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NASA NTRS2005

Results of a 2000 Hour Wear Tof the NEXIS Ion Engine

The Nuclear Electric Xenon Ion System (NEXIS) ion thruster was developed for potential outer planet robotic missions under NASA's Prometheus program. This engine was designed to operate at power levels ranging from 16 to over 20 kWe at specific impulses of 6000 to 7500 s for burn times of up to 10 years, satisfying the requirements of nuclear electric propulsion systems such as that on the proposed Prometheus 1 mission to explore the icy moons of Jupiter. State-of-the-art performance and life assessment tools were used to design the thruster. Following the successful performance validation of a Laboratory Model thruster, Development Model hardware was fabricated and subjected to vibration and wear testing. The results of a 2000-hour wear test are reported herein. Thruster performance achieved the target requirements and was steady for the duration of the test. Ion optics performance was similarly stable. Discharge loss increases of 6 eV/ion were observed in the first 500 hours of the test and were attributed to primary electron energy decreases due to cathode insert conditioning. Relatively high recycle rates were observed and were identified to be high-voltage-to-ground arcs in the back of the thruster caused by wire insulation outgassing and electron penetration through the plasma screen. Field emission of electrons between the accelerator and screen grids was observed and attributed to evolution of field emitter sites at accelerator grid aperture edges caused by ion bombardment. Preliminary modeling and analysis indicates that the NEXIS engine can meet mission performance requirements over the required lifetime. Finally, successful validation of the NEXIS design methodology, design tools, and technologies with the results of the wear test and companion performance and vibration tests presents significant applicability of the NEXIS development effort to missions of near-term as well as long-term interest for NASA.

Thruster performance↗

NASA NTRS2015

High Intensity Resistive and Rowing Exercise Countermeasures Do Not Prevent Orthostatic Intolerance Following 70 Days of Bed Rest

More than 60% of US astronauts participating in Mir and early International Space Station missions (greater than 5 months) were unable to complete a 10‐min 80 deg head‐up tilt test on landing day. This high incidence of post‐spaceflight orthostatic intolerance may be related to limitations of the inflight exercise hardware that prevented high intensity training. PURPOSE: This study sought to determine if a countermeasure program that included intense lower‐body resistive and rowing exercises designed to prevent cardiovascular and musculoskeletal deconditioning during 70 days of 6 deg head-down tilt bed rest (BR), a spaceflight analog, also would protect against post‐ BR orthostatic intolerance. METHODS: Sixteen males participated in this study and performed no exercise (Control, n=10) or performed an intense supine exercise protocol with resistive and aerobic components (Exercise, n=6). On 3 days/week, exercise subjects performed lower body resistive exercise and a 30‐min continuous bout of rowing (greater than or equal to 75% max heart rate). On 3 other days/week, subjects performed only high‐intensity, interval‐style rowing. Orthostatic intolerance was assessed using a 15‐min 80 deg head‐up tilt test performed 2 days (BR‐2) before and on the last day of BR (BR70). Plasma volume was measured using a carbon monoxide rebreathing technique on BR‐3 and before rising on the first recovery day (BR+0). RESULTS: Following 70 days of BR, tilt tolerance time decreased significantly in both the Control (BR‐2: 15.0 +/- 0.0, BR70: 9.9 +/- 4.6 min, mean +/- SD) and Exercise (BR‐2: 12.2 +/- 4.7, BR70: 4.9 +/- 1.9 min) subjects, but the decreased tilt tolerance time was not different between groups (Control: ‐34 +/- 31, Exercise: ‐56 +/- 16%). Plasma volume also decreased (Control: ‐0.56 +/- 0.40, Exercise: ‐0.48 +/- 0.33 L) from pre to post‐BR, with no differences between groups (Control: ‐18 +/- 11%, Exerciser: ‐15 +/-1 0%). CONCLUSIONS: These findings confirm previous reports in shorter BR studies that the performance of an exercise countermeasure protocol by itself during BR does not prevent orthostatic intolerance or plasma volume loss. This suggests that protection against orthostatic intolerance in astronauts following long‐duration spaceflight will require an additional intervention, such as periodic orthostatic stress, fluid repletion, and/or lower‐body compression garments.

