ALBERT

Description: A brief overview is given of the scope of the NASA space solar cell research and development program. Silicon cells, gallium arsenide cells, indium phosphide cells, and superlattice solar cells are addressed, indicating the state of the art of each type in outer space and their advantages and drawbacks for use in outer space. Contrasts between efficiency in space and on earth are pointed out.

Description: This paper presents results of development testing of various solar thermal parabolic dish concentrators. The concentrators were mostly designed for the production of electric power using dish-mounted Rankine, Brayton or Stirling cycle engines, intended to be produced at low cost. Measured performance for various dishes included optical efficiencies ranging from 0.32 to 0.86 at a geometric concentration ratio of 500, and from about 0.09 to 0.85 at a geometric concentration ratio of 3000. Some malfunctions were observed. The tests should provide operating information of value in developing concentrators with improved performance and reduced maintenance.

Description: A survey of the batteries used in the low earth orbit (LEO) and geosynchronous earth orbit (GEO) missions at the Goddard Space Flight Center is described. For each spacecraft, tentative launch date is given, along with relevant battery parameters including battery size and description, depth-of-discharge, predicted mission temperature, and life requirement.

Description: The planetary program has historically used batteries to supply peak power needs for mission specific applications. Any time that additional power has been required in order to meet peak power demands or those applications where only limited amounts of power were required, batteries have always been used. Up until the mid to late 70's they have performed their task admirably. Recently, however, we have all become aware of the growing problem of developing reliable NiCd batteries for long mission and high cycle life applications. Here, the role rechargeable batteries will play for future planetary and earth observing spacecraft is discussed. In conclusion, NiCds have been and will continue to be the mainstay of the power system engineers tools for peak power production. Recent experience has tarnished its once sterling reputation. However, the industry has stood up to this challenge and implemented wide ranging plans to rectify the situation. These efforts should be applauded and supported as new designs and materials become available. In addition, project managers must become aware of their responsibility to test their batteries and insure quality and mission operating characteristics. Without this teamwork, the role of NiCds in the future will diminish, and other batteries, not as optimum for high performance applications (low mass and volume) will take their place.

Description: LIPS 3 is a member of the Living Plume Shield series of spacecraft. In each LIPS project, the plume shield, a simple sheet metal cone, was structurally stiffened, and an active satellite was then built around it. The original purpose of the plume shield was to prevent the plume from solid propellent engines, which are fired outside the atmosphere after the aerodynamic shroud is jettisoned, from reaching the primary payload. The surface of LIPS 3 facing the plume also functioned in this manner, but the anterior surfaces were unaffected, and it was there that all solar arrays, sensors, and experiments were mounted. The purpose of LIPS 3 was to provide a test bed for new space power sources. With the long delays projected for schedules of the STS and other major launch systems, it appeared that a decade might pass before long term flight data could be obtained on many new and innovative power sources. The fact that a launch scheduled for early in 1987 required a plume shield was seen as a unique opportunity to obtain some of this data in a timely manner. The LIPS 3 system, the experiments placed aboard, and the experiment data acquisition subsystem are described. Various problems were encountered during integration and after launch; those which appear to effect the accuracy of experimental results are discussed. A preliminary description is given of the accuracy of the flight experiment data.

Description: Multijunction thin film solar cells utilizing GaAs and CuInSe2 as semiconductor absorbers are rapidly developing, becoming a viable technology for space power systems with an unparalleled combination of high efficiency, low mass, and high radiation tolerance. The prospect for evolutionary improvement of this type of cell towards efficiency of approximately equals 30 percent and specific power greater than 1 kW/kg while retaining the attribute of high radiation tolerance are good. Limitations of the present configuration and possible avenues for circumventing these problems are presented.

Description: Phase 2 of the Advanced Photovoltaic Solar Array (APSA) program, started in mid-1987, is currently in progress to fabricate prototype wing hardware that will lead to wing integration and testing in 1989. The design configuration and key details are reviewed. A status of prototype hardware fabricated to date is provided. Results from key component-level tests are discussed. Revised estimates of array-level performance as a function of solar cell device technology for geosynchronous missions are given.

Description: A first principles pn junction device model has predicted new designs for high voltage, high efficiency InP solar cells. Measured InP material properties were applied and device parameters (thicknesses and doping) were adjusted to obtain optimal performance designs. Results indicate that p/n InP designs will provide higher voltages and higher energy conversion efficiencies than n/p structures. Improvements to n/p structures for increased efficiency are predicted. These new designs exploit the high absorption capabilities, relatively long diffusion lengths, and modest surface recombination velocities characteristic of InP. Predictions of performance indicate achievable open-circuit voltage values as high as 943 mV for InP and a practical maximum AM0 efficiency of 22.5 percent at 1 sun and 27 C. The details of the model, the optimal InP structure and the effect of individual parameter variations on device performance are presented.

Description: The application of a Bearing and Power Transfer Assembly (BAPTA) to a Solar Array Drive for communications satellites is presented. The basic principles which were used as guidelines for design and development are developed and the three main subassemblies are described in detail. The results of vibration qualification and thermal vacuum life tests are included.

Description: The Jet Propulsion Laboratory is involved in a Research and Development program sponsored by NASA/OAST on the development of ambient temperature secondary lithium cells for future space applications. Some of the projected applications are planetary spacecraft, planetary rovers, and astronaut equipment. The main objective is to develop secondary lithium cells with greater than 100 Wh/kg specific energy while delivering 1000 cycles at 50 percent Depth of Discharge (DOD). To realize these ambitious goals, the work was initially focused on several important basic issues related to the cell chemistry, selection of cathode materials and electrolytes, and component development. The performance potential of Li-TiS2, Li-MoS3, Li-V6O13 and Li-NbSe3 electrochemical systems was examined. Among these four, the Li-TiS2 system was found to be the most promising system in terms of realizable specific energy and cycle life. Some of the major advancements made so far in the development of Li-TiS2 cells are in the areas of cathode processing technology, mixed solvent electrolytes, and cell assembly. Methods were developed for the fabrication of large size high performance TiS2 cathodes. Among the various electrolytes examined, 1.5M LiAsF6/EC + 2-MeTHF mixed solvent electrolyte was found to be more stable towards lithium. Experimental cells activated with this electrolyte exhibited more than 300 cycles at 100 percent Depth of Discharge. Work is in progress in other areas such as selection of lithium alloys as candidate anode materials, optimization of cell design, and development of 5 Ah cells. The advances made at the Jet Propulsion Laboratory on the development of secondary lithium cells are summarized.

Description: The promise of very high specific energy and power was not yet achieved for practical battery systems. Some recent approaches are discussed for new approaches to achieving high performance for lithium/DeS2 cells and sodium/metal chloride cells. The main problems for the development of successful LiAl/FeS2 cells were the instability of the FeS2 electrode, which has resulted in rapidly declining capacity, the lack of an internal mechanism for accommodating overcharge of a cell, thus requiring the use of external charge control on each individual cell, and the lack of a suitable current collector for the positive electrode other than expensive molybdenum sheet material. Much progress was made in solving the first two problems. Reduction of the operating temperatures to 400 C by a change in electrolyte composition has increased the expected life to 1000 cycles. Also, a lithium shuttle mechanism was demonstrated for selected electrode compositions that permits sufficient overcharge tolerance to adjust for the normally expected cell-to-cell deviation in coulombic efficiency. Sodium/sulfur batteries and sodium/metal chloride batteries have demonstrated good reliability and long cycle life. For applications where very high power is desired, new electrolyte coinfigurations would be required. Design work was carried out for the sodium/metal chloride battery that demonstrates the feasibility of achieving high specific energy and high power for large battery cells having thin-walled high-surface area electrolytes.

Description: Sodium-sulfur batteries were identified as the most likely successor to nickel-hydrogen batteries for space applications. One advantage of the Na/S battery system is that the usable specific energy is two to three times that of nickel-hydrogen batteries. This represents a significant launch cost savings or increased payload mass capabilities. Sodium-sulfur batteries support NASA OAST's proposed Civil Space Technology Initiative goal of a factor of two improvement in spacecraft power system performance, as well as the proposed Spacecraft 2000 initiative. The sodium-sulfur battery operates at between 300 and 400 C, using liquid sodium and sulfur/polysulfide electrodes and solid ceramic electrolyte. The transport of the electrode materials to the surface of the electrolyte is through wicking/capillary forces. These critical transport functions must be demonstrated under actual microgravity conditions before sodium-sulfur batteries can be confidently utilized in space. Ford Aerospace Corporation, under contract to NASA Lewis Research Center, is currently working on the sodium-sulfur battery space flight experiment definition study. The objective is to design the experiment that will demonstrate operation of the sodium-sulfur battery/cell in the space environment with particular emphasis on evaluation of microgravity effects. Experimental payload definitions were completed and preliminary designs of the experiment were defined.

Description: A sufficient production, test and operational database is now available to permit design technology optimization for the next decade. The evolved battery cell design features standardized technology intended to support multiple type missions (e.g., both GEO and LEO). Design analyses and validation test cells demonstrate improved performance plus attractive specific-energy characteristics will be achieved.

