Advancing Commercial Space

Innovators at NASA's Glenn Research Center have developed two novel technologies that make Stirling engines more efficient and less costly. First, Glenn's thermoacoustic power converter uses sound to turn heat into electric power. Utilizing heat-driven pressures and volume oscillations from thermoacoustic sources to power piezoelectric alternators or other power-converter technologies, this device can generate electricity with unprecedented efficiencies. Unlike conventional Stirling-based devices, this thermoacoustic engine achieves high thermal-to-electrical efficiencies with no moving parts. Glenn's second advancement for Stirling engines replaces the conventional linear alternator with a magnetostrictive alternator that converts the oscillating pressure wave into electric power (see cut-away diagram above). These innovations offer a reliable and efficient way to generate power from any heat source, benefiting applications such as combined heat and power (CHP) systems, distributed generation, solar power generation, and heating and cooling systems.

NASA’s Glenn Research Center introduces the “Closed Strayton” generator design to efficiently deliver lightweight and sustainable electric power for clean energy applications. Optimized for hydrogen-based, zero-emission electrified aircraft propulsion from kW to MW range, the design builds on the core “Strayton” engine technology, which combines both Stirling and Brayton cycle elements to overcome the size and performance limitations of conventional turbines and heat engines. In its closed-cycle configuration, the design provides fuel-source agnostic, maintenance-free, quiet power generation for applications with challenging footprint and noise constraints. With additional support for open-cycle and combined-cycle implementations, as well as the capability to scale to higher power outputs, this early-stage technology offers broad applicability for both today and tomorrow’s clean energy and power systems.

NASA's Glenn Research Center has developed a method and apparatus for in situ health monitoring of solar cells. The innovation is a novel approach to solar cell monitoring, as it is radiation-hard, consumes few system resources, and uses commercially available components. The system operates at temperatures from -55°C to 225°C, allowing it to reside close to the array in direct sunlight. The circuitry measures solar cell current versus voltage (I-V) curves using relatively inexpensive electronics, a single switchable +28 volt power bus, and two analog-to-digital (A/D) converter channels. A single transistor is used as a variable resistive load across the cell, rather than the large resistor arrays or active current sources normally used to characterize cells. Originally developed for space, the technology can be adapted for use in terrestrial solar power generation systems and other applications.

Innovators at NASA's Glenn Research Center have developed a high-efficiency multi-junction solar cell that uses a thin interlayer of selenium as the bonding material between wafers. Selenium is a unique semiconductor in that its transparent to light at photon energies below the band gap (infrared), enabling light to pass from the multi-junction top cell to the silicon-based bottom cell. The innovation allows a multi-junction solar cell to be developed without the constraint of lattice matching, and with a low-cost, robust silicon wafer as the supporting bottom substrate and bottom cell. This approach enables a cell that is simultaneously lower in cost, more rugged, and more efficient than existing space-based photovoltaic cells. This high-efficiency solar technology takes advantage of inexpensive silicon wafers and provides a more robust design for next-generation solar cells in space. For terrestrial applications, it can provide unprecedented efficiencies for auxiliary power units in vehicles, solar roof tiles, power plants, and smart grid systems.

NASA’s Universal Modular Interface Converter (UMIC) innovation is a bidirectional AC/DC power converter designed to connect lunar surface power assets and enable power sharing over long distances between sources (e.g. solar) and loads. The UMIC module is intended to be lightweight and readily deployable. The UMIC innovation can essentially serve as the backbone of an electrical power grid for lunar surface exploration and development missions operated by NASA or the commercial space industry. The UMIC architecture is flexible to different grid voltages and frequencies, as well as to different controller and communication systems. The NASA inventors of this technology envision it becoming a standardized system that all users can access similarly.

An innovation from NASA's Glenn Research Center increases the efficiency and versatility of fuel cell stacks for power generation. When there is a large increase in the power demand from a fuel cell system, the voltage of the fuel cell system decreases, sometimes below the lowest acceptable threshold. To meet the requirements of a fuel cell system, engineers have typically added direct-current-to-direct-current (DC-to-DC) converters that boost the voltage produced at the ends of the fuel cell stack or added additional fuel cell systems to manage the increased power demand. However, adding DC-to-DC converters or additional fuel cell systems increases cost, reduces efficiency, and adds both mass and volume. NASA's innovative technique features multiple power points that connect different numbers of cells in an electrical series to a device connected to the fuel cell system, allowing the fuel cell system to maintain the desired voltage to the device under very large electrical power demand changes. This capability eliminates DC-to-DC converter electronics, thereby reducing cost and simplifying the system.