Lee, Stuart M. C.↗

NASA NTRS2017

Ionizing Radiation Affects Gene Expression in Mouse Skin and Bone

Future long-duration space exploration beyond low earth orbit will increase human exposure to space radiation and microgravity conditions as well as associated risks to skeletal health. In animal studies, radiation exposure (greater than 1 Gy) is associated with pathological changes in bone structure, enhanced bone resorption, reduced bone formation and decreased bone mineral density, which can lead to skeletal fragility. Definitive measurements and detection of bone loss typically require large and specialized equipment which can make their application to long duration space missions logistically challenging. Towards the goal of developing non-invasive and less complicated monitoring methods to predict astronauts' health during spaceflight, we examined whether radiation induced gene expression changes in skin may be predictive of the responses of skeletal tissue to radiation exposure. We examined oxidative stress and growth arrest pathways in mouse skin and long bones by measuring gene expression levels via quantitative polymerase chain reaction (qPCR) after exposure to total body irradiation (IR). To investigate the effects of irradiation on gene expression, we used skin and femora (cortical shaft) from the following treatment groups: control (normally loaded, sham-irradiated), and IR (0.5 Gy 56Fe 600 MeV/n and 0.5 Gy 1H 150 MeV/n), euthanized at one and 11 days post-irradiation (IR). To determine the extent of bone loss, tibiae were harvested and cancellous microarchitecture in the proximal tibia quantified ex vivo using microcomputed tomography (microCT). Statistical analysis was performed using Student's t-test. At one day post-IR, expression of FGF18 in skin was significantly greater (3.8X) than sham-irradiated controls, but did not differ at 11 days post IR. Expression levels of other genes associated with antioxidant response (Nfe2l2, FoxO3 and Sod1) and the cell cycle (Trp53, Cdkn1a, Gadd45g) did not significantly differ between the control and IR groups at either time point. Radiation exposure resulted in a 27.0% increase in FGF18-positive hair follicles at one day post-IR and returned to basal levels at 11 days post-IR. A similar trend was observed from FGF18 gene expression analysis of skin. In bone (femora), there was an increase in the expression of the pro-osteoclastogenic cytokine, MCP-1, one day after IR compared to non-irradiated controls. FGF18 expression in skin and MCP- 1 expression in bone were found to be positively correlated (P less than 0.002, r=0.8779). Further, microcomputed tomography analysis of tibia from these animals showed reduced cancellous bone volume (-9.9%) at 11 days post- IR. These results suggest that measurements of early radiation induced changes in FGF18 gene expression in skin may have value for predicting subsequent loss of cancellous bone mass. Further research may lead to the development of a relatively simple diagnostic tool for bone loss, with the advantage that hair follicles and skin are relatively easy to acquire from human subjects.

space radiation↗

NASA NTRS2019

Overview of the New Version 3 NASA Micro-Pulse Lidar Network (MPLNET) Automatic Precipitation Detection Algorithm

