Physical Sciences

A Multifunctional Active-Excitation Spectral Analyzer

A portable, near-room-temperature instrument would optically probe chemical compositions of surfaces. A highly sensitive, low-power, low-noise multifunctional active-excitation spectral analyzer (MAESA) that would span the wavelength range of 0.5 to 2.5 µm and would operate near room temperature is undergoing development. The fully developed MAESA is expected to be a portable and highly miniaturized version of a prototype of the instrument that has been demonstrated in a laboratory. The MAESA is intended primarily for use in remote sensing of chemical compositions of mineral surfaces on planets or on Earth.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Physical Sciences


Development of Sensors for Detecting Leaks of O2 and H2

Both commercial and noncommercial sensors show promise. The Propulsion group at Dryden Flight Research Center is performing analyses of the effectiveness of chemical-species sensors for detecting and assessing leakage. The group is also studying relationships between (1) rates at which high-energy species leak from the propellant-feed systems of advanced aircraft and spacecraft and (2) the rates of leakage of inert species substituted for the high-energy species in the same systems. Several commercial sensors and a prototype noncommercial sensor have been and continue to be subjected to tests of their ability to detect their respective chemical species accurately and quickly. Analysis of the data from these tests is expected to determine whether it is possible to develop instruments capable of detecting propellant leaks over a wide range of temperature and pressure. If suitable, the instruments can be employed in various flight experiments in which there are requirements for such leak-detection capability. Analysis of data from inert- and high-energy-propellant leak testing will help in scaling leakage from gaseous propellant feed systems without the need to use high-energy propellants during subsequent leak tests.

Posted in: Briefs, Physical Sciences, Failure analysis, Sensors and actuators, Propellants, Gases, Fuel injection, Test procedures


Micromachined Emitter/Bolometer Structures for Infrared Gas Sensors

Small, inexpensive, mass-producible gas sensors would be enabled by these novel micromachined wavelength-selective emitter/bolometers.Infrared gas sensors that could be mass-produced at relatively low cost have been proposed for a variety of applications — for example, detecting carbon monoxide in air inside houses. A sensor of this type would include a housing into which ambient air could diffuse. The gas of interest would be detected via an infrared absorption measurement. The novel micromachined emitter/bolometer structure being developed is a heated strip of lithographically patterned, single-crystal silicon that will function as both an emitter of infrared radiation at a precise wavelength and as a bolometer. The emitted radiation would traverse a path within the sensor housing and would be reflected back along that path to the emitter/bolometer. In the presence of an infrared-absorbing gas, the amount of radiation returning to the emitter/ bolometer would decrease, causing the emitter/bolometer to come to thermal equilibrium at a lower temperature than it would in the absence of such a gas. The temperature-dependent electrical resistance of the emitter/bolometer would be measured and used to infer the concentration of the infrared-absorbing gas.

Posted in: Briefs, TSP, Physical Sciences, Architecture, Sensors and actuators, Air pollution, Gases


Deployable Shell Structures With Shape-Control Actuators

Hierarchical distributed control systems would effect both deployment and fine shape control. Advanced control systems that include built-in smart-material elastic-deformation structural actuators have been proposed for deployable thin-shell structures that are required to be maintained in precise shapes once deployed. This approach to structural shape control was conceived to enable the development of lightweight telescope mirrors, radar reflectors, and the like that could be stowed compactly for launching and transport, then deployed in outer space to required precise shapes at much larger dimensions (of the order of 10 m). The concept may also be applicable to similar, but probably smaller structures for terrestrial use.

Posted in: Briefs, TSP, Physical Sciences, Sensors and actuators, Smart materials


Software for Simulating Two-Phase Systems

Møtran (signifying "multi-phase transient") is a package of software for simulating flows in two-phase (gas/liquid) fluid systems like networks of such components as pipes, T junctions, pumps, evaporators, and condensers. The software is based on a two-fluid formulation that can accommodate unequal velocities and temperatures for the two phases. Møtran provides for single-phase, bubbly, slug, stratified, and annular flow regimes. Mechanistic models are used for establishing the boundaries between flow regimes and for constitutive relations that represent wall shear, interfacial shear, wall heat transfer, interfacial heat transfer, and phase change. Constitutive models are provided for each of the flow regimes, and all are selected and calculated dynamically during solution for each grid point in the network. The software is applicable at all levels of gravitation, whether steady or time varying. Møtran includes a state-of-the-art graphical user interface (GUI) and an integrated fluid-property database. The user assembles the representation of the fluid system (which can be of arbitrary topology) through drag-and-drop operations on the GUI. The software predicts pressures, volume fractions, temperatures, and velocities of the phases throughout the system.

Posted in: Briefs, Physical Sciences, Simulation and modeling, Computer software and hardware


Software for Improved Processing of DRWP Signals

The Automated Adaptive Signal Processing (AASP) computer program extracts wind data from the outputs of Doppler-radar wind profilers (DRWPs). Unlike prior software used for this purpose, AASP does not rely on manual intervention to prevent a DRWP system from locking onto and tracking interfering signals (e.g., signals from side lobes of radar beams). AASP identifies interference signals in the range-gated spectra produced by a DRWP, then tracks the height- and time-continuous atmospheric signal in each radar beam. AASP then combines the radial velocity components from three or five beams and computes the horizontal and vertical wind components. AASP produces high-quality wind profiles within a single radar cycle, without need for averaging for quality control. It also calculates an indication of the level of confidence with each wind estimate. The single-cycle capability enables users to detect temporal shifts in wind earlier and with greater confidence than was possible by use of prior software. AASP comprises two coupled software subsystems: (1) a subsystem that implements signal-processing algorithms and (2) a subsystem that provides a quality-control capability and that generates displays of spectra, of wind estimates, and of the performances of the DRWP hardware.

Posted in: Briefs, Physical Sciences, Computer software and hardware, Data acquisition and handling, Radar


Large-Aperture Telescope Synthesized From Small Mirrors

A report proposes a design concept for synthesizing a reflecting telescope with a large-aperture (diameter ≈100 m) primary mirror from a sparse arrangement of four smaller (diameter ≈10 m) primary mirrors. The telescope would be placed in orbit for viewing Earth with high resolution. The primary and secondary mirrors would be mounted on a lightweight structure that would be deployed in orbit.

Posted in: Briefs, TSP, Physical Sciences, Mirrors, Test equipment and instrumentation


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