Innovators at NASA's Glenn Research Center have developed a novel thermoelectric material that raises the bar for solid-state power conversion devices. There is growing momentum in the aerospace and automotive industries to harvest energy from heat (such as exhaust from combustion), but advances have been hampered by the lack of environmental durability and performance levels of thermoelectric materials currently in use. Glenn's breakthrough material is a ruthenium-doped gadolinium orthotantalate that excels at directly converting heat into energy. More important, this material does not break down at higher temperatures or air environments - even without special coatings or inert packaging. Glenn's pioneering material enables designers to make great strides in developing solid-state power conversion devices for application in aerospace, automotive, and power-generation industries.

NASA's Glenn Research Center has developed a novel design for a fully premixed high-pressure burner capable of operating on a variety of gaseous fuels and oxidizers, including hydrogen-air mixtures, with a low pressure drop. The burner provides a rapidly and uniformly mixed fuel-oxidizer mixture that is suitable for use in a fully-premixed combustion regime that has the benefit of low pollutant emissions. Further, it is free from harmful flashback effects, combustion instabilities, and thermal meltdown problems that are normally associated with premixed combustion systems operating at high pressures. This burner can be easily scaled for use in practical low-emissions combustion systems such as stationary power plants or hydrogen-air combustion for vehicles. This technology is also applicable to process gas heaters, chemical processing, process gas afterburners, kiln or furnace burners, utility boiler burners, gas reforming burners, and fuel cell processing burners.

Innovators at NASA’s Goddard Space Flight Center have developed a groundbreaking extravehicular activity (EVA)-compatible Battery Charger Module (BCM) as part of the Lunar Experiment Support System and Handling (LESSH) package. This first-of-its-kind technology is designed to provide wired battery charging capabilities to astronauts on the lunar surface or other harsh environments. With the Artemis III mission and beyond, NASA plans to deploy cutting-edge science instruments near the lunar South Pole landing site. To support extended lunar science operations, the EVA-compatible LESSH BCM offers seamless recharging and reliable hard-line data transfer at the modular interface bank on the Human Landing System (HLS) or other Artemis systems (rovers, vehicles, habitats, etc.). Engineered for astronaut ease-of-use, the LESSH BCM delivers an ergonomic interface to connect instruments to power and data systems. By combining battery charge monitoring with flexible data transfer capabilities, the BCM empowers astronauts to extend the scope and duration of operations on the Moon. The NASA invention is integral to creating a recharging infrastructure that enables sustainable, long-term lunar exploration.

Isolated power converters (IPCs) provide safety and performance benefits like noise reduction by separating current flow between a circuit’s input and output. Existing IPCs require bootstrapping the main converter on startup by using a dedicated converter to supply isolated power from the output to the input. The need for two converters decreases efficiency, increases size, weight, and power (SWaP) requirements, and adds complexity to the overall power converter. The bootstrapping problem is significant in space flight applications where SWaP considerations are critical. In response, engineers at NASA's Goddard Space Flight Center developed the Self-Bootstrapping IPC to eliminate the need for an isolated bootstrap converter by allowing bi-modal operation of a single converter. Specifically, the invention operates in transition mode for bootstrapping and then migrates to fixed frequency mode via closed feedback. This bi-modal converter allows users to benefit from reduced mass and volume, increased power density, and improved efficiency (91-94%).

NASA Johnson Space Center is developing a passive thermal management cooling system for a fuel cell. The cooling system uses a radiator comprising a shape memory alloy (SMA) actuator, and a thermosyphon-based system for heat transport that can eliminate the need of moving parts. Relying upon partial gravity for operation, the innovation, called “PaCeSS” for short, is highly promising for power generation and storage in lunar and planetary surface operations, and may be compelling for terrestrial industries interested in passive thermal management. Current fuel cells require active thermal management components such as pumps to push liquid coolant through a fuel cell stack and electronic control valves to operate radiator panels. These components have moving parts presenting several disadvantages: they limit the operational lifetime and reliability of a fuel cell system, and are a source of parasitic power draw because they consume energy from the fuel cell stack to power their operations. PaCeSS could eliminate the wear-and-tear of moving parts and reduce complexity associated with fuel cell system thermal management. It is a system-level solution that spans heat acquisition, heat transport, and heat rejection by incorporating a two-phase thermosyphon for passively removing heat from a fuel cell stack through a transport path. It then uses an SMA mechanism to actuate a radiator panel that can vary the heat rejection rate into space.

