Tech Briefs

Improved High-Voltage Gas Isolator for Ion Thruster

A report describes an improved highvoltage isolator for preventing electrical discharge along the flow path of a propellant gas being fed from a supply at a spacecraft chassis electrical potential to an ion thruster at a potential as high as multiple kilovolts. The isolator must survive launch vibration and must remain electrically nonconductive for thousands of hours under conditions that, in the absence of proper design, would cause formation of electrically conductive sputtered metal, carbon, and/or decomposed hydrocarbons on its surfaces.

Posted in: Briefs, TSP, Physical Sciences, High voltage systems, High voltage systems, Propellants, Gases, Insulation, Fuel injection, Spacecraft
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Hybrid Mobile Communication Networks for Planetary Exploration

A paper discusses the continuing work of the Mobile Exploration System Project, which has been performing studies toward the design of hybrid communication networks for future exploratory missions to remote planets. A typical network could include stationary radio transceivers on a remote planet, mobile radio transceivers carried by humans and robots on the planet, terrestrial units connected via the Internet to an interplanetary communication system, and radio relay transceivers aboard spacecraft in orbit about the planet. Prior studies have included tests on prototypes of these networks deployed in Arctic and desert regions chosen to approximate environmental conditions on Mars. Starting from the findings of the prior studies, the paper discusses methods of analysis, design, and testing of the hybrid communication networks. It identifies key radio-frequency (RF) and network engineering issues. Notable among these issues is the study of wireless LAN throughput loss due to repeater use, RF signal strength, and network latency variations. Another major issue is that of using RF-link analysis to ensure adequate link margin in the face of statistical variations in signal strengths.

Posted in: Briefs, Electronics & Computers, Design processes, Architecture, Internet, Radio equipment, Wireless communication systems, Architecture, Internet, Radio equipment, Wireless communication systems, Spacecraft
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Recirculation of Laser Power in an Atomic Fountain

Optical and electronic subsystems of a frequency standard can be simplified.

A new technique for laser-cooling atoms in a cesium atomic fountain frequency standard relies on recirculation of laser light through the atom-collection region of the fountain. The recirculation, accomplished by means of reflections from multiple fixed beam-splitter cubes, is such that each of two laser beams makes three passes. As described below, this recirculation scheme offers several advantages over prior designs, including simplification of the laser system, greater optical power throughput, fewer optical and electrical connections, and simplification of beam power balancing.

Posted in: Briefs, TSP, Physical Sciences, Lasers, Lasers
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Recirculation of Laser Power in an Atomic Fountain

Optical and electronic subsystems of a frequency standard can be simplified.

A new technique for laser-cooling atoms in a cesium atomic fountain frequency standard relies on recirculation of laser light through the atom-collection region of the fountain. The recirculation, accomplished by means of reflections from multiple fixed beam-splitter cubes, is such that each of two laser beams makes three passes. As described below, this recirculation scheme offers several advantages over prior designs, including simplification of the laser system, greater optical power throughput, fewer optical and electrical connections, and simplification of beam power balancing.

Posted in: ptb catchall, Tech Briefs, Briefs, Photonics, Lasers, Lasers, Cooling
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Simplified Generation of High-Angular-Momentum Light Beams

Inherent properties of a WGM resonator and optical fiber are exploited.

A simplified method of generating a beam of light having a relatively high value of angular momentum (see figure) involves the use of a compact apparatus consisting mainly of a laser, a whispering-gallery-mode (WGM) resonator, and optical fibers. The method also can be used to generate a Bessel beam. (“Bessel beam” denotes a member of a class of non-diffracting beams, so named because their amplitudes are proportional to Bessel functions of the radii from their central axes. High-order Bessel beams can have high values of angular momentum.)

Posted in: ptb catchall, Tech Briefs, Briefs, Photonics, Fiber optics, Lasers, Fiber optics, Lasers, Performance upgrades, Acoustics, Acoustics
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Complex Type-II Interband Cascade MQW Photodetectors

Multiple active subregions, each optimized for a different color, would enable multicolor operation.

Multiple-quantum-well (MQW) photodetectors of a proposed type would contain active regions comprising multiple superlattice subregions. These devices would have complex structures: The superlattice of each subregion would be designed for enhanced absorption of photons in a desired wavelength band (typically in the infrared) and multiple subregions of different design would be cascaded for multicolor operation.

Posted in: ptb catchall, Tech Briefs, Briefs, Photonics, Architecture, Optics, Sensors and actuators, Architecture, Optics, Sensors and actuators, Product development
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Interferometric Quantum-Nondemolition Single-Photon Detectors

These detectors would function independently of frequency.

Two interferometric quantum-nondemolition (QND) devices have been proposed: (1) a polarization-independent device and (2) a polarization-preserving device. The prolarization-independent device works on an input state of up to two photons, whereas the polarization-preserving device works on a superposition of vacuum and single-photon states. The overall function of the device would be to probabilistically generate a unique detector output only when its input electromagnetic mode was populated by a single photon, in which case its output mode would also be populated by a single photon.

Posted in: ptb catchall, Tech Briefs, Briefs, Photonics, Measurements, Lasers, Lasers
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Ring-Down Spectroscopy for Characterizing a CW Raman Laser

Parameters of operation can be obtained from a single ring-down scan.

A relatively simple technique for characterizing an all-resonant intracavity continuous- wave (CW) solid-state Raman laser involves the use of ring-down spectroscopy. As used here, “characterizing” signifies determining such parameters as threshold pump power, Raman gain, conversion efficiency, and quality factors (Q values) of the pump and Stokes cavity modes.

Posted in: ptb catchall, Tech Briefs, Briefs, Photonics, Calibration, Lasers, Spectroscopy, Lasers, Spectroscopy
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Advances in Measurement of Skin Friction in Airflow

This system implements a combination of established experimental techniques and advanced image processing.

The surface interferometric skin-friction (SISF) measurement system is an instrument for determining the distribution of surface shear stress (skin friction) on a wind-tunnel model. The SISF system utilizes the established oil-film interference method, along with advanced image-data-processing techniques and mathematical models that express the relationship between interferograms and skin friction, to determine the distribution of skin friction over an observed region of the surface of a model during a single wind-tunnel test.

Posted in: Briefs, Test & Measurement, Mathematical models, Test equipment and instrumentation, Wind tunnel tests, Aerodynamics
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Calibration Test Set for a Phase-Comparison Digital Tracker

Four equal-amplitude signals are generated at selectable phase increments of 0.1°.

An apparatus that generates four signals at a frequency of 7.1 GHz having precisely controlled relative phases and equal amplitudes has been designed and built. This apparatus is intended mainly for use in computer-controlled automated calibration and testing of a phase-comparison digital tracker (PCDT) that measures the relative phases of replicas of the same Xband signal received by four antenna elements in an array. (The relative direction of incidence of the signal on the array is then computed from the relative phases.) The present apparatus can also be used to generate precisely phased signals for steering a beam transmitted from a phased antenna array.

Posted in: Briefs, TSP, Electronics & Computers, Calibration, Antennas, Antennas, Test equipment and instrumentation
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