Nelson, Thomas M .; and Otto, Edward W. : Effect of Sur-face Energy on the Liquid-Vapor I nterface Configuration During Weight-lessness. NASA TN D-1582, 1963.3. Wallner, Lewis E.; and Nakanishi, Shigeo: A Study of L iquid Hydrogen i nZero Gravity. NASA TM X -723, 1963.4. Petrash, Donald A.; Kussle, Ralph C.; and Otto, Edward W.: Effect of Con-

tact Angle and Tank Geometry on the Configuration of the L iquid-VaporI nterface During Weightlessness. NASA TN D-2075, 1963.5. K noll, R ichard H.; Smolak, George R.; and Nunamaker, Robert R .: Weight-

lessness Experiments with L iquid Hydrogen i n Aerobee Sounding Rockets;Uniform Radiant Heat Addition - Flight 1. NASA TM X-484, 1962.6. Anon.: Design Report for RLlOA-3 Rocket Engine. Rept. No. PWA FR-324C,Fratt and Whitney A i rcraft, J an. 31, 1964.7. Pinson, Larry D.: Longitudinal Spring Constants f or L iquid Propell ant Tankswith E l l ipsoidal Ends. NASA TIV D-2220, 1964.8. Bauer, Helmut F.: Fl uid Osci l lations i n the Containers of a Space Vehicleand Their I nfluence Upon Stabi l i ty . NASA TR R-187, 1964.9. Smer, Irving E. ; Stofan, Andrew J .; and Shramo, Daniel L . : ExperimentalSloshing Characteristics and a Mechanical Analogy of L iquid Sloshing i n aScale-Model Centaur L iquid Oxygen Tank. NASA TM X-999, 1964.

10. A rnett, R. W.; and Mi l lhiser, D. R.: AMethod for Analyzing Thermal Strat-i f i cation and Sel f-Pressurization i n a Fluid Container. Rept. No. 8777,NBS, Apr. 1965.

19


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20

IA620T 284CA623T 291CA626T 297CA537T 302CA540T 310CAM3T 318C AW T 326CA549T 334CA552T 342 CA609TCA612TCA615TCA618TCA621T ~CA624TCA627TCA538TCAMlTC A m TCA602T 360 CA547T

CA550TCA553TCA556TCA603T

CA555T 351 t3248259269278286293299304312320328336344353363

CA622TCA625TCA628TCA539TCA542TCA545TCA548TCA551TCA554TCA557TCA604T

CA708TCA496T

Figure 1 - AC-4 hydrogen tank external skin temperature measurements.

288295301306314322330338346355364

Stat on465465

QuadrantI1I V


23/42

drA-4ravity I)ositive.__ .

\\c-1, c-$1 LA-^ - .I op view4

P -I

I \ R O I I rotationP(rPos itive pitch// rotation

-x, 180"-Pitchaxis

+ositive yawrotationYaw axis 1 Rear view-y#270"Figure 2 - Location of attitude control and propellant settlingengines.

21


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u38:\Uvalcmmcm

-.-ccealUA Z0,1

-.-

-.53

. 53(a) Yaw rate signal low range.

8.51

-8.51(b ) Yaw rate signal high range.

12.76

-12.77

420

-4. 20 572.8Time from lift-off, sec

(d) Roll rate signal high rangeFigure 3 - AC-4 vehicle rotational rates during coast.

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(9) Longitudinal acceleration.

572.8 800Time from lift-off, sec(h)Longitudinal acceleration fine range.

Figure 3 - Concluded.

23


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y-y axisA-4 A-1@ -x axisA -3 P 2Engin e location; view looking forwa rd

P - 1 I I I I I I I I I IP - 2 --1 I I I I I I I IA -2 IA -3A -4 I mYIH- I I I m i I 111 1111I 11imii I 11 I 11 II I II I I 1 I I I I I I I I II I II I I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I l l 1 1 1 II I 1 1 1 1 1 I I I I l l I I I I II I0 20 40 60 80 100 120 140 160 180

T i m e f r om f i r s t MECO, SecF i gur e 4 - Hydrogen peroxide engin e commands.

Disturbance

At t i tude control> engines

Time, secF i gur e 5 - Typical yaw rate gy ro signal.

24


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CA605T-CA608T-CA611T-CA614T-CA617T-CA620TCA623TCA626TCA540TCA543TCA537T

CA546TCA549TCA552TCA555TCA602T-

Station

----------

(a) Positive y-axis.

