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Near-Infrared Cameras Indicate Signature of Water on the Moon

InGaAs shortwave infrared (SWIR) cameras Sensors Unlimited, Goodrich Corp. Princeton, NJ 609-520-0610 www.sensorsinc.comShortwave infrared (SWIR) cameras from Sensors Unlimited were instrumental in NASA’s LCROSS mission to find water on the Moon. The cameras were selected for the mission more than three years ago, and were integrated into the imaging payload of the shepherding spacecraft.

Posted in: Application Briefs, Sensors, Optics, Water, Spacecraft

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Insulation-Testing Cryostat With Lifting Mechanism

Cryogenic-insulation specimens can be tested reliably under typical conditions of use. The figure depicts selected aspects of an apparatus for testing thermal-insulation materials for cryogenic systems at temperatures and under vacuum or atmospheric conditions representative of those encountered in use. This apparatus, called “Cryostat-100,” is based on the established cryogen-boil-off calorimeter method, according to which the amount of heat that passes through an insulation specimen to a cryogenic fluid in a container, and thus the effective thermal conductance of the specimen, is taken to be proportional to the amount of the cryogenic fluid that boils off from the container.

Posted in: Briefs, Physical Sciences, Insulation, Materials properties, Test equipment and instrumentation

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Optical Testing of Retroreflectors for Cryogenic Applications

Commercial uses include cryogenic metrology on aerospace structures and optical metrology instrumentation. A laser tracker (LT) is an important coordinate metrology tool that uses laser interferometry to determine precise distances to objects, points, or surfaces defined by an optical reference, such as a retroreflector. A retroreflector is a precision optic consisting of three orthogonal faces that returns an incident laser beam nearly exactly parallel to the incident beam. Commercial retroreflectors are designed for operation at room temperature and are specified by the divergence, or beam deviation, of the returning laser beam, usually a few arcseconds or less. When a retroreflector goes to extreme cold (≈35 K), however, it could be anticipated that the precision alignment between the three faces and the surface figure of each face would be compromised, resulting in wavefront errors and beam divergence, degrading the accuracy of the LT position determination.

Posted in: Briefs, Physical Sciences, Lasers, Optics, Test equipment and instrumentation

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Measuring Cyclic Error in Laser Heterodyne Interferometers

Amplitude modulation, instead of phase modulation, associated with displacement oscillations is measured. An improved method and apparatus have been devised for measuring cyclic errors in the readouts of laser heterodyne interferometers that are configured and operated as displacement gauges. The cyclic errors arise as a consequence of mixing of spurious optical and electrical signals in beam launchers that are subsystems of such interferometers. The conventional approach to measurement of cyclic error involves phase measurements and yields values precise to within about 10 pm over air optical paths at laser wavelengths in the visible and near infrared. The present approach, which involves amplitude measurements instead of phase measurements, yields values precise to about ≈0.1 pm — about 100 times the precision of the conventional approach.

Posted in: Briefs, TSP, Physical Sciences, Finite element analysis, Measurements, Lasers

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Self-Referencing Hartmann Test for Large-Aperture Telescopes

Full aperture testing of large-aperture telescopes is performed without the need for an equally large-aperture autocollimating flat.A method is proposed for end-toend, full aperture testing of large-aperture telescopes using an innovative variation of a Hartmann mask. This technique is practical for telescopes with primary mirrors tens of meters in diameter and of any design. Furthermore, it is applicable to the entire optical band (near IR, visible, ultraviolet), relatively insensitive to environmental perturbations, and is suitable for ambient laboratory as well as thermal-vacuum environments. The only restriction is that the telescope optical axis must be parallel to the local gravity vector during testing.

Posted in: Briefs, TSP, Physical Sciences, Optics, Test procedures

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Measuring a Fiber-Optic Delay Line Using a Mode-Locked Laser

Fractional error is no more than about 3 × 10–6. The figure schematically depicts a laboratory setup for determining the optical length of a fiber-optic delay line at a precision greater than that obtainable by use of optical time-domain reflectometry or of mechanical measurement of length during the delay-line-winding process. In this setup, the delay line becomes part of the resonant optical cavity that governs the frequency of oscillation of a mode-locked laser. The length can then be determined from frequency- domain measurements, as described below.

Posted in: Briefs, Physical Sciences, Measurements, Fiber optics, Lasers

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Compact, Reliable EEPROM Controller

This controller prevents inadvertent writes in an EEPROM. A compact, reliable controller for an electrically erasable, programmable readonly memory (EEPROM) has been developed specifically for a space-flight application. The design may be adaptable to other applications in which there are requirements for reliability in general and, in particular, for prevention of inadvertent writing of data in EEPROM cells.

Posted in: Briefs, Semiconductors & ICs, Computer software and hardware, Electronic control units, Semiconductors, Reliability, Spacecraft

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