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NASA Technical Memorandum 4325
Enabling the Space Exploration
Initiative: NASA's Exploration
Technology Program in Space Power
Gary L. Bennett and Ronald C. Cull
NASA Office of Aeronautics and Exploration Technology
Washington, D.C.
National Aeronautics andSpace Administration
Office of Management
Scientific and Technical
Information Program
1991
https://ntrs.nasa.gov/search.jsp?R=19920001913 2019-04-03T22:23:31+00:00Z
Enabling the Space Exploration Initiative:NASA's Exploration Technology Program
in Space Power
Gary L. Bennett and Ronald C. Cull
Propulsion, Power and Energy Division
National Aeronautics and Space Administration
Washington, D. C.
ABSTRACT
With the President's Space Exploration Ini-tiative (SEI) of returning to the Moon and
then going to Mars, NASA will need to developa number of enabling technologies, chiefamong them being power for spacecraft andsurface bases. The SEI power technology pro-gram will build upon ongoing efforts in the
areas of advanced photovoltaics, energy stor-age, power management, nuclear power, andhigher conversion efficiency systems. Recentstudies have identified space nuclear power asa key technology for SEI. Nuclear power of-fers tremendous advantages for manned lunarbases and it greatly enhances manned Marsbases. Nuclear power can also be used topower nuclear electric propulsion (NEP)spacecraft such as piloted and cargo missionsto Mars as well as unmanned science missionsthroughout and beyond the Solar System.
THE _PAGE EXPLORATION
INITIATIVE
President George Bush inaugurated the SpaceExploration Initiative (SEI) with his speechon 20 July 1989 commemorating the 20thanniversary of the Apollo 11 landing on theMoon when he stated:
"And next -- for the new century -- back tothe Moon. Back to the future. And this time,back to stay.
And then -- a journey into tomorrow -- ajourney to another planet -- a manned mis-sion to Mars".
National S Dace Policy
The President subsequently codified this vi-sion in the National Space Policy which estab-lishes as one of the overall goals of UnitedStates space activities the expansion of humanpresence and activity beyond Earth orbit intothe solar system [White House 1989]. All ofthese activities had a foundation in earlier
studies such as the report of the NationalCommission on Space [NCOS 1986] and thereport to the Administrator of NASA by Dr.Sally K. Ride [Ride 1987]. This report wasfollowed by case studies conducted by NASA'sOffice of Exploration.
General Goals and Architecture=
Overall the Space Exploration Initiative es-tablishes a long-term goal for the civil spaceprogram of returning to the Moon and carry-ing out human exploration of Mars. SEI pro-vides a strategic horizon which can focus andintegrate many current and future activities.In this sense SEI serves as a framework forguiding the investment of limited resources
and for measuring progress in the space pro-gram. Figure 1 provides an overview of pastand current SEI-related activities.
In general the various studies conducted onhuman exploration of the Moon and Mars have
identified a number of technology develop-ments (including power) required before themissions can be undertaken. While the stud-
ies differ in emphasis they generally identifythe need for precursor robotic missions toscout the territory followed by human mis-sions. These robotic missions can includeor-
biters, rovers, samplers, and penetrators or
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other surfacestations. The humanmissionscan be conducted in several ways including
all-up missions and split missions in whichthe cargo is sent ahead on a robotic cargo ve-hicle to be followed by the lighter, manned
spacecraft which typically goes on a reducedflight time trajectory. The human presenceon the Moon and Mars will evolve from the
initial landing installation to outposts andeventually full-up self-supporting bases.The power requirements will span the rangefrom hundreds of watts for robotic precursormissions to tens of megawatts for permanentbases and for electric propulsion on pilotedvehicles.
NASA 90-Day Study
The follow-on 90-day study by NASA, which
synthesized several years of explorationmission studies and defined feasible mission
options and their requirements, identifiednuclear surface power as one of the key tech-
nologies required for lunar and Mars explo-ration. The general scenario described in the90-day study envisioned the initial lunarbase as being powered by photovoltaic arrayswith regenerative fuel cells (RFCs). TheRFCs would be used during the long (14-Earth-day) lunar night when solar cellswould not be functional. As base power re-quirements increased to match the increasingactivities of an expanded human presence onthe Moon the power source would evolve into anuclear reactor power system which can op-erate continuously day or night and is lighterthan the equivalent solar/RFC power system[NASA 1989c]. Figures 2 and 3 show howsuch a lunar base might evolve while Figure 4shows the mass advantage for nuclear reac-tors.
National Research Council Report
The Vice President in his capacity as Chair-man of the National Space Council (NSpC)"requested that the National Research Council
(NRC) assess the scope and content of theNASA 90-day study as well as alternative ap-proaches and various technology issues". TheNRC established a Committee on Human Ex-
ploration of Space which reviewed the NASA
study and provided a number of findings andconclusions. In the power area the Committeeconcluded that "To meet the heavy demands for
power on the Moon or Mars, nuclear electricpower eventually will be essential" [NRC
1990].
As part of the "outreach" program to solicitand evaluate new ideas that might be applica-ble to SEI, the American Institute of Aeronau-tics and Astronautics (AIAA) solicited ideasgenerated by individuals associated with theaerospace industry. The AIAA recommendedadvanced technology development on nuclearpower, specifically continuing the develop-ment of the SP-100 space nuclear reactor
power system with advanced converters, foruse as a power source on the surfaces of theMoon and Mars. The AIAA also noted a number
of other technologies that could be applied toSEI missions such as photovoltaic arrays,RFCs, dynamic isotope power systems(DIPS), power beaming, and improved ther-mal management [AIAA 1990].
