NASA Technical Memorandum 102366

The Fuel Cell in Space: Yesterday,

Today and Tomorrow

Marvin Warshay and Paul R. Prokopius

Lewis Research Center

Cleveland, Ohio

Prepared for the

Grove Anniversary (1839-- 1989) Fuel Cell Symposium

sponsored by the Royal Institution

London, Great Britain, September 18-21, 1989

NOU- 1 1 _,0-_

THE FUEL CELL IN SPACE" YESTERDAY, TODAY AND TOMORROW

Marvin Warshay and Paul R. Prokopius

National Aeronautics Space Administration

Lewis Research Center

Cleveland, Ohio 44135

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0

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SUMMARY

The past, present, and future of space fuel cell power systems is

reviewed, starting with the first practical fuel ceil by F.T. Bacon which led

to the 1.5 kW Apollo alkaline fuel ce11. However, the first fuel cell to be

used for space power was the Gemini 1.0 kN acid IEM fuel cell.

The successor to the Apollo fuel cell is today's 12 kW Orbiter alkaline

fuel cell whose technology is considerably different and considerably better

than that of its ancestor, the Bacon cell. And in terms of specific weight

there has been a steady improvement from the past to the present, from the

close to 200 Ib/kW of Apollo to the 20 Ib/kW of the orbiter.

For NASA future Lunar and Martian surface power requirements the regenerative fuel cell (RFC) energy storage system is enabling technology, with the

alkaline and the PEM the leading RFC candidate systems. The U.S. Air Force

continues to support fuel cell high power density technology development for

its future short-duration applications.

INTRODUCTION

The first practical fuel cell resulted from work begun in England in 1932

by F.T. Bacon. Eventually a 5 kW hydrogen-oxygen, alkaline electrolyte system

developed by Bacon demonstrated its capability by powering a welding machine, a

circular saw, and a 2-ton fork lift truck. With these and other demonstrations

of the applications of this "new" power device, the fuel cell had finally

apparently emerged from the laboratory. However, it was the worldwide attention to NASA space missions that introduced "fuel cell" to the vocabulary of

millions of people. Ironically, it has probably been the announcement, during

space flights, of real or suspected fuel cell malfunctions, rather than the

usual smooth performance of the fuel cells in space, that has given fuel cells

their wide recognition. (The aborted Apollo 13 flight was a case in point. A

prelaunch malfunction of an oxygen feed control component - not the proclaimed

fuel cell problem - was the real cause of the near disaster that attracted the

attention of many millions of people.)

THE PAST

In the early years of U.S. space flight, the fuel cell was selected over

other competing power systems because of its greater promise to meet the

on-board power requirements of planned NASA extended duration manned missions.

In addition to satisfying the power, efficiency, weight, life, reliability,
safety, mlssion flexib111ty, development maturity, etc. requirements, the fuel

cell offered a numberof special advantages over competing power systems.

Noteworthy amongthese advantages was the abillty of the hydrogen-oxygen fuel

cell to supply potable water (the product of the electrochemical reaction) for

crew consumption and for cabin air humidlfication.

What emerged as a result of the NASA selectlon of the fuel cell was an

almost explosive growth in fuel cell research and development (primarily sponsored by NASA and other U.S. government organizations) in industries, in

universities, and in government laboratories.

For the Gemini earth-orbiting mission (1962 to 1965) fuel cells were successful in supplying power in a reliable manner. The General Electric (GE)

fuel cells that were used for seven fights of that mission utilized solid

polymer electrolytes (called an ion-exchange membrane (IEM) at that tlme) consisting of a cationic membrane of sulfonated polystyrene resin. This type of

electrolyte had mobile H+ ions in well-defined electrolyte boundaries. The

advantage of the obvious ease of electrolyte containment was offset by the

ohmic resistance of the membrane, which contributed to the lower performance

(voltage efficiency) of the IEM than of alkaline Cuel cell systems such as that

used for the Apollo missions that followed. Making the membrane thin mlnlmized, as much as possible, the effect of high ohmic resistance. (In the

1980's there has been considerable improvement in the performance of this concept, now called the Proton Exchange Membrane, or PEM. This is dlscussed in

"The Future" section.)

