Miniaturized Laser Heterodyne Radiometer

The technology is a solid state, Carbon Dioxide (CO2) sensor configured for sensitive detection of CO2 having a concentration within the range of about 100 Parts per Million (ppm) and 10,000 ppm in both dry conditions and high humidity conditions (e.g., > 80% relative humidity). The solid state CO2 sensor achieves detection of high concentrations of CO2 without saturation and in both dynamic flow mode and static diffusion mode conditions. The composite sensing material comprises Oxidized Multi-Walled Carbon Nanotubes (O-MWCNT) and a metal oxide, for example O-MWCNT and iron oxide (Fe2O3) nanoparticles. The composite sensing material has an inherent resistance and corresponding conductivity that is chemically modulated as the level of CO2 increases. The CO2 gas molecules absorbed into the carbon nanotube composites cause charge-transfer and changes in the conductive pathway such that the conductivity of the composite sensing material is changed. This change in conductivity provides a sensor response for the CO2 detection. The solid state CO2 sensor is well suited for automated manufacturing using robotics and software controlled operations. The solid state CO2 sensor does not utilize consumable components or materials and does not require calibration as often as conventional CO2 sensors. Since the technology can be easily integrated into existing programmable electronic systems or hardware systems, the calibration of the CO2 sensor can be automated.

In conjunction with academia and industry, NASA's Glenn Research Center has developed a range of microelectromechanical systems (MEMS)-based and Silicon Carbide (SiC)-based microsensor technologies that are well-suited for many applications. The suite of technologies includes hydrogen and hydrocarbon leak detection sensors; emissions sensor arrays; and high-temperature contact pads for wire bond connections. Currently used to protect astronauts on the International Space Station, the hydrogen and leak detection sensors have many Earth-based applications as well. They can function as a single-sensor unit or as part of a complete smart sensor system that includes multiple sensors, signal conditioning, power, and telemetry. The system can comprise sensors for hydrogen, hydrocarbons, oxygen, temperature, and pressure. The emissions sensor array features a gas-sensing structure that detects various combustion emission species (carbon monoxide, carbon dioxide, oxygen, hydrocarbons, and nitrogen oxides) over a wide range of concentrations. In addition, the emissions sensor array remains highly sensitive and stable while providing gas detection at temperatures ranging from 450 to 600°C. These new sensors provide a combination of responsiveness and durability that offers great value for a wide range of applications and industries.

Conventional ambient-temperature oxygen sensors are limited in various ways: optically based sensors can be expensive and challenging to manufacture; electrochemical cells with liquid electrolytes can have limited lifetimes and become leak sources; and both types of sensors are difficult to miniaturize. These problems are addressed with Glenn's novel ambient temperature oxygen microsensor, which is based on a Nafiontm polymer electrolyte, microfabricated using thin-film technologies. In the past, one drawback of Nafiontm film has been that it can lose conductivity when the moisture content in the film is too low, potentially affecting sensor operation. Glenn researchers devised a method to use certain salts to hold water molecules in the Nafiontm film structure at room temperature. The presence of these salts provides extra sites in the film to promote proton (H+) mobility, thus improving film conductivity and overall sensor performance, particularly in arid and high-temperature environments. The innovative use of metal/metal oxide as the reference electrode enables miniaturization by eliminating the reference gas and sealing the reference electrode. The combination of interdigitized electrodes with the unique metal/metal oxide reference electrode permits sensor operation in either potentiometric or amperometric mode, as appropriate. In potentiometric mode, which measures voltage differences between working and reference electrodes in different gases, the voltage differences can be monitored with a voltmeter; however, the sensor itself does not need a power source. In room-temperature testing, the sensor achieved repeatable responses to 21 percent oxygen in nitrogen (using nitrogen as a baseline gas), and also detected oxygen from 7 to 21 percent, making Glenn's breakthrough technology usable for personal health monitoring as well as fire detection, fuel-leak detection, and environmental monitoring.

Environmental Control and Life Support Systems (ECLSS) used for extended space missions must recover and process wastewater to provide potable water for crew consumption and oxygen generation. Exploration mission spacecraft will have a smaller crew than the ISS, meaning demands would typically be less than what full-featured commercial TOC analyzers are designed to provide. Current analyzer technology also has limitations and uncertainties for spaceflight integration, such as part traceability, reliability, material properties for flammability or off-gassing, software and interface that are inconsis-tent with spaceflight needs, human factors, and structural reliability. The MiniTOCA provides a compact solution to the performance demands of onboard water quality analysis for crewed exploration missions through a unique core technology process that facilitates the detection of trace organic compounds in a water sample. It utilizes an ultra-violet oxidation method to activate the dissolved oxygen in the water which results in oxidation of the organic chemicals into carbon dioxide. The carbon dioxide is then measured by a Miniature Tunable Laser Spectrometer (MTLS) by sweeping the carbon dioxide out of the water in a gas / liquid separator using nitrogen gas. This novel process allows for small system sample volumes, small overall size/mass, zero consumables, low average power con-sumption (less than 60W), projected long-life (~10 years), and reliable analytical performance – all addressing critical performance gaps within the current TOC analyzer industry. Lab and environmental testing demonstrated that the MiniTOCA’s architecture is both feasible and is excellent in performance. Potential commercial applications for the MiniTOCA include, but are not limited to, ultra-pure water (UPW) systems; remote, mobile, and distributed environmental water quality monitoring; and specialized industrial process control. Technologies comprising the device lend themselves to miniaturization and are forward leaning in exploration applications. The MiniTOCA is scheduled to be flown and imple-mented aboard the ISS in late 2025.

The OH Gas Detector combines the properties of Gas Correlation Radiometry (GCR) with Broad Band Cavity Enhanced Absorption Spectroscopy (BBCEAS) to measure the absorption of OH remotely. GCR utilizes a precise filter with a high spectral resolution that is matched to the absorption features of a specific gas. BBCEAS measures light intensity through a stable optical cavity. OH gas absorbs strongly at specific wavelengths in ultraviolet light. Using the sun as a light source, modulated sunlight is split into two, independent gas cells. One gas cell contains a vacuum and the other gas cell contains OH gas. The OH Gas Detector uses the gas cell containing OH gas as a precise bandpass filter for GCR. Due to the short lifespan and reactivity of OH gas, OH gas must be actively generated to use as a reference and only a limited amount can be generated. BBCEAS is used to increase the path length within the gas cell for a measurement to be possible using the small amount of OH gas present within the gas cell. The OH Gas Detector measures the absorption rate of each gas cell, which is ratioed to determine the remote level of OH absorption.