Technolooy Needs
In response to a Congressional request NASAsubmitted a report outlining specific technol-ogies that will be needed to meet thedevelopment and operational requirements oftheSEI. This report noted that surface opera-tions are the primary purpose of the SEI andthat surface operations ;equired systems withhigh reliability and reasonable operationscosts. Among the technologies requiring de-velopment to meet the requirements of sur-face operations were [Mankins and Buoni1990 and NASA 1990]:
• space nuclear power• planetary rovers (with surface
mobility systems)• surface solar power (with chemical
energy storage)
Advisory Committee Re Dort
The Advisory Committee On the Future of theU.S. Space Program (which was chaired by
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Norman R. Augustine and is sometimes re-ferred to as "The Augustine Committee")stated that ".. we share the view of the
President that the long term magnet for themanned space program is the planet Mars --the human exploration of Mars, to be specific.It needs to be stated straightforwardly thatsuch an undertaking probably must be justi-tied largely on the basis of intangibles -- thedesire to explore, to learn about one's sur-roundings, to challenge the unknown and tofind what is to be found. Surely such an en-deavor must be preceded by further unmannedvisits, and by taking certain important stepsalong the way, including returning for ex-tended periods to the Moon in order to refineour hardware and procedures and to develop
the skills and technologies required for longterm planetary living" [Advisory Committee1990].
The Advisory Committee offered the followingrecommendations related to SEI [AdvisoryCommittee]:
Recommendation 4: That the Mission from
Planet Earth be established with the long-term goal of human exploration of Mars, un-derpinned by an effort to produce significantadvances in space transportation and spacelife sciences.
Recommendation 5: That the Mission fromPlanet Earth be configured to an open-endedschedule, tailored to match the availability offunds.
Recommendation 7: That technology be pur-sued which will enable a permanent, possiblyman-tended outpost to be established on theMoon for the purposes of exploration and forthe development of the experience base re-quired for the eventual human exploration ofMars. That NASA should initiate studies ofrobotic precursor missions and lunar out-posts.
Recommendation 8: That NASA, in concertwith the Office of Management and Budget andappropriate Congressional committees, estab-lish an augmented and reasonably stable shareof NASA's total budget that is allocated to ad-
vanced technology development. A two- tothree-fold enhancement of the current modest
budget seems not unreasonable. In addition,we recommend that an agency-wide technologyplan be developed with inputs from the Asso-ciate Administrators responsible for themajor development programs, and that NASAutilize an expert, outside review process,managed from headquarters, to assist in theallocation of technology funds.
The Synthesis Group
The Synthesis Group, which integrated the in-formation developed during the outreachprogram, recommended initiation of "a spacenuclear power technology development pro-gram based on the Space Exploration Initiativerequirements" [Synthesis Group 1991].
Among the supporting technologies that TheSynthesis Group identified as requiringdevelopment for the "safe and cost effectiveexploration of the Moon and Mars" were nu-clear electric surface power to megawatt lev-els and nuclear electric propulsion for fol-low-on cargo missions [Synthesis Group1991].
SPACE POWER REQUIREMENTS
FOR SEI
The foregoing studies have identified a rangeof space power requirements for SEI mis-sions. These will be summarized according tothe specific application.
Robotic Missions
Before humans actually set forth back to theMoon and on to Mars it is planned that therewill be precursor robotic missions to
advance scientific understanding anddevelop the basis for human scienceexploration
• determine suitable/desirable landingand outpost sites
• provide design data for human missionelements
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demonstrate the technologies andoperational concepts for humanmissions
Lunar Spacecraft
For the Moon the emphasis will be on select-ing the landing/outpost site. For this purposea Lunar Observer spacecraft (see Figure 5)would be needed to characterize the Moon
globally from a low (~100-km) polar map-ping orbit (with a gravity subsatellite in anelliptical orbit) since the Apollo data arelimited to a band near the lunar equator. Sucha Lunar Observer mission would be used to
• map the surface chemistry
• map the gravity field
• verify requirements for surfaceequipment and excursion vehicles
• select the outpost site
• plan lunar surface operations
• assess availability of resources
• select sites of scientific potential
The Lunar Observer spacecraft would be solarpowered and it could benefit from some of thetechnology advances in higher efficiency solarcells and light-weight solar arrays.
Mars Spacecraft
For Mars the emphasis for robotic missionswill be on science and human mission success.A candidate robotic mission set for Mars couldinclude:
• Mars Observer
• Site Reconnaissance Orbiter
• Mars Landers
• Mars Sample Return/Rovers
The solar-powered Mars Observer has beenscheduled for a 1992 launch. Similarly,other orbital spacecraft such as a Site Recon-naissance Orbiter can benefit from improvedsolar cell/array and battery technology. Justas the Viking Orbiters were solar poweredwhile the Viking Landers, which operated in amore hostile environment (dust and tempera-ture extremes), were powered by RTGs andbatteries so, too, will nuclear power play arole in the robotic craft sent to the surface ofMars.
NASA's Office of Space Science andApplications (NASA/OSSA) has been studyingSEI-related missions that will challenge thespace power community. One mission set in-
volves distributing a relatively large number(~20) of small robotic landers on Mars toexplore the structural, mineralogical, andchemical characteristics of the Martian soil,search for evidence of subsurface ice, and
collect long-term seismological andmeteorological data over a period of ten years.These studies have been termed the Mars Glo-
bal Network (MGN) at JPL [JPL 1989] andthe Mars Environmental Survey (MESUR) atNASA's Ames Research Center [ARC 1990].Typical power requirements are in the rangeof 2 We to 12 We per lander.
Rovers will allow humans Io conduct advance
exploration of the surface of Mars. In an as-sessment of the technology needs for humanexploration missions it was noted that "Most,if not quite all, of the mission scenarios underconsideration include the use of mobile sur-
face vehicles to conduct exploration, gathersamples, and deploy scientific payloads. Es-tablishing permanent human presence onother worlds will require surface
transportation systems to support both con-struction and surface mining operations.These systems may be autonomous, teleoper-ated, or piloted" [NASA 1989b].
One assessment of NASA's needs for advanced
nuclear power sources categorized the follow-ing planetary surface rover power require-ments [NASA 1989a]:
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Unmanned scientific rovers
Power range: 0.5 kWe to 1.0 kWeLifetime: 1 yearPossible power source(s): RTGs with
energy storage
Unmanned advanced scientific rovers
Power range: 1 kWe to 10 kWeLifetime: >1 yearPossible power source(s): Advanced
radioisotope power source withenergy storage
Figure 6 is an artist's illustration of a possi-ble configuration for an unmanned scientificrover.
Recent analyses of the Viking Lander solar in-solation data have shown that photovoltaicsare a viable option for certain Mars surfaceoperations [Appelbaum and Flood 1989].
