Physical Sciences

Delta-Doped CCDs as Detector Arrays in Mass Spectrometers

Improved performance is obtained with reduced size, mass, and power. Delta-doped, back-illuminated charge-coupled devices (CCDs) are used as detector arrays in high-performance double- focusing miniature mass spectrometers of Mattauch-Herzog design (described below). The uses of delta-doped CCD detector arrays eliminates the need for microchannel plates (MCPs) and the high-voltage power supplies, that, heretofore, have been used in detection schemes in mass spectrometers; this makes it possible to reduce the sizes, masses, and power demands of mass spectrometers. The use of delta-doped CCDs enables the direct and simultaneous measurement of ions with different masses separated along the focal plane.

Posted in: Physical Sciences, Briefs, TSP

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Array of Bolometers for Submillimeter-Wavelength Operation

This is a prototype of arrays for astrophysical imaging and photometry. A feed-horn-coupled monolithic array of micromesh bolometers is undergoing development for use in a photometric camera. The array is designed for conducting astrophysical observations in a wavelength band centered at 350 μm. The bolometers are improved versions of previously developed bolometers comprising metalized Si3N4 micromesh radiation absorbers coupled with neutron-transmutation-doped Ge thermistors. Incident radiation heats the absorbers above a base temperature, changing the electrical resistance of each thermistor. In the present array of improved bolometers (see figure), the thermistors are attached to the micromesh absorbers by indium bump bonds and are addressed by use of lithographed, vapor-deposited electrical leads. This architecture reduces the heat capacity and minimizes the thermal conductivity to 1/20 and 1/300, respectively, of earlier versions of these detectors, with consequent improvement in sensitivity and speed of response.

Posted in: Physical Sciences, Briefs, TSP

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Optimal Calibration of the Spitzer Space Telescope

A document discusses the focal-plane calibration of the Spitzer Space Telescope by use of the instrument pointing frame (IPF) Kalman filter, which was described in “Kalman Filter for Calibrating a Telescope Focal Plane” (NPO-40798), NASA Tech Briefs, Vol. 30, No. 9 (September 2006), page 62. To recapitulate: In the IPF Kalman filter, optimal estimates of both engineering and scientific focal-plane parameters are obtained simultaneously, using data taken in each focal-plane survey activity. The IPF Kalman filter offers greater efficiency and economy, relative to prior calibration practice in which scientific and engineering parameters were estimated by separate teams of scientists and engineers and iterated upon each other. In the Spitzer Space Telescope application, the IPF Kalman filter was used to calibrate 56 frames for precise telescope pointing, estimate >1,500 parameters associated with focal-plane mapping, and process calibration runs involving as many as 1,338 scientific image centroids. The final typical survey calibration accuracy was found to be 0.09 arc second. The use of the IPF Kalman filter enabled a team of only four analysts to complete the calibration processing in three months. An unanticipated benefit afforded by the IPF Kalman filter was the ability to monitor health and diagnose performance of the entire end-to-end telescope- pointing system.

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Integral Radiator and Storage Tank

Weight and volume are reduced. A simplified, lightweight system for dissipating heat of a regenerative fuel- cell system would include a heat pipe with its evaporator end placed at the heat source and its condenser end integrated into the wall of the regenerative fuel cell system gas-storage tanks. The tank walls act as heat-radiating surfaces for cooling the regenerative fuel cell system. The system was conceived for use in outer space, where radiation is the only physical mechanism available for transferring heat to the environment. The system could also be adapted for use on propellant tanks or other large-surface-area structures to convert them to space heat-radiating structures.

Posted in: Physical Sciences, Briefs, TSP

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Compensation for Phase Anisotropy of a Metal Reflector

A multilayer dielectric coating would introduce an opposing phase anisotropy. A method of compensation for the polarization-dependent phase anisotropy of a metal reflector has been proposed. The essence of the method is to coat the reflector with multiple thin alternating layers of two dielectrics that have different indices of refraction, so as to introduce an opposing polarization- dependent phase anisotropy.

Posted in: Physical Sciences, Briefs, TSP

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Multispectral Imager With Improved Filter Wheel and Optics

“Dead” time is reduced substantially, relative to prior systems of the same type. Figure 1 schematically depicts an improved multispectral imaging system of the type that utilizes a filter wheel that contains multiple discrete narrow-band-pass filters and that is rotated at a constant high speed to acquire images in rapid succession in the corresponding spectral bands. The improvement, relative to prior systems of this type, consists of the measures taken to prevent the exposure of a focal-plane array (FPA) of photodetectors to light in more than one spectral band at any given time and to prevent exposure of the array to any light during readout. In prior systems, these measures have included, variously the use of mechanical shutters or the incorporation of wide opaque sectors (equivalent to mechanical shutters) into filter wheels. These measures introduce substantial “dead” times into each operating cycle — intervals during which image information cannot be collected and thus incoming light is wasted. In contrast, the present improved design does not involve shutters or wide opaque sectors, and it reduces dead times substantially.

Posted in: Physical Sciences, Briefs, TSP

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High-Resolution, Wide-Field-of-View Scanning Telescope

Narrow-angle scanning over a wide field would be achieved without slewing the entire telescope. A proposed telescope would afford high resolution over a narrow field of view (<0.10°) while scanning over a total field of view nominally 16° wide without need to slew the entire massive telescope structure. The telescope design enables resolution of a 1-m-wide object in a 50-km-wide area of the surface of the Earth as part of a 200-km-wide area field of view monitored from an orbit at an altitude of 700 km. The conceptual design of this telescope could also be adapted to other applications — both terrestrial and extraterrestrial — in which there are requirements for telescopes that afford both wide- and narrow-field capabilities.

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