Precipitation modifies atmospheric column thermodynamics through the process of evaporation and serves as a proxy for latent heat modulation. For this reason, a correct precipitation parameterization (especially for low-intensity precipitation) within global scale models is crucial. In addition to improving our modeling of the hydrological cycle, this will reduce the associated uncertainty of global climate models in correctly forecasting future scenarios, and will enable the application of mitigation strategies. In this manuscript we present a proof of concept algorithm to automatically detect precipitation from lidar measurements obtained from the National Aeronautics and Space Administration Micropulse lidar network (MPLNET). The algorithm, once tested and validated against other remote sensing instruments, will be operationally implemented into the network to deliver a near real time (latency <1.5 h) rain masking variable that will be publicly available on MPLNET website as part of the new Version 3 data products. The methodology, based on an image processing technique, detects only light precipitation events (defined by intensity and duration) such as light rain, drizzle, and virga. During heavy rain events, the lidar signal is completely extinguished after a few meters in the precipitation or it is unusable because of water accumulated on the receiver optics. Results from the algorithm, in addition to filling a gap in light rain, drizzle, and virga detection by radars, are of particular interest for the scientific community as they help to fully characterize the aerosol cycle, from emission to deposition, as precipitation is a crucial meteorological phenomenon accelerating atmospheric aerosol removal through the scavenging effect. Algorithm results will also help the understanding of long term aerosol–cloud interactions, exploiting the multi-year database from several MPLNET permanent observational sites across the globe. The algorithm is also applicable to other lidar and/or ceilometer network infrastructures in the framework of the Global Aerosol Watch (GAW) aerosol lidar observation network (GALION).

Simone Lolli↗

DOE OSTI2015

Stochastic generation of hourly rainstorm events in Johor

Engineers and researchers in water-related studies are often faced with the problem of having insufficient and long rainfall record. Practical and effective methods must be developed to generate unavailable data from limited available data. Therefore, this paper presents a Monte-Carlo based stochastic hourly rainfall generation model to complement the unavailable data. The Monte Carlo simulation used in this study is based on the best fit of storm characteristics. Hence, by using the Maximum Likelihood Estimation (MLE) and Anderson Darling goodness-of-fit test, lognormal appeared to be the best rainfall distribution. Therefore, the Monte Carlo simulation based on lognormal distribution was used in the study. The proposed model was verified by comparing the statistical moments of rainstorm characteristics from the combination of the observed rainstorm events under 10 years and simulated rainstorm events under 30 years of rainfall records with those under the entire 40 years of observed rainfall data based on the hourly rainfall data at the station J1 in Johor over the period of 1972–2011. The absolute percentage error of the duration-depth, duration-inter-event time and depth-inter-event time will be used as the accuracy test. The results showed the first four product-moments of the observed rainstorm characteristics were close with the simulated rainstorm characteristics. The proposed model can be used as a basis to derive rainfall intensity-duration frequency in Johor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRSDate not supplied

Crew Scheduling Performance

As NASA considers long-duration exploration missions (LDEMs), it is envisioned that crew will behave more autonomously as compared to low-Earth orbit missions. The necessary shift of Ops Planners’ complete management of scheduling and planning to provide flexibility for crew to manage their own schedule in real-time requires significant research and investigation in evaluation of concepts of operations, of software tools to support tasks, and of crew performance to complete scheduling tasks. Our research objective is to characterize the human performance envelope for the task of planning and scheduling (crew self-scheduling), develop countermeasures to mitigate adverse performance effects due to plan complexity, and inform performance standards and guidelines based on research results. In our efforts to understand and characterize scheduling performance of crew members, we have conducted subject matter expert interviews to obtain feedback on scheduling plan complexity drivers and plan goodness. Following the pilot study conducted last year, we designed a study and have begun remote human subject testing to evaluate non-expert human performance, workload, and situational awareness for the task of planning and scheduling. This study investigates the effects of the number and type of constraints on human performance, and the differences in scheduling metrics between scheduling and rescheduling tasks. Subject testing is currently in progress, and we aim to collect data from approximately thirty subjects. We will summarize the methods used and impacts of the number and type of scheduling constraints. We will also present lessons learned as well as relevant results of the study.

