AlAA 93-2273 Design and Integration of a Cryogenic Propellant Crossfeed Svstem for Parallel Burn Vehicles Charles J. -Sosa, James W. Howarth, Michael V. Merlin, Stephen P. Petrilla and Seshagirirao V. Vaddey Rockwell International - Space Systems Division Downey, CA

AI AWSAEI AS M El AS E E 29th Joint Propulsion

Conference and Exhibit June 28-30, 1993 / Monterey, CA

For perrnlsslon to copy or republlsh, contact the Arnerlcan Instltuta .) Aeronautics and Astronautics 370 L'Enfant Promenade, S.W., Washlngton, D.C. 20024

U

DESIGN AND INTEGRATION OF A CRYOGENIC PROPELLANT CROSSFEED SYSTEM FOR PARALLEL BURN VEHICLES

James. Stephen P.

Charles J. &sa*

Rockwell International Space Systems Division

Downey, California

W. Howarth*, Michael V. Merlin** Petrille* and Seshagirirao V. Vaddey**

. Sr. EngineerIAnalyst EngineerIAnalys! ..

A b s t r a

A study was madc to design and intcgralc a cryogcnic propellant crossfeed system into an orbitcrlboostcr vehicle set having parallel burning slriges. A crossfccd system configuration has been devclopcd that providcs a solulion for crossfeeding multi-parallel-burn stages for HLLV and AMLS vehiclcs. With a crossfccd systcm, the NASALangIey Research Center (LaRC) predicted wcight Savings of =26% in gross weight and =23% in dry wcight can be achieved. The crossfced configuration succcss is highly dependent on componcnt sclcction and the opcra- tional sequence chosen to achievc systcm pcrformancc objectives. These componcnts and a flight sequcncc arc identified. Emphasis is placed on minimizing vchicle complexity and obtaining low boostcr residuals. The related sub-system concerns for propcllant loading, - pressurization, venting, in-flight scparablc umbilical disconnects and reuaction are addressed. Guidelines and design objectives were also established for large diameter, separable disconnect design development.

Proposed heavy lift launch vchiclcs (HLLV) and the two stage Advanced Manned Launch Systcm (AMLS) vehicle each have parallel burning stages during asccnt. Thesc vehicles lend themselves to increasing the overall performance capabilities by employing propcllant crossfeed systems. LaRC showed improvement in gross weight of 25.6% and in dry weight of 22.6% for the AMLS two stage vehicle using crossfecd.lCrossfeed enables the vehicle to consume propellants from only the booster tanks, with booster and orbiter engines running, during the first part of thc asccnt mission. On staging, thc depleted booster is dropped. Thc orbitcr (with full tanks at staging) proceeds to orbit. Vehiclc performance is improved when the high mass fraction stage (thc orbiter) bums for the longest time. Thc AMLS vehicle employs "Derived SSMEs" (Space Shuttle Main Engine) running at 80% thrust during ascent. I f one engine goes out on either stage the remaining engines can maintain thc thrust profile by running at 100%. Table 1 summarizes AMLS propulsion system parameters.

-"Copyright c 1993 by thc Amcrican Institute of Aeronautics and Astronautics, Inc. All rights rcscrvcd.

Introduct inn

1

Ascent Opcration 1st Stage Parallel Bum - Booster and Orbiter 2nd Stage Single Bum * Orbiter Only

Tanks Booster - LO2 Forward Mounted (AI-Lithium)

5 Boostcr Engines Vac Thrust 497,000 Ibs (Derived SSMEs) Vac Isp 440 secs

Orbiter - LO2 Aft Mounted

Mixture ratio: 611 Expansion Ratio = 3 5 1

S Orbitcr Engines Vac Thrust 513,500 Ibs (Dcrivcd SSMEs) Vac Isp 453.5 secs

Mixture ratio: 6/1 Expansion Ratio = 7 7 5 1

(50 x 100 Nautical mile Orbit) Payload 40,000 Ibm +Crew

Table 1 - AMLS Propulsion Description

Thc challenge in this study was addressing the concern that a crossfeed system, though beneficial, would add high com- plexity to the involved vehicle. We have established:

1 .) The required complexity of a crossfeed system. 2.) Thc key issucs to be addressed.

