NASA Technical Memorandum 105650

05o_ o

Thermal Control System for Space Station

Freedom Photovoltaic Power Module(NASA-TM-I05650) THERMAL CONTROL

SYSTEM FOR SPACE STATION FREEDOM

PHOTOVOLTAIC POWER MODULE (NASA)

13 p

N94-24825 _;':

Uncl as

G3/18 0205030

Thomas H. HachaNational Aeronautics and Space Administration

Lewis Research Center ........

Cleveland, Ohio

and

Laura Howard __Rockwell International .......

Canoga Park, California

Prepared for the22nd International Conference on Environmental System

sponsored by the Society of Automotive EngineersSeattle, Washington, July 13-16, 1992 _

https://ntrs.nasa.gov/search.jsp?R=19940020352 2020-06-21T03:01:01+00:00Z

Thermal Control System for Space Station Freedom Photovoltaic Power Module

Thomas H. HachaNational Aeronautics and Space Administration

....... Lewis Research Center ....Cleveland, Ohio 44135

and

Laura S. HowardRockwell InternationalRocketdyne Division

Canoga Park, California 91303

ABSTRACT

The electric power for Space Station Freedom(SSF) is generated by the solar arrays of the photo-voltaic power modules (PVM's) and conditioned, con-trolled, and distributed by a power management anddisVibution system. The PVM's are located outboard ofthe alpha gimbals of SSF. A single-phase thermalcontrol system is being developed to provide thermalcontrol of PVM electrical equipment and energy storagebatteries. This system uses ammonia as the coolantand a direct-flow deployable radiator. This paper pre-sents the description and development status of thePVM thermal control system.

INTRODUCTION

The electric power system for Space StationFreedom (SSF) provides utility grade power to the userinterface via a modular and expandable network ofpower generation, energy storage, control, and dis-tribution equipment. This system is being developed byRockwell International_ocketdyne Division under con,tract with NASA Lewis Research Center. The powersystem uses 160-Vdc electrical buses for the primarydistribution of power and converts it to 120-Vdc second-ary distribution power for the user interface. It alsoprovides 28-Vdc power to the space shuttle.

All of the SSF electric power is generated byphotovoitalc power modules (PVM's), which providedirect and stored energy at 160 Vdc to the centralstation for distribution to the users. The thermalconditioning of the electrical equipment and the energystorage systems in the PVM is provided by both activeand passive thermal control systems.

This paper descries the active thermal controlsystem being developed to thermally control the PVMelec_'ical equipment and energy storage batteries. Thesystem is located outboard of the port and starboardalpha gimbals on SSF and separate from the inboard

active thermal control system. A PVM and the loca-tions of the three PVM's on SSF are shown In Fig. 1.

PHOTOVOLTAIC POWER MODULE (PVM)

The SSF at permanently manned configuration isequipped with three PVM's: two on the starboard sideand one on the port side. Each PVM has a ratedcapacity of 18.75 kW average and 25 kW peak. Thisrepresents a rated capacity of 56.25 kW average and75 kW peak at permanently manned configuration.

The major subassemblies of the PVM are two betagimbal/photovoltalc array assemblies and the integratedequipment assembly (lEA). The beta gimbal/photovoltalc array assemblies convert radiant energyfrom the sun into dc electric power, which is supplied toSSF through the lEA. The lEA conditions and storesthe electric power collected by the photovoltalc arraysfor use in SSF operations. The PVM thermal controlsystem heat acquisition, heat transport, and heatrejection (radiator) systems are part of the lEA.

PHOTOVOLTAIC POWER MODULE THERMALCONTROL SYSTEM

The PVM thermal control system ('I'CS) acquiresexcess heat from the energy storage (batteries) andelectrical equipment assemblies located on the lEA andtransports this =heat to a dedicated radiator for rejectionto space. The TCS is a single-phase system that usesammonia as the coolant. All fluid-handling surfaces areconstructed with corrosion-resistant stainless steel,which provides excellent material compatibility withammonia. The TCS maintains the battery cell tempera-tures between 0 and 10 °C, and the electrical equip-ment baseplate temperature below 41 °C. All of theheat-generating sources cooled by the TCS are orbitalreplacement units (ORU's) located on the lEA. TheseORU's, their basic functions, maximum heat generationrates, and quantity are listed in Table I. Although heatloads vary throughout each orbit, the TCS is designed

to reject an orbital average heat load of approximately "7.5 kW.

