Tech Briefs

Formation Flying of Tethered and Nontethered Spacecraft

A paper discusses the effect of the dynamic interaction taking place within a formation composed of a rigid and a deformable vehicle, and presents the concept of two or more tethered spacecraft flying in formation with one or more separated freeflying spacecraft.

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Microwave-Spectral Signatures Would Reveal Concealed Objects

This technique should prove superior to conventional ground-probing radar. A proposed technique for locating concealed objects (especially small antipersonnel land mines) involves the acquisition and processing of spectral signatures over broad microwave frequency bands. This technique was conceived to overcome the weaknesses of older narrow-band electromagnetic techniques like ground-probing radar and low-frequency electromagnetic induction.

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Part 2 of a Computational Study of a Drop-Laden Mixing Layer

This second of three reports on a computational study of a mixing layer laden with evaporating liquid drops presents the evaluation of Large Eddy Simulation (LES)models.The LES models were evaluated on an existing database that had been generated using Direct Numerical Simulation (DNS).The DNS method and the data- tively coated thin electroactive-polymer (EAP)films be developed for use in spaceborne microwave and optical systems.

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Digital Averaging Phasemeter for Heterodyne Interferometry

One instrument performs functions for which separate instruments were previously needed. A digital averaging phasemeter has been built for measuring the difference between the phases of the unknown and reference heterodyne signals in a heterodyne laser interferometer. This phasemeter performs well enough to enable interferometric measurements of distance with accuracy of the order of 100 pm and with the ability to track distance as it changes at a speed of as much as 50 cm/s. This phasemeter is unique in that it is a single, integral system capable of performing three major functions that, heretofore, have been performed by separate systems: (1) measurement of the fractional-cycle phase difference, (2) counting of multiple cycles of phase change, and (3) averaging of phase measurements over multiple cycles for improved resolution. This phasemeter also offers the advantage of making repeated measurements at a high rate: the phase is measured on every heterodyne cycle. Thus, for example, in measuring the relative phase of two signals having a heterodyne frequency of 10 kHz, the phasemeter would accumulate 10,000 measurements per second. At this high measurement rate, an accurate average phase determination can be made more quickly than is possible at a lower rate.

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Imaging of ³-Irradiated Regions of a Crystal

Electron-trapping and photorefractive effects are exploited. A holographic technique has been devised for generating a visible display of the effect of exposure of a photorefractive crystal to γ-rays. The technique exploits the space charge that results from trapping of electrons in defects induced by  γ rays.

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Rapid Chemometric Filtering of Spectral Data

Target species would be identified in real time.   A method of rapid, programmable filtering of spectral transmittance, reflectance, or fluorescence data to measure the concentrations of chemical species has been proposed. By "programmable" is meant that a variety of spectral analyses can readily be performed and modified in software, firmware, and/or electronic hardware, without need to change optical filters or other optical hardware of the associated spectrometers. The method is intended to enable real-time identification of single or multiple target chemical species in applications that involve high-throughput screening of multiple samples. Examples of such applications include (but are not limited to) combinatorial chemistry, flow cytometry, bead assays, testing drugs, remote sensing, and identification of targets.

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Preparing and Analyzing Iced Airfoils

SmaggIce version 1.2 is a computer program for preparing and analyzing iced airfoils.It includes interactive tools for (1)measuring ice-shape characteris- tics,(2)controlled smoothing of ice shapes,(3)curve discretization,(4)gen- eration of artificial ice shapes,and (5)de- tection and correction of input errors. Measurements of ice shapes are essential for establishing relationships between characteristics of ice and effects of ice on airfoil performance.The shape-smoothing tool helps prepare ice shapes for use with already available grid-generation and computational-fluid-dynamics soft- ware for studying the aerodynamic effects of smoothed ice on airfoils.The artificial ice-shape generation tool supports para- metric studies since ice-shape parameters can easily be controlled with the artificial ice.In such studies,artificial shapes gen- erated by this program can supplement simulated ice obtained from icing re- search tunnels and real ice obtained from flight test under icing weather condition. SmaggIce also automatically detects geometry errors such as tangles or dupli- cate points in the boundary which may be introduced by digitization and provides tools to correct these.By use of interactive tools included in SmaggIce version 1.2,one can easily characterize ice shapes and prepare iced airfoils for grid genera- tion and flow simulations.

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