The LaRC two stage reuseable AMLS vehicle was used in this study due to the maturity of its configuration. Figure 1 illustrates the AMLS vehicle, while Figure 2 schematically shows the AMLS vehicle tank arrangement. The AMLS is composcd of an unmanned booster stage and a manned orbiter stage. Each stage has 5 "Derived SSME's". All engines start prior to lift-off. booster engines are shut down during staging, and the orbiter engines continue to run until orbital insertion velocity is rcached. The AMLS vehicle uses low pressure propellant tanks (20 to 40 p i a ) and gravity feed to supply the engines as recommend- ed in a previous study. Loading is through the booster rise-off umbilical disconnects (disc).

Orbiter

- Figure 1 AMLS Launch Vehicle

BOOSTER

TO ENGINES

ORBITER

c LIQUID LEVU.

TO ENGINES

'igure 2. AMLS Roo ster and Orbiter prowellant Tank Arrangemen1

iLImcmh The design integration of the crossfeed system into the AMLS vehicle was derived using the following steps:

1 . ) Development of guidelines and design objectives for the selection of a "large internal diameter (ID) inflight separable" disconnect set. Costs are discussed

2.) Assessment and integration of the crossfeed system and the loading/draining, venting and pressurization processes.

3.) Analysis was performed in system definition, flowate evaluations for line sizing, for staging crossfeed transient performance evaluation, and propellant depletion.

Note: 1. Analysis efforts were concentrated on the LO2 system due to the greater concern for surge with L02. 2. For leakage and seal design concerns, the efforts were directed to the LH2 systems. 3. Engine conditioning was not addressed.

\d

L

Crossfeed Sv stem Descrintion

'-' An inteiratcd cryogenic propcllant crossfeed dcsign con- figuration will provide crossfccd for parallcl burning stages. The key features of the dcvelopcd LO2 crossfccd configuration, for thc AMLS vchiclc, arc detailed schematically in Figure 3. Thc overall LH? and LO2 crossfeed configuration is illustrated in Figurc 4. Thc LH? and LO2 disconncct scts would bc mountcd in parallcl and separate umbilicals. In Figure 3, the LO2 flow pattcrns for loading/draining

and propellant feed arc illustrated by flow direction ar- rows. The LO2 disconncct set is separablc. Thc booster disconnect has a bcllows and mating scal. and includes a normally open motorized closing valve. The orbitcr disconnect has a latched opcn swing pivot closurc. that when unlatched will close to scal off thc linc bcforc separation. The crossfecd configuration w'as arrivcd a( through the review of disconncct dcsigns, system integration evaluations and systcm analyscs. We observcd that a disconncct configuration may begin with a generalized or universal approach (onc fits all), but in the final analysis, the sysiem requirements and limita- tions govern design selection. The overall crossfeed design configuration as illustrated in

Figure 4, employs separable disconncct scts (one orbiter and one booster half per set), orbiter LO2 & LH2 pro- pellant tank isolation valves (isovalves), orbiter LO2

'V throttlable bypass topping/replcnish (T/R) valve (with position control), booster LH2 propcllant tank isovalve, booster LH2 throttlable bypass (T/R) valve (with position control), orbiter and booster drain isovalves and discon- nects, and interconnecting plumbing. The booster LO2 disconnect closure is shown on edge to illustrate the open position; however, for flow stability the closure axis would be vertical, on the paper. The crossfeed componcnts permit tcrmination of booster

crossfeed flow, initiation of orbiter propcllant tank flow, depletion of booster stage propellant tanks, and facilitates propellant loading/draining operations. The orbiter isovalves are rcquired to preclude orbiter propellant flow during thc first stage burn, whcn booster propcllants are being consumed. Thc booster LH2 tank isovalvc and the throttlable bypass T/R valve are rcquired to pcrinil control of the tank liquid level. Umbilical rctraction (bcllows compression or line flcxure) is required on thc booster side to permit stage scparation. Retraction of 2.5 inches is estimated to hc rcquircd. The Booster disconnects will bc exposed to thc ambient

air stream, which is relatively benign, during the return to the launch sitc. Orbiter umbilicals will bc isolatcd from re-entry heating by closing the crossfeed umbilical doors (similar to the Space Shuttle Orbiter). The booster and orbiter will individually prcssurizc thcir

V' own propellant tanks during ascent (no crossfeed), see Figure 9.