Description: Effects of KOH concentrations on failure modes and mechanisms of nickel-hydrogen cells were studied using long cycled boiler plate cells containing electrolytes of various KOH concentrations ranging 21 to 36 percent. Life of these cells were up to 40,000 cycles in an accelerated low earth orbit (LEO) cycle regime at 80 percent depth of discharge. An interim life test results were reported earlier in J. Power Sources, 22, 213-220, 1988. The results of final life test, end-of-life cell performance, and teardown analyses are discussed. These teardown analyses included visual observations, measurements of nickel electrode capacity in an electrolyte-flooded cell, dimensional changes of cell components, SEM studies on cell cross section, BET surface area and pore volume distribution in cycled nickel electrodes, and chemical analyses. Cycle life of a nickel-hydrogen cell was improved tremendously as KOH concentration was decreased from 36 to 31 percent and from 31 to 26 percent while effect of further concentration decrease was complicated as described in our earlier report. Failure mode of high concentration (31 to 36 percent) cells was gradual capacity decrease, while that of low concentration (21 to 26 percent) cells was mainly formation of a soft short. Long cycled (25,000 to 40,000 cycles) nickel electrodes were expanded more than 50 percent of the initial value, but no correlation was found between this expansion and measured capacity. All electrodes cycled in low concentration (21 to 26 percent) cells had higher capacity than those cycled in high concentration (31 to 36 percent) cells.

Description: In most instances separate electrocatalysts are needed to promote the reduction of O2 in the fuel cell mode and to generate O2 in the energy storage-water electrolysis mode in aqueous electrochemical systems operating at low and moderate temperatures (T greater than or equal to 200 C). Interesting exceptions are the lead and bismuth ruthenate pyrochlores in alkaline electrolytes. These catalysts on high area carbon supports have high catalytic activity for both O2 reduction and generation (1,2). Rotating ring-disk electrode measurements provide evidence that the O2 reduction proceeds by a parallel four-electron pathway. The ruthenates can also be used as self-supported catalysts to avoid the problems associated with carbon oxidation, but the electrode performance so far achieved in the research at Case Western Reserve University (CWRU) is considerably less. At the potentials involved in the anodic mode the ruthenate pyrochlores have substantial equilibrium solubility in concentrated alkaline electrolyte. This results in the loss of catalyst into the bulk solution and a decline in catalytic activity. Furthermore, the hydrogen generation counter electrode may become contaminated with reduction products from the pyrochlores (lead, ruthenium). A possible approach to this problem is to immobilize the pyrochlore catalyst within an ionic-conducting solid polymer, which would replace the fluid electrolyte within the porous gas diffusion O2 electrode. For bulk alkaline electrolyte, an anion-exchange polymer is needed with a transference number close to unity for the Oh(-) ion. Preliminary short-term measurements with lead ruthenates using a commercially available partially-fluorinated anion-exchange membrane as an overlayer on the porous gas-fed electrode indicate lower anodic polarization and virtually unchanged cathodic polarization.

Description: Dow Chemical's research activities in fuel cell devices revolves around the development and subsequent investigation of the perfluorinated inomeric membrane separator useful in proton-exchange membrane systems. Work is currently focusing on studying the effects of equivalent weight, thickness, water of hydration, pretreatment procedures, as well as the degree of water management required for a given membrane separator in the cell. The presentation will include details of certain aspects of the above as well as some of the requirements for high and low power generation.

Description: Hydrogen-oxygen SPE fuel cells and SPE electrolyzers (products of Hamilton Standard) both use a Proton-Exchange Membrane (PEM) as the sole electrolyte. The SPE cells have demonstrated a ten year life capability under load conditions. Ultimate life of PEM fuel cells and electrolyzers is primarily related to the chemical stability of the membrane. For perfluorocarbon proton-exchange membranes an accurate measure of the membrane stability is the fluoride loss rate. Millions of cell hours have contributed to establishing a relationship between fluroride loss rates and average expected ultimate cell life. Several features were introduced into SPE fuel cells and SPE electrolyzers such that applications requiring greater than or equal to 100,000 hours of life can be considered. Equally important as the ultimate life is the voltage stability of hydrogen-oxygen fuel cells and electrolyzers. Here again the features of SPE fuel cells and SPE electrolyzers have shown a cell voltage stability in the order of 1 microvolt per hour. That level of stability were demonstrated for tens of thousands of hours in SPE fuel cells at up to 500 amps per square foot (ASF) current density. The SPE electrolyzers have demonstrated the same at 1000 ASF. Many future extraterrestrial applications for fuel cells require that they be self recharged. To translate the proven SPE cell life and stability into a highly reliable extraterrestrial electrical energy storage system, a simplification of supporting equipment is required. Static phase separation, static fluid transport and static thermal control will be most useful in producting required system reliability. Although some 200,000 SPE fuel cell hours were recorded in earth orbit with static fluid phase separation, no SPE electrolyzer has, as yet, operated in space.

Description: High power density fuel cell systems for defense and civilian applications are being developed. Taking into consideration the main causes for efficiency losses (activation, mass transport and ohmic overpotentials) the only fuel cell systems capable of achieving high power densities are the ones with alkaline and solid polymer electrolyte. High power densities (0.8 W/sq cm at 0.8 V and 1 A/sq cm with H2 and O2 as reactants), were already used in NASA's Apollo and Space Shuttle flights as auxiliary power sources. Even higher power densities (4 W/sq cm - i.e., 8 A sq cm at 0.5 V) were reported by the USAF/International Fuel Cells in advanced versions of the alkaline system. High power densities (approximately 1 watt/sq cm) in solid polymer electrolyte fuel cells with ten times lower platinum loading in the electrodes (i.e., 0.4 mg/sq cm) were attained. It is now possible to reach a cell potential of 0.620 V at a current density of 2 A/sq cm and at a temperature of 95 C and pressure of 4/5 atm with H2/O2 as reactants. The slope of the linear region of the potential-current density plot for this case is 0.15 ohm-sq cm. With H2/air as reactants and under the same operating conditions, mass transport limitations are encountered at current densities above 1.4 A/sq cm. Thus, the cell potential at 1 A/sq cm with H2/air as reactants is less than that with H2/O2 as reactants by 40 mV, which is the expected value based on electrode kinetics of the oxygen reduction reaction, and at 2 A/sq cm with H2/air as reactant is less than the corresponding value with H2/O2 as reactants by 250 mV, which is due to the considerably greater mass transport limitations in the former case.

Description: In a continuing effort to develop NiH2 bipolar technology to a point where it can be used efficiently in space flight, testing of a second 40 Ahr, 10-cell bipolar battery has begun. This battery has undergone extensive characterization testing to determine the effects of such operating parameters as charge and discharge rates, temperature, and pressure. The fundamental design of this actively cooled bipolar battery is the same as the first battery. Most of the individual components, however, are from different manufacturers. Different testing procedures as well as certain unique battery characteristics make it difficult to directly compare the two sets of results. In general, the performance of this battery throughout characterization produced expected results. The main differences seen between the first and second batteries occurred during the high-rate discharge portion of the test matrix. The first battery also had poor high-rate discharge results, although better than those of the second battery. Minor changes were made to the battery frame design used for the first battery in an attempt to allow better gas access to the reaction sites for the second build and hopefully improve performance. The changes, however, did not improve the performance of the second battery and could have possibly contributed to the poorer performance that was observed. There are other component differences that could have contributed to the poorer performance of the second battery. The H2 electrode in the second battery was constructed with a Goretex backing which could have limited the high-rate current flow. The gas screen in the second battery had a larger mesh which again could have limited the high-rate current flow. Small scale 2 x 2 batteries are being tested to evaluate the effects of the component variations.

Description: The nickel-hydrogen secondary battery system is now the one of choice for use in GEO satellites. It offers superior energy density to that of nickel-cadmium, with a lifetime that is at least comparable in terms of both cycle life and overall operating life. While the number of deep cycles required for GEO use is small, LEO satellites with long lifetimes (5 to 10 years) will require secondary battery systems allowing 30,000 to 60,000 useful cycles which are characterized by an approximately 2C charge rate and C average discharge rate. Recent work has shown that birnessite MnO2 doped with bismuth oxide can be cycled at very high rates (6C) over a very large number of cycles (thousands) at depths-of-discharge in the 85 to 90 percent range, based on two electrons, which discharge at the same potential in a flat plateau. The potential is about 0.7 V vs. hydrogen, with a cut-off at 0.6 V. At first sight, this low voltage would seem to be a disadvantage, since the theoretical energy density will be low. However, it permits the use of lightweight materials that are immune from corrosion at the positive. The high utilization and low equivalent weight of the active material, together with the use of teflon-bonded graphite for current collection, result in very light positives, especially when these are compared with those in a derated nickel-hydrogen system. In addition, the weight of the pressure vessel falls somewhat, since the dead volume is lower. Calculations show that a total system will have 2.5 times the Ah capacity of a derated nickel-hydrogen LEO battery, so that the energy density, based on 1.2 V for nickel-hydrogen and 0.7 V for MnO2-hydrogen, will be 45 percent higher for comparable cycling performance.

