Tech Briefs

System Measures Optical Spectrum Components While Preserving Spatial Detail of Object Surface

An imaging spectrograph system performs data analysis with no need for a frame grabber or PC. Conventional commercial spectrometers or spectrophotometers are usually able to measure optical spectrum from a specified surface area at one point. This is done either with one detector scanning the spectrum in narrow wavelength bands or with an array detector, in which case all the spectral components are acquired at once. If one desires to measure the spectrum at several spatial locations of the specified surface, the target under examination or the measuring instrument has to be mechanically scanned.

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Reconditioned Test Equipment as a Key Driver in Reducing Life Cycle Support Costs

Previously owned test and measurement equipment has been purchased for over 50 years by the United States military, agencies of the Federal gov- ernment, and prime contractors that support these organizations. Yet, despite the significant amount of previously owned equipment purchased regularly, there are very few guidelines (either official or understood) for the research and procurement of this equipment. There are many reasons why an engineer or organization may choose to procure previously owned test equipment assets; however, they are generally one or all of the following: Need to save money. Need to save time over delivery of a new asset. Need to replace with an exact model/configuration that is no longer available as new. Electronic Test Equipment — commonly referred to in the military as TMDE (Test, Measurement and Diagnostic Equipment) or GPETE (General Purpose Electronic Test Equipment) — has been a key component in the lifecycle management of electronic systems since the earliest communication systems were deployed in field, air, and shipboard programs. Today, this equipment continues to play a valuable role in maintaining operational readiness for our military services. In many cases, when a new system is being deployed or repair is required to an existing one, the engineer and/or procurement official will have the option of purchasing new test equipment or previously owned. The availability of previously owned equipment in these cases is usually correlated to the degree in which the equipment is new, cuttingedge technology usually found in design work. The vast majority of federal and military projects, however, typically involve manufacturing, maintenance, or production that relies on “proven” previously deployed and tested technology. Hence, there is usually adequate supply of previously owned equipment. If this is the case, the decision to purchase new or used may be influenced by budget or urgency. Purchasing previously owned equipment may end up costing less than 50% of the list price of the new asset, and may be delivered more quickly. However, there are factors that would-be purchasers of previously owned equipment should keep in mind: Search for the model within one’s own company/organization. If it is not available inside the department or organization and you choose to procure previously owned equipment, always know your source. Specifically, who is guaranteeing quality, warranty, and right of return? The best way to procure this asset is through an informal bidding process where only bona fide test equipment dealers are invited to compete. Do not allow substitutions unless it is clearly understood that the asset will work as configured. If delivery is the main issue, make sure the asset is definitely available from the dealer and that the manufacturer/distributor is unable to expedite delivery. Avoid buying from end users directly, as there are hidden costs that make this an unacceptable choice for anyone other than organizations with complete evaluation, calibration, and repair facilities. Because military systems evolve and, in many cases, have their operational life extended, the original test systems must still be available and maintainable. Today, two factors combine to make system support more difficult. First, the lifespan of military systems is being extended as the government struggles with the dual budget pressures of being squeezed by rising personnel costs and being hit by massive increases in the acquisition cost of new systems. Therefore, in many cases, the procedures to test older systems are based on test equipment that, if removed, must be replaced with product that is a form, fit, and function substitution, or proper system functionality will be at serious risk, requiring a software rewrite and a complete system re-validation. Second, product lifecycles are shortening even as the move to Commercial Off the Shelf (COTS) equipment accelerates. Manufacturers are not stocking spares for long-term support to the extent they did in the past. This makes test equipment harder to support and maintain. The manufacturer’s solution may be to supply a replacement instrument. Before integrating such a replacement instrument, the support facility must consider the switching costs carefully, including physical size and weight, power consumption, cooling requirements, electrical specifications, programming language and interface, and software drivers. Replacing an instrument in a test system with anything other than an original piece of equipment requires engineering expertise, not only in the understanding of the original test procedure, but also the characteristics of the original Device Under Test (DUT) and the specifications and capabilities of the original instrument. So what are the alternatives when a critical system needs to be replicated, repaired, or made more reliable and maintainable? The answer lies in the use of “exact replacement” instruments that are drawn from a broad pool of existing products in the commercial and government sectors. By applying a rigorous inspection, evaluation, and reconditioning process, existing instruments can be brought up to “new” standards with a useful life equal to the original. In most cases, it is possible to source a broad range of exact replacement equipment from the secondary market supply chain. There are many suppliers in this chain that operate refurbishing programs that can bring an existing malfunctioning unit up to the condition and specifications of a new unit, making it a “zero time” product that performs as if it were a new item. Reconditioned instruments provide a viable and cost-effective way to extend the life of existing support systems. Using products from the commercial and government secondary market also allows significant cost savings in current and future maintenance requirements. This article was written by Peter Ostrow, President and CEO of TestMart/NAVICPmart, San Bruno, CA. For more information, visit www.navicpmart.com.