3

Thc tank vent systems should be kept separate (no crossfeed). Crossfeccding the vent systems would add complexity and weight to the crossfeed umbilicals. Electrical feed through the crossfeed umbilicals may not be

rcquircd. Vcrification of crossfeed flow characteristics can hc performed

in sub-scalc flow tcsts.

Selection of a Laree I/D Disconnect

One of thc key elements of the Crossfeed technology study was to establish a configuration for a large internal diameter (ID), and separable in-flight disconnect design to satisfy boostcr half closure, orbiter half closure, external sealing and separation mechanism requirements. A largc internal diameter, separable disconnect enables

propcllant cxchangc between the booster tanks for orbiter cnginc fccd. Disconncct closure devices shut off propellant crossfccd flow passages before booster separation. Guidclincs, design objcctives, and a series of potential

options were idcntificd. An optimal dcsign for crossfeed flow was sclccted. In the design process use of innovative concepts can lead

to design simplicity and to lower costs.

Guidelines and Design Objectives:

Guidelines:

A. Eliminate reauirementts) for active actuation s- m . By incorporating self opening/closing features into the

design, complex actuation systems using pneumatics, hydraulics or electromagnetic actuators can be avoided. If not avoided. they can be minimized.

B. Reduce or eliminate use of dynamic seals. This requirement can be extended to include elimination of

external protrusions through the housing which would re- quire dynamic seals, or even static seals. Experience with thc Shuttlc 17" & 14" disconnects as well as other Shuttle componcnts show that dynamic seals (shaft seals) significantly add time and effort during manufacturing, and have a higher potcntial for external leakage vs static seals. Design of thc dynamic seals and mating parts must meet

stringent tolerances, which require special tooling and handling processes. If external protrusions cannot be avoided it is rccommendcd that coverplates with static body seals be thc primary means of sealing. Static seals can be designed with sufficient compliance to assure tight leakage control during all thermal conditions and imposition of mechanical loads.

DOWCOMER(S) FROM ROOSTER WZTANK -

31 " or

'wo 21"

FILL

t FEED 6 DRAIN

FEED 6 DRAIN

21"

FILL

t -

TO SSMES AND BOOSTER RISE-OFF UMBILICALS

DISC VALVT.SHOW VALVE SHOWN 015K. I O m . CLOSED mSTnOh

Is PI w . W M BOOSTER c w s ~ ~ m s m ~ o ~ N W T O M

I I I I I I I I

IMERFACE (ilF) BOOSTERORBnER

ORBITER 'EED

DRAIN

21"

TOORBliER w e s

Figure 3 LO2 CROSSF EED FOR AMLS VEHICLE

+ TOPPING, REPLENISH

4

21"

t

0 w \

PROPELLANT FEED DURING BOOSTER BURN

21 "

SEPARATION

w

PLANE I I I I

Figure 4. AMLS Ascent Propellant Crossfeed System

5

C. Enhanced rotatinc or slidine mechanisms. Rotating or sliding mechanisms rcquirc bcarings, bushings,

rollers, guides, special lubricants or othcr mcans of facilitating motion. This adds cost and complexity. I f mc- chanism motion cannot be avoidcd, i t is rccommcndcd that multiple rotating or sliding surfaccs bc dcsigncd wi th conservativcly low bcaring loads This protects the (lcsign from single point failures due to binding or excessive wcar.

D. Lower Darts count. Reducing the overall parts count reduccs manufacturing and

assembly time, minimizes thc number of potcntial failure modes, and reduces documenfation and quality control requirements because of fewer parts to makc, inspcct. handlc, and inventory.