Description: The Monolithic Solid Oxide Fuel Cell (MSOFC) is an oxide-ceramic structure in which appropriate electronic and ionic conductors are fabricated in a honeycomb shape similar to a block of corrugated paperboard. These electronic and ionic conductors are arranged to provide short conduction paths to minimize resistive losses. The power density achievable with the MSOFC is expected to be about 8 kW/kg or 4 kW/L, at fuel efficienceis over 50 percent, because of small cell size and low resistive losses in the materials. The MSOFC operates in the range of 700 to 1000 C, at which temperatures rapid reform of hydrocarbon fuels is expected within the nickel-YSZ fuel channels. Tape casting and hot roll calendering are used to fabricate the MSOFC structure. The performance of the MSOFC has improved significantly during the course of development. The limitation of this system, based on materials resistance alone without interfacial resistances, is 0.093 ohm-sq cm area-specific resistance (ASR). The current typical performance of MSOFC single cells is characterized by ASRs of about 0.4 to 0.5 ohm-sq cm. With further development the ASR is expected to be reduced below 0.2 ohm-sq cm, which will result in power levels greater than 1.4 W/sq cm. The feasibility of the MSOFC concept was proven, and the performance was dramatically improved. The differences in thermal expansion coefficients and firing shrinkages among the fuel cell materials were minimized. As a result of good matching of these properties, the MSOFC structure was successfully fabricated with few defects, and the system shows excellent promise for development into a practical power source.

Description: Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium-sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 Wh/kg theoretical). Energy densities in excess of 180 Wh/kg were realized in practical batteries. Other technological advantages include its chemical simplicity, absence of self-discharge, and long cycle life possibility. More recently, other high temperature sodium batteries have come into the spotlight. These systems can be described as follow: Na/Beta Double Prime-Al2O3/NaAlCl4/Metal Dichloride Sodium/metal dichloride systems are colloquially known as the zebra system and are currently being developed for traction and load leveling applications. The sodium-metal dichloride systems appear to offer many of the same advantages of the Na/S system, especially in terms of energy density and chemical simplicity. The metal dichloride systems offer increased safety and good resistance to overcharge and operate over a wide range of temperatures from 150 to 400 C with less corrosion problems.

Description: Advanced secondary batteries operating at intermediate temperatures (100 to 200 C) have attracted considerable interest due to their inherent advantages (reduced corrosion and safety risks) over higher temperature systems. Current work in this laboratory has involved research on a class of intermediate temperature Na/beta double prime- alumina/RSSR batteries conceptually similar to Na/S cells, but operating within a temperature range of 100 to 150 C, and having an organosulfur rather than inorganic sulfur positive electrode. The organosulfur electrodes are based on the reversible, two electron eduction of organodisulfides to the corresponding thiolate anions, RSSR + 2 electrons yield 2RS(-), where R is an organic moiety. Among the advantages of such a generic redox couple for battery research is the ability to tailor the physical, chemical, and electrochemical properties of the RSSR molecule through choice of the organic moiety. The viscosity, liquidus range, dielectric constant, equivalent weight, and redox potential can in fact be verified in a largely predictable manner. The current work concerns the use of multiple nitrogen organosulfur molecules, chosen for application in Na/RSSR cells for their expected oxidizing character. In fact, a Na/RSSR cell containing one of these materials, the sodium salt of 5-mercapto 1-methyltetrazole, yielded the highest open circuit voltage obtained yet in the laboratory; 3.0 volts in the charged state and 2.6 volts at 100 percent discharge. Accordingly, the cycling behavior of a series of multiple nitrogen organodisulfides as well as polymeric organodisulfides are presented in this manuscript.

Description: The results of a survey on advanced secondary battery systems for space applications are presented. The objectives were: to identify advanced battery systems capable of meeting the requirements of various types of space missions, with significant advantages over currently available batteries, to obtain an accurate estimate of the anticipated improvements of these advanced systems, and to obtain a consensus for the selection of systems most likely to yield the desired improvements. Few advanced systems are likely to exceed a specific energy of 150 Wh/kg and meet the additional requirements of safety and reliability within the next 15 years. The few that have this potential are: (1) regenerative fuel cells, both alkaline and solid polymer electrolyte (SPE) types for large power systems; (2) lithium-intercalatable cathodes, particularly the metal ozides intercalatable cathodes (MnO2 or CoO2), with applications limited to small spacecrafts requiring limited cycle life and low power levels; (3) lithium molten salt systems (e.g., LiAl-FeS2); and (4) Na/beta Alumina/Sulfur or metal chlorides cells. Likely technological advances that would enhance the performance of all the above systems are also identified, in particular: improved bifunctional oxygen electrodes; improved manufacturing technology for thin film lithium electrodes in combination with polymeric electrolytes; improved seals for the lithium molten salt cells; and improved ceramics for sodium/solid electrolyte cells.

Description: A brief overview of the current set of unmanned missions that are currently in operation and those planned for the next 5 to 10 years was presented. The important role of batteries in the development of successful missions was discussed. The workhorse battery, the NiCd, and its use throughout historical missions was explored. Its role on Observers and Landers was discussed, and the success those batteries had. The recent events in the issues of quality and life for NiCd batteries were discussed. These discussions focused on the current design activities for Mars Observer (MO), TOPEX, and Mariner Mark II. Separator selection and the need for uniform testing procedures to develop a quality battery product that can perform to mission requirements were discussed. The recent experiences with the GRO battery failure and the other events have led JPL to the decision to develop a testing program in conjunction with other NASA centers to determine the best separator material for these two missions. The decision for separator material and battery design must be made a year from now. Thus there will not be time to perform a total 2-year accelerated test. The JPL plan for coping with this compromise was discussed. A discussion of where NiH2 batteries are beginning to have an impact and the difficulties with their implementation were addressed. Such missions at Earth Observing System (EOS) and the NOAA series of satellites rely upon NiH2 for success but were not chosen for TOPEX or MO due to their large volume requirements.

Description: In July, 1989, Cosmic Background Explorer (COBE) will be launched from a Delta rocket to study the big bang theory. The COBE, which is in a LEO/Polar orbit, will have two 20 Ah NiCd batteries, and 18 cells per battery, made by McDonnell Douglas Company. In December, 1989, National Oceanic and Atmospheric Administration (NOAA-D) will be launched from an Atlas rocket for weather observation purposes. NOAA-D, which is in a LEO/Polar morning orbit, will have two 26.5 Ah NiCd batteries, and 17 cells per battery, made by Ge-Astro East Windor. NOAA-I, which is scheduled for May, 1991 launch in a LEO/Polar afternoon orbit, will have three 26.5 Ah NiCd batteries, 17 cells per battery, made by GE-Astro East Windor. In April, 1990, Gamma Ray Observatory (GRO) will be launched from STS37 to study the gamma ray radiation phenomenon. GRO, which is in a LEO orbit, will have two modular power systems (MPS) made by McDonnell Douglas, each MPS consisting of three 50 Ah NiCd batteries, 22 cells per battery. In July, 1990, Geostationary Operational Environmental Satellite (GOES-I) will be launched from an Atlas I rocket for weather observation purposes. GOES-I, which is in a GEO orbit, will have two 12 Ah NiCd batteries, 28 cells per battery, made by Ford Aerospace and Communications Company. In December, 1990, Tracking and Data Relay Satellite (TDRS-E) will be launched from STS43 for communication purposes. TDRS-E, which is in a GEO orbit, will have three 40 Ah NiCd batteries, 24 cells per battery, made by TRW. In August, 1991, Extreme Ultraviolet Explorer (EUVE) will be launched from a Delta rocket. EUVE, which is in a LEO orbit, will have one modular power system (MPS) made by McDonnell Douglas. In December, 1991, Upper Atmosphere Research Satellite (UARS) will be launched from STS50 to study the Earth's ozone layer and other environmental concerns. UARS, which is in a 56 deg inclination LEO orbit, will have one modular power systems (MPS) made by McDonnell Douglas.

Description: Extensive characterization testing has been done on a second 40 amp-hour (Ahr), 10-cell bipolar nickel-hydrogen (Ni-H2) battery to study the effects of such operating parameters as charge and discharge rates, temperature, and pressure, on capacity, Ahr and watt-hour (Whr) efficiencies, end-of-charge (EOC) and mid-point discharge voltages. Testing to date has produced many interesting results, with the battery performing well throughout all of the test matrix except during the high-rate (5C and 10C) discharges, where poorer than expected results were observed. The exact cause of this poor performance is, as yet, unknown. Small scale 2 x 2 inch battery tests are to be used in studying this problem. Low earth orbit (LEO) cycle life testing at a 40 percent depth of discharge (DOD) and 10 C is scheduled to follow the characterization testing.

Description: The nickel-hydrogen secondary battery system, developed in the early 1970s, has become the system of choice for geostationary earth orbit (GEO) applications. However, for low earth orbit (LEO) satellites with long expected lifetimes the nickel positive limits performance. This requires derating of the cell to achieve very long cycle life. A new system, rechargeable MnO2-Hydrogen, which does not require derating, is described here. For LEO applications, it promises to have longer cycle life, high rate capability, a higher effective energy density, and much lower self-discharge behavior than those of the nickel-hydrogen system.

Description: Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 Wh/kg theoretical). Energy densities in excess of 180 Wh/kg have been realized in practical batteries. More recently, cathodes other than sulfur are being evaluated. Researchers at JPL are evaluating various new cathode materials for use in high energy density sodium batteries for advanced space applications. The approach is to carry out basic electrochemical studies of these materials in a sodium cell configuration in order to understand their fundamental behaviors. Thus far studies have focused on alternate metal chlorides such as CuCl2 and organic cathode materials such as tetracyanoethylene (TCNE).