The Gemini l kW powerplant consisted of three stacks of 32 cells. The heat

generated by the fuel cell stack was removed by a clrcu]ating coolant. Two

]-kW powerplants were on board to handle maximum load requirements. The average power that was produced on the Gemini flights was 620 W. The hydrogen and

oxygen reactants were stored in their cryogenic states. The nominal hydrogen

supply pressure was 1.7 psi above water pressure, that of the oxygen 0.5 psi

above the hydrogen pressure. The cell operating temperature was 70 °F. The

anode and cathode consisted of titanlum screens upon which unsupported Pt

catalysts with PTFE were deposited. The catalyst loading was 28 mg Pt/cm2/

electrode. This IEM fuel cell technology was subsequently (1967) used for the

Biosatellite spacecraft. An important change in the IEM fuel cell technology

for this application was the use of a new membrane, namely the perfluorosulfonic acid ionomer. The membrane called Nafion (registered trademark) was

developed by DuPont. These type of cationic membranes became the standard for

this type of fuel cell, which continues to this day.

A special problem of the Gemini IEM fuel cell was its sensitivity to membrane water content. Nith insufficient water the membrane would dry out and

often crack. On the other hand, the membrane could not hold too much water.

A flooded electrode was often the result. Both extremes would result in a

severe performance loss. To avoid the problem of excess water, the Gemini fuel

cell design utilized wicks to carry excess water to a ceramic porous separator

where the water was separated from the oxygen and sent to an accumulator for

storage.

The fuel cell technology that went to the moon was not based upon the

Gemini IEM fuel cell of the ]960's, but rather upon the Bacon cell that preceded
the GEIIEM fuel cell work. Through the British National Research and Development Council and Leesona-Moos Laboratories, Pratt & Whitney acquired the patent

to Bacon's fuel cell technology in 1959 and applied the technology to the NASA

Apollo mission. However, for space use, the heavy, high pressure Bacon cell

was not directly suitable. For the Apollo fuel cell, the pressure was lowered

from 600 to 50 psi. To prevent the KOH from boiling at 205 °C, the KOH concentration was increased from 30 to 75 percent. But, at ambient temperature

75 percent KOH is solid. However, this proved not to be a significant problem.

Finally, the temperature was raised to 260 °C to recover the performance lost by

the pressure reduction. The Apollo fuel cell included Bacon's double-porosity

layer nickel electrodes designed to maintain the gas-electrolyte interface at

the boundary between the pore size regions. The anode was porous nickel while

the cathode was lithiated, oxidized porous nickel. Because of the high temperature <maximum) of 260 °C a highly active catalyst like Pt was not needed as

can the case of the Gemini fuel cell which operated at 70 °F. At 260 °C and a

current density of 150 A/ft 2 the voltage was 0.87 V/cell, while at its nominal

operating temperature of 204 °C it produced 0.72 V at 150 A/ft 2. The performance of the Gemini fuel cell was lower.

The Apollo fuel cell 1.5 KN powerplant consisted of three modules connected electrically in parallel. Heat and water removal were by hydrogen circulation. A glycol-water secondary coolant loop was also employed. The power

range was 563 to 1420 W. Peak power capability was 2295 W at 20.5 V. It

weighed 220 lb. The module rating was 400 hr; but it ran 690 hr without failing. The Apollo missions were from 1968 to 1972.

The KOH-H20 electrolyte solution was pressurized to 53.5 psia while each

reactant gas cavity was maintained at 63 psia. The operating pressure of the

system and relative pressure differentials affected the fuel cell performance.

The latter determined the location of the reactant-electrolyte interface.

