Physical Sciences

Mars-Optimized Solar Cells

NASA’s Jet Propulsion Laboratory, Pasadena, California

Commercial triple junction solar cell designs were modified in their junction thicknesses, contact grid densities, and anti-reflective (AR) coating thicknesses to better match the Mars surface solar spectrum. Resulting cells show up to approximately 8% relative improvement in efficiency under the Mars solar spectrum, compared to non-optimized space solar cells, in testing performed at JPL.

Posted in: Briefs, Physical Sciences, Solar energy
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Alternating Magnetic Field Forces for Satellite Formation Flying

John F. Kennedy Space Center, Florida

Orbiting a large number of satellites in fixed formations will be critical to many future space missions, especially large-scale interferometers, telescopes, antennas, and gravity wave detectors. Consequently, extensive research has been devoted over the last 20 years to formation flying architectures, concentrating not only on the mission objective, but also on the technologies required to achieve a stable satellite formation. Several proposals have been suggested for determining the location of the satellites, but the more difficult problem is developing a system that can hold the satellites at those desired locations and orientations. The two most common solutions are to use microthrusters, though these require propellant and will eventually be depleted, or to choose orbital patterns that minimize relative perturbations, but for highly precise positioning, this is not adequate. Neither of these approaches solves the problem for long-duration missions such as a multi-element telescope where the mirrors must be located and oriented to a tolerance less than an optical wavelength.

Posted in: Briefs, TSP, Physical Sciences, Flight management systems, Flight management systems, Satellites
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Thermal Materials Protect Priceless Personal Keepsakes

Thermal protection technology used on the shuttles keeps valuables safe from fire.

Most of us cannot comprehend the task of building something to withstand temperatures over 4,000 °F, but NASA can. The space shuttles endured such temperatures when returning to Earth’s atmosphere because of aerodynamic heating, or heating due to the combination of compression and surface friction from Earth’s atmosphere. For the vehicle to survive these conditions, NASA constructed a complex thermal protection system (TPS) for the exterior of the shuttle.

Posted in: Articles, Materials, Physical Sciences, Fire
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Nanosensor/Cellphone Hybrid for Detecting Chemicals and Concentrations

Based on solid-state technology, the sensor requires no reagents and can be refreshed with an ultraviolet diode.

Ames Research Center, Moffett Field, California

Nanosensors have been developed for chemical detection using carbon nanotubes (CNTs). Unlike other chemical sensors, this solid-state approach requires no reagents and can be refreshed with a solid-state ultraviolet (UV) diode. The sensors possess high sensitivity (ppbv), fast response (≈2 s), high selectivity, low power (μW), and very small size (1 cm2 or less based on advanced miniaturization), and they are ideally suited for integration with wireless networks or cellphone type devices.

Posted in: Briefs, Physical Sciences, Sensors, Sensors and actuators, Sensors and actuators, Chemicals
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Coated or Doped Carbon Nanotube Network Sensors as Affected by Environmental Parameters

Applications include medical diagnostics, gas leak detection, and homeland security and defense.

Ames Research Center, Moffett Field, California

Chemical sensors have been developed over the past decades to detect gases and vapors at various concentration levels for deployment in a wide range of industrial applications. The detection usually centers on a change of a particular property or status of the sensing material, such as temperature, electrical, and optical characteristics. Other types of sensors include electrochemical cells, conducting polymer sensors, surface acoustic wave sensors, and catalytic bead sensors. Sensors based on nanotechnology promise to provide improved performance on all of these sensors compared to current micro and macro sensors.

Posted in: Briefs, Physical Sciences, Sensors, Sensors and actuators, Sensors and actuators, Chemicals, Gases
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Regenerable Internal CO Scrubber for Hydrogen Sensors

A guard electrode would protect the sensing electrode to maintain sensor sensitivity toward hydrogen.