Description: The results of a survey on advanced secondary battery systems for space applications are presented. Fifty-five battery experts from government, industry and universities participated in the survey by providing their opinions on the use of several battery types for six space missions, and their predictions of likely technological advances that would impact the development of these batteries. The results of the survey predict that only four battery types are likely to exceed a specific energy of 150 Wh/kg and meet the safety and reliability requirements for space applications within the next 15 years.

Description: The solar arrays on Navstars 1 to 6 have been limiting the electrical power capabilities in the extended life (beyond the 5 year design life). The departure from predicted performance consists of an extra 2.5 percent per year degradation beyond the radiation model estimates. This degradation is unusual in showing a linear rather than exponential decay with time. The performance of the arrays on these satellites has been examined in order to predict future behavior and to make refined projections on the Navstar 7 to 11 solar arrays. Evidence obtained from flight experiments on Navstar 5 and 6, and from laboratory experiments, suggests that contamination of the solar arrays while on orbit may be responsible. The evidence for photo-induced contamination of spacecraft surfaces is presented, and the effect on solar array output in the case of the GPS satellites is shown to be consistent with the observed anomalies.

Description: Over the past three years, NASA Lewis and Entech, Inc. have been investigating the use of high efficiency refractive photovoltaic concentrators for use in space. The design currently under investigation uses a square domed Fresnel lens to focus light on a GaAs concentrator cell. A prismatic cell cover, which directs light away from the front contacts and thus eliminates metalization losses, is applied to the top of the GaAs cell to further enhance array efficiency. The latest experimental results based on testing the GaAs cell/prism cover assembly at standard and operating conditions are presented.

Description: Recent experience in producing GaAs solar cells, to meet the full requirements of space-array manufacturers is reviewed. The main problems have been in extending MOCVD technology to provide high throughput of high quality epitaxial layers, and to integrate the other important factors needed to meet the full range of user requirements. Some discussion of evolutionary changes is also given.

Description: Gold based alloys, commonly used as ohmic contacts for solar cells, are known to react readily with GaAs. It is shown that the contact interaction with the underlying GaAs can continue even at room temperature upon aging, altering both the electrical characteristics of the contacts and the nearby pn junction. Au-Ge-Ni as-deposited (no heat-treatment) contacts made to thin emitter (0.15 microns) GaAs diodes have shown severe shunting of the pn junction upon aging for several months at room temperature. The heat-treated contacts, despite showing degradation in contact resistance, did not affect the underlying pn junction. Au-Zn-Au contacts to p-GaAs emitter (0.2 microns) diodes, however, showed slight improvement in contact resistance upon 200 C isothermal annealing for several months, without degrading the pn junction. The effect of aging on electrical characteristics of the as-deposited and heat-treated contacts and the nearby pn junction, as well as on the surface morphology of the contacts are presented.

Description: High conversion efficiency and low weight are obviously desirable for solar cells intended for space applications. One promising structure is GaAs on Ge. The advantages of using Ge wafers as substrates include the following: they offer high efficiency by forming a two-junction tandem cell; low weight combined with superior strength allows usage of thin (3 mil) wafers; and they are a good substrate for GaAs, being lattice matched, thermal expansion matched, and available as large-area wafers.

Description: Design concepts for ultra-thin (2 to 10 microns) high efficiency single-crystal silicon cells are discussed. Light trapping allows more light to be absorbed at a given thickness, or allows thinner cells of a given Jsc. Extremely thin cells require low surface recombination velocity at both surfaces, including the ohmic contacts. Reduction of surface recombination by growth of heterojunctions of ZnS and GaP on Si has been demonstrated. The effects of these improvements on AM0 efficiency is shown. The peak efficiency increases, and the optimum thickness decreases. Cells under 10 microns thickness can retain almost optimum power. The increase of absorptance due to light trapping is considered. This is not a problem if the light-trapping cells are sufficiently thin. Ultra-thin cells have high radiation tolerance. A 2 microns thick light-trapping cell remains over 18 percent efficient after the equivalent of 20 years in geosynchronous orbit. Including a 50 microns thick coverglass, the thin cells had specific power after irradiation over ten times higher than the baseline design.

Description: The results of a study into the potential impact of advanced solar cell technologies on the characteristics (weight, cost, area) of typical planar solar arrays designed for low, medium and geosynchronous altitude earth orbits are discussed. The study considered planar solar array substrate designs of lightweight, rigid-panel graphite epoxy and ultra-lightweight Kapton. The study proposed to answer the following questions: Do improved cell characteristics translate into array-level weight, size and cost improvements; What is the relative importance of cell efficiency, weight and cost with respect to array-level performance; How does mission orbital environment affect array-level performance. Comparisons were made at the array level including all mechanisms, hinges, booms, and harnesses. Array designs were sized to provide 5kW of array power (not spacecraft bus power, which is system dependent but can be scaled from given values). The study used important grass roots issues such as use of the GaAs radiation damage coefficients as determined by Anspaugh. Detailed costing was prepared, including cell and cover costs, and manufacturing attrition rates for the various cell types.

Description: A survey was conducted on past studies of hole traps in InP. An experiment was designed to evaluate hole traps in Zn-doped InP after fabrication, after electron irradiation and after annealing using deep level transient spectroscopy. Data similar to that of Yamaguchi was seen with observation of both radiation-induced hole and electron traps at E sub A=0.45 eV and 0.03 eV, respectively. Both traps are altered by annealing. It is also shown that trap parameters for surface-barrier devices are influenced by many factors such as bias voltage, which probes traps at different depths below the surface. These devices require great care in data evaluation.

Description: Indium phosphide solar cells with very thin n-type emitters have been made by both ion implantation and metalorganic chemical vapor deposition. Air mass zero efficiencies as high as 18.8 percent (NASA measurement) have been achieved. Although calculations show that, as is the case with GaAs, a heterostructure is expected to be required for the highest efficiencies attainable, the material properties of InP give the shallow-homojunction structure a greater potential than in the case of GaAs. The best cells, which were those made by ion implantation, show open-circuit voltage (V sub oc) of 873 mV, short-circuit current of 357 A/sq m (35.7 mA/sq cm), and fill factor of 0.829. Improvements are anticipated in all three of these parameters. Internal quantum efficiency peaks at over 90 percent in the red end of the spectrum, but drops to 54 percent in the blue end. Other cells have achieved 74 percent in the blue end. Detailed modeling of the data indicates that a high front surface recombination velocity is responsible for the low blue response, that the carrier lifetime is high enough to allow good carrier collection from both the base and the emitter, and that the voltage is base-limited.

Description: The development of the first commercial, ultralight, flexible, deployable, PV array for aerospace applications is discussed. It is based on thin-film, amorphous silicon alloy, multijunction, solar cells deposited on a thin metal or polymer by a proprietary, roll-to-roll process. The array generates over 200 W at AM0 and is made of 20 giant cells, each 54 cm x 29 cm (1566 sq cm in area). Each cell is protected with bypass diodes. Fully encapsulated array blanket and the deployment mechanism weigh about 800 and 500 g, respectively. These data yield power per area ratio of over 60 W/sq m specific power of over 250 W/kg (4 kg/kW) for the blanket and 154 W/kg (6.5 kg/kW) for the power system. When stowed, the array is rolled up to a diameter of 7 cm and a length of 1.11 m. It is deployed quickly to its full area of 2.92 m x 1.11 m, for instant power. Potential applications include power for lightweight space vehicles, high altitude balloons, remotely piloted and tethered vehicles. These developments signal the dawning of a new age of lightweight, deployable, low-cost space arrays in the range from tens to tens of thousands of watts for near-term applications and the feasibility of multi-100 kW to MW arrays for future needs.

Description: The tandem cells consisting of GaAs single crystal and CuInSe2 polycrystalline thin films are being developed under the joint program of the Boeing Co. and Kopin Corp. to meet the increasing power needs for future spacecraft. The updated status of this program is presented along with experimental results such as cell performance, and radiation resistance. Other cell characteristics including the specific power of and the interconnect options for this tandem cell approach are also discussed.

Description: This talk outlines a simple process for the fabrication of n(+)-p solar cells in indium phosphide. Large area cells (greater than 0.25 sq cm) have been made by this process, with a photovoltaic conversion efficiency of 15.21 percent under AM0 conditions of illumination. An ideality factor of 1.1 and a saturation current density of 8 x 10 to the minus 15th power A/sq cm have been observed for these cells. The technique for cell fabrication involves the diffusion of sulfur into InP by an open tube process, and gives highly reproducible results from run to run. A vacuum-deposited layer of gallium sulphide (Ga2S3) was used as the source for sulfur diffusion, with a chemically vapor deposited SiO2 cap layer to prevent decomposition of the InP surface during heat treatment. Diffusions were carried out in a flowing nitrogen ambient at 585 to 708 C, and characterized by their surface carrier concentration and the diffusion constant. The diffusion profile for sulfur in InP is estimated to be of the complementary error function type. The activation energy of the diffusion was estimated to be 1.94 eV. The technique described here is ideally suited for the fabrication of shallow n(+)-p junctions in InP, and has been used for space-borne solar cells.

Description: N/P InP homojunction solar cells with an In sub 0.53 Ga sub 0.47 As contacting layer were fabricated by liquid phase epitaxy (LPE). Electron-Beam-Induced-Current (EBIC) measurements were performed on several selected samples. It was found that the background doping level in the base region sometimes results in a deep junction, which greatly affects the cell performance.