crew scheduling↗

NASA NTRSDate not supplied

Functional Volume Assessment of an Early Version of the Mars Transit Habitat

During the summer of 2020, the NASA Mars Architecture Team (MAT) conducted a functional volume assessment of the Transit Habitat (TH). The TH has evolved substantially since that time and the current TH does not share the same internal configuration, but the insights gained from the assessment remain relevant. In virtually all architectures involving chemical, electric, or nuclear propulsion, the majority of the crew mission is spent aboard the TH. The Earth to Mars transit durations may vary from architecture to architecture, but all are on the order of hundreds of days, regardless of whether an opposition or conjunction class trajectory is selected, and regardless of whether the propulsion system is chemical, electric, or nuclear. Thus, the TH must provide capabilities appropriate to a very long duration. So, despite significant changes in the current Mars architecture over the past few years, this evaluation still provides useful recommendations in the form of habitability guidance that can be applied to current and future TH concepts. This assessment had six primary objectives: provide a sanity check to the BOC-derived TH layout; understand if we can fit the hardware and functional tasks in the volume; provide a high-level assessment of how aggressive the layout is; generate a list of challenges or assumptions necessary to make it work; generate a list of future work to refine understanding; and identify proposed requirements. All of this information is critical to drive habitat sizing studies and key architecture decisions. It was clear that a human-in-the-loop (HITL) evaluation of some kind would be necessary, but several challenges were immediately identified. The most information could be gleaned from a Desert Research and Technology Studies (DRATS) type of mission operations test (MOT), but the TH concept was too low fidelity to construct the type of prototype necessary to conduct a MOT, nor were their financial resources to do so. The next best option – and really the one most appropriate for the BOC’s stage of maturity – is a Virtual Reality (VR) walk-through evaluation. However, NASA was in a shutdown state due to the COVID-19 pandemic and the VR labs were inaccessible. As a result, a tabletop evaluation was created, using .jpg imagery from the ECM CAD model along with Excel-based datasheets. High-level crew living and working functions within the habitat were identified for evaluation. Questionnaires using Likert scales assessed acceptability of habitat functions and sim quality – the degree to which the function was represented in CAD. This enabled the evaluation to be conducted by personnel working remotely. Each function was evaluated individually along with several overarching habitability parameters and vehicle subsystems. The results of this evaluation are discussed, including methodological challenges and rating challenges. Acceptability results are discussed for functions that the participants were able to rate and participant comments for functions that could not be related are also described. Final conclusions are described, including challenges or assumptions needed to make the TH design acceptable, future work needed to refine understanding of the TH, and proposed habitat requirements based on test data.

Transit Habitat↗

NASA NTRS2017

ISS Training Best Practices and Lessons Learned

Training our crew members for long duration exploration-class missions (LDEM) will have to be qualitatively and quantitatively different from current training practices. However, there is much to be learned from the extensive experience NASA has gained in training crew members for missions on board the International Space Station (ISS). Furthermore, the operational experience on board the ISS provides valuable feedback concerning training effectiveness. Keeping in mind the vast differences between current ISS crew training and training for LDEM, the needs of future crew members, and the demands of future missions, this ongoing study seeks to document current training practices and lessons learned. The goal of the study is to provide input to the design of future crew training that takes as much advantage as possible of what has already been learned and avoids as much as possible past inefficiencies. Results from this study will be presented upon its completion. By researching established training principles, examining future needs, and by using current practices in spaceflight training as test beds, this research project is mitigating program risks and generating templates and requirements to meet future training needs.

ISS↗

DOE OSTI2022

A Real-Time Data Dashboard for Monitoring Travel Behavior

When running a smartphone app-based travel behavior study, it is important to keep participants engaged in contributing data. Long study durations and/or large samples make it difficult to engage participants in reporting their travel behavior. We developed a dashboard web application called 'emdash' to facilitate and ease the data collection maintenance task. It allows deployers to view trip trajectories, track which participants are uploading data, and generate report ready plots. Emdash can also be useful for deployers to identify ways to best encourage a particular transportation mode shift and to provide feedback and reporting to participants. Using the dashboard, a single admin was able to support a classic travel study with 80 participants. The dashboard is currently deployed in a two-year electric bike (e-bike) pilot study called CanBikeCO, conducted in six locations across Colorado, USA. CanBikeCO targets carbon emissions reduction and equity improvement by evaluating changes to participants' travel behavior when they are offered free e-bikes. Each CanBikeCO location has access to their own version of emdash to help them monitor and support participants. After testing and gathering feedback, we made improvements to the dashboard's usability and scalability, and proposed a method to make detecting data issues easier. Improvements include configurable options and limiting the volume of data sent to the dashboard as study size and duration increase.