The major assemblies and components in the PVMthermal control system are (1) the-pump and flow con-trol subassemblies (PFCS's), which are orbital replace-ment units located on the IF_A,(2) a direct-flow deploy-able radiator subassembly, which is an ORU attachedto the lEA structural framework, (3) radiant fin heatexchangers (RFX's) and associated fluid tubing whichare located within the lEA structural framework, and (4)fluid quick disconnects (FQD's), which connect fluidlines from the lEA tubing to the PFCS and radiator.

Figure 2 shows the lEA and the location of theheat source ORU's (batteries, dc switching units(DCSU's), battery charge and discharge units(BCDU's), and dc-to-dc converter units (DDCU's)), thePFCS's, and the radiator in the stowed position.

A flow schematic of the PVM thermal control sys-tem is shown in Fig. 3. This schematic is for the firstPVM launch, which has redundant PFCS's on the lEAfor failure tolerance requirements. Subsequent PVMlaunches will have a single PFCS. Single-phaseammonia liquid coolant is pumped by one of the twopumps in the PFCS at a constant flow rate of approxi-mately 1180 kg/hr to the fluid lines in the lEA. Heat isacquired via radiant fin heat exchangers (RFX's) fromthe batteries, BCDU's, DCSU's, and DDCU's by aparallel-series flow arrangement. After heat acquisitionthe fluid flows through one of the two redundant flowloops in the radiator, where heat is radiated to space.The redundant flow loops in the radiator are activatedand deactivated by the radiator FQD isolation valves.After heat rejection the fluid is returned to the PFCSand reclrculatad. A flow control valve in the PFCS

varies the flow through the radiator via a bypass whilemaintaining nearly constant flow to the RFX's in thelEA. Battery cell temperatures are maintained withintheir prescribed range by circulating more flowthroughthe radiator during high heat loads and less flowthrough the radiator during low heat loads. Fluid accu-mulators located in the PFCS and the radiator allowfluid expansion and contraction over the TCS operatingtemperature range and maintain system pressureabove saturation pressure. FQD's connect and dis-connect the PFCS and radiator fluid lines to the lEA

during ORU replacement. A FQD is also used forcoolant filling and draining of the system. Both theaccumulators and the FQD's are used to facilitate leakdetection and isolation.

COLDPLATE SUBASSEMBLIES - The TCS sys-tem collects heat via a unique application of fin, heatsink, and heat exchanger technology. One unusualfeature of this design is that the heat-sink-like baseplateof the energy storage subsystem (batteries and BCDU)and electrical equipment (DCSU and DDCU) ORU'stransfer excess heat by mechanism of radiation ratherthan the traditional mechanism of convection from thefins. This radiant heat is then received by the finned

heat exchanger subassemblies that make up the TCS

coldplate subassemblies. The coldplate subassembliesserve as components of the TCS as well as structuralmembers of the lEA structural framework. Each cold-

plate assembly consists of two or more radiant fin heatexchanger subassemblies. Each heat exchangersubassembly consists of a stainless steel serpentinetube soldered to an aluminum finned plate.

Figure 4 illustrates the RFX thermal interface witha typical ORU. The following heat transfer processoccurs during normal operation of the PVM. Heat isgenerated by the battery cells or other electrical com-ponents and is transferred to the ORU box baseplateby conduction. This heat is then transferred to themating fins of the heat exchanger subassembly by radi-ation. The fins conduct the heat away, transferring itto the solder material, where it is convectively drawnaway by the ammonia coolant in the serpentine linesattached to it.

Each coldplate subassembly consists of two ormore RFX's interconnected by manifold tubes. Fluidheaders hydraulically connect the manifold tubing of thecoldplate assemblies to one another. The remainingcomponents of the TCS are interconnected by interimtubing. A coldplate subassembly for two battery ORU'sand a battery charge and discharge unit ORU is illus-trated in Fig. 5.

This design was driven by a variety of challengingfactors. Although this radiant exchang_betw#e n fins isnot the most efficient ther{'nald=esTgn,-itis a-solutionthat enables on-orbit maintenance flexibility not possibleby conventional means of active cooling. In addition,for optimum manufacturing and heat transfer capabili-ties, it would have been more common to use the samematerial for serpentine tube and tinplate. However,because the tube material must be compatible with theselected coolant, it was necessary to use a dissimilarmetal for the tubing and the tinplate. The differences incoefficient of thermal expansion necessitated selectionof a solder material with good creep capability.