Description: Progress, dating from the start of the Lewis program, is reviewed emphasizing processing techniques which have achieved the highest efficiencies in a given year. To date, the most significant achievement has been attainment of AM0 total area efficiencies approaching 19 percent. Although closed tube diffusion is not considered to be an optimum process, reasonably efficient 2cm x 2cm and 1cm x 2cm InP cells have been produced in quantity by this method with a satellite to be launched in 1990 using these cells. Proton irradiation of these relatively large area cells indicates radiation resistance comparable to that previously reported for smaller InP cells. A similar result is found for the initial proton irradiations of ITO/InP cells processed by D. C. sputtering. With respect to computer modelling, a comparison of n/p homojunction InP and GaAs cells of identical geometries and dopant concentrations has confirmed the superior radiation resistance of InP cells under 1 MeV electron irradiations.

Description: The Space Power needs for the 21st Century and the program in photovoltaics needed to achieve it are discussed. Workshops were conducted in eight different power disciplines involving industry and other government agencies. The Photovoltaics Workshop was conducted at Aerospace Corporation in June 1987. The major findings and recommended program from this workshop are discussed. The major finding is that a survivable solar power capability is needed in photovoltaics for critical Department of Defense missions including Air Force and Strategic Defense Initiative. The tasks needed to realize this capability are described in technical, not financial, terms. The second finding is the need for lightweight, moderately survivable planar solar arrays. High efficiency thin III-V solar cells can meet some of these requirements. Higher efficiency, longer life solar cells are needed for application to both future planar and concentrator arrays with usable life up to 10 years. Increasing threats are also anticipated and means for avoiding prolonged exposure, retraction, maneuvering and autonomous operation are discussed.

Description: The goal is to develop secondary lithium cells with a 100 Wh/kg specific energy capable of 1000 cycles at 50 percent DOD. The approach towards meeting this goal initially focused on several basic issues related to the cell chemistry, selection of cathode materials and electrolytes and component development. The performance potential of Li-TiS2, Li-MoS3, Li-V6O13 and Li-NbSe3 electrochemical systems was examined. Among these four, the Li-TiS2 system was found to be the most promising system in terms of achievable specific energy and cycle life. Major advancements to date in the development of Li-TiS2 cells are in the areas of cathode processing technology, mixed solvent electrolytes, and cell assembly. A summary is given of these advances.

Description: A sufficient production, test and operational database is now available to permit design technology optimization for the next decade. The evolved battery cell design features standardized technology intended to support multiple type missions (e.g., both GEO and LEO). Design analysis and validation test cells demonstrate that improved performance plus attractive specific-energy characteristics will be achieved.

Description: A controlled experiment evaluating the capacity loss experienced by nickel electrodes stored under various conditions of temperature, hydrogen pressure, and electrolyte concentration was conducted using nickel electrodes from four different manufacturers. It was found that capacity loss varied with respect to hydrogen pressure, and storage temperature as well as with respect to electrode manufacturing processes. Impedance characteristics were monitored and found to be indicative of electrode manufacturing processes and capacity loss. Cell testing to evaluate state-of-charge effects on capacity loss were inconclusive as no loss was sustained by the cells tested in this experiment.

Description: Studies are currently underway to further the development of lightweight nickel electrode technology. Work is focused primarily on the space nickel-hydrogen system and nickel-iron system but is also applicable to the nickel-cadmium and nickel-zinc systems. The goal is to reduce electrode weight while maintaining or improving performance, thereby increasing electrode energy density. Two basic electrode structures are being investigated. The first is the traditional nickel sponge produced from sintered nickel-carbonyl powder. The second is a new material for this application which consists of a non-woven mat of nickel fiber. Electrodes are being manufactured, tested, and evaluated at the electrode and cell level.

Description: KOH concentration effects on cycle life of a Ni/H2 cell have been studied by carrying out a cycle life test of ten Ni/H2 boiler plate cells which contain electrolytes of various KOH concentrations. Failure analyses of these cells were carried out after completion of the life test which accumulated up to 40,000 cycles at an 80 percent depth of discharge over a period of 3.7 years. These failure analyses included studies on changes of electrical characteristics of test cells and component analyses after disassembly of the cell. The component analyses included visual inspections, dimensional changes, capacity measurements of nickel electrodes, scanning electron microscopy, BET surface area measurements, and chemical analyses. Results have indicated that failure mode and change in the nickel electrode varied as the concentration was varied, especially, when the concentration was changed from 31 percent or higher to 26 percent or lower.

Description: Impedance measurements have been made on several Ni/Cd and Ni/H2 flightweight cells using the case as a reference electrode. For these measurements the voltage of the case with respect to the anode or cathode is unimportant provided that it remains stable during the measurement of the impedance. In the cells measured so far, the voltages of the cell cases with respect to the individual electrodes differ from cell to cell even at the same overall cell voltage, but they remains stable with time. The measurements can thus be used to separate the cell impedance into the contributions of each electrode, allowing improved diagnosis of cell problems.

Description: Electrochemical impedance spectra of rolled and bonded and sintered porous nickel battery electrodes were recorded periodically during charge/discharge cycling in concentrated KOH solution at various temperatures. A transmission line model (TLM) was adopted to represent the impedance of the porous electrodes, and various model parameters were adjusted in a curve fitting routine to reproduce the experimental impedances. Degradation processes for rolled and bonded electrodes were deduced from changes in model parameters with electrode cycling time. In developing the TLM, impedance spectra of planar (non-porous) electrodes were used to represent the pore wall and backing plate interfacial impedances. These data were measured over a range of potentials and temperatures, and an equivalent circuit model was adopted to represent the planar electrode data. Cyclic voltammetry was used to study the characteristics of the oxygen evolution reaction on planar nickel electrodes during charging, since oxygen evolution can affect battery electrode charging efficiency and ultimately electrode cycle life if the overpotential for oxygen evolution is sufficiently low. Transmission line modeling results suggest that porous rolled and bonded nickel electrodes undergo restructuring during charge/discharge cycling prior to failure.

Description: Very high-efficiency GaAs Cassegrainian solar cells have been fabricated in both the n-p and p-n configurations. The n-p configuration exhibits the highest efficiency at concentration, the best cells having an efficiency eta of 24.5 percent (100X, AM0, temperature T = 28 C). Although the cells are designed for operation at this concentration, peak efficiency is observed near 300 suns (eta = 25.1 percent). To our knowledge, this is the highest reported solar cell efficiency for space applications. The improvement in efficiency over that reported at the previous SPRAT conference is attributed primarily to lower series resistance and improved grid-line plating procedures. Using previously measured temperature coefficients, researchers estimate that the n-p GaAs cells should deliver approximately 22.5 percent efficiency at the operating conditions of 100 suns and T = 80 C. This performance exceeds the NASA program goal of 22 percent for the Cassegrainian cell. One hundred Cassegrainian cells have been sent to NASA as deliverables, sixty-eight in the n-p configuration and thirty-two in the p-n configuration.

Description: A significant impediment to the widespread use of GaAs solar cells in space is the cost and weight of the GaAs substrate. In order to overcome these problems, Spectrolab is pursuing thin cell technologies encompassing both liquid phase epitaxy (LPE) GaAs on GaAs and MOCVD GaAs on Ge cells. Spectrolab's experience in the manufacture of 4 to 6 mil 2 cm x 4 cm GaAs cells on a LPE production line is discussed. By thinning the cells at a late state of processing, production yields comparable to 12 mil cells have been achieved. Data are presented showing that GaAs cells can be welded without degradation and have achieved minimum average efficiencies of 18 percent AM0, 28 C with efficiencies up to 20 percent. Spectrolab, in conjunction with Spire Corporation has also been pursuing GaAs on Ge cell technology in support of larger area lighter weight power systems. Data are presented showing that individual 2 cm x 2 cm, 8 mil cell efficiencies up to 21.7 percent have been achieved. Efficiencies up to 24 percent AM0 will be possible by optimizing the GaAs/Ge interface. Cells have been welded without degradation using silver interconnects and have been laid down on an aluminum honeycomb/graphite facesheet substrate to produce a small coupon. The efficiency was 18.1 percent at AM0, 28 C.

Description: Researchers have calculated the expected performance dependence of near-optimally designed shallow homojunction n+pp+InP solar cells on incident intensities up 200 AM0 and temperatures up to 100 C (373K). Both circular and rectangular cells have been considered, the former for use in a Cassegrainian concentrator array at 100 AM0, 80 to 100 C and the latter for use in a Slats type concentrator array at 20 AM0 80 to 100 C. Calculation of the temperature dependence of the performance parameters I sub sc, V sub oc, FF and eta was done by first verifying that the use of the measured temperature variation of I sub sc, of the best published value of the temperature dependence of the bandgap of InP, and of the temperature dependences of the lifetimes and mobilities of electrons and holes the same as in equivalently doped GaAs, gave calculated results that closely matched measured data on the temperature variation of I sub sc, V sub oc, and FF of four existing InP cells at 1 AM0. It was then assumed that the same temperature dependences of I sub sc, the bandgap and lifetimes and mobilities would hold in the near-optimally designed cells at the higher concentrations.