Human Missions
Power will be required both for the trips tothe Moon and Mars and for operations on thesurfaces of the Moon and Mars. Round triptimes for lunar missions will be on the order
of seven days whereas round trip times formissions to Mars can be as long as two years.Power requirements for human missions willspan the range of tens of kilowatts needed formanned spacecraft, landers, surface excur-sion vehicles and habitats to tens of megawattsfor electric propulsion and self-sufficientbases with in situ resource utilization.
Initially a lunar outpost may only be mannedduring the lunar day but eventually full-timeoperation will be desirable even during thelong (14-Earth-day) lunar night whichplaces a premium on being able to supplypower in the absence of sunlight. Supplyingpower for full-time operation on Mars willbe somewhat easier because the Martian day isonly slightly longer (24.6-h equatorial rota-tion) than that on Earth; however, unlike theMoon, Mars receives less than half as muchsolar energy flux as does the Earth.
Human missions to the Moon and Mars will
undoubtedly include initial outposts, scientif-
ic laboratories, full-up operational bases,partially tended installations, and surface ex-cursion vehicles [NASA 1989c, Petri et al.1990, and Synthesis Group 1991]. Figure 7illustrates a man-tended radioastronomy ob-
servatory on the lunar farside. In each casepower will be critical. It has been noted that"a rudimentary lunar base for 6 people witha fully closed life support system would ap-pear to require almost 100 kW for the astro-nauts to merely perform rudimentary work.Full industrialization will likely drive powerdemands into the megawatt class" [Brandhorst1991].
In an assessment of NASA's needs for advanced
nuclear power sources it was noted that utili-
ty power and manned rovers would require 10kWe to 25 kWe with lifetimes on the order of
5 years. Possible power sources could in-clude fuel cells, solar photovoltaic power withregenerative fuel cells, nuclear reactorpower systems, and beamed power (satelliteto surface) [NASA 1989a]. In aworkshop onpower for planetary rovers it was noted thatexploration-class missions would require thefollowing kinds of piloted rovers [Roberts1989]:
• Piloted, unpressurized (4.3 kWe)
• Piloted, pressurized (10 - 30 kWe)
Construction machines, generalpurpose (10 - 30 kWe)
CraneExcavator/DozerTruck
User accommodation equipment,special purpose (1 kWe)
VLFA (Very Low Frequency Array)construction deviceOther
• Mining machines (undefined) (10 -30 kWe)
These power levels are consistent with simi-lar studies of vehicle power req_Jirements[Petri et al. 1990].
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The use of electrical power for electric pro-pulsion systems is a possible candidate fortransporting humans to and from Mars. Fig-ure 8 shows some of the transportation op-tions for manned missions to Mars. While
electric propulsion for unmanned missionssuch as cargo vehicles to Mars can be accom-plished with powers on the order of a fewmegawatts piloted missions will require tensof megawatts. NASA has defined a program todevelop megawatt-class electric propulsionfor piloted missions to Mars [Bennett et al.1990a].
Because of the human presence the require-ments on reliability will be even greater forthe human missions. The Synthesis Group hasstated that "Habitats must have their own
highly reliable power source for safety. Basepower includes power for mining, in situ op-erations, fabrication, emergency power forhabitats and power for regeneration of fuelcells. Habitat power must be highly reliable,greater than 99.5%, while base power can beabout 95% reliable. Power units should bemade operational with a minimum of supportactivities, have lifetimes compatible with thebase, be serviceable and, if nuclear, be refu-elable and disposable. Evolutionary system
designs are preferable to specific point de-signs without growth potential" [SynthesisGroup 1991].
Based on its outreach activities and assess-
ments of alternative architectures The Syn-thesis Group developed a set of functionalpower requirements which are summarized inTable 1 [Buden et al. 1991 and SynthesisGroup 1991]. The next section describesNASA's planning to meet the estimated powerrequirements of the Space Exploration Initia-tive.
XPLORATION TEC:HNOLOG.YPROGRAM
foundation
Begin now to make the necessaryinvestments to meet the long-rangetechnology needs and establish acommitment to long-term explorationtechnology development
Seek out innovative technologicalsolutions to exploration technologydevelopment
Perform technology development inparallel with exploration missiondesign studies
The planning to meet the space power re-quirements of SEI follows the foregoing strat-egy for technology development. The spacepower program has been planned to addressthe technology development challenges and"drivers" such as
Develop power systems for and extendtheir life in functional environments
(LEO, GEO, Moon, planetary)
Increase power density of powersystem
• Reduce power system mass
• Increase power system reliability
• Enable power system operation athigher temperatures
The technology benefits of this research in-clude reduced launch mass; increased powerfor the same mass; increased lifetime; in-creased reliability; reduced costs; extendedrange of power system capabilities; and re-duced volume. Some of the benefits of im-
provements in the electrical power system(EPS) can be seen in Figures 9 and 10 takenfrom Brandhorst 1991.
The planning for exploration technology de-velopment has lour themes [Mankins andBuoni 1990]:
• Capitalize on the existing nationalspace research and technology
The EPS generally consists of the powersource, energy storage, and power manage-ment and distribution (PMAD). Tied in close-ly with the EPS is the thermal management ofthe space system. All of these elements are
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important to improved EPS performance.Thus, the technology development approachthat is being planned includes
Development and evaluation of high-efficiency, radiation-hard solar cellsand light-weight array systemcomponents
Development of advanced, high-specific-energy, high-energy-density, long-cycle-life energystorage systems
• Development of improved thermal-to-electric conversion systems
Development of light-weight, smart,high-temperature, compact powermanagement and control (PMAC)
Development of innovative, low-massthermal transport and radiatorconcepts
• Development of the SP-100 spacenuclear reactor power system
• Development of a laser power beamingcapability
• Development of improved powersystem materials
Development of models for
environmental interactions and designguidelines for future space powersystems
Under current planning the technology devel-opment would be carried out in two parallelthrusts. Firstly, NASA has an ongoing baseresearch and technology (R&T) program inspace energy conversion which is designed toprovide the technology to meet power systemrequirements for future space missions,including growth Space Station, Earth orbit-ing spacecraft, lunar and planetary bases, and
solar system exploration [Bennett 1989].This base R&T program provides the techno-logical foundation for the second thrust whichcovers focused space applications such as SEI.
