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All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Spatially coherent radiation from an array of GaAs lasers

Spatially coherent radiation from a monolithic array of three homostructure GaAs lasers is reported. The three lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent beam formation makes use of the Fourier transformation property of the internal lenses. The transverse mode control is performed by a spatial filter. The optical peak power at room temperature of the device was measured to be 5 W, three times the power of a single laser in the array. From the synthesized far-field distribution which was evaluated, we conclude that the laser radiation is of spatial coherence.

Philipp-Rutz, E. M.↗
NASA NTRS1981

Conceptual performance of a satellite borne, wide swath synthetic aperture radar

A satellite borne synthetic aperture radar can image a wide swath in the order of 700 km with one-look 100-m resolution. If the design meets the ambiguity constraints at the far edge of the swath, the maximum swath width is independent of both radar wavelength and shape of the physical antenna aperture. The antenna pattern can be a pencil beam scanned in the elevation plane, or a fan beam formed by a long antenna. The scanning pencil beam antenna may be a phased array or multiple-feed reflector which may be more practical than a long antenna to image a wide swath. Design performance trade computations are presented involving resolution, swath width, antenna area, average transmitter power and digital data rate.

Tomiyasu, K.↗
NASA NTRS1991

A high radiometric performance CCD for the third generation stratospheric aerosol and gas experiment

A third-generation SAGE instrument is about to be designed as part of the NASA Earth Observational System. Previous instruments have used individual diodes as detectors. The new instrument will use a custom design CCD to dramatically enhance the study of the gas and aerosol components of the upper atmosphere. The CCD is a 3 by 400 imaging array that has a single serial register and an exposure control drain. It will be used at the focal plane of a spectrometer covering the spectral range from 288 nm to 1.02 micron.

Delamere, Alan↗
NASA NTRS2008

[The Extrasolar Planetary Imaging Coronagraph]

The Extrasolar Planetary Imaging Coronagraph (EPIC) is a proposed NASA Exoplanet Probe mission to image and characterize extr asolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC will provide insights into the physical nature of a variety of planets in other solar systems complimenting radial velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets identified by radial velocity surveys, deter mine orbital inclinations and masses, characterize the atmospheres around A and F type stars which cannot be found with RV techniques, and observe the inner spatial structure and colors of debris disks. EPIC has a heliocentric Earth trailing drift-away orbit, with a 5 year mission lifetime (5 year goal). The robust mission design is simple and flexible ensuring mission success while minimizing cost and risk. The science payload consists of a heritage optical telescope assembly (OTA), and visible nulling coronagraph (VNC) instrument. The instrument achieves a contrast ratio of 10(exp 9) over a 4.84 arcsecond field-of-view with an unprecedented inner working angle of 0.14 arcseconds over the spectral range of 440-880 nm. The telescope is a 1.65 meter off-axis Cassegrain with an OTA wavefront error of /9, which when coupled to the VNC greatly reduces the requirements on the large scale optics, compressing them to stability requirements within the relatively compact VNC optical chain. The VNC features two integrated modular nullers, a spatial filter array (SFA) and an E2V-L3 photon counting CCD. Direct null control is accomplished from the science focal plane mitigating against complex wavefront and amplitude sensing and control strategies.

Clampin, Mark↗
NASA NTRS1993

Morphological Changes in the NGC 6251 Jet

The giant radio galaxy NGC 6251 is a particularly good object for observational tests of relativistic jet models. Due to its high declination and similar 0.5 Jy radio nucleus, high quality VLBI images of the central regions of the source can be made with northern hemisphere arrays. In addition, the large-scale radio morphology strongly suggests that the radio axis lies close to the plane of the sky, so Doppler boosting should be less extreme than in the core-dominated superluminal sources. Earlier 18-cm VLBI observations of NGC 6251 revealed an unexpectedly large jet/counterjet brightness ratio and small transverse motion of a feature in the parsec-scale jet. These early results are difficult to reconcile with the simplest symmetric relativistic jet models.

Wehrle, A. E.↗
NASA NTRS1984

Singular value decomposition with systolic arrays

Systolic arrays for determining the singular value decomposition of a mxn, m n, matrix A of bandwidth w are presented. After A has been reduced to bidiagonal form B by means of Givens plane rotations, the singular values of B are computed by the Golub-Reinsch iteration. The products of plane rotations form the matrices of left and right singular vectors. Assuming each processor can compute or supply a plane rotation, O(wn) processors accomplish the reduction to bidiagonal form in O(np) steps, where p is the number of superdiagonals. A constant number of processors then determines each singular value in about 6n steps. The singular vectors are computed by rerouting the rotations through the arrays used for the reduction to bidiagonal form, or else along the way by employing another rectangular array of O(wm) processors.

Ipsen, I. C. F.↗
NASA NTRS2014

The X-ray Integral Field Unit (X-IFU) for Athena

Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload consists of a large aperture high angular resolution X-ray optics (2 m2 at 1 keV) and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), oering 2.5 eV spectral resolution, with approximately 5" pixels, over a field of view of 5' in diameter. In this paper, we present the X-IFU detector and readout electronics principles, some elements of the current design for the focal plane assembly and the cooling chain. We describe the current performance estimates, in terms of spectral resolution, effective area, particle background rejection and count rate capability. Finally, we emphasize on the technology developments necessary to meet the demanding requirements of the X-IFU, both for the sensor, readout electronics and cooling chain.