Description: Their excellent radiation resistance and conversion efficiencies greater than 20 percent, measured under global conditions, make InP shallow-homojunction solar cells very attractive for space or terrestrial application. In addition, modeling studies show that, for optimized design, efficiencies of these devices should exceed 20 percent even under AM0 conditions. However, a systematic experimental investigation of the influence of the various cell design parameters on cell performance has not as yet been made. For the n+/p/p+ structures investigated in the previous modeling study, the design parameters include the impurity concentrations and thicknesses of the emitter and base layers. In the work reported here, researchers discuss an experimental investigation of the effects on cell performance of varying the impurity concentrations of the emitter and base and thickness of the emitter.

Description: Hydrogen-oxygen solid polymer electrolyte (SPE) fuel cells and SPE electrolyzers (products of Hamilton Standard) both use a Proton-Exchange Membrane (PEM) as the sole electrolyte. These solid electrolyte devices have been under continuous development for over 30 years. This experience has resulted in a demonstrated ten-year SPE cell life capability under load conditions. Ultimate life of PEM fuel cells and electrolyzers is primarily related to the chemical stability of the membrane. For perfluorocarbon proton exchange membranes an accurate measure of the membrane stability is the fluoride loss rate. Millions of cell hours have contributed to establishing a relationship between fluoride loss rates and average expected ultimate cell life. This relationship is shown. Several features have been introduced into SPE fuel cells and SPE electrolyzers such that applications requiring greater than or equal to 100,000 hours of life can be considered. Equally important as the ultimate life is the voltage stability of hydrogen-oxygen fuel cells and electrolyzers. Here again the features of SPE fuel cells and SPE electrolyzers have shown a cell voltage stability in the order of 1 microvolt per hour. That level of stability has been demonstrated for tens of thousands of hours in SPE fuel cells at up to 500 amps per square foot (ASF) current density.

Description: Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outlined. The results of tests utilizing a new experimental membrane useful in proton-exchange membrane fuel cells are presented. The high voltage at low current densities can lead to higher system efficiencies while, at the same time, not sacrificing other critical properties pertinent to membrane fuel cell operation. A series of tests to determine response times indicated that on-off cycles are on the order of 80 milliseconds to reach 90 percent of full power. The IR free voltage at 100 amps/sq ft was determined and the results indicating a membrane/electrode package resistance to be .15 ohm-sq cm at 100 amps/sq ft.

Description: Of all the fuel cell systems only alkaline and solid polymer electrolyte fuel cells are capable of achieving high power densities (greater than 1 W/sq cm) required for terrestrial and extraterrestrial applications. Electrode kinetic criteria for attaining such high power densities are discussed. Attainment of high power densities in solid polymer electrolyte fuel cells has been demonstrated earlier by different groups using high platinum loading electrodes (4 mg/sq cm). Recent works at Los Alamos National Laboratory and at Texas A and M University (TAMU) demonstrated similar performance for solid polymer electrolyte fuel cells with ten times lower platinum loading (0.45 mg/sq cm) in the electrodes. Some of the results obtained are discussed in terms of the effects of type and thickness of membrane and of the methods platinum localization in the electrodes on the performance of a single cell.

Description: A brief comparative analysis was made for three concepts of supplying large-scale electrical energy to Earth from space. The concepts were: (1) mining helium-3 on the Moon and returning it to Earth; (2) constructing solar power satellites in geosynchronous orbit from lunar materials (the energy is beamed by microwave to receivers on Earth); and (3) constructing power collection and beaming systems on the Moon itself and transmitting the energy to Earth by microwave. This analysis concerned mainly space transportation and operations, but each of the systems is briefly characterized to provide a basis for space transportation and operations analysis.

Description: The capacity of global power systems must be increased by a factor of ten to provide the predicted power needs of electric power by the year 2050. The Lunar Power System (LPS) would collect solar energy at power bases located on opposing limbs of the moon as seen from Earth. LPS can provide dependable, economic, renewable, and environmentally benign solar energy to Earth. A preliminary engineering and cash flow model of the LPS was developed. Results are shown for a system scaled to a peak capacity of 355 GWe on Earth and to provide 13,600 GWe-Yrs of energy over a 70 year life cycle of construction and full operation. The growth in capacity of the reference system from start of installation on the moon in 2005 to completion of its nominal life cycle in the year 2070 is shown. World needs for power could be accommodated by expansion in capacity of the reference LPS beyond 344 GWe. This would be done by steadily incorporating newer technology during full operation and by establishing additional bases. The results presented encourage consideration of a faster paced program than is assumed herein.

Description: A general discussion of various types of large space structures is presented. A brief overview of the history of space structures is presented to provide insight into the current state-of-the art. Finally, the results of a structural study to assess the viability of very large solar concentrators are presented. These results include weight, stiffness, part count, and in-space construction time.

Description: Procedures for measuring the air mass zero (AM0) current versus voltage characteristics and calculating the efficiency are discussed. The various factors influencing the determination of the efficiency include the I-V measurement system, reference cell calibration, standard reporting conditions, area measurement, light source characteristics, temperature measurement and control, and the measurement procedures. Each of these sources contributes to the precision index and bias limit which is combined to obtain the total uncertainty in the efficiency. These factors are discussed as well as how to minimize differences in the reported AM0 efficiency of a given PV cell between various laboratories.

Description: The wide range of cells that must be available from present-day production lines for space solar cells are described. After over thirty years of space-cell use, there is very little standardization in solar cell design. It is not generally recognized what a wide range of designs must remain available on cell production lines. This range of designs is surveyed.

Description: Results of micron-spaced geometries produced by wet chemical etching and subsequent OMCVD growth on various GaAs surfaces are presented. The polar lattice increases the complexity of the process. The slow-etch planes defined by anisotropic etching are not always the same as the growth facets produced during MOCVD deposition, especially for deposition on higher-order planes produced by the hex groove etching.

Description: Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies.

Description: A comparison of the radiation tolerance of MOCVD-grown GaAs cells and GaAs/Ge cells was undertaken using 1 MeV electrons. The GaAs/Ge cells are somewhat more tolerant of 1 MeV electron irradiation and more responsive to annealing than are the GaAs/GaAs cells examined in this study. However, both types of cells suffer a greater degradation in efficiency than has been observed in other recent studies. The reason for this is not certain, but it may be associated with an emitter thickness which appears to be greater than desired. The deep level transient spectroscopy (DLTS) spectra following irradiation are not significantly different for the GaAs/Ge and the GaAs/GaAs cells, with each having just two peaks. The annealing behavior of these peaks is also similar in the two samples examined. It appears that no penalty in radiation tolerance, and perhaps some benefit, is associated with fabricating MOCVD GaAs cells on Ge substrates rather than GaAs substrates.

Description: The performance and safety characteristics Li-SOCl2 cells were evaluated at -40 C. Tests were conducted on cells of several defferent designs to determine the influence of cell design on performance and safety. The cells exhibited low operating voltages, poor voltage regulation, and low capacity at -40 C. The performance of the cells was found to be critically dependent on the cell design. No safety problems were observed during discharge to 2.0 V under constant current and constant load operating conditions. Cells subjected to prolonged periods of continuous drain at constant-load did not vent/rupture upon warm-up. Cells subjected to prolonged reversal were found to be potentially hazardous. Microcalorimetry and electrochemical impedance spectroscopy studies performed on the cells suggested that those containing a catalyst may exhibit poor shelf life.

Description: The X-ray diffraction patterns of 100 percent discharged Schawinigan black cathodes from Li/SOCl2-LiAlCl4 cells were obtained using a high resolution Guinier camera. The previous assignments of the diffraction lines to Li2O2 and rhombohedral sulfur are all found to be incorrect; all sharp Bragg diffraction lines not assignable to anhydrous LiCl can be assigned to LiCl.H2O.

Description: Energy conversion efficiency of metalorganic chemical vapor deposited CdTe as an intrinsic active layer in n-i-p solar cell structures is reported. Small-area devices with efficiencies over 9 percent have been demonstrated. I-V characteristics, photospectral response, and the results of Auger profiling of structural composition for typical devices will be presented. Also presented are preliminary results on similar photovoltaic devices having Cd(0.85)Mn(0.15)Te in place of CdTe as an i layer.

Description: The properties of the alkali metal thermoelectric converter (AMTEC) are discussed together with those of an efficient AMTEC electrode. Three groups of electrodes were prepared and tested for their performance as AMTEC electrodes, including WPt-T3, WRh-B1, and WRh-B2. The best electrodes of both WPt and WRh types typically exhibited low porosity, and thickness greater than 0.8 micron, which indicated that transport in these electrodes does not occur by a purely free-molecular flow mode. The observed values of the exchange current were found to be within the range of those observed for oxide-free Mo electrodes under similar conditions.

Description: Highlights of the InP solar cell research program are presented. Homojunction cells with efficiencies approaching 19 percent are demonstrated, while 17 percent is achieved for ITO/InP cells. The superior radiation resistance of the two latter cell configurations over both Si and GaAs cells has been shown. InP cells aboard the LIPS3 satellite show no degradation after more than a year in orbit. Computed array specific powers are used to compare the performance of an InP solar cell array to solar dynamic and nuclear systems.

Description: A GaAs solar cell with a V-grooved front surface is described. It shows improved optical coupling and higher short-circuit current compared to planar cells. The GaAs homojunction cells, manufactured by OrganoMetallic Chemical Vapor Deposition (OMCVD), are described. The V-grooves were formed by anisotropic etching. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls.