The programmatic objective of the focusedspace power R&T program is to provide thefocused technology to meet power system re-quirements for lunar and planetary bases,planetary rovers, penetrators, Earth-orbit-ing spacecraft, and deep-space missions. Fig-ure 11 shows the organization of the spaceenergy conversion R&T program to meet bothtechnological and focused applications.
Base Research & Technoloay Pro_aram
The base R&T program is organized as shownin Figure 12. Table 2 summarizes thestate-of-the art in each of the elements of the
base R&T program and lists the objectives ofthese program elements. The basic elementswill be described in the following sections.
Photovoltal¢ Energy Conversion
The objective of the photovoltaic energy con-version program element is to provide thetechnology for photovoltaic arrays with im-proved conversion efficiency, reduced mass,reduced cost, and increased operating life foradvanced space missions. The photovoltaic el-ement is organized around solar cell researchcarried out through NASA's Lewis ResearchCenter (LeRC) and advanced solar array re-search carried out through NASA's Jet Pro-pulsion Laboratory (JPL).
Research at LeRC has led to advances in cell
technologies including thin gallium arsenide(GaAs) and indium phosphide (InP) cells.Studies of thin film technology show the po-tential to develop a 1000 W/kg flexible solararray blanket [Flood et al. 1989]. As part ofthe ongoing NASA-sponsored activity of devel-oping a 300-W/kg solar array JPL and TRWhave developed the advanced photovoltaic solararray (APSA) which for a baseline 5.8-kWewing has a beginning-of-life (BOL) specificpower and power density of 137.9 W/kg and
140.1 W/m 2 (based on total panel area) re-
spectively. Corresponding end-of-life (EOL)
values are 92.5 W/kg and 94.0 W/m 2 for a10-year mission in a geosynchronous Earthorbit (GEO) [Stella and Kurland 1991].
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Chemical Energy Conversion
The objective of the chemical energy conver-sion program element is to provide the tech-nology base for advanced electrochemical en-ergy conversion and storage systems requiredto support the low- to high-power needs andcycle life requirements for future space mis-sions.
Work sponsored by LeRC has led to the suc-cessful completion of over 40,000 low-Earthorbit (LEO) cycles at 80% depth of discharge(DOD) in boiler plate nickel hydrogen cellsand over 10,000 cycles in bipolar nickelhydrogen batteries [Smithrick and Hall 1991and Manzo 1989]. JPLhassuccessfullycom-pleted over 700 cycles at 50% DOD in 1-A-hlithium titanium disulfide cells [Halpert et al.1991]. An overview of the NASA research andtechnology program on batteries may be foundin Bennett 1990b.
Thermal Energy Conversion
The objectives of the thermal energy conver-sion program element are to
Develop the technology base to provideadvanced, high-efficiency, high-temperature, long-life solar dynamicStirling/Brayton power systems
Develop new thermoelectric materialswith significantly higher figures ofmerit
Investigate and demonstrate thefeasibility of high-power, long-lifealkali metal thermal-to-electric
converter (AMTEC)
At LeRC research is being sponsored on ad-vanced concentrator technology and advancedreceiver technology for solar dynamic powersystems. Under this program the feasibilityof fabrication techniques for concentrator
aluminum panels with microsheet glass hasbeen demonstrated. This technology has ap-plication for both Earth orbital and lunar
missions [Calogeras et al. 1991 and Richter1991]. In the area of thermoelectrics,
preliminary studies at JPL have shown that
ruthenium silicide has the potential to pro-vide figure of merit values four times higherthan conventional silicon-germanium ther-moelectric materials [Ohta et al. 1991]. Im-provements in AMTEC electrode current col-lection have been achieved at JPL by usingmolybdenum grids to decrease sheet and con-tact resistance in the rhodium-tungsten andplatinum-tungsten electrodes [Ryan et al.1991].
Power Management
The objectives of the power management pro-gram element are to
Develop the electrical power systemsconditioning, control, and distributiontechnology for future space missions
Develop the capability to model powersystems (including environmentalinteractions)
Develop advanced concepts (e.g., powerbeaming and advanced powermanagement materials)
A number of accomplishments have occurredunder this program element, including suc-cessfully testing a silicon-carbide metal oxidesemiconductor (MOS) field effect transistor(FET) power switch to 723 K; developing aMonte Carlo model for atomic oxygen erosion;and demonstrating a seven-fold increase inatomic oxygen durability with chemical-va-por-deposited (CVD) silica on carbon/carboncomposite radiator surfaces. Work is also
proceeding on the development of monolithicpower integrated circuits (PICs) technologyfor space applications. This effort offers thepotential for up to 80% reductions in massand volume and up to 90% reductions in thepiece parts count in a typical PMAD system.
Separately, as part of the Power Managementprogram element, researchers at NASA's Lan-
gley Research Center (LaRC) have beenpursuing the use of solar-pumped lasers totransmit power [Kwon and Lee 1989]. Beampower may provide an alternative to nuclear
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and photovoltaic/chemical power sources forbases or rovers on the surfaces of the Moon
and Mars [De Young et al. 1991]. LaRC hasproduced 14 W of continuous wave (CW)power at 1.3 p.m from a solar-simulator-
pumped iodide laser and LaRC has operated theworld's first solar-pumped iodide laser am-plifier.
Thermal Management
The objectives of the thermal managementprogram element are to
Develop the technology base forversatile thermal managementsystems for the next generation ofspace missions
Provide advanced thermal managementtechnology for both high and moderatetemperatures, including technologyfor thermal control of instrument
systems
Research carried out through NASA's GoddardSpace Flight Center (GSFC) has resulted inthe fabrication and successful testing of oxy-gen and nitrogen cryogenic heat pipes. Re-search carried out through LeRC has demon-strated the stability of a liquid sheet radiatorat 1-G and verified the analytical predictions[Juhasz and Chubb 1991].
Focused Research & Technolo_ayEr.o.gzam_
Figure 13 shows the proposed work break-down structure (WBS) for the focused spaceenergy conversion research and technologyprogram. The following sections will describethe planned program elements.