Lyndon B. Johnson Space Center, Houston, Texas

Amperometric electrochemical sensors are commonly used for the detection of carbon monoxide (CO) and hydrogen (H2) in air. The electrochemistry of heterogeneous CO and H2 oxidations is similar enough that the sensors show significant cross-sensitivities between the two gases. Thus, in applications where H2 is being monitored in the presence of CO, amperometric hydrogen sensors will produce false positive responses due to the presence of CO. This error is further aggravated by the fact that the sensor’s response to CO is typically at least twice that for hydrogen on a volumetric basis. Furthermore, chronic CO exposure will poison or fatigue the H2 sensor electrodes and reduce the sensor sensitivity toward hydrogen.

Posted in: Briefs, Physical Sciences, Sensors, Sensors and actuators, Sensors and actuators, Carbon monoxide
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Nanostructure Sensor Determines Presence and Concentration of a Target Molecule in Fluid

This sensing system works with resonant frequencies.

Ames Research Center, Moffett Field, California

Several methods are presently being developed to sense the presence of a target molecule in small or modest concentration in a fluid. However, estimation of the concentration of the target molecule is unavailable where the fluid is substantially motionless relative to the sensor, in part because the fluid in equilibrium will have substantially the same concentration everywhere.

Posted in: Briefs, Physical Sciences, Sensors, Sensors and actuators, Sensors and actuators
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Floating Ultrasonic Transducer Inspection System for Nondestructive Evaluation

Langley Research Center, Hampton, Virginia

This floating ultrasonic transducer inspection system is based on a “momentary touching” scheme wherein the ultrasonic transducer is in contact with the structure being scanned for a relatively short time while performing the measurement. A vibrating element is a fundamental component, allowing the probe to lift up and down quickly over the surface being scanned. The measurement duty cycle would be long enough to acquire the data. Using this configuration reduces the coefficient of friction significantly by more than 95% based on the measurement duty cycle.

Posted in: Briefs, Physical Sciences, Sensors, Inspections, Non-destructive tests
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Multiplexer for Multiple Sensors in a Vacuum Chamber

The multiplexer reduces the number of required feedthroughs and ports.

John F. Kennedy Space Center, Florida

Vacuum chamber testing at large facilities can require hundreds of instruments, necessitating even more feedthroughs. The number of instruments and sensors that can be fed into a vacuum chamber is limited by the number of feedthrough ports dedicated to instrumentation. Thus high-pin-count, mil-spec-style feedthroughs have been developed, but these are all custom-made and also expensive to make and replace. The high-pin-count feedthroughs also make it much harder to troubleshoot individual wires in case of a problem. By using a multiplexer within the vacuum chamber, the number of wires required per instrument can be reduced to much less than one. The multiplication of wires from within a vacuum chamber allows a drastic increase in sensor and instrumentation channel count, while using the same number of sensor ports and feedthroughs within an existing vacuum system.

Posted in: Briefs, TSP, Physical Sciences, Sensors, Sensors and actuators, Sensors and actuators
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Miniaturized Schottky Diode Sensors for Hydrogen and Hydrocarbon Detection at High Temperatures

The sensors have application in fuel leak detection, environmental monitoring, fire detection, security monitoring, and engine emission monitoring.

John H. Glenn Research Center, Cleveland, Ohio

A miniaturized Schottky diode hydrogen and hydrocarbon sensor with the structure of catalytic metal-metal oxide-silicon carbide (SiC) has been developed. The major innovation of this work is the use of the metal oxide, palladium oxide (PdOx), as a barrier layer between the catalytic metal and the SiC in the gas-sensing structure. A major advantage of adding a PdOx barrier layer between the gate metal and the SiC is to prevent and alleviate chemical reactions between the gate metal and the SiC. Without the PdOx barrier layer, the gate metal and the substrate can easily form metal silicides at high temperature, leading to diode structure disruption. The metal oxide barrier layer can be incorporated into a gas-sensing structure by standard deposition techniques in a controlled manner. This oxide naturally forms with Pd in Pd-based gas sensor systems and can disrupt the gas sensor structure when formed in situ in an uncontrolled manner. However, purposely including this oxide in the Schottky barrier structure produces a stable barrier layer that enables a stable and sensitive gas sensor structure.

Posted in: Briefs, Physical Sciences, Sensors, Sensors and actuators, Sensors and actuators, Exhaust emissions, Fire detection
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