Description: The Solar Concentrator Advanced Development Project has successfully designed, fabricated, and tested a full scale prototypical solar dynamic concentrator for space station applications. A Truss Hexagonal Panel reflector was selected as a viable solar concentrator concept to be used for space station applications. This concentrator utilizes a modular design approach and is flexible in attainable flux profiles and assembly techniques. The detailed design of the concentrator, which included structural, thermal and optical analysis, identified the feasibility of the design and specific technologies that were required to fabricate it. The needed surface accuracy of the reflectors surface was found to be very tight, within 5 mrad RMS slope error, and results in very close tolerances for fabrication. To meet the design requirements, a modular structure composed of hexagonal panels was used. The panels, made up of graphite epoxy box beams provided the strength, stiffness and dimensional stability needed. All initial project requirements were met or exceeded by hardware demonstration. Initial testing of structural repeatability of a seven panel portion of the concentrator was followed by assembly and testing of the full nineteen panel structure. The testing, which consisted of theodolite and optical measurements over an assembly-disassembly-reassembly cycle, demonstrated that the concentrator maintained the as-built contour and optical characteristics. The facet development effort within the project, which included developing the vapor deposited reflective facet, produced a viable design with demonstrated optical characteristics that are within the project goals.

Description: Electrochemical cells have been fabricated for the simultaneous generation of oxygen and lithium from a Li2O containing molten salt (Li2O-LiCl-LiF). The cell utilizes an oxygen vacancy conducting solid electrolyte, yttria-stabilized zirconia (YSZ), to effect separation between oxygen evolving and lithium reduction half-cell reactions. The cell, which operates at 700 to 850 C, possesses rapid electrode kinetics at the lithium-alloy electrode with exchange current density (i sub o) values being greater than 60mA sq cm. When used in the electrolytic mode, lithium produced at the negative electrode would be continuously removed from the cell for later use (under lunar conditions) as an easily storable reducing agent (compared to H2) for the chemical refining of lunar ores. Because of the high reversibility of this electrochemical system, it has also formed tha basis for the lithium oxygen secondary battery system which possesses the highest theoretical energy density yet investigated.

Description: Electrocatalysts and supports for the positive electrode of moderate temperature single-unit rechargeable alkaline fuel cells are being investigated and developed. Candidate support materials were drawn from transition metal carbides, borides, nitrides and oxides which have high conductivity (greater than 1 ohm/cm). Candidate catalyst materials were selected largely from metal oxides of the form ABO sub x (where A = Pb, Cd, Mn, Ti, Zr, La, Sr, Na, and B = Pt, Pd, Ir, Ru, Ni (Co) which were investigated and/or developed for one function only, O2 reduction or O2 evolution. The electrical conductivity requirement for catalysts may be lower, especially if integrated with a higher conductivity support. All candidate materials of acceptable conductivity are subjected to corrosion testing. Materials that survive chemical testing are examined for electrochemical corrosion activity. For more stringent corrosion testing, and for further evaluation of electrocatalysts (which generally show significant O2 evolution at at 1.4 V), samples are held at 1.6 V or 0.6 V for about 100 hours. The surviving materials are then physically and chemically analyzed for signs of degradation. To evaluate the bifunctional oxygen activity of candidate catalysts, Teflon-bonded electrodes are fabricated and tested in a floating electrode configuration. Many of the experimental materials being studied have required development of a customized electrode fabrication procedure. In advanced development, the goal is to reduce the polarization to about 300 to 350 mV. Approximately six support materials and five catalyst materials were identified to date for further development. The test results will be described.

Description: Carbons activated with macrocyclics have attracted increasing attention as alternative electrocatalysts for oxygen reduction. Initial activity of these catalysts is good, but performance declines rapidly. Pyrolyzing the macrocyclic on the carbon support leads to enhanced stability and the catalysts retain good activity. The approach described is designed to develop bulk doped catalysts with similar structures to pyrolyzed macrocyclic catalysts. The transition metal and coordinated ligands are dispersed throughout the bulk of the conductive carbon skeleton. Two approaches to realizing this concept are being pursued, both involving the doping of carbon precursors. In one approach, the precursor is a solid phase carbon-containing ion-exchange resin. The precursor is doped with a transition metal and/or nitrogen, and the resulting mixture is pyrolyzed. In the other approach, the precursor is a gas-phase hydrocarbon. This is introduced with a transition metal species and nitrogen species into a reactor and pyrolyzed. Several studies have been conducted to determine if there is a synergistic effect between the transition metal and nitrogen and the effect of different methods of introducing the metal-nitrogen (M-N) coordination on performance. One approach was to introduce the metal and nitrogen separately, for example, by sequentially doping FeCl3 and NH4OH into the resin. Catalysts were prepared from an undoped ion-exchange resin, a resin doped only with N, a resin doped only with Fe, and a resin doped with both Fe and N. Introduction of nitrogen alone has no beneficial effect on the performance of the catalysts. The introduction of the Fe alone significantly improves the performance in both the high and low current density regions. When both Fe and N are introduced, the performance at lower current densities (catalytic activity) is increased beyond that of the Fe-doped carbon, but the performance at higher current densities is similar to the carbon containing only Fe. Catalysts prepared from resins-Fe(bipy)3SO4 precursors have performance that is only slightly less then CoTMPP adsorbed and pyroloyzed on Vulcan XC-72. Their performance is much better than carbons which have had the N and Fe introduced separately.

Description: In support of the U.S. Department of Energy's Stirling Engine Highway Vehicle Systems program, the NASA Lewis Stirling engine performance code was evaluated by comparing code predictions without engine-specific calibration factors to GPU-3, P-40, and RE-1000 Stirling engine test data. The error in predicting power output was -11 percent for the P-40 and 12 percent for the Re-1000 at design conditions and 16 percent for the GPU-3 at near-design conditions (2000 rpm engine speed versus 3000 rpm at design). The efficiency and heat input predictions showed better agreement with engine test data than did the power predictions. Concerning all data points, the error in predicting the GPU-3 brake power was significantly larger than for the other engines and was mainly a result of inaccuracy in predicting the pressure phase angle. Analysis into this pressure phase angle prediction error suggested that improvements to the cylinder hysteresis loss model could have a significant effect on overall Stirling engine performance predictions.

Description: The effect of series and voltage-matched configurations on the performance of multijunction solar cells in a radiation environment was investigated. It was found that the configuration of the multijunction solar cell can have a significant impact on its radiation tolerance characteristics.

Description: Hydrogenated amorphous silicon thin films were irradiated with 2.00 MeV helium ions using fluences ranging from 1E11 to 1E15 cm(-2). The films were characterized using photothermal deflection spectroscopy and photoconductivity measurements. The investigations show that the radiation introduces sub-band-gap states 1.35 eV below the conduction band and the states increase supralinearly with fluence. Photoconductivity measurements suggest the density of states above the Fermi energy is not changing drastically with fluence.

Description: A new technique has been developed to capture, digitize, and enhance the image of light emission from a forward biased direct bandgap solar cell. Since the forward biased light emission from a direct bandgap solar cell has been shown to display both qualitative and quantitative information about the solar cell's performance and its defects, signal processing techniques can be applied to the light emission images to identify and analyze shunt diodes. Shunt diodes are of particular importance because they have been found to be the type of defect which is likely to cause failure in a GaAs solar cell. The presence of a shunt diode can be detected from the light emission by using a photodetector to measure the quantity of light emitted at various current densities. However, to analyze how the shunt diodes affect the quality of the solar cell the pattern of the light emission must be studied. With the use of image enhancement routines, the light emission can be studied at low light emission levels where shunt diode effects are dominant.

Description: The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

Description: Development of a three solar cell stack can lead to practical efficiencies greater than 30 percent (1x,AM0). A theoretical efficiency limitation of 43.7 percent at AM0 and one sun is predicted by this model. Including expected losses, a practical system efficiency of 36.8 percent is anticipated. These calculations are based on a 1.93eV/1.43eV/0.89eV energy band gap combination. AlGaAs/GaAs/GaInAsP materials can be used with a six-terminal wiring configuration. The key issues for multijunction solar cells are the top and middle solar cell performance and the sub-bandgap transparency. AstroPower has developed a technique to fabricate AlGaAs solar cells on rugged, self-supporting, transparent AlGaAs substrates. Top solar cell efficiencies greater than 11 percent AM0 have been achieved. State-of-the-art GaAs or InP devices will be used for the middle solar cell. GaInAsP will be used to fabricate the bottom solar cell. This material is lattice-matched to InP and offers a wide range of bandgaps for optimization of the three solar cell stack. Liquid phase epitaxy is being used to grow the quaternary material. Initial solar cells have shown open-circuit voltages of 462 mV for a bandgap of 0.92eV. Design rules for the multijunction three solar cell stack are discussed. The progress in the development of the self-supporting AlGaAs top solar cell and the GaInAsP bottom solar cell is presented.

Description: It is desirable to employ a corrosion screening test for catalyst or support candidates for the fuel cell cathode before entering upon optimization of the candidate or of the catalytic electrode. To this end, corrosion test electrodes, intended for complete immersion and maximum wetting, have been made with 30 to 40 vol. pct Teflon; with perovskites this is about 10 to 15 pct. The candidates were synthesized by methods intended for single-phase product without special emphasis on high surface area, although the substances tested were no coarser than 2 m squared/g. A typical loading was 25 mg/cm sq of the pure substance, usually on gold screen, a few mm squared of which were left bare for contacting. Contact to the gold lead wire was made by welding with a micro-torch or a spot-welder. Corrosion testing consisted of obtaining current-voltage data under flowing inert gas in the potential region for reduction of O2. The electrode was immersed in 30 pct KOH. Observations were made at 20 C and 80 C, and the results compared with data from gold standards. Results with some perovskites, pyrochlores, spinels, and interstitial compounds will be discussed.