A producibility sample in the form of a battery RFXwas fabricated and tested. Thermal cycling and ran-dom vibration testing have exhibited hardware designintegrity.

PUMP AND FLOW CONTROL SUBASSEMBLY

(PFCS) -The PFCS provides fluid transport for theTCS, regulates flow through the radiator, performs avariety of electrical control and interface functions, andallows for fluid volume changes in the TCS. The majorcomponents in the PFCS are two pumps, a flow controlvalve (FCV), a fluid accumulator, a local data interface .(LDI), a signal conditioning interface (SCI), and sevenmotor controllers. The PFCS is being developed byUnited Technologies Corporation, Hamilton StandardDivision, under contract with Rocketdyne. A diagran_ 0fthe PFCS is shown in Fig. 6.

Circulation of the ammonia coolant is provided byone of two identical centrifugal pumps in the PFCS.Each pump is powered by a hermetically sealed120-Vdc canned motor and designed to provide

P

2

approximately1180kg/hrat a 172-kPa head. Althoughonly one pump is operating, the second pump isprovided for reliability requirements. Bacldlow throughthe nonoperating pump is prevented by a dual checkvalve.

The flow corr_oi valve is a three-way spool valvethat controls the percentage of total system flowthrough the radiator and radiator bypass. The valve isdesigned to provide 0- to 100-percent radiator flow with100 discrete valve positions. Full motion of the valve isaccomplished in 10 sec. Valve contoured ports main-tain constant fluid system pressure drop at all positionsto maintain nearly constant flow through the RFX's.The flow control valve is actuated by a 28-Vdc steppermotor. Hermetic sealing of the valve is achieved by amagnetic coupling between the spool and the motor.

Fluid accumulators are provided to accommodatethe fluid volumetric changes over a temperature rangefrom -77 to 4g °C and to insure single-phase operationby maintaining the system pressure above the fluidsaturation pressure. In addition to the single accu-mulator in the PFCS, two accumulators are located inthe radiator subassembly (one for each flow loop). Theaccumulator contains fluid coolant and pressurizedn_ogen gas separated by a metal bellows. Fluid volu-metric changes caused by system temperature excur-sions result in bellows motion and compression orexpansion of the nitrogen cover gas. During normaloperation the system pressure is nominally maintainedby the accumulators between 793 and 1550 kPa. Fluidinventory is determined by sensing the bellows position.This information is used in system leak detection andisolation, described later.

The local data interface is the data link to the sen-sors and effectors in the TCS. This interface convertscommands from the PVM controller located on the lEA

to discrete signals used to control the TCS and pro-vides data to the PVM controller.

The signal conditioning interface provides signalconditioning for the TCS instrumentation, supplies lowvoltage to the local data interface end FQD motor con-trollers, and performs control functions to actuate theflow control value.

Seven motor controllers are located in the PFCS.Four controllers located in the FQD controller housingoperate the fluid quick disconnects (FQD's) located inthe PFCS and radiator. These controllers also providethe mate-demate position status of the FQD's. Threecontrollers perform the control functions to operate thetwo pump motors and the flow control valve motor.

RADIATOR SUBASSEMBLY - Heat rejection tospace is accomplished by the PVM radiator (PVR).The PVR is a direct-flow deployable radiator that is inthe folded (stowed) position during launch in the shuttleand during on-orbit assembly. When the PVM is acti-vated, the radiator is deployed to full extension of ap-proxlmately 15.2 m in length. Ammonia coolant flowsthrough tubes located in the radiator panels, transfer-ring heat to the panel surface. A high-emissivity, low-

absorptivity coating on the panel surface radiates thewaste heat to space. The PVR is being developed byLTV Aerospace and Defense Company, L'I'V Missilesand Electronics Group, Missiles Division, under contractwith Rocketdyne. Figure 7 illustrates the PVR in boththe stowed and deployed position.

The PVR has eight 3.56- by 1.98-m panels (approx-imately 93 m2 of radiating area) to reject the requiredwaste heat at the required operational end environ-mental conditions. The panels are constructed of analuminum honeycomb matrix with stainless-steel flowpassages that extend across the panel. Thesestainless-steel flow tubes are connected to inlet andoutlet manifolds that extend along the panel edges. Tofacilitate good thermal conduction, the stainless steeltubes are bonded with a silver-filled epoxy to aluminumextrusions that conduct heat to the panel surface. Aradiator panel and manifolds are shown in Fig. 8.