Space Nuclear Power
As noted earlier space nuclear power has beenidentified as one of the key technologies forSEI. Accordingly, NASA has been participatingwith the Department of Energy (DOE) and theStrategic Defense Initiative Organization(SDIO) in the SP-100 space nuclear reactorpower system program. The objectives of this
program are to develop and validate the tech-nologies for safe and reliable space nuclearreactor power systems to support lunar andMars exploration missions. The payoff willbe a flexible power source that can span arange of power levels up to 1 MWe for spaceand surface bases with improved specificmass and lifetime[Armijo et al. 1991]. Fig-ure 14 is an artist's illustration of a lunar
base powered by an SP-100 reactor using aStirling conversion system.
High Capacity Power
To augment the SP-100 space nuclear reactorpower program NASA is sponsoring the highcapacity power program which has the objec-
tives of developing and demonstrating low-mass, reliable, long-lived power conversiontechnologies for space nuclear reactor powersystems. Specifically, this program is aimedat developing and demonstrating a 1300 KStirling conversion system (35% efficiency)
in time for early SEI use. This program willprovide SP-100 with the conversion technol-ogy to scale up to 1 MWe [Dudenhoefer andWinter 1991 and Winter 1989].
Surface Power and Thermal
Management
As noted in the discussion of the mission sce-
narios the initial lunar and Mars operationswill probably be solar-powered. NASA isplanning a surface power and thermal man-agement program to develop solar-basedpower and low-grade-heat thermal manage-ment technologies to support lunar and Marssurface system operations. This program willprovide a light-weight, reliable, solar-basedpower system for the first exploration/out-post missions to the Moon and Mars as well as
providing a backup source of power [Petri etal. 1990]. Because the largest fraction of the
solar-based power system for lunar applica-tions is in energy storage the near-term focusfor the surface power program has been ondeveloping regenerative fuel cells with spe-cific energies of 500 to 1000 W-h/kg withoperational lifetimes of at least 20,000 h.The photovoltaic array goal is 300 W/kg. Thegoal for the overall power system is to
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achieve 25 kWe at 3 We/kg on the Moon and 8
We/kg on Mars.
Earth Orbiting Platform Power andThermal Management
The objectives of this planned program are todevelop and demonstrate integrated power andthermal management technologies for near-Earth missions. This program would allowinitiation of a new thrust to develop planar
and concentrator arrays immune to the spaceenvironment with 100 W-h/kg battery sys-
tems; integrated, high-efficiency autonomousPMAC; and integrated thermal management forhigh-temperature electronics. This programwould benefit the Earth-orbiting platforms(such as data relay satellites) for SEI as wellas other Earth-orbiting applications.
Spacecraft Power and ThermalManagement (Deep Space)
The objectives of this planned program are todevelop and demonstrate integrated spacecraftbus technologies for deep-space applications.(SEI does not stop with Mars.) This programwould initiate a new thrust to
Demonstrate a high-power-densitysolar array with deployment and low-intensity, low-temperature (LILT)resistance
Develop advanced static or dynamicconversion systems for radioisotopesources and define integrationissues/advantages of reactor-poweredscience spacecraft
• Develop energy storage subsystems for
penetrators
• Develop advanced PMAC and thermalmanagement for deep-space missions
The payoff will be the provision of high-spe-
cific-power solar arrays and high-efficiencyconverters with advanced PMAC and energystorage to reduce mass and/or increase thepower of deep-space missions.
Laser Power Beaming
The Synthesis Group report noted that "Powerbeaming for surface-to-surface power dis-tribution may greatly reduce the mass of rov-ers and other mobile surface systems, assum-ing line of site can be met. If nuclear electricpropulsion is developed for use in the lunaror Mars cargo vehicle, the orbiting transfervehicle may be a convenient power source forsurface operations. If power beaming can bedemonstrated at a reasonable cost, long termdevelopment could provide attractive bene-fits" [Synthesis Group 1991]. Accordingly aprogram on laser power beaming has beenproposed to develop and demonstrate the tech-nologies and subsystems for laser powerbeaming from the Earth to the Moon. Discus-sions of this approach have appeared before,most recently in Landis 1991. The use of anorbiting laser diode array to power a lunarrover has been discussed recently by De Younget al. 1991.
Mobile Surface Systems (Power)
Since surface exploration vehicles are antici-pated to play a key role in SEI (see Figure 6)a mobile surface systems power program hasbeen proposed to develop compact power tech-nologies to a level of readiness sufficient toenable mobile and portable extraterrestrialsurface power systems. This program willinclude work on system integration, powergeneration (both nuclear and nonnuclear),energy storage, tribology, PMAD, small free-piston Stirling engine, convective heat ex-changers for Martian surface mobile and/orportable dynamic isotope power systems. Theend objective is to provide mobile power sys-tem options that can span the range from <1kWe to >20 kWe with varying power ratiosand usages for a hostile, dusty environment.
Some of the specific technical objectives in-clude development of a 14%-efficient ther-moelectric element and a 30%-efficient solar
cell. Energy storage goals are >50 W-h/kgfor batteries and >350 W-h/kg for fuel cells.
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SUMMARY AND CONCLUSIONS
The Space Exploration Initiative (SEI) willrequire several different types of powersources and energy storage systems to spananticipated power requirements ranging fromhundreds of watts for robotic precursor mis-sions to tens of megawatts for mature, mannedbases and for electric propulsion on pilotedvehicles. The ongoing NASA research andtechnology program in space energy conver-sion provides a foundation from which to buildthe focused technology programs to meet theSEI power requirements. An augmented pro-gram focusing on space nuclear power, highcapacity power, surface power and thermalmanagement, Earth orbiting platform powerand thermal management, spacecraft powerand thermal management for deep-space ve-hicles, laser power beaming, and mobile sur-face systems power has been defined to devel-op the specific focused technologies for SEI
applications.
REFERENCES
Advisory Committee (1990) Report of theAdvisory Committee On the Future of the U.S.Space Program, U.S. Government Printing Of-
rice, Washington, D. C.
AIAA (1990) Final Report to the Office ofAeronautics, Exploration and Technology Na-tional Aeronautics and Space Administrationon Assessment of Technologies for the SpaceExploration Initiative (SEI), American Insti-tute of Aeronautics and Astronautics, Wash-
ington, D. C.