ADVANCED PROPULSION SYSTEMS,MATHEMATICS AND COMPUT↗

NASA NTRS2010

FeatherSail - Design, Development and Future Impact

To the present day, the idea of using solar sails for space propulsion is still just a concept, but one that provides a great potential for future space exploration missions. Several notable solar propulsion missions and experiments have been performed and more are still in the development stage. Solar Sailing is a method of space flight propulsion, which utilizes the light photons to propel spacecrafts through the vacuum of space. This concept will be tested in the near future with the launch of the NanoSail-D satellite. NanoSail-D is a nano-class satellite, <10kg, which will deploy a thin lightweight sheet of reflective material used to propel the satellite in its low earth orbit. Using the features of the NanoSail-D architecture, a second-generation solar sail design concept, dubbed FeatherSail, has been developed. The goal of the FeatherSail project is to create a sail vehicle with the ability to provide steering from the sails and increase the areal density. The FeatherSail design will utilize the NanoSail-D based extendable boom technology with only one sail on each set of booms. This design also allows each of the four sails to feather as much as ninety degrees. The FeatherSail concept uses deployable solar arrays to generate the power necessary for deep space missions. In addition, recent developments in low power, low temperature Silicon-Germanium electronics provide the capability for long duration deep space missions. It is envisioned that the FeatherSail conceptual design will provide the impetus for future sail vehicles, which may someday visit distant places that mankind has only observed.

Alhorn, Dean C.↗

NASA NTRS2011

Evaluation of the Monotonic Lagrangian Grid and Lat-Long Grid for Air Traffic Management

The Air Traffic Monotonic Lagrangian Grid (ATMLG) is used to simulate a 24 hour period of air traffic flow in the National Airspace System (NAS). During this time period, there are 41,594 flights over the United States, and the flight plan information (departure and arrival airports and times, and waypoints along the way) are obtained from an Federal Aviation Administration (FAA) Enhanced Traffic Management System (ETMS) dataset. Two simulation procedures are tested and compared: one based on the Monotonic Lagrangian Grid (MLG), and the other based on the stationary Latitude-Longitude (Lat- Long) grid. Simulating one full day of air traffic over the United States required the following amounts of CPU time on a single processor of an SGI Altix: 88 s for the MLG method, and 163 s for the Lat-Long grid method. We present a discussion of the amount of CPU time required for each of the simulation processes (updating aircraft trajectories, sorting, conflict detection and resolution, etc.), and show that the main advantage of the MLG method is that it is a general sorting algorithm that can sort on multiple properties. We discuss how many MLG neighbors must be considered in the separation assurance procedure in order to ensure a five-mile separation buffer between aircraft, and we investigate the effect of removing waypoints from aircraft trajectories. When aircraft choose their own trajectory, there are more flights with shorter duration times and fewer CD&R maneuvers, resulting in significant fuel savings.

Kaplan, Carolyn↗

NASA NTRS2013

Vapor Compression and Thermoelectric Heat Pump Heat Exchangers for a Condensate Distillation System: Design and Experiment

Maximizing the reuse of wastewater while minimizing the use of consumables is critical in long duration space exploration. One of the more promising methods of reclaiming urine is the distillation/condensation process used in the cascade distillation system (CDS). This system accepts a mixture of urine and toxic stabilizing agents, heats it to vaporize the water and condenses and cools the resulting water vapor. The CDS wastewater flow requires heating and its condensate flow requires cooling. Performing the heating and cooling processes separately requires two separate units, each of which would require large amounts of electrical power. By heating the wastewater and cooling the condensate in a single heat pump unit, mass, volume, and power efficiencies can be obtained. The present work describes and compares two competing heat pump methodologies that meet the needs of the CDS: 1) a series of mini compressor vapor compression cycles and 2) a thermoelectric heat exchanger. In the paper, the system level requirements are outlined, the designs of the two heat pumps are described in detail, and the results of heat pump performance tests are provided. A summary is provided of the heat pump mass, volume and power trades and a selection recommendation is made.