Description: An update is given on work to design and build a Fuel Cell Energy Storage System (FCESS) bench-tested unit for the Space Station Freedom Extravehicular Mobility Unit (EMU). Fueled by oxygen and hydride-stored hydrogen, the FCESS is being considered as an alternative to the EMU zinc-silver oxide battery. Superior cycle life and quick recharge are the main attributes of FCESS. The design and performance of a nonventing, 28 V, 34 Ahr system with 7 amp rating are discussed.

Description: The modeling of the Debye Approximation electron sheaths in the edge and strip geometries was completed. Electrostatic potentials in these sheaths were compared to NASCAP/LEO solutions for similar geometries. Velocity fields, charge densities and particle fluxes to the biased surfaces were calculated for all cases. The major conclusion to be drawn from the comparisons of our Debye Approximation calculations with NASCAP-LEO output is that, where comparable biased structures can be defined and sufficient resolution obtained, these results are in general agreement. Numerical models for the Child-Langmuir, high-voltage electron sheaths in the edge and strip geometries were constructed. Electrostatic potentials were calculated for several cases in each of both geometries. Velocity fields and particle fluxes were calculated. The self-consistent solution process was carried through one cycle and output electrostatic potentials compared to NASCAP-type input potentials.

Description: NaS batteries have been identified as the most likely successor to space Ni-H2 or Ni-Cd batteries, primarily due to a mass reduction by a factor 2 to 3 over Ni-H2 and by a factor of 4 over Ni-Cd. This yields major launch cost reductions or payload mass improvements. NaS batteries support NASA OAST's proposed Civil Space Technology Initiative goal of a factor of two improvement in spacecraft 2000 initiative. Since Ni-H2 and Ni-Cd batteries have been space flight proven, it is essential to have the flight experiment to establish a national space technology base to demonstrate the operation of the NaS battery for space applications.

Description: The feasibility of the monolithic solid oxide fuel cell (MSOFC) concept has been proven, and the performance has been dramatically improved. The differences in thermal expansion coefficients and firing shrinkages among the fuel cell materials have been minimized, thus allowing successful fabrication of the MSOFC with few defects. The MSOFC shows excellent promise for development into a practical power source for many applications from stationary power, to automobile propulsion, to space pulsed power.

Description: Current/voltage data was obtained for specially made corrosion electrodes of some oxides and of gold materials for the purpose of developing a screening test of catalysts and supports for use at the cathode of the alkaline fuel cell. The data consists of measurements of current at fixed potentials and cyclic voltammograms. These data will have to be correlated with longtime performance data in order to fully evaluate this approach to corrosion screening. Corrosion test screening of candidates for the oxygen reduction electrode of the alkaline fuel cell was applied to two substances, the pyrochlore Pb2Ru2O6.5 and the spinel NiCo2O4. The substrate gold screen and a sample of the IFC Orbiter Pt-Au performance electrode were included as blanks. The pyrochlore data indicate relative stability, although nothing yet can be said about long term stability. The spinel was plainly unstable. For this type of testing to be validated, comparisons will have to be made with long term performance tests.

Description: Recent results for Li-Al/FeS2 cells and bipolar battery design have shown the possibility of achieving high specific energy (210 Wh/kg) and high specific power (239 W/kg) at the cell level for an electric vehicle application. Outstanding performance is also projected for sodium/metal chloride cells having large electrolyte areas and thin positive electrodes.

Description: The doping of solid phase precursors followed by pyrolysis or the copyrolysis of gas phase precursors has allowed us to produce catalysts with good activity toward oxygen reduction. Efforts are currently underway to better understand the reasons for the catalytic activity of the bulk doped catalysts with a view toward further improving their activity.

Description: In most instances separate electrocatalysts are needed to promote the reduction of O2 in the fuel cell mode and to generate O2 in the energy storage-water electrolysis mode in aqueous electrochemical systems operating at low and moderate temperatures (T greater than or equal to 200 C). Interesting exceptions are the lead and bismuth ruthenate pyrochlores in alkaline electrolytes. These catalysts on high area carbon supports have high catalytic activity for both O2 reduction and generation. Rotating ring-disk electrode measurements provide evidence that the O2 reduction proceeds by a parallel four-electron pathway. The ruthenates can also be used as self-supported catalysts to avoid the problems associated with carbon oxidation, but the electrode performance so far achieved in the research at Case Western Reserve University (CWRU) is considerably less. At the potentials involved in the anodic mode the ruthenate pyrochlores have substantial equilibrium solubility in concentrated alkaline electrolyte. This results in the loss of catalyst into the bulk solution and a decline in catalytic activity. Furthermore, the hydrogen generation counter electrode may become contaminated with reduction products from the pyrochlores (lead, ruthenium).

Description: The 1989 solar cell calibration balloon flight was successfully completed on August 9, 1989, meeting all objectives of the program. Forty-two modules were carried to an altitude of 118,000 ft (36.0 km). The calibrated cells can now be used as reference standards in simulator testing of cells and arrays.

Description: Work is presented on heterojunction solar cells which were studied under the NASA/Arizona State University intern program. The heterojunction solar cells were fabricated by the liquid phase epitaxy method. The basic conversion efficiency was measured at 5 percent. It was determined that a thicker epilayer is needed, and that the density of recombination center should be reduced to give a smaller saturation current and hence a larger open-circuit voltage.

Description: The current status of work on an electrochemical technology for the simultaneous generation of oxygen and lithium from a Li2O containing molten salt (Li2O-LiCl-LiF) is discussed. The electrochemical cell utilizes an oxygen vacancy conducting solid electrolyte, yttria-stabilized zirconia, to effect separation between the oxygen evolving and lithium reduction half-cell reactions. The cell, which operates at 700 to 800 C, possesses rapid electrode kinetics at the lithium-alloy electrode with exchange current density values being greater than 60 mA/sq cm, showing high reversibility for this reaction. When used in the electrolytic mode, lithium produced at the negative electrode would be continuously removed from the cell for later use (under lunar conditions) as an easily storable reducting agent (compared to H2) for the chemical refining of lunar ores via the general reaction: 2Li + MO yields Li2O + M where MO represents a lunar ore. Emphasis to this time has been on the simulated lunar ore ilmenite (FeTiO3), which we have found becomes chemically reduced by Li at 432 C. Furthermore, both Fe2O3 and TiO2 have been reduced by Li to give the corresponding metal. This electrochemical approach provides a convenient route for producing metals under lunar conditions and oxygen for the continuous maintenance of human habitats on the Moon's surface. Because of the high reversibility of this electrochemical system, it has also formed the basis for the lithium-oxygen secondary battery. This secondary lithium-oxygen battery system posses the highest theoretical energy density yet investigated.

Description: Researchers summarize previous Raman spectroscopic results and discuss important structural differences in the various phases of active mass and active mass precursors. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to x rays (i.e., does not scatter x rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging are discussed. The oxidation states and dopant contents are explained in terms of the nonstoichiometric structures.

Description: The primary objective of this program is the investigation and development of electrocatalysts and supports for the positive electrode of moderate temperature single-unit rechargeable alkaline fuel cells. Approximately six support materials and five catalyst materials have been identified to date for further development.

Description: Work was conducted that could lead to a high energy density electrochemical capacitor, completely free of liquid electrolyte. A three-dimensional RuO sub x-ionomer composite structure has been successfully formed and appears to provide an ionomer ionic linkage throughout the composite structure. Capacitance values of approximately 0.6 F/sq cm were obtained compared with 1 F/sq cm when a liquid electrolyte is used with the same configuration.

Description: Impedance concepts can be applied to the analysis of battery electrodes, yielding information about the structure of the electrode and the processes occurring in the electrode. Structural parameters such as the specific area (surface area per gram of electrode) can be estimated. Electrode variables such as surface overpotential, ohmic losses, and diffusion limitations may be studied. Nickel and cadmium electrodes were studied by measuring the ac impedance as a function of frequency, and the specific areas that were determined were well within the range of specific areas determined from BET measurements. Impedance spectra were measured for the nickel and cadmium electrodes, and for a 20 A-hr NiCd battery as functions of the state of charge. More work is needed to determine the feasibility of using frequency response as a nondestructive testing technique for batteries.

Description: Impedances of fifteen electrodes form each of the four U.S. manufactures were measured at 0.200 V vs. the Hg/HgO reference electrode. This corresponds to a voltage of 1.145 for a Ni/H2 cell. Measurements were also made of a representative sample of these at 0.44 V. At the higher voltage, the impedances were small and very similar, but at the lower voltage there were major differences between manufacturers. Electrodes from the same manufacturers showed only small differences. The impedances of electrodes from two manufacturers were considerably different in 26 percent KOH from those in 31 percent KOH. These preliminary results seen to correlate with the limited data from earlier life testing of cells from these manufacturers. The impedances of cells being tested for Space Station Freedom are being followed, and more impendance measurements of electrodes are being performed as functions of manufacturer, voltage, electrolyte concentration, and cycle history in hopes of finding better correlations of impedance with life.