Appelbaum, J. and D. J. Flood (1989) "Pho-tovoltaic Power System Operation in the MarsEnvironment", Proceedings of the 24th
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Armijo, J. S., A. T. Josloff, H. S. Bailey, and
D. N. Matteo (1991) "SP-100 - The National
Space Reactor Power System Program in Re-sponse to Future Needs", Proceedings of the26th Intersociety Energy Conversion Engi-neering Conference held in Boston, Massachu-setts, 4-9 August 1991.
Bennett, G. L. (1989) "The OAST SpacePower Program", Space Photovoltaic Re-search and Technology - 1989, NASA Confer-ence Publication 3107, published in 1991;
proceedings of a conference held at NASALewis Research Center, Cleveland, Ohio, 7-9November 1989.
Bennett, G. L., M. A. Watkins, D. C. Byers, andJ. W. Barnett (1990a) Enhancing SpaceTransportation: The NASA Program To DevelopElectric Propulsion, NASA Technical Memo-randum 4244, prepared forAIAA/DGLR/JSASS 21st International Electric
Propulsion Conference held in Orlando, Flori-da, 18-20 July 1990.
Bennett, G. L. (1990b) "The NASA Researchand Technology Program on Batteries",Proceedings of the 25th Intersociety EnergyConversion Engineering Conference held inReno, Nevada, 12-17 August 1990.
Brandhorst, Jr., H. W. (1991) "Key Issuesin Space Nuclear Power Challenges for theFuture", Proceedings of the 8th Symposiumon Space Nuclear Power Systems, CONF-910116, held in Albuquerque, New Mexico,6-10 January 1991.
Buden, D., D. Bartine, S. Harrison, J. Fore-man, and K. Biringer (1991) "The StaffordCommission Synthesis Group Evaluation ofPower for the Space Exploration Initiative",Proceedings of the 26th Intersociety EnergyConversion Engineering Conference held inBoston, Massachusetts, 4-9 August 1991.
Calogeras, J. E., M. O. Dustin, and R. R. Se-cunde (1991) "Solar Dynamic Power forEarth Orbital and Lunar Applications",Proceedings of the 26th Intersociety EnergyConversion Engineering Conference held inBoston, Massachusetts, 4-9 August 1991.
-11-
De Young, R. J., M. D. Williams, G. H. Walker,G. L. Schuster and J. H. Lee (1991) "A LunarRover Powered by an Orbiting Laser DiodeArray" Proceedings of the Eighth Symposiumon Space Nuclear Power Systems, CONF-910116, held in Albuquerque, New Mexico,6-10 January 1991.
Dudenhoefer, J. E. and J. M. Winter (1991)"Status of NASA's Stirling Space Power Con-verter Program", Proceedings of the 26th
Intersociety Energy Conversion EngineeringConference held in Boston, Massachusetts, 4-
9 August 1991.
Flood, D. J., M. Piszczor, Jr., P. Stella, andG.L. Bennett (1989) "NASA Advanced SpacePhotovoltaic Technology - Status, Potentialand Future Mission Applications",Proceedings of the European Space PowerConference (European Space Agency publica-tion ESA SP-294, August 1989), Madrid,Spain, 2-6 October 1989 (also published asNASA Technical Memorandum 102093).
Halpert, G., S. Surampudi and A. Atria (1991)
"The Status of Rechargeable Li-TiS 2 Cell
Technology", Proceedings of the 26th Inter-society Energy Conversion EngineeringConference held in Boston, Massachusetts, 4-
9 August 1991.
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Exploration Precursor Task Team, Jet Pro-pulsion Laboratory, Pasadena, California.
Juhasz, A. J. and D. L. Chubb (1991) "DesignConsiderations for Space Radiators Based onthe Liquid Sheet (LSR) Concept", Proceedingsof the 26th Intersociety Energy ConversionEngineering Conference held in Boston, Mas-sachusetts, 4-9 August 1991.
Kwon, J. H. and J. H. Lee (1989) "Far FieldBeam Pattern of One MW Combined Beam of
Laser Diode Array Amplifiers for SpacePower Transmission", paper number899592 in Proceedings of the 24th Interso-
ciety Energy Conversion EngineeringConference, held in Crystal City, Virginia, 6-11 August 1989.
Landis, G. A. (1991) "Space Power byGround-Based Laser Illumination",Proceedings of the 26th Intersociety EnergyConversion Engineering Conference held in
Boston, Massachusetts, 4-9 August 1991.
Mankins, J. C. and C. M. Buoni (1990)"Technology and Mars Exploration" AIAApaper 90-3797, prepared for AIAA SpacePrograms and Technologies Conference held inHuntsville, Alabama, 25-28 September1990.
Manzo, M. A. (1989) "Bipolar Nickel-Hy-drogen Battery Development: A Program Re-view", Proceedings of the 24th IntersocietyEnergy Conversion Engineering Conferenceheld in Crystal City, Virginia, 6-11 August1989.
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Exploration Missions, NASA Office ofExploration Document No. Z-89-1.2-001,Washington, D. C.
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-12-
Ohta, T., C. B. Vining, and C. E. Allevato(1991) "Characteristics of a Promising NewThermoelectric Material: Ruthenium Sili-
cide", Proceedings of the 26th IntersocietyEnergy Conversion Engineering Conferenceheld in Boston, Massachusetts, 4-9 August1991.
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Ryan, M. A., B. Jeffries-Nakamura, R. M.Williams, M. L. Underwood, D. O'Connor andS. Kikkert (1991)"Directly Deposited Cur-rent Collecting Grids for AMTEC Electrodes",Proceedings of the 26th Intersociety EnergyConversion Engineering Conference held inBoston, Massachusetts, 4-9 August 1991.
Smithrick, J. J. and S. W. Hall (1991) "Ef-fect of KOH Concentration on LEO Cycle Life ofIPV Nickel-Hydrogen Flight Cells - An Up-date", Proceedings of the 26th IntersocietyEnergy Conversion Engineering Conferenceheld in Boston, Massachusetts, 4-9 ALJgust1991.