Design Objectives:

1. The disconnects shall be self aligning. 2. Orbiter and boostcr half closures are normally closcd n,hcn

3. Booster to orbiter structure maintains disconnects mated. 4. Mechanical detents hold closures open and stablc whcn

5. When separated, closures can be manually cycled. 6. Provide a clean flow path. 7. Use low cost manufacturing techniques and avoid complex

8. Static seals shall be used for body penetrations. 9. Interface seals shall have the sufficient compliance to ac-

comodate component squirm and load induced distortions (thermal and mechanical)

Vendor Suppor t and Costs:

Discussions were held with various vendors to evaluate design concepts and cost drivers. A products' dcsign will influence manufacturing costs. Engr-: :-ring costs to manage, design, analyze. and document

the design are the majority of non-recurring costs. The remaining non-recurring costs are due to tcsting (dcvclopmcnt and certification), tooling, etc. Streamlining thc dcsign process, by reducing program management and docmcnration requirements, will reduce non-recurring costs. Using inno- vative design and analysis techniques to simplify the dcsign will facilitate testing and production. 20% of recurring costs is required for production acccptance

testinj:. and 20-30% can be directly attributed to the stringent quality control requirements. Manufacturing, material and documentation account for the remainder of recurring costs. Recurring costs can be reduced by minimizing documentation and quality control requirements imposed on vendors.

separated and open upon mating.

mated and flowing propellants.

internal and external body contours.

As production quantities increase (loo's to 1000's of thc cost per unit can be significantly reduced. For low production quantities. typical in the aerospace industry, it is apparent that the process of designing a component is a more significant percentage of the cost than manufacturing. Low quantity production costs can also be reduced by employ-

ing parts or derivatives, that are being produced at high pro- duction rates.

Configuration Selection:

Three different disconnect concepts were developed to satisfy various system and performance requirements.

Thc first conceu. a dual poppet disconnect, was found to be the simplcst. but is hindered by having a long length, a large diametcr envelope and a long engagement stroke (= 1 2 ) . see Figurc 5. This dcsign is applicable to a rise-off disconnect or f o r Atlas-booster-type separation (where the separation direc- tion is parallcl to thc disconnect centerline).

The second concent, has a poppet in one half and a 'D' cross-section in the other half. This offers improved flow paths to minimize cavitation susceptibility and flow tur- bulcnce. This design also has a long stroke (7.5") and large diameter envelope, see Figures 6 and 6A.

The third conceu, with split flappers (closures), is the most complex. However, a large diameter disconnect is packaged in a small length envelope, while obtaining clean flow passages, scc Figure 7. An alternate o f the third conceut. employs a single pivoted

swing closure in each half. I t has a large envelope and short Icngth: but, has desirable design features: clean flow path, no dynamic external seals, short engagement stroke (=1.5"), and is can be manually operated (see Fig 3, Orbiter LO2 Disc.).

AMLS Confirruration; Except for the third option alternate, the three concepts are

not optimal for the AMLS vehicle. The AMLS configuration is not conducive to long separation stroke ( = 7.5" IO ~ 1 2 ) . Disconnect separation and retraction can be achieved in a short

distance. The Shuttlc Orbiter and External Tank Disconnect scparation occurs in 1.5" and retraction is 2.5 ". Analysis requires that the AMLS LO2 disconnects have a

controllcd profile closing valve on one half (booster) and a swing closure on the other (orbiter). Therefore the AMLS LO2 disconnect configuration shown schematically in Figure 3 was devcloped. This configuration enables performing the crossfeed staging sequence.

v

6

Figure 5. Dual Poppet Disconnect

Figure 6. Poppet and "D" Cross-section

Figure 7. Split Flapper

Figure 6A. Flapper Drive Linkage

The key design features for the AMLS LO2 disconnect set configuration are:

1. Disconnect interface mating seal.loaded by booster discon- nect bellows

2. Orbiter disc employs latchable swing pivot closure: manual open and latch. remote control unlatch, close return spring.

3. Booster disc has a controlled profile closing closure. 4. Short guided engagement length of = 1.5". alignment. 5. Booster and orbiter structure holds disconnects in the mated

position. and provides initial interface seal load through bellows compression.

(4.5"). 6. Booster line and disconnect retraction required is short

7. No external dynamic seals on orbiter disconnect. 8. One sided, single set of redundant shaft seals (dynamic) is

Note: LH2 bellows is required to be vacuum jacketed.

Five of the nine design objectives were met, and three others were uartiallv satisfied.

required on booster.