On-orbit deployment of the PVR is accomplishedwith a scissors-type deployment mechanism. Thepanels are connected by hinges, and the panel fluidmanifolds are connected by flex_le metal hoses. Themechanism deploys and retracts using a 120-Vdc brush-less motor and a cable drive system. The deploymentsystem provides the capability of manual deploymentand retraction in case of motor failure, in the stowedposition, a cinching mechanism is used to secure thepanels so that the PVR can withstand launch loads.Decinching prior to deployment and cinching prior toORU removal is done manually.

The PVR has two independent flow circuits. Eachcircuit contains one fluid accumulator. One circuit isoperating while the second circuit is closed to the cir-culating system by the FQD's. This redundant fluidsystem helps ensure against loss of the radiator andTCS due to penetration of the fluid lines by micro-meteorites or orbital debris. With this redundancy there

will be 95-percent probability of not losing heat rejectioncapability for a period of 10 years.

FLUID QUICK DISCONNECTS (FQD) - Fluid quickdisconnect couplings are used to connect and discon-nect the fluid lines of the PFCS and radiator ORU's tothe fluid lines in the IF_A,thereby allowing on-orbitreplacement of these ORU's. FQD's are also used tofacilitate leak detection and isolation. Each FQD hastwo independent flow passages operated by a 120-Vdcbrush-type motor. Each coupling has two halves: apassive half and an active half. The passive half isfixed to the lEA, whereas the active half, which includesthe motor _nd drive train, is attached to the ORU's.Mating and demating is accomplished automatically ormanually by translation of the active half to and _omthe passive half. Spring-loaded Teflon seals wereselected for fluid compatibility and low-temperaturesurvivability. The FQD is being developed by MoogInc., under contract with Rocketdyne. A FQD is illus-trated in Fig. 9.

The FQD's have three discrete positions, asfollows:

(1)Mated- Bothactive and passive halves arecoupled and sealed. Isolation valves in both halves areopen to flow.

(2) Engaged - Same as mated except that isolationvalves in both halves are closed to flow.

(3) Demated - Isolation valves in both halves areclosed to flow, and the halves are separated by motionof active haft from passive half.

A unique feature of the FQD design is a replace-able cartridge for the passive halves. This featureallows ground and on-orbit replacement of the passivehalf seals for routine maintenance or in case of sealleakage. A special tool removes the old cartridge,which contains all the seals and moving parts from theFQD passive half housing, and inserts and secures anew cartridge into the housing. This is accomplished atsystem pressures with only a minor loss of fluid. Sincethe iEA fluid lines are of all-welded construction, thisFQD maintenance feature greatly enhances the lEAreliability.

LEAK DETECTION AND ISOLATION - The TCSinstrumentation used for leak detection and isolationmeasures pressure, temperature, and accumulatorposition (Fig. 3). This instrumentation in conjunctionwith on-orbit software algorithms will be capable ofautonomously detecting time-critical coolant leaks dur-ing TCS operation. On-orbit leaks will be detected by atemperature-compensated, pressure decay method.Coolant leaks that are not time critical will be detectedby ground monitoring personnel. In addition, the soft-ware will be capable of isolating leaks by means ofTCS instrumentation, FQD's, and accumulators. Thistechnique is limited to leak isolation to the PVR, PFCS,and lEA.

Leak isolation will be performed by using the FQDcouplings, which separate the PFCS and the PVR fromthe lEA. These FQD's will be sequentially commandedto connect or isolate portions of the ammonia fluid inthe TCS for isolation purposes. The FQD's are se-quenced in such a manner that the lEA is never com-pletely isolated _om a TCS accumulator located in thePFCS or the PVR. Electrical inhibitsensure that thelEA will always maintain an open fluid path to anaccumulator (a necessary safety requirement to ensurethat the lEA does not become overpressudzed).

SUMMARY

The Space Station Freedom (SSF) electric powersystem provides utility grade power to the user inter-face. All of the SSF electric power is generated byphotovoltaic power modules (PVM's).

The batteries and major electrical equipment loca-ted on the PVM are cooled by a single-phase thermalcontrol system (TCS), with ammonia as the coolant. Allmetal surfaces contacted by the coolant are construc-ted of corrosion-resistant stainless steel for coolantcompatibility. The major components of the TCS are a

pump and flow conVol subassembly (PFCS), a radiatorsubassembly, radiant fin heat exchangers (RFX's), andfluid quick disconnects (FQD's).