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-13-
Table 1. Power Requirements and Mass Allocation[Buden et al. 1991]
Functions
SpacecraftManned
Moon MarsP_er Mass Power Mass
_bca_on
to 20 kW 2 MT(1 ) to 30 kW 2 MT
Unmanned 5kW 1MT 5kW 1MT
Lander 20 kW 300 kg 20 kW 300 kg
Electric propulsion
Surface Activities
Day onlyHabitat/lab
IOC
toSMWto5OMT to5MW toSOMT==
2O kW 150 kg
to 30 kW 2MT toS0 kW 3MT
NOCBase Power
_3c (3)NOC(4)
RoversUnloader/ConstructionPressurized
.,._C(pe_ trip)NOC (pertrip)
Unpressurized
50kW 3MT lO0kW 4MT
tolO0kW 4MT tol00kW 4MTto800 kW 10MT to1MW 12 M'I"
240 kW-hr 240 kg 240 kW-hr 240 kg
1900 kW-hr 2 MT 1900 kW-hr 2 MT4800 kW-hr 5 MT 4800 kW-hr 5. MT
lO0kW-hr 100kg 10OkW-hr 100kg(1) 1 MT (metric ton) = 1000 kg(2) Depends on final power level(3) }OC stands for Initial Operational Capability(4) NOC stands for Next Operational Capability(5) In-situ methane and oxygen produced on Mars may substitute for fuel cells.
SuggestedTechnoloov
Fuel cells (Moon)Nuclear/photovoltaics
(Mars)(2)Fuel cells (Moon)Photovoltaics
(Mars)Fuel cells (w/wophotovoltaicsNuclear
Photovoltaics
Photovoltaics ornuclear (2)Nuclear
NuclearNuclear
Fuel cells (5)
Fuel cells (5)Fuel cells (5)Fuel cells (5)
-±4-
0t-- i
o oq- C
4rap
0
0
C
c®o
0¢-
dk_mO
0C
e,,,e_
k- o¢U
¢0
oA_
_> _=_o
oo
^oo03A
,-3.X
£o
0 _ t_ =
WI-
o
E EO 121
O9k- oZLU
'" 0
"' 0
0
0.
E3oa
u3
J_
o
c-
o c__- A
_ bE E
>-
ZlZZ
w©Z--
_oz_OmOT
oC
o
^
U
"0
v
>-
rrZwO
JIU
_zn"Owo-rI-
E
o
6 ^A
0
V
l-ziJ.l
_w
In_z
E
0
o
l--z
"i- z
-15-
Studies
r-{ National Commission on Space Report
[] "Leadership and America's Future in Space" (Ride Report)
I ...... ) Office of Exploration Case Studies
/_ President Announces Moon/Mars Goal
['7 NASA's 90-Day Study
_ National Space Policy
,/_ White House SEI Policy Direction - Arch_ectureOptions
_'_ Synthesis I" TechnologyPriorilies
I " EarlyAccomplishments
[NASA Trade Studies l" "lSynthesis Support Ii i L
[__.________J .......... [_] Modify "Near-Term" Plan
Develop "Near-Term" PlanI " ArchilectureStudies
[ I-TechnologyDev.
/_ Architecture Decision
Architecture ImplementationProgram Planning
• ManagementStructure - Roles/ Missions- ProcurementStrategy - International
Figure 1. Overview of Past and Current Activities
Related to the Space Exploration Initiative
Strategy: Early Outpost Power Needs Later Outpost Power Needs
• Power Generation- Photovoltaic Arrays or
Solar Dynamic Modules• Low-Moderate Mass/kW
• Near Term Development• Can Be Located Near Outpost• Ease of Deployment
• Daytime Power Only. Power Storage Required• Moderate Spares• Moderate Crew Support
• Power Storage- Batteries
• Near Term Development
• High Initial Mass/kW• Short Lived Systems
- Regenerative Fuel Cells• Longer Term Developmenl• Moderate Mass/kW
• Short Lived Systems• High Spares/Resupply
• Nuclear Power- Continuous Day/Night Power- No Power Storage Required- Low Initial Mass/kW
- Lowest Spares/Resupply- Long Lile Systems- Minimum Crew Support
- Longer Term Development- Must Be Remote to Outpost- Radiation Shielding- Political
Figure 2. Lunar Surface Power System Options
-16-
_ _",_ _ _ ..... _'_'-_i= >_'"_"_- ' "'_K_ '_ _" i
Figure 3.
PHOTOVOLTAIC ARRAY/
REGENERATIVE FUEL CELL
• Initial outpost power source
• 25/12.5 kW day/night capability
• State-of-the-art technology with
large experience base
• Low power/mass ratio (1.5-3
W/kg)
• High resupply and sparing mass
requirements (1 t/year/unit)
SP- I O0 NUCLEAR REACTOR
• Dynamic engine powerconversion
• 100 kW day/night capability
• High power/mass ratio (25-60
W/kg)
• Long life, high reliability system
(7 year life)
Surface Power Systems for a Lunar Base
Tolal System Mass,t
160
140
120
100
SO
60
40
20
0
Pholovollai¢ Arrayswith Regenerative Fuel
C¢115
Nuclear
Example:
Systems to Provide 100 kW
Continuous Day/Night Power
ID Spares/Resupply =r'l ]nilial Mass II
Figure 4. Lunar Surface Power System Options -lO-Year Life Comparison
-17-
Figure 5. Artist's Concept of a Lunar Observer
Spacecraft
Figure 6, Concept for a Mars Robotic Rover
-18-
OF POOR QUALrI'Y"
Figure 7. Lunar Radioastronomy Observatory
Mars Excursion
Cry_janK; Vehicle (MEV IAerobr aka
Cryogentc/Aerobrake Reference
Configuration
Aarobrake for Mars Transfer Vehacle
Cryogenic Mars Lancling OnlyTankage (MTV)
] LH2 Tank I
I ,/ I LH..+Ta_ag. I+",a,:_a_,,
MEV
Cryogenic/All Propulsive Nuclear Thermal Propulsion
Configuration Configuration
Ir_rt Thruslar_l
Reacloq_owar I
Assembly Radiator I
_j__ Argon
/MEV
- m m --. • t_/ropellan,Nuclear Electric Propulsion _ "
Configuration I
Solar Electric Propulsion
Configuration
Solar Array
' /i} \I i
_ -
ion Thrusters
Mars Transit Habnal
Fissionable Fuel
GCR w/Contro_ Supply I HEU z'_ )
Drum Jacket I_1 _ Equipment Shield
-_q _ / . _ LH _, Tanks
Aerobrakel
l MTV_MEV
I/
I '
I/+
MEV
LH z +
Space StationPump & Electron¢ Derived Truss
Control Drives
Gas Core Nuclear Reactor
Configuration
Figure 8. Mars Transportation Concepts
-19-
ORIGINAL PAGE ISOF POOR (_JALITf
106
104
TRANSPORTATIONCOST, 1_1
1.1 1 10 100 1,g(_ 10,000 1H,0(X)
DISTANCEFROMEARTH,lO00'z n.m.