Erickson, Lisa R.↗

NASA NTRS2015

Fluid Shifts

INTRODUCTION: Mechanisms responsible for the ocular structural and functional changes that characterize the visual impairment and intracranial pressure (ICP) syndrome (VIIP) are unclear, but hypothesized to be secondary to the cephalad fluid shift experienced in spaceflight. This study will relate the fluid distribution and compartmentalization associated with long-duration spaceflight with VIIP symptoms. We also seek to determine whether the magnitude of fluid shifts during spaceflight, as well as the VIIP-related effects of those shifts, can be predicted preflight with acute hemodynamic manipulations, and also if lower body negative pressure (LBNP) can reverse the VIIP effects. METHODS: Physiologic variables will be examined pre-, in- and post-flight in 10 International Space Station crewmembers including: fluid compartmentalization (D2O and NaBr dilution); interstitial tissue thickness (ultrasound); vascular dimensions and dynamics (ultrasound and MRI (including cerebrospinal fluid pulsatility)); ocular measures (optical coherence tomography, intraocular pressure, ultrasound); and ICP measures (tympanic membrane displacement, otoacoustic emissions). Pre- and post-flight measures will be assessed while upright, supine and during 15 deg head-down tilt (HDT). In-flight measures will occur early and late during 6 or 12 month missions. LBNP will be evaluated as a countermeasure during HDT and during spaceflight. RESULTS: The first two crewmembers are in the preflight testing phase. Preliminary results characterize the acute fluid shifts experienced from upright, to supine and HDT postures (increased stroke volume, jugular dimensions and measures of ICP) which are reversed with 25 millimeters Hg LBNP. DISCUSSION: Initial results indicate that acute cephalad fluid shifts may be related to VIIP symptoms, but also may be reversible by LBNP. The effect of a chronic fluid shift has yet to be evaluated. Learning Objectives: Current spaceflight VIIP research is described, including novel hardware and countermeasures.

Stenger, M. B.↗

NASA NTRS2018

ISS Training Best Practices and Lessons Learned

Training our crew members for long-duration Deep Space Transport (DST) missions will have to be qualitatively and quantitatively different from current training practices. However, there is much to be learned from the extensive experience NASA has gained in training crew members for missions on board the International Space Station (ISS). Furthermore, the operational experience on board the ISS provides valuable feedback concerning training effectiveness. Keeping in mind the vast differences between current ISS crew training and training for DST missions, the needs of future crew members, and the demands of future missions, this ongoing study seeks to document current training practices and lessons learned. The goal of the study is to provide input to the design of future crew training that takes as much advantage as possible of what has already been learned and avoids as much as possible past inefficiencies. Results from this study will be presented upon its completion. By researching established training principles, examining future needs, and by using current practices in spaceflight training as test beds, this research project is mitigating program risks and generating templates and requirements to meet future training needs.