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Wedge Heat-Flux Indicators for Flash Thermography

Wedge indicators have been proposed for measuring thermal radiation that impinges on specimens ill- uminated by flash lamps for thermographic inspection. Heat fluxes measured by use of these indicators would be used, along with known thermal, radiative, and geometric properties of the specimens, to estimate peak flash temperatures on the specimen surfaces. These indicators would be inexpensive alternatives to high-speed infrared pyrometers, which would otherwise be needed for measuring peak flash surface temperatures. The wedge is made from any suitable homogenous material such as plastic. The choice of material is governed by the equation given below. One side of the wedge is covered by a temperature sensitive compound that decomposes irreversibly when its temperature exceeds a rated temperature (Trated). The uncoated side would be positioned alongside or in place of the specimen and exposed to the flash, then the wedge thickness (d) at the boundary between the white and blackened portions measured. The heat flux (Q) would then be estimated by Q = (cρ/εb)(Trated–Tambient)d, where c and ρ are the specific heat and mass density, respectively, of the wedge material; εb is the emissivity of the black layer of the sheet material, and Tambient is the ambient temperature.

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Earth-Space Link Attenuation Estimation via Ground Radar Kdp

A method of predicting attenuation on microwave Earth/ spacecraft comm- unication links, over wide areas and under various atmospheric conditions, has been developed. In the area around the ground station locations, a nearly horizontally aimed polarimetric S-band ground radar measures the specific differential phase (Kdp) along the Earthspace path. The specific attenuation along a path of interest is then computed by use of a theoretical model of the relationship between the measured S-band specific differential phase and the specific attenuation at the frequency to be used on the communication link. The model includes effects of rain, wet ice, and other forms of precipitation. The attenuation on the path of interest is then computed by integrating the specific attenuation over the length of the path. This method can be used to determine statistics of signal degradation on Earth/spacecraft communication links. It can also be used to obtain real-time estimates of attenuation along multiple Earth/spacecraft links that are parts of a communication network operating within the radar coverage area, thereby enabling better management of the network through appropriate dynamic routing along the best combination of links.

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Update on Area Production in Mixing of Supercritical Fluids

The paper “Turbulence and Area Production in Binary-Species, Super- critical Transitional Mixing Layers” presents a more recent account of the research sum- marized at an earlier stage in “Area Production in Super- critical, Transitional Mixing Layers” (NPO-30425), NASA Tech Briefs, Vol. 26, No. 5 (May 2002) page 79. The focus of this research is on supercritical C7H16/N2 and O2/H2 mixing layers undergoing transitions to turbulence. The C7H16/N2 system serves as a simplified model of hydrocarbon/air systems in gasturbine and diesel engines; the O2/H2 system is representative of liquid rocket engines. One goal of this research is to identify ways of controlling area production to increase disintegration of fluids and enhance combustion in such engines. As used in this research, “area production” signifies the fractional rate of change of surface area oriented perpendicular to the mass-fraction gradient of a mixing layer. In the study, a database of transitional states obtained from direct numerical simulations of the aforementioned mixing layers was analyzed to investigate global layer characteristics, phenomena in regions of high density-gradient magnitude (HDGM), irreversible entropy production and its relationship to the HDGM regions, and mechanisms leading to area production.

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Dyakonov-Perel Effect on Spin Dephasing in n-Type GaAs

A paper presents a study of the contribution of the Dyakonov-Perel (DP) effect to spin dephasing in electron-donor-doped bulk GaAs in the presence of an applied steady, moderate magnetic field perpendicular to the growth axis of the GaAs crystal. (The DP effect is an electron-wave- vectordependent spin-state splitting of the conduction band, caused by a spin/orbit interaction in a crystal without an inversion center.) The applicable Bloch equations of kinetics were constructed to include terms accounting for longitudinal optical and acoustic phonon scattering as well as impurity scattering. The contributions of the aforementioned scattering mechanisms to spin-dephasing time in the presence of DP effect were examined by solving the equations numerically. Spin-dephasing time was obtained from the temporal evolution of the incoherently summed spin coherence. Effects of temperature, impurity level, magnetic field, and electron density on spin-dephasing time were investigated. Spin-dephasing time was found to increase with increasing magnetic field. Contrary to predictions of previous simplified treatments of the DP effect, spin-dephasing time was found to increase with temperature in the presence of impurity scattering. These results were found to agree qualitatively with results of recent experiments.

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Continuous Tuning and Calibration of Vibratory Gyroscopes

Vibrational excitation is periodically switched between orthogonal axes to derive calibration data. A method of control and operation of an inertial reference unit (IRU) based on vibratory gyroscopes provides for continuously repeated cycles of tuning and calibration. The method is intended especially for application to an IRU containing vibratory gyroscopes that are integral parts of microelectromechanical systems (MEMS) and that have cloverleaf designs, as described in several previous NASA Tech Briefs articles. The method provides for minimization of several measures of spurious gyroscope output, including zero-rate offset (ZRO), angle random walk (ARW), and rate drift. These benefits are afforded both at startup and thereafter during continuing operation, in the presence of unknown rotation rates and changes in temperature.

Posted in: Mechanics, Briefs, TSP

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