Coolant is circulated through the system by a cen-trifugal pump. Heat from the batteries and electricalequipment is acquired by the fluid via RFX's and rejec-ted to space by a direct-flow deployable radiator. TheTCS maintains the battery cell temperatures between0 and 10 °C by controlling the flow through the radiatorwith a flow control valve that allows fluid to bypass theradiator at low heat loads while maintaining nearlyconstant flow through the RFX's.

The RFX collects heat by a unique application offin, heat sink, and heat exchanger technology. Theheat sources transfer heat to a finned baseplate byconduction. This heat is transferred to the mating finsof the RFX by radiation, then transfen'ed to the coolanttubes by conduction. This design enables on-orbitequipment replacement flexibility not poss_le with con-ventional thermal design.

The PFCS contains redundant pumps, a flow con-trol valve, a fluid accumulator, and various electricalequipment. The centrifugal pumps are designed toprovide approximately 1180-kg/hr flow at a 172-kPahead.

The flow control valve regulates the flow throughthe radiator to control battery cell temperatures withinthe required range. Ruid volume_'ic changes over thetemperature range -77 to 49 °(3 are accommodated bythe accumulator in the PFCS and accumulators in the

radiator subassembly. The electrical equipment in thePFCS performs a variety of electrical control and inter-face functions.

The radiator subassembly is a direct-flow deploy-able radiator that is in the folded (stowed) positionduring launch and is deployed when the PVM is acti-vated on-orbit. The radiator has eight panels withapproximately 93-m 2 radiating area. The panels areconstructed of an aluminum honeycombed matrix. On-orbit deployment is achieved with a motor-poweredscissors-type mechanism. Manual deployment andretraction capability is also provided. The radiator hastwo Independent flow circuits for protection against lossdue to micrometeorites or orbital debris.

Fluid quick disconnects (FQD's) are employed tofacilitate on-orbit replacement of the PFCS and radiator.FQD's are also used in the leak detection and isolation

method employed for the TCS. A unique feature of theFQD design is a replaceable carlz'idge, which allows on-orbit replacement of the seals and moving parts whilemaintaining system pressure.

TCS instrumentation in conjunction with on-orbitsoftware algorithms will be capable of autonomouslydetecting time-critical leaks during TCS operation.Leak detection is accomplished by a temperature-compensated, pressure decay method. Isolation will beperformed by using the FQD isolation feature.

Ir

ACRONYMS

BAT batteryBCDU battery charge and discharge unitDCSU dc switching unitDDCU dc-to-dc converter unit

. FCV flow control valveFQD fluid quick disconnect

lEAORUPFCSPVMPVRRFXTCS

integrated equipment assemblyorbital replacement unitpump and flow control subassemblyphotovoltaic power modulePVM radiatorradiant fin heat exchangerthermal control system

TABLE I. - ORBITAL REPLACEMENT UNITS (ORU's) CONTROLLED BY PVM

ORU

dc Switching unit(DCSU)

Battery

Battery charge anddischarge unit(SCDU)

dc-to-dc Converter

unit (DDCU)

THERMAL CONTROL SYSTEM

Maximum Numberheat of ORU's

generation per PVMper ORU,

W

420 2

1150 12

420 6

545 2

Function

Provides transfer of power toand from various electrical

equipment on PVM andcentraJ station.

Provides energy storageduring insolation period andpower during eclipse period.

Regulates power to and frombatteries.

Converts pdmary 160-Vdc

power to secondary 120oVdcutility-grade power from PVM

usage.

5

PVM ---_

/_- PVM's \.

/ / \\ _ <_

(a) Space Station Freedom permanently manned configuration.

Integrated

equipment

assembly --_

imbaJ

Radiator/

(b] PhotovoltaJc power module.

Figure 1 .m Space Station Freedom and photovoltaJc power module.

6

Radiator _ -_-_._.

(stowed) --_ -

J

v

Figure 2.-- Integrated equipment assembly.

PUMPS - -- F DUAL PUMPS 7 LEGENDDUAL ' :

I _7 1_ -=°=_

I_T _ )C_J

" "_ _'_. l IL_LF:::::_ T ,uuuu,,_i

I.tT

FIt,IJDRAIN FQD L

INTEGRATED EOUtPMENT ASSEMBLY _IEA)

Rgure 3.-- PVM thermal control system flow schematic.