NASA seeks interested parties to license the Battery Management System (BMS) developed by innovators at Johnson Space Center. NASA's BMS features the ability to monitor and balance the charge of individual battery cells that are in series and provide fault detection of individual cells in parallel within a battery pack of hundreds of cells. The circuit uses fewer connections (pins) than competing technologies, which reduces complexity and improves reliability. It offers a safe and potentially low-cost management system for high-voltage battery systems, including lithium-ion (Li-ion) battery systems that are used in electric vehicles and other next-generation renewable energy applications. This NASA Technology is available for your company to license and develop into a commercial product. NASA does not manufacture products for commercial sale.

Innovators at NASA Johnson Space Center have developed an adaptive battery cell chamber, or “ABCC” for short, whose chamber halves com-press and constrain a battery pouch cell or a prismatic cell while it is induced into thermal runaway (TR) for analysis. The device comprises an adaptive diaphragm to accommodate variations in the thickness of these types of battery cells without requiring significant changes in the hard-ware. While NASA’s previous cell chamber design was state-of-the-art, the ABCC brings numerous enhancements to the prior NASA design. The prior design required two technicians and approximately one and a half hours for setup between consecutive tests. This down-time was partially caused by the needed separation of the cell chamber from the fractional thermal runaway calorimeter (FTRC) bore where the thermal energy from a TR event is measured when expelled by the ABCC. Addi-tionally, various internals such as heating elements and thermal sensors required refurbishment between each test in which TR was achieved. The ABCC incorporates a novel two-pin quick-disconnect whereby the cell chamber is easily separated from the FTRC. This quick release de-sign increases battery testing throughput while reducing complexity and number of parts. Furthermore, the ABCC internal hardware was designed to be fully reusable, lending itself to more reliable and consistent energy yield calculations sought after by battery cell testing and manufacturing industries.

Innovators at NASA Johnson Space Center have developed a high-powered infrared (IR) laser that can trigger Li-ion battery cells into thermal runaway (TR) without perforating the battery’s can wall like previous methods. Inducing TR in a battery cell allows engineers to test and improve the safety performance of overheated batteries that can potentially catch fire or explode. The primary advantage of this method is the heat energy delivered by the laser can be localized to the exact target spot on the battery cell minimizing thermal biasing to adjacent cells. This laser method does not require any internal modification of the test subject cell design nor require patch heating to trigger a short-circuit. Triggering Li-ion Cells with Laser Radiation could work on any commercial battery cell design with only exterior surface treatment required, which can be done by the user.

Innovators at NASA Johnson Space Center have developed a battery testing technology called ThermoArc that uses a plasma arc to drive a Li-ion battery cell into thermal runaway (TR) by inducing a localized short circuit. The short circuit is created when the plasma arc breaches the cell and melts a small section of the internal separator causing the anode and cathode to come into contact. This "short" yields rapid heat generation that, if not contained, can potentially cause a fire or explosion. This situation becomes especially dangerous if a single cell’s TR event propagates to other cells within a battery pack, such as those used commercially in aerospace and electric vehicles. Therefore, various testing methodologies have been adopted by battery manufacturers to study TR and the results, and thereby improve TR containment. ThermoArc presents a method that uses a plasma arc to deliver thermal energy to heat up only a small area of a Li-ion battery cell to trigger a TR event. This method ensures that the total heat applied is minimal and does not affect the cell’s thermal properties nor does it make significant electrical or mechanical alterations to the cell. Additionally, ThermoArc technology can be implemented to initiate hundreds of repeatable Li-ion battery cell TR tests significantly cheaper than other TR testing method-ologies given that the only consumables are inexpensive electrodes.

Innovators at NASA Johnson Space Center have developed a device that projects a dome-ended nail at a Li-ion battery cell can wall to initiate a thermal runaway (TR) event by denting it. The dent and resulting internal stress wave tears the separator between the anode and cathode within the battery cell causing a short circuit that leads to TR and battery deflagration. Initiating TR in battery cells is an important part of Li-ion battery R&D to better understand the effects of TR, and to make related safety improvements. The novelty of this technology is that the separator is destroyed from the inside without perforating the battery cell can itself or adding thermal energy as a trigger mechanism. This approach results in a more accurate simulation of field-like short circuits and TR for Li-ion battery research and development compared to current state of the art (SoT). Additionally, this device could be used to enhance or supplant traditional testing methods such as those that implement heat-based TR initiation, or mechanical insult where the material integrity of a battery cell is compromised. The Ram-Dent Thermal Runaway Triggering Device was designed to be used in conjunction with NASA’s fractional thermal runaway calorimeters (FTRC) to obtain calorimetry measurements of TR events for fast Li-ion battery failure evaluation. However, this device could be modified to work with other calorimeters designed for the testing of a single Li-ion battery cell or battery-pack.