CA606T-CA609TCA612TCA615TCA618TCA621TCA624TCA627TCA538TCA541TCA544TCA547TCASSOTCA553TCA556TCA603T

23024025026 027 028029030031 032033 034035 036037 00 Mo 400 600 800 l oo0 1200Ti me from l i f t

----------------

1400-off, sec 1600 1800(b) Positive x-axis.

Figure 6 . - Liquid-hydrogen tan k wa ll l iquid indication.

2000 2200

2 5


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.Sensor Station

CA608TCA6lOTCA613TCA616TCA622TCA625TCA628TCA539TCAM2T

CA619T

CA545TCA548TCA551TCA5MTCA557TCA6MT

--

---------

-----

Time from lift-off, sec(c )Negative y-axis.

Figure 6 - Concluded.' 1 1

' Temperature Station

550 560 570 580 590 600 610Time from lift-off, secFigure 7 - Temperature his tory near main engine cutoff. Forwardbulkhead area.


29/42

,-Possible liquid slosh existing atrRe circulation- line flow- ackflow from ducts

orward motion due to , MECO (not prevalent on AC-4)

,r Boost-pump-volute bleed line, 2-in. diam.

line, 0.625-in. diam.

Figure 8. - Residual liquid-hydrogen motion after main engine cutofffor AC-4 flight.

27


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-.53

.53(a) Yaw rate signal low.

8.51

-8.51lb) Yaw rate signal high.

i i . 76

-12.77(c) Pitch rate signal high.

4.M

-4. 20800 840 1032Time from lift-off, sec

(d) Roll rate signal high.Figure 9. - AC-4 vehicle rotational rates during Coast.

28


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I I I I i r r I I I I \ I I ~ ~ I I I I I I I I I I-. -

-.005

, 005(g) Longitudinal acceleration

,0005

-.0005 1032Time from lift-off, sec

(h) Longitudinal acceleration fine.F igure 9. - Concluded.

29


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01UE-.-9

ai-LIa

.a

. 4

0-.4

4

3

2

1

0840 850 860 870 880 890 900 910 920 930 940 950 960Time from lift-off, Sec

Figure 10. - Coast-phase vent and vehicle instabil ity.

~I l l l l l l l l l l l lVenturitemper- rUllaqe temperatureature, .

30


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12.

-12.

I 1

G H ~ 1 i-low rate-. \0 -r1200 1300 1400 1500 1600 1700 1800 1900- I C . : : ,Time from lift-off, sec

Figure 12. - Coast-phase venting and vehicle y a w rate.

4Lockandburp

1!r 1 - m : , rh-1900 2M)o 2100

2

01200 1300 1400 1500 1600 1700 1800Time from lift-off, secFigure 12. - Coast-phase venting and vehicle y a w rate.

*iM)o 2100

76

I I 1 1 1 I \ A I1 I I I I I I I I 1 I I I I I I I77 l l l l l l l l l l l- (a) P itch rate signal high.c

4.20eaVc0 )>-.-

I I 1 I 1 \ 1 1 I I \ I / I Y I \ V I I T 1\11 T 1 - 1 I I I- 4 . 2 0 1 1 I I 1 1 1 1 I I W 1 9 I I 1 1 1 1 I I 1 1 1 1 11248 1298 1398 1478Time from lift-off, sec

( b) Roll rate signal high.Figure 13. - AC-4 vehicle rotational rates during coast.

31


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Time from lift-off, secFigure 14. - AC-4 liquid-oxygen and liquid-hydroyen ullage temperatures.

Time from lift-off, secFigure 15. - Hydrogen tank pressure and boost-pump performance at second main enginestart

32 4Luwmf


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Figure 16. - A C - 4 liquid-oxygen and liquid-hydrogen tank pressures.

33


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Payload (spacecrafth

A

34

-J ettisonable nosefairing

-J ettisonable insulationpanel)g'"-Centaur stage

-Interstage adapterB usta inert'rAtlas stage

i!;j f ; ; ; ; ; ;,,-Booster

Azusaantenna-

Sustainer-Boosters

(a) General arrangement.Figure 17. - Atlas-Centaur vehicle.

A

---Electronicand guidancepackages--LH2 tank

LO X tank

'-LOX tank

rF uel tank/

,-Vernier

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