7 W

Comoonent Weiehts:

Weights for booster and orbiter cryogcnic propcllant system components were collected and estimated. This dala is plot- ted in Figure 8. and can be bcncficial in projecting systcm weights.

Assessment of Crossfeed Interrration

Propulsion systems on a vehiclc or stagc must bc pro- perly integratcd to providc start, stop and safing functions from prelaunch through separation, orbital inscrtion, re-entry and landing. Also, gcncral vchiclc dcsign philo- sophy is to simplify the vchiclc systems, and if ncccssary, penalize the GSE and not the vehiclc for system com- plexity or system weights. An example of vehicle penalization is the *'clean pad"

concept, where all vehiclc to ground support equipment (GSE) interfaces ( IF) are located at thc basc of Ihc launch vehicle. For many configurations, that may bc an cvxIIcnt approach, but for tall cryogenic propellant st;igcs, this approach poses many problems. The most cihvious, is routing tank vent lines to thc vchiclc basc. Wcight penalties of long lines and vent flow resiswncc drivc up vehicle weight and decrease propellant performancc. For the LO2 tanks, venting to the atmosphere is a normal practice. Cost considerations must aslo be evaluated. I f vchicle

performance margins are high, then these vehicle wcight increases may be off-set by GSE savings

- - - - -

250

= 200 0 - - - -

150 3s 4 E = = !

> 50 - -

2 E

> -

- -

100

. Li:

a 4

For the AMLS configuration loading, draining, venting and prcssuriwtion system impacts. were evaluated for the cros

The results of these evaluations are discussed below:

Loadina:

Thc loading process includes preconditioning, slow fill, fast f i l l , and topping/rcplenish (T/R), which blends well with the crossfecd system. The crossfeed is transparent to these opera- tions. Because the crossfeed is in place, i t is not necessary to duplicatc the f i l l system on the orbiter stage, which saves wcight. However, due to the different elevations of L02/LH2 tanks,

thc lower tanks need to be isolated (shut-off). Isolation valves (isovalve) and throttlablc bypass T/R valves (with position control) arc used. These valves are shown in Figure 5. Thc rationale for use of these valves is as follows: 1. To avoid high pressure in the orbiter LO2 tank ullage. which

2. Necd to bc able to vent the lower tanks at anytime. 3. Necd to individually control tank liquid levels ( independent

control), otherwise performance uncertainties arise. 4. Low ullage pressure in each tank permits loading and

maintaining highest density LH2 and LO2 for launch.

.

fccd configuration. ir,

would rcquire a heavier orbiter LO2 tank.

PREDICTED 21" VALVEDISC HALF

/. - 1- COMPONENT WEIGHT ONLY.

DOES NOT INCLUDE EXTERNAL INSULATION, OK ACTUATION AND STRUCTURAL SUPPORT

' I7"DISC HALF

/ --

12" PREVALVE

/ --

X" F/D VALVE 1-2" DISC HALF/. ..m-' 9'' DISC HALF o , , , , , , , , , , I , , , , : , , , , : , , , , I

Note: Topping and replenishing of the upper tanks is expected to be performed by controlling the fill flow from the GSE.

L d

Figure 8 Valve/Disconnect Half Weight vs Internal Diameter

8

The draining of the AMLS is limitcd by thc clcvation of thc 'crossfecd line. On the orbitcr and boostcr thc SSME inlct supply manifolds would bc lcft ful l . scc Figurc 4. To effect a complete drain of maniflods. scvcral options

were available; lower thc crossfccd linc. pcrmit largc amounts of LH?/L02 io slowly boil-off. or configure the vehicle io pcrmii draining ihc SSME inlci supply maniflods. To minimize largc linc routings and rcsiduals. drain lincs were added to thc SSME inlci supply m:inifolds. For thc boostcr and orbiter small diamctcr drain lincs wcre addcd. For the orbiter isolation valves and disconnccls wcrc also addcd. In addition, the LH2 bypass T/R vitlvc on thc boostcr, was placed bciwecn thc fill linc and thc LH2 SSME inlct supply manifold. This enahlcs using ihc LH? T/R valvc as a manifold drain valvc. Thcsc drain systcms will avoid opcraiional timc consmints

and the wcight pcnaliy is sm;ill.