,'-- ORU box/I

/

r-- Integral/ t-tuned ORU

baseplate

Integralfinned

cold plate

Solder ._z _-- Serpentinefluid coolant

tubes

Figure 4.m ORU box radiant heat exchanger interface.

Battery BCDU location _,\ ______

ORU \_ '

Iocation-/_ ,. _ _ "/ / \\ \¢____

//Ill

<4(a) Finned side.

_ine tubing

(b) Tube side.

Figure 5.-- Cold plate assembly for battery and BCDU ORU's.

8

=f

FQD

controller

Accumulator| v

#

FQD

Pump

controller

0 0 0 0

SCI

IFCVl|

O

um / 0

v

FQD

Figure 6.-- Pump and flow control subassembly (PFCS). (Drawing courtesy of United Technologies Corporation-)

Panelhingles(interior)--_

Flexhoses

Cross-flowtubes-J

L-Scissors

beam

(a) Deployed position.

Manifold

cover

F" Panel hinges/

/

/

341 ¢m

Deployment

" pulley

housing -J"

/-- Cinch cables

I

) _ Base

I structure

63.5 cm

204cm

(b) Stowed position.

Figure 7.-- Radiator subassembly. (Drawing courtesy of LTV Aerospace and Defense Company).

10

r177 cm

panel

L

315 cm

Scissor I" panel "1beam

A

I

_=rp_=.====

< 342 cm

Scissor Primary Secondarybeam manifold manifold

• tube tube

extension

Aluminum Aluminumskin flow tube

extrusion\ /

/ \Stainless Flow tube

steel tube closeoutextrusion

Detail A

Aluminum honeycomb

l,-,,,i Primary ------_. \

-- tube spacing I \ _j_

Aluminum tube spacing /honeycomb Flow tube

assembly(see detail A)

View A - A View B - B

Figure 8.-- Radiator panel and manifold details (all dimensions approximate). (Drawing .courtesy of LTV Areospace and DefenseCompany.)

Fluid

/- Drive

/ motor

(a) Demated`

half

(b) Mated.

Figure 9.-- Fluid quick disconnect coupling. (Drawing courtesy of Moog Inc.)

11

4. TITLE AND SUBTrrLE

Thermal Control System for Space Station Freedom Photovoltaic

Power Module

AUTHOR(S)

Thomas H. Hacha and Laura Howard

PERFORMING ORGAN|ZATION NAME(S) AND AODRESS(ES)

National Aeronautics and Space Administration

Lewis Research CenterCleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and SpaceAdministrationWashington, D.C. 20546-0001

WU-474--46-10

8. PERFORMING ORGANIZATIONREPORT NUMBER

E-7014

10. SPO NSORING/MCP qTORINGAGENCY REPORT NUMBER

NASA TM- 105650

11. SUPPLEMENTARY NOTESPrepared for the 22rid Imemational Conference on Environmental Systems, sponsored by the Society of Automotive Engineer, Seattle,

Washington, July 13-16, 1992. Thomas H. Hacha, NASA Lewis Research Center and Laura Howard, Rockwell I.ntemational

Rocketdyne Division, Canoga Park, California 91303. Responsible person, Thomas H. Hacha, (216) 433-8319.

DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified -UnlimitedSubject Categories 18, 20 and 34 12b. DIs] FdBUTION CODE

ABSTRACT (Maximum 200 words)

The electric power for Space Station Freedom (SSF) i_ generated by the solar arrays of the photovoltaic power modules

(PVM's) and conditioned, controlled, and distributed by a power management and distribution system. The PVM's arelocated outboard of the alpha gimbals of SSF. A single-phase thermal control system is being developed to providethermal control of PVM electrical equipment and energy storage batteries. This system uses ammonia as the coolantand a direct-flow deployable radiator. This paper presents the description and development status of the PVM thermal

control system.

14. SUBJECT TERMS

Photovoltaic; Electric power; Thermal; Space Station

SECURR'Y CLASSIRCATIONOF REPORT

Unclassified

NSN 7540-01-280-5500

18. SECUHIq-lr CLASSIFICATION

OF THIS PAGE

Unclassified 19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF P*A-GES13

16. PRICE CODEA03

20. LIMITATION OF AB:_ACT

Standard Form 298 (Rev. 2-89)Pre_d by ANSI Std. z3g-18298-102