training↗

NASA NTRSDate not supplied

Dynamic Radioisotope Power Systems Development Status and Path to Flight

Dynamic power conversion offers the potential to produce Radioisotope Power Systems (RPS) that generate higher power outputs and utilize the Pu-238 radioisotope more efficiently. Additionally, dynamic power conversion offers the potential of producing generators with minimal degradation resulting in more power at the end of the mission, when the power is needed. Dynamic power conversion technologies being developed for space applications include the Stirling and Brayton thermodynamic cycle machines. Machines can be built based on these cycles while eliminating wear mechanisms of the moving components, enabling long design life necessary for space missions. The Dynamic Radioisotope Power Systems (DRPS) project at NASA Glenn Research Center (Glenn Research Center) is pursuing the realization of this type of power source on a flight mission. The project currently has three convertor development contracts that will deliver prototype hardware in 2020. This hardware will undergo a gamut of experimental performance verification efforts at NASA GRC. In parallel, the project has also initiated generator design efforts based on these underlying convertor options, and is also on track to build an in-house version of a generator for laboratory system-level testing. The project is also funding control electronics technology, which are necessary to convert alternating current from the dynamic devices to direct current for use by a spacecraft. A lunar mission is being targeted as the first use of this new technology, as DRPS enables a wide range of high-return scientific missions on the moon, while the mission being short in duration (2 years rather than 10 years for an outer planets mission).

Salvatore M Oriti↗

NASA NTRSDate not supplied

Dynamic Radioisotope Power Systems Status and Path to Flight

Salvatore Oriti↗

NASA NTRS2002

Advanced Life Support Food Subsystem Salad Crop Requirements

As the National Aeronautics and Space Administration (NASA) begins to look towards longer duration space flights, the importance of fresh foods and varied menu choices increases. Long duration space missions require development of both a Transit Food System and a Lunar or Planetary Food System. These two systems are intrinsically different since the first one will be utilized in the transit vehicle in microgravity conditions while the second will be used in conditions of partial gravity (hypogravity). The Transit Food System will consist of prepackaged food of extended shelf life. Microgravity imposes significant limitations on the ability of the crew to handle food and allows only for minimal processing. Salad crops will be available for the planetary mission. Supplementing the transit food system with salad crops is also being considered. These crops will include carrots, tomatoes, lettuce, radish, spinach, chard, cabbage, and onion. The crops will be incorporated in the menu along with the prepackaged food. The fresh tasting salad crops will provide variety, texture, and color in the menu. This variety should provide increased psychological benefit. Preliminary studies on spinach, tomatoes, and bok choy have been completed. Sensory and analytical tests, including color and moisture were conducted on the chamber grown crops and compared to store bought spinach, tomatoes, and bok choy. Preliminary studies of the appropriate serving sizes and number of servings per week have also been conducted.

Perchonok, Michele H.↗

NASA NTRS2008

Composite Cathodes for Dual-Rate Li-Ion Batteries

Composite-material cathodes that enable Li-ion electrochemical cells and batteries to function at both high energy densities and high discharge rates are undergoing development. Until now, using commercially available cathode materials, it has been possible to construct cells that have either capability for high-rate discharge or capability to store energy at average or high density, but not both capabilities. However, both capabilities are needed in robotic, standby-power, and other applications that involve duty cycles that include long-duration, low-power portions and short-duration, high-power portions. The electrochemically active ingredients of the present developmental composite cathode materials are: carbon-coated LiFePO4, which has a specific charge capacity of about 160 mA h/g and has been used as a high-discharge-rate cathode material and Li[Li(0.17)Mn(0.58)Ni(0.25)]O2, which has a specific charge capacity of about 240 mA h/g and has been used as a high-energy-density cathode material. In preparation for fabricating the composite material cathode described, these electrochemically active ingredients are incorporated into two sub-composites: a mixture comprising 10 weight percent of poly(vinylidine fluoride); 10 weight percent of carbon and 80 weight percent of carbon coated LiFePO4; and, a mixture comprising 10 weight percent of PVDF, and 80 weight percent of Li[Li(0.17)Mn(0.58)Ni(0.25)]O2. In the fabrication process, these mixtures are spray-deposited onto an aluminum current collector. Electrochemical tests performed thus far have shown that better charge/discharge performance is obtained when either 1) each mixture is sprayed on a separate area of the current collector or (2) the mixtures are deposited sequentially (in contradistinction to simultaneously) on the same current-collector area so that the resulting composite cathode material consists of two different sub-composite layers.

Whitacre, Jay↗