VcnlinK

Thc veni systcm is critical for assuring low tcmpcraiurc propcllants for cnginc optraiion and bcsi vchiclc pcr- formance. Long or smoll diamctcr vent lincs causc highcr ullagc prcssurcs. As propcllants must sit for hours prior to launch, thc lowcr thc ullagc prcssurc (assuming similar insulation hcat Icak) thc Iowcr thc propcll;int tcmpcraiurc. Thcrcforc, thc vcni systcms should not bc hurdcncd with routing penaltics (io thc bottom of thc slrigc or itcross slagcs) and/or unnccccsary flow rcstriciions. Crossfccd. i f uscd in a clcan pad approach. would add

complcxily duc to thc nccd to crossfccd thc vcnt systcms. This doublcs thc number of crossfcui umhilical disconnccts and crcatcs orbitcr problcms for vcnting, bcforc and ahcr scparation. A crossfccd Ycni sysicm is not recommcndcd. If ihc AMLS

iwo slagc vchiclc has thc pcrformmcc margins in thc configuration. vcnt linc rouLing to ihc si:igc b;tsc could bc lolcraicd.

i/

W

BOOSTER

I c 1

ORBKER

Figure 9. Flight Pressurization System

In summary. the crossfeed svsiem inteerates verv well with the AMLS vchiclc propellant loaoding, draining and feed systems. Crossfccding of Ihc vent and pressurization systems is not advantagcous.

Svstem Analvsis

Concept Development:

Thc crossfwd systcm configuration was driven by early analysis rcsulis. During a rcview of flow characteristics involved

Prcssurizaiion:

The tank prcssurization systcm can bc arrangcd to bc indcpcndcnt for cach slage on AMLS. To makc thc systcms indcpcndcnt of crossfccd, thc follo\ving dcsign leaiurcs, arc rcquircd: 1 . Each AMLS stagc must haw a GSE prc-prcssurization

linc for each lank. 2. Thc booster LHZLO? tanks flight pressurization gases

must comc from its own boosicr cngincs. 3. Thc orbircr LH2 and LO? tanks prcssurcs must bc main-

laincd by thc orbiicr cngincs. Thc prcssurization modulc must permit no/low flow Link prcssurization through staging inilialion, high flow during staging to enginc shuidown. - SCC Figurc 9 for ihc flight prcssurizaiion sysicms.

in crossfccd and its tcrmination, it was realized that there is a potcntial for suddcn flow reversals. Two observations were made that addrcsscd corrccdng this problem:

1 .) Stcp prcssurization of thc booster tanks might be necessary w,hcn ihc orbiter propellanr isolation valve was opening and thc LO? lcvcl in thc booster tank is low, and/or

2.) A chcck vnlvc in the crossfwd line could permit booster flow and would inhibit orbiter reverse flow to the booster

This sccond approach is schematically illusuaied in Figure 10. Thc chcck valvc and crossfeed flow (inb, whFh can go nega- t i x ) arc shown in Figure IO. Chcck valve IS in the disc.

9

Verification of Line Sizing:

Analysis was performed to check the feedline diamenical linc sizing. The analysis established that the AMLS line sizcs could be reduced over what is used as the baseline. The 21" ID LO2 downcomer lines could he 17" ID, and the individual LO2 Booster engine lines could be 9" ID while still satisfying engine NPSH requirements. The LO2 Orbiter tank outlet line would be 21" (no change) and the LO2 Orbitcr engine lincs would be I O ID. Thc LH2 engine lines would be 12" ( n o change). The wcight of the baseline vehicle LO2 lines could be reduced. However, for commonality the LH2 and LO2 engine lines

would rcmain at 12".

Transient Evaluation:

v,

A transient model was dcvcloped that is representative of thc AMLS two stage booskr/orbiter LO2 crossfeed config- uration. The LH2 side was not analyzed. The putpose of the model is to determine if a workable sequence is feasible. The model used the 21"ID line configuration with the flow to the booster and orbiter engines. Each SSMEs operates at 80 % thrusl. The frictional losses, in these lines, were accounted for in the model. The booster and orbiter isovalve opening characteristics are assumed to be linear with time.