PRESENT

Bacon might not recognize the "grandchild" of his alkaline fuel cell

today, the Orbiter fuel ceil. The high pressure, very heavy construction of

Bacon's fuel cell was already gone in the Apollo fuel cell. In the Orbiter

fuel cell, United Technologies Corp. (the new name for the Pratt & Whitney fuel

cell organization) dropped the dual porosity electrodes. In the place of free

electrolyte, the Orbitor electrolyte held the 32 percent KOH electrolyte in an

asbestos matrix. ,Another change was the cell temperature, which was reduced to

93 °C. At this temperature an electrocatalyst was required to achieve a reasonable performance. The operating pressure is 60 psia. The electrodes consisted of gold plated Ni screens upon which a catalyst layer and PTFE was

applied. The hydrophobic PTFE provided gas passages through the electrode.

The catalyst loading on each electrode is 20 mg/cm L Au Pt alloy on the cathode

and lO mg/cm 2 Pt on the anode.

Heat generated by the fuel cell reaction is transferred to the fuel cell's

coolant system. The fuel cell coolant system, containing a fluorinated hydrocarbon dielectric liquid, transfers the heat through the Orbiter's heat

exchangers to the freon coolant system.
The Space Shuttle Orbiter is equipped with three fuel cell powerplants

supplying 12 kN at peak and 7 kW average power. Each powerplant weighs 250 lb.

The Orbiter's fuel cell powerplants are 50 Ib lighter and deliver up to 8 times

as much power as those of Apollo.

The fuel cell powerplants are started approximately 8 hr prior to launch,

using ground-suppl_ed hydrogen and oxygen reactants. Approximately 7 min is

required to bring the powerplants to full operating capacity. After startup,

the fuel cells share spacecraft electrical loads with ground power support.

About 3 min prior to launch, the spacecraft automatically switches to onboard

reactant supply and the fuel cells become the sole source of electrical power

for the spacecraft for the duration of the mission. Approximately every 8 hr

during the mission each fuel cell powerplant is ourged for 2 min to remove

Inert gases from the system.

THE FUTURE

NASA's planning for the future exploration of the Solar System includes

the establishment of manned outposts, as well as central base stations on the

Moon and Mars. Supportlng human expeditions to, and operations on, the surface

of the Moon or Mars represents a substantial technology challenge for current

and projected power system capabilities. The high levels of power associated

with an operational base, somewhere in the I00 to lO00 kW, will require nuclear

power systems. During the installation of these permanent nuclear systems,

power systems based on solar energy hold the greatest promise for supplying

needed power. These systems will also be required to augment and serve as

back-up power sources for the permanent nuclear-powered bases.

Because the solar-based surface power system must supply usable power contlnuously, that is during the day as well as the night, a regenerative system

is required. During the daylight hours the power generation subsystem will

recharge the energy storage subsystem and also supply power directly to the

system's electrical loads. Thus, continuous power is supplied to the load: it

is provided by the power generation subsystem during sun periods and from the

energy storage subsystem during periods of darkness.

In a Lunar application, the period of darkness extends for 2 weeks, while

a Mars application presents a more manageable 12-hr night. Both applications

require very high energy density and reliable energy storage systems. The

highest potential for successfully achieving surface power storage capabilities

for these applications lies in the regenerative fuel cell (RFC) concept. The

regenerative fuel cell system is depicted in figure I. During the light portion of the orbit the photovoltaic solar arrays generate sufficient power to

service the system electrical loads plus a water electrolysis unit. The amount

of electrical energy required by the electrolysis unit is dictated by the

amount of hydrogen and oxygen needed to generate power in a fuel cell, which

supplies the electrical loads during the dark portion of the orbit. In generating this power, water is produced by the fuel cell as a by-product of the

electrochemical reaction. To complete the cycle, the by-product water is collected and stored for use in the electrolyzer during the succeeding orbit.