Figure 9. Cost of Delivering 100 kWe of Usable Power[Brandhorst 1991]
100-(100kWe,1988U.S,TRANSPORTATIONCOSTS)
COST$ BILLION
10
! I I !
Ni/H2 NalS RFC RFCSOA PV SOA PV SOA PV ADV. PV
! !
SP-IO0 ADV.NUCLEAR
Figure 10. Impact of Power Technology Advances onTransportation Costs
[Brandhorst 1991]
-20-
J POWER TECHNOLOGY JI
I I
i,R&TBASE ELEMENTSI IFOCUSED TECHNOLOGY PROGRAMSI
- PHOTOVOLTAIC ENERGYCONVERSION
CHEMICAL ENERGY CONVERSION
THERMAL ENERGY CONVERSION
POWER MANAGEMENT
THERMAL MANAGEMENT
- SPACE NUCLEAR POWER
- HIGH CAPACITY POWER
- SURFACE POWER & THERMAL MANAGEMENT
MOBILE SURFACE SYSTEMS (POWER)
LASER POWER BEAMING
EARTH ORBITING PLATFORMS POWER &THERMAL MANAGEMENT
SPACECRAFT POWER & THERMAL MANAGEMENT
Figure 11. Proposed Organization of the NASA SpaceEnergy Conversion Research & Technology Program
- 2 I _
m
LL
0
I,-,-
Q)
-2?-
Imm
,,I.=
Clm
U_
m
>,0)0m
Or-r-U
mm
:3I)n:3.I)m
l.U
CO
>-
(t) ,..
UJrr
09 V
LU
=-I
rm
o=s
n
r. vo
r.- r'-,
°°= g o.= -
0 r-
,_ _ o .____ = _ _ 6o :S _>., ";" >"
:>, r- 0 >" _ J= ":"
I I I I I l
8_ o'_ 0
_ =
_ _ • E= _. o
-23-
ORIGINAL PAGE 15OF POOR QUALITY
*JASA
Figure 14. Artist's Concept of a Lunar Base Powered byan SP-100 Class Nuclear Reactor with Stirling Cycle
Conversion
-2A-
Form ApprovedREPORT DOCUMENTATION PAGE OMBNO.0704-0188
Pu0hc reporDr_g burden for this collection of ir_forrnatpon is esDrflated to average 1 hOLJrper response, including the time for reviewing instructions, sear_htn9 existing data sources.cjathe_mg _nd maintaining the data needed, and comDletln 9 and rev,ew_ng the .:otlectJonof informatPOn Send comments regarding this b_Jrden eslimate or any other aspect of thiscollection of rr_formatlon, _ncludlng sugcjestions for reducing this burden _o Washrngton Headauar_er$ Services, Directorate/or _nformation Operations and RepOrts, 1215 JeffersonDaws Hic3h_ay. Suite 1204. _r_nngton, VA 22202-4]02¸ and to the Offi<e of Ma_agemer_t _ncl Budget. Paperwork Reduction Project (0104-0188). Washrngton. DC 2050]
1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
October 1991 Technical Memorandum
4. TITLE AND SUBTITLE S. FUNDING NUMBERS
Enabling the Space Exploration Initiative: NASA's
Exploration Technology Program in Space Power
6. AUTHOR(S)
Gary L. Bennett and Ronald C. Cull
7. PERFORMINGORGANIZATIONNAME(S}ANDADDRESS(ES)
NASA Office of Aeronautics and Exploration Technology
Washington, D.C.
9. SPONSORING/MONITORINGAGENCYNAME(S}ANDADDRESS(ES)
NASA Headquarters (Code RP)
Washington, DC 20546
11."SUPPLEMENTARY NOTES
8. PERFORMING ORGANIZATIONREPORT NUMBER
10. SPONSORING / MONITORINGAGENCY REPORT NUMBER
NASA TM-4325
From the AIAA/NASA/OAI Conference on Advanced SEI Technologies
12a. DISTRIBUTION/AVAILABILITY STATEMENT
Unclassified - Unlimited
Subject Category 20
12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words)
With the President's Space Exploration Initiative (SEI) of returning to the Moon and
then going to Mars, NASA will need to develop a number of enabling technologies,
chief among them being power for spacecraft and surface bases. The SEI power for
spacecraft and surface bases. The SEI power technology program will build uponongoing efforts in the areas of advanced photovoltaics, energy storage, power
management, nuclear power, and higher conversion efficiency systems. Recent studies
have identified space nuclear power as a key technology for SEI. Nuclear power offer_tremendous advantages for manned lunar bases and it greatly enhances manned Mars
bases. Nuclear power can also be used to power nuclear electric propulsion (NEP)spacecraft such as piloted and cargo missions to Mars as well as unmanned science
missions throughout and beyond the Solar System.
14. SUBJECTTERMS Mars Observer; site reconnaissance; lunar bases;
Space Exploration Technology; National Space Policy; SP-100;
space nuclear power; planetary rovers; surface solar power
17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATIONOF REPORT OF THIS PAGE
Unclassified Unclassified
_s_ 7540.0_280s500
15. NUMBER OF PAGES
28
16. PRICE CODE
A03
19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACTOF ABSTRACT
Unclassified Unlimited
Standard Form 298 (Rev 2-89)Prescrabecl by ANSF _ld Z]9-18298-102
NASA-Langley, 199l