Researchers at NASA have developed new methods to manufacture carbon materials (e.g., nanotubes, graphene) with holes through the graphitic surface of the particles. The methods generate materials with increased accessible surface area, increased functional groups at damage sites, and improved through-surface molecular transport properties. The materials generated using these techniques are anticipated to be applicable to a variety of industries, especially energy storage (e.g. super-capacitors and batteries) and separation membranes (e.g. for gas, ions, organics, proteins, etc.).

Solvent-free methods were developed to create arrays of holes with lateral dimensions of 10 micrometers and above on holey graphene-based articles from dry compression (such as films, discs, pellets) to form holey graphene mesh (HGM). HGM is enabled by the uniqueness in the dry compressibility of holey graphene and the processibility of the dry-compressed monolithic articles, both of which are unavailable with pristine graphene.

Innovators at the NASA Langley Research Center (LaRC) have developed the Multi-Layer Nuclear Thermionic Avalanche Cell (NTAC), a novel electrical generator which transforms nuclear gamma-ray photon energy directly to electric power by liberating intra-band atomic inner shell electrons. The invention consists of several NTAC layers arranged in a radially concentric series separated by a vacuum gap space. A large number of electrons liberated within the emitter material are emitted from the surface, which has a tightly spaced array of nanometer-scale emitter points. Liberated electrons go across the vacuum gap and arrive at the collector to efficiently convert energy derived from radioactive materials into usable electricity. The device provides a compact, reliable, and continuous electrical source with high power density capable of long-life operation without refueling. The Multi-Layer NTAC is based on previous work at NASA LaRC in which a single emitter device captured high energy photons; use of a multilayer structure greatly improves the performance of the electrical generator.

Nuclear Thermionic Avalanche Cells with Thermoelectric (NTAC-TE) offers direct conversion of energy carried by gamma radiation and beta particles into electricity, as well as direct energy conversion of the heat byproduct without steam driven turbines. This process is considerably more efficient, especially with the addition of Cobalt-60 and sodium-22, than traditional nuclear power generation. In the NTAC-TE system, even the Cesium byproduct of Uranium 235 fission contributes additive energy for more power output. Upgrading, or using NTAC-TE in conjunction with nuclear power plants increases power derived from the fission process. NTAC-TE cells can also use up all radioactive emission energy from radioactive materials without allowing any radioactive emission from the device. NTAC-TE can even use existing fission waste as a viable fuel and operate as a safe and mobile remote energy source.

Ideal power sources for portable equipment ideally should be small, compact, lightweight, and provide continuous power with high power density. Batteries meet all but the continuous power requirement. Radioisotope thermoelectric generators (RTG) meet the continuous power condition but none of the others. However, a compact, thermionic-based cell that converts heat to electricity can meet all the above requirements . A tightly spaced array of nanometer-scale emitter points efficiently converts the heat from Plutonium-238 (238 Pu) into usable electricity. The thermionic cell uses metals with low work-function, not semiconductors, and escapes many of the RTG limitations such as lower carrier concentration and mobility, and the difficult requirement of high electrical and low thermal conductivity. It delivers an estimated 10-20% vs. 7% efficiency for an equivalent-sized, 238Pu-based RTG. Such a power cell would be ideal for remote, hazardous or otherwise isolated applications such as remote sensors/transmitters in severe environments.

NASA Langley Research Center has developed a system to increase the effective piezoelectric constant and the mechanical energy input to energy harvesting transducers. This results in practical performance advantages including higher mechanical-electrical coupling and conversion efficiencies, and more efficient operation across a range of vibrational frequencies.

Innovators from the NASA Langley and NASA Glenn Research Centers have developed materials and processes to use carbon nanomaterials as bipolar membranes or plates for separating solid-state battery unit cells. Using carbon materials over current bipolar plates will be an enabling technology for lightweight, high energy density solid-state batteries. Bipolar membranes or plates provide a chemically inert but electrically conductive layer separating solid-state battery unit cells that allow them to be stacked within a single package. Here, the developed bipolar plate materials include films or membranes of graphene, holey graphene, and carbon nanotubes. These carbon materials provide a significant weight savings over currently used metallic materials while maintaining the necessary performance characteristics of the bipolar plates. These new bipolar membranes or plates may be employed in high energy density solid-state batteries for electrified aircraft, electric vehicles, or a variety of electric devices that require high performance batteries.