The mass and specific energy benefits to be realized by employing a regenerative fuel cell system are displayed in figure 2. Low system mass for a
given power level is a central requirement for achieving acceptance of transportation costs to the Moon or Mars. Another requirement, even more challenging, |s appreciable system lifetime without sacrificing performance even after

an extended period of dormancy. Also a relatively high power level requirement of 25 kW is projected to support an initial surface outpost of four to

six astronauts. To develop the technology base for a system which will meet

these requirements, a program has been initiated as one of the elements of NASA

Project Pathfinder. This program was developed and is being managed by NASA

Lewis Research Center. It focuses on the technology areas of solar power generation, energy storage and electrical power management. Advancing these technologies and coupling their performance potentials with an advanced low mass,

reliable electrical power management subsystem can lead to surface power systems having a reliable life in excess of 20 OOO hr with system specific powers

of 3 W/kg for Lunar application and 8 W/kg for Martian applications. These

projected specific powers represent substantial improvements over the state-ofthe-art, up to a factor of 30. System mass reductions of this magnitude,

coupled to the expected factor of IO increase in life, should enable extraterrestrial surface missions where life and mass are the driving forces for

success.

The Energy Storage element of the Pathfinder Surface Power Program is a

IO-year effort culminating in the verification of a regenerative fuel cell system breadboard operating in a relevant environment. The near-term, 5-year,

Phase I effort, will provide the development and verification of the system

critical components, those being the fuel cell and electrolyzer stacks. The

second 5-year phase will focus on the development and verificatlon of the complete RFC breadboard system.

The two candidate fuel cell and electrolyer technologies for the Pathfinder system are the alkaline and proton exchange membrane (PEM). Because

alkaline was the system of choice for both Apollo and the Space Shuttle, the

state-of-the-art of alkaline systems had been advanced considerably over that

of the PEM technology. However, the recent technology efforts on fuel cells

for transportation applications have advanced the PEM technology.

The major deficiency facing the alkaline technology in the Pathfinder

application is the lack of long term catalyst layer stability, which translates

into performance degradation with time. Unlike with PEM and other acid-type

fuel cells, a stabilizing catalyst support has not been developed for the alkaline system. PEM, on the other hand, offers a stable, long life system but one

whose efficiency has, until recently, been significantly lower than alkaline.

Recent improvements in the conductivity of PEM membranes increase the probability that this technology could replace alkaline as the Pathfinder RFC baseline.

At present, the weakness in the PEM technology stems From the fact that the

membrane technology improvements are very recent and, therefore, the data base

needed to justify committment to this technology does not exist. Accordingly,

a technology assessment has been undertaken to provide guidelines for selecting

the technology to be carried into full development in the Pathfinder Program.

Since the late 1960's the U.S. Air Force has been supporting fuel cell

technology development for future space applications requiring very high power

densities for much shorter periods than for NASA missions. Figure 3 illustrates the steady progress over the years in alkaline fuel cell power density
performance improvement. The work was carried out by UTC (this part of UTC Is

now called the Internatlonal Fuel Ceils Corp., IFC).

The Solid Oxide Fuel Cell (SOFC) in its monollth configuration has the

potential for even higher power density performance than does the alkallne fuel

cell system. However, the high power density alkallne fuel cell system is much

further along In Its development than is the SOFC for the Air Force Space

applications. The government funding for the SOFC monolith concept has been

directed at the NASP (National Aerospace Plane) application. Finally, the

alkallne fuel cell system holds particular promise for the proposed National

Space Transportation System (NSTS), sometimes referred to as the a11-electrlc

shuttle. Here the fuel cell is to supply both on-board power and high power

density, short burst power for electrical control system accuators.

The European space program also plans to use fuel cell systems to satisfy

spacecraft power requirements. Hermes, the European manned reusable space

plane will requlre 3 to 4 kW for low earth orbit missions. Its electrical system will utl]Ize fuel cells as the primary power source and lithium primary

batteries as a back-up/peak power supply (peak of 15 kW). For future European

spacecraft hlgh power requirements, European organizations have been studying

RFC systems.