The results of this transient analysis have established 1 .) The crossfeed shutdown can be accomplished in 3.5 scconds with minor surging expected. However, the b m s t e i d (or orbiter) crossfeed disconnect half closure must be molorized in order to control closing. The closing would shutdown crossfeed flow over a 3.5 second time period. The orbiter motorized LO2 tank isovalve would slowly open within this time frame. Figure 11 reflects the LO2 Booster disconnect closure position (%) vs time, and also shows the crossfeed and the orbiter flows (%) vs time. Figure 12 rcflecic the crossfeed line static pressures (ft of L02) at the booster disconnect inlet and at the orbiter disconnect line outlct vs time. The LO2 pressures stays within a 160 ft (79 psi) to 230 ft (1 13.4 psi) range (assumes 2g gravity field). Thc AMLS peak g load is =2.5g's, which would not raise thc surge to unacceptable levels. The shuttle orbiter LO2 linc is designed for =I85 psi working pressures (220 psi after separation) and surge pressures to 265 psi. 2.) A 10 second period could also be used to complete the crossfeed shutdown with the same two motorized valves, and produce no noticeable surge. This extended time would create a longer separation sequence. This longer time would in- crwse the booster residuals, but the AMLS mission is not relatively sensitve to booster residuals. On the orbiter side. thc impact would be more noticeable to mission perfor- mance. Howcver, the extra 6.5 seconds is estimated as not to hc crucial to the mission. This longcr time would be beneficial for minimizing

cycling stress loads (slowing opening and closing times) on thcsc large diameter valves.

300STER I ORBITER --t+P7 Flow

I Check;alve I I In

mO I/F

t I

r' BOOSTER TANK FLOW

Note:

ORIHTER TANK FLOW

ORRITER ENGINE FLOW

Check valve enabled in staging sequence.

Figure 10. Crossfeed Check Valve The first approach, 1 . Step pressurization, is not viable.

Insufficient time is available to raise the pressure in thc empty booster tanks in either 3.5 or 10 seconds (time to terminate cross feed).

The second approach, 2. Add a Gheck valve, is viable. A crossfeed configuration was dcrived using latchable and swine valve closures in the disconnecl. This providcs the check valve function when the closure is unlatchcd. This design effects the following during crossfeed termination: I.) Prevents potential backflow instabilities, and 2.) Closes off orbiter flow (liquid or gas) prior to separation. The same latchable closure (flapper) was to be uscd on the

booster side to seal off the crossfecd system beforc to separation. Note: These check valves (swing closures) are latchcd opcn

before loading and until crossfeed shutdown is started. Subsequent transient analysis dictated that a flow restriction

was required in the LO2 crossfeed line in order to permit the orbiter tank feed to reach full flow during crossfeed termina- tion. This change requires a revision to the original conccpt by requiring the use of a programmed closing closurc in thc boostcr disconnect half. The conccrn for reverse flow IS no longer a problem. The first concept was not a complctc loss, as the orhitcr latchable, pivoted, swing closure is still employed.

10

1.2

I

0.8

2 2 2

3 0.6

3

0.4

0.2

0 0 0.5 I 1 .S 2 2.5 3 3.5 4

BME-SECONDS

Figure 11. Predicted Valve Position (%) and Flowrates (Yo) vs Time

250

225

N 2 m 9 E t

175

2 2 E 150

125

im 0 0.5 1 1.5 2 2.5 3 3.5 4

TIME-SKI

Figure 12. Predicted Crossfeed Pressures vs Time

11

Summary The cryogenic propellant crossfeed system design pre- scntcd in this paper shows the feasibility of using parallel

The timing to be used for crossfeed termination favors the 3.5 scconds if performance is to be maximized. Concerns regarding the relatively fast operation of large

diamelcr valves (21" ID) dictates use of a longer cross- fccd termination time.

