Physical Sciences

Narrowband Tunable Optical Filter Using Fiber Bragg Gratings

Research at Langley Research Center has developed a special fiber- Bragg grating optical filter for use in aircraft or spaceborne differential absorption lidar (DIAL) systems for measuring water vapor in the atmosphere of the Earth. The filter is an optical fiber containing two Bragg gratings that afford high reflectance in 10-pm-wide wavelength bands at wavelengths of 946.0 and 949.5 nm. The optical fiber would be glued to a piezoelectric ceramic, to which a voltage could be applied to stretch the gratings and thereby adjust their peak-reflection wavelengths to correspond to atmospheric water vapor lines of interest. The concept of multiple Bragg gratings in a single optical fiber tuning such gratings by stretching the fiber is not new. The novelty of this research lies partly in the application of these concepts to make tunable ultra-narrowband filters for the specific water vapor wavelengths in question. Another element of novelty in the proposal lies in the design of the DIAL instrument in which the filters would be used: The design calls for a unique optical receiver that would couple a lidar signal from a telescope to a filter of the type proposed, then using an optical circulator the light would be detected.

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Temperature-Compensation Method for High-Temperature Strain Gauges

Strain gauge and temperature-compensation element are exposed to the same temperature. A relatively simple and inexpensive method of fabricating a temp- erature-compensation element for high- temperature strain gauges has been devised. This element, connected in the adjacent arm of a Wheatstone bridge, provides temperature compensation for an active strain gauge attached to the substrate. A method for accurately measuring structural static strains in harsh environments is an important requirement for future flight research of hypersonic vehicles and ground test articles. Sturdy, flight-worthy strain sensors must be developed for attachment to superalloys, new composite materials, and thermal-protection systems. With little deviation from standard Rokide flame-spray installation procedures, preliminary tests indicate viable data can be produced to operating temperatures of at least 1,700 °F (927 °C).

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System for Detecting Hazardous Gases at Multiple Locations

The Hazardous Gas Detection System 2000 (HGDS 2000) is the latest in a series of instrumentation systems for detecting gases leaking from a space shuttle on a launch pad. The HGDS is a fully redundant system that includes analog and digital electronic control circuitry and a sub- system for sampling gases at multiple locations and delivering the samples to two independent commercial quadrupole mass spectrometers. [The sampling subsystem was described in “System for Delivering Gas Samples to Multiple Instruments” (KSC-12123), NASA Tech Briefs, Vol. 25, No. 6 (June 2001), page 60.] The system is rugged enough to withstand the launch-pad environment, is easy to operate, and can be fully automated. When in automated operation, the system notifies an operator if an unusual situation or a fault is detected. An operator interacts with the system via a personal computer by use of mouse and keyboard commands. Operation of the HGDS 2000 is expected to take substantially smaller amounts of operators’ time and to cost substantially less, relative to operation of the older instrumentation systems in this series. Although the HGDS 2000 is optimized for detecting leaking spacecraft-propellant gases, it can also be used to detect many other gases.

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Advanced Hardware and Software for Monitoring Contamination

Sensor readings can be viewed both locally and remotely. An instrumentation system measures the concentrations of three principal contaminants (nonvolatile residue, hydrocarbon vapor, and particle fallout) in real time. The system includes a computer running special-purpose application software that makes it possible to connect the system into a network (which can, in turn, be connected to the Internet) to enable both local and remote display and analysis of its readings. The system was developed for use in a Kennedy Space Center facility that was required to be maintained at a specified high degree of cleanliness for processing a spacecraft payload that was highly sensitive to contamination. The system is also adaptable to monitoring contamination in other facilities and is an example of an emerging generation of sophisticated instrumentation systems that communicate data with other equipment.

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Making Hydrogen by Electrolysis of Methanol

The cost is about half that of making hydrogen by electrolysis of water. Scientists at NASA's Jet Propulsion Laboratory are developing apparatuses for electrolysis of methanol to produce pure hydrogen for use at industrial sites, in scientific laboratories, and in fuel cells. The state-of-the-art onsite hydrogen generators now in use are based on electrolysis of water to produce hydrogen, with oxygen as a byproduct that has no commercial value in this context. The developmental methanol electrolyzers consume less than half the electrical energy of water electrolyzers in producing a given amount of hydrogen. Even when the cost of methanol is included, the cost of producing hydrogen by electrolysis of methanol is still only about half that of producing hydrogen by electrolysis of water.

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Miniature NMR Spectrometers Without Magnets

These spectrometers would be used to characterize ferromagnetic minerals. Miniature, lightweight nuclear-magnetic-resonance (NMR) spectrometers suitable for characterizing ferromagnetic minerals in the field are undergoing development. In previously developed miniature NMR spectrometers, more than half the weight is contributed by permanent magnets. The present developmental miniature NMR spectrometers can be made much lighter because they do not contain permanent magnets: Unlike other NMR spectrometers, they are designed to operate without applied magnetic fields; instead, they exploit the natural magnetic fields of the mineral phases to be studied.

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Aircraft-Mounted Cloud-Water-Content Probe

This relatively simple instrument contains no heater or pump. An aircraft-mounted instrument for high- resolution, in situ measurement of the abundances of liquid water and ice in clouds is undergoing development. This instrument is intended to overcome the dis- advantages of instruments developed previously for the same purpose. The disadvantages include various combinations of complexity, dependence on heaters and/or pumps, insensitivity to ice crystals, or dependence on droplet/crystal size. The present instrument is relatively simple, does not include a heater or a pump, and is expected (when fully developed) to be sensitive to both water droplets and ice crystals of any size.

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