CONCLUDING REMARKS

Figure 4 is a graphic depiction of the progress in space fuel cell power,

as well as the hope for the future In particular applications. (However, thls

flgure does not depict the progress leading to the important future NASA space

fuel cell application discussed In this paper, namely the RFC for Lunar and

Mars surface power energy storage.) In terms of specific weight it illustrates

the steady improvement from the past to the present, from the close to

200 Ib/kN of the Apollo 1.5 kW powerplant to the 20 Ib/kW of the Orbiter 12 kN

fuel cell powerplant of today. Based on technology development both underway

and planned, it forecasts meeting the goals of (1) about 1.5 Ib/kW, in about

1993, for the 300 KW NSTS fuel cell powerplant, and (2) about 0.5 lb/kW for

the very high power density, short duration applications at the beginning of

the 21st century.
kWe

MAIN

POWER

BUS

ENERGY

STORAGE

SYSTEM

ELECTROLYZER I _

"_ FUELCELL J

kWe

kWe

POWER

LOADS

FIGURE1: REGENERATIVEFUEL CELLSYSTEMSCHEMATIC

7
SPECIFIC ENERGY OF 25 kWe ENERGY STORAGE SYSTEM

2000'

IOOO  ̧

!+¢,._j¢ IOOUJ

Q.

(/)

10

...... i , .... ,,'i , , • ,,'"i

I I0 I00

DISCHARGE TIME, HRS.

RFC's

I000

TECHNOLOGY IMPACTS

25kW SURFACE POWER SYSTEM

Z

MJ

M,I

iv0A

LUNAR MARS

0.0 °

Ni/H2

SOA PV

Na/S RFC Ni/H2 Na/S

SOA PV SOA PV SOA PV SOA PV

RFC

SOAPV

FIGURE 2: ADVANTAGESOF REGENERATIVE FUEL CELL

ENERGY STORAGE VERSUS BATTERY SYSTEMS

FOR LONG DISCHARGE APPLICATIONS
Cell

voltage

0.8

0.6

'-21

1.0

7

i9710_i_r_'__

I 2000I I 4_0I i 6000I

I I

8000

Current density - Ampslft 2

FIGURE 3: ALKALINE HIGH POWER DENSITY PERFORMANCE

Specific

weight

Lb/kW

200

20-

1.5 1.0 I

0.5_

1960

D

Apollo--l.5 kW

Orbiter--12 kW

NSTS--300 kW

lO0's MW •

J I I I I I I I

1965 1970 1975 1980 1985 1990 1995 2000

Year

FIGURE 4: PROGRESS IN FUEL CELL SPACE POWER

9
Nallonal Aeronautics and

Space Adm_nlsl_allen

1. Report No.

NASA TM- 102366

4. Title and Subtitle

The Fuel Cell in Space: Yesterday, Today and Tomorrow

7. Author(s)

Marvin Warshay and Paul R. Prokopius

9. Performing Organization Name and Address

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135-3191

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, D.C. 20546-0001

Report Documentation Page

2. Government Accession No. 3. Recipient's Catalog No.

5. Report Date

6. Performing Organization Code

8. Performing Organization Report No.

E-5084

!10. Work Unit No.

591-14-3A

11. Contract or Grant No.

13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared lbr the Grove Anniversary (1839--1989) Fuel Cell Symposium sponsored by the Royal Institution,

London, Great Britain, September 18-21, 1989.

16. Abstract

The past, present, and future of space fuel cell power systems is reviewed, starting with the first practical fuel

cell by F.T. Bacon which led to the 1.5 kW Apollo alkaline fuel cell. However, the first fuel cell to be used for

space power was the Gemini 1.0 kW acid IEM fuel cell. The successor to the Apollo fuel cell is today's 12 kW

Orbiter alkaline fuel cell whose technology is considerably different and considerably better than that of its

ancestor, the Bacon cell. And in terms of specific weight there has been a steady improvement from the past to

the present, from the close to 200 lb/kW of Apollo to the 20 lb/kW of the orbiter. For NASA future Lunar and

Martian surface power requirements the rege_aerative fuel cell (RFC) energy storage system is enabling technology,

with the alkaline and the PEM the leading RFC candidate systems. The U.S. Air Force continues to support fuel

cell high power density technology development for its future short duration applications.

17. Key Words (Suggested by Author(s))

Fuel cell

Power space

Lunar

Martian

18. Distribution Statement

Unclassified- Unlimited

Subject Category 20

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