Thc key design issues in the development of the cross. fccd configuration were as follows:

1. The crossfeed disconnect requires a motorized closing valve, combined with a motorized opening isovalve in thc orbiter to control crossfeed propellant flow. Surges arc low using a 3.5 second sequence, reference Figure 12. 2. A propellant isolalon valve is required at the inlet of each of the low tanks (LO2 on orbiter and LH2 on booster) for the purpose of loading. Each isovalve q u i r e s a throttlablc bypass topping/replenish valve for liquid level control, once the low tanks are loaded. 3. The propellant tank vent systems should be indepen- dent of the crossfeed system. 4. The booster and orbiter shall have independent pre- pressurization and flight pressurization systems. 5. Loading and draining arc fully supported by the crossfeed system. Spccial valves and line routing were required to drain the engine supply manifolds.

Future Considerations

burning stages for future vehicle missions. u

u Location (Usage)

LO2 Liquid Level Sensof'dry" (Crossfeed Termination) Top of Crossfeed Line (SSME Shutdown Transient) Mid SSME Supply Manifold

The addition of a controlled closure in the mating crossfccd dis- connect set also gives grcatcr flcxihlity on separating, or staging at any time during ascent (especially for emergcncics). The results of the transient analysis requircd a change LO the

original configuration approach (use of pivotcd and latchablc swing closures). These changes arc already reflected in Figurc 3. The LO2 booster disconnect half must include a motor control- Icd closure dcvice. The opening of thc orbiter LO2 isovalvc must be coordinated with, and fall within thc booster disconnect closure closing time.The booster disconnect valve closurc creates the needed Ap (from booster sidc to orbiter side) that permit.. thc orbiter system to reach full flow in a short period of time, = 3.5 seconds (sec).

Exuected Booster Residuals The flow shutdown termination would occur when thc LO2

liquid level sensor, near thc top of thc downcomer line, is activated. Using the twin 21" ID lines, the hcight required for the LO2 sensor is -60 ft above the top of the crossfeed line, see figure 2. This height is based on using =22,400 Lbs of LO2 during the 3.5 seconds of crossfeed termination. Also, somc 5.200 Ibs of LO2 are used during booster engines shutdown. The post shutdown LO2 rcsidual will approach 4500 Ibs. Table 2. reflects locations, times, and LO2 propellant masscs and usage (A mass).

Time LO2 Muss (set) (A mass) 0.0 32,400 Ibs

(22,400 Ibs) 3.5 10,000 Ibs

5,200 Ibs 6.0 4,800 Ibs

1. Crossfeed weight estimates should be made and corn. pared to LaRC's estimate. 2. Fluid simulation of crossfeed termination should be performed. 3. The LH2 configuration should be evaluated in more dcplh.

The expected staging sequence is identified as follows: (The target conditions (at T= 0.0 seconds) would be to reach Mach Acknowledgement: 3.0 when the LO2 staging depletion liquid sensor is rcachcd.)

Thanks to Ms Jacqueline C. Guerrero for her assistance Mach 3.0 in providing a technical and constructive review of this T= 0.0 1. Booster LO2 downcomer line level sensors dry "on". paper. Technical discussions with NASAILaRC were

2. Start closing booster LO2 disconnect closure. fruilrul in honing this study. References 3. Start opening orbiter LO2 tank isovalve closure.

T= 0.9 4. Orbiter LO2 disconnect swing flappcr unlatchcd. T= 3.5 5. Booster LO2 disconncct closurc closed "on". 1. Douglas 0. Stanley, Theodore A.Talay, Roger A. Lepsch,

6. Orbiter LO2 propellant isovalve open "on". W. Douglas Morris, and Kathryn E.Wurster "Conceptual T=3.6 7. Booster engines shutdown command "on". Dcsign of a fully Reusable Manned Launch System." AIAA

8. Booster Disconnect Line Retracted. Paper 91-0537, Presented at the 29thAcrospace Sciences 9. Booster stage separation enabled. Mccting, January 1991.

T= 6.0 IO. Booster engine main LO2 valves closed "on". 2. T.J.Gormley and Seshagirirao V. Vaddey "Crossfeed Tech- This sequence refects the expected operation of the two parallel nologies for NLS Evolution" AIAA Paper 92-1555, Presented burning stages during crossfeed termination, and boostcr/orbiter to the AIAA Space Programs and Technologies Conference, staging/separation. March 1992. L

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