X-ray↗
NASA NTRS1979

Non-linear phenomena in films of solar arrays

The paper assesses nonlinear effects in films which are associated with the instability of their shape as a result of contractions during longitudinal and transverse in-plane oscillations. The following problems are solved analytically: transverse in-plane oscillations, longitudinal oscillations in films of rotating solar sail, transverse in-plane oscillations in films of a rotating solar sail, and effect of damping in films of a rotating solar sail. The reason for damping lies in the loss of kinetic energy during absorption of the film particles by root wrinkles without reflection (absolutely inelastic shock).

Zak, M.↗
NASA NTRS1983

Integrating indium antimonide linear arrays at 65K and below

A schematic is presented of a simplified electronic architecture of experimental 128 element infrared imager. Tables are given of sample diode responsivity, 512 element focal plane performance summary, and 128 element FPA mechanical and electrical characteristics. Typical 43 x 43 micron detector IV characteristics at 84 K are given, along with typical 43 x 43 micron Indium Antimonide CV characteristic at 83 K.

Bailey, Gary C.↗
NASA NTRS2002

The 12x32 Pop-Up Bolometer Array for the SHARC II Camera

SHARC II is a 350 micron facility camera for the Caltech Submillimeter Observatory (CSO) expected to come on-line in 2002. The key component of SHARC II is a 12x32 array of doped silicon 'pop-up' bolometers developed at NASA/Goddard and delivered to Caltech in March 2002. Each pixel is 1 mm x 1 mm, coated with a 400 Omega/square bismuth film, and located lambda/4 above a reflective backshort to maximize radiation absorption. The pixels cover the focal plane with greater than 95% filling factor. Each doped thermistor occupies nearly the full area of the pixel to minimize 1/f noise. We report some results from the first cold measurements of this array. The bolometers were located inside a dark cover, and 4x32 pixels were read simultaneously. In the best 25% of winter nights on Mauna Kea, SHARC II is expected to have an NEFD at 350 microns of 1 Jy s(sup 1/2) or better.

Dowell, C. Darren↗
NASA NTRS1983

Directivity of planar array feeds for satellite reflector applications

Array-fed reflector antennas are used extensively in today's contour and multiple beam satellite antennas. To determine the directivity of these antennas theoretically, the total radiated power of the array feed must be accurately computed. In this paper, a closed-form expression for the radiated power is obtained for arrays with the well-known (cos theta q-type element patterns. The formulation is general, and takes into account polarization, nonsymmetric E- and H-plane element patterns, nonuniform element spacings and arbitrary complex excitation coefficients. Selective numerical data are presented to demonstrate the usefulness of this result. Comparisons are made with the available results obtained using direct numerical integration techniques, and with other available data based on less general formulations. Excellent agreement is observed for all cases. In particular, data are presented on the directivity of seven-element cluster feeds used in multiple beam designs, and an array feed for producing a contour beam covering the United States Eastern Time Zone (ETZ).

Rahmat-Samii, Y.↗
NASA NTRS2001

Microshutter Arrays for the NGST NIRSpec

We are developing a programmable multiobject field selector for the NGST NIRSpec. This device is a microshutter array, a close-packed 2000 x 2000 array of 100 micrometer x 100 micrometer shutters fabricated with Micro-ElectroMechanical Systems (MEMS) technologies. The shutters are opened using a magnet scanned over the array. The shutters are held open by electrostatic potentials on adjacent vertical electrodes. Modeling of the magnetic actuation of the microshutters allowed optimization of the magnetic field configuration, the distance between magnet and shutters, and the force and torque produced by the magnet. The results of laboratory tests are consistent with our modeling. We have demonstrated actuation, latching and addressing. We are able to rotate shutters out of the plane up to 90 degree and more, to latch them electrostatically to the walls and release them selectively. During the last six month all critical elements of the array have been demonstrated. Fabrication processes were developed to deposit vertical electrodes on support grid side walls and insulated light-shields that block the gaps between shutters and the support grid. Physical optics analysis was performed to assess the expected optical performance of the microshutters. A preliminary Fourier optics analysis on the microshutter array performance has been carried out. More detailed analysis of wave propagation through 3D structures is a next step. An optical test station for verifying optical parameters of the shutter array at room temperature has been developed. It allows to measure parameters, such as transmission, scattering, contrast ratio, and diffraction of the array structure. Initial data have been acquired and are being analyzed and compared to theoretical predictions.

Moseley, Harvey↗
NASA NTRS2003

Step Free Surface Heteroepitaxy of 3C-SiC Layers on Patterned 4H/6H-SiC Mesas and Cantilevers

Most SiC devices are implemented in homoepitaxial films grown on 4H/6H-SiC wafers with surfaces 3 degrees to 8 degrees off-axis from the (0001) basal plane. This approach has not prevented many substrate crystal defects from propagating into SiC epilayers, and does not permit the realization of SiC heteropolytype devices. This presentation describes recent advances in SiC epitaxial growth that begun to overcome the above shortcomings for arrays of mesas patterned into on-axis 4H/6H-SiC wafers. First, we demonstrated that atomic-scale surface steps can be completely eliminated from 4H/6H-SiC mesas via on-axis homoepitaxial step-flow growth, forming (0001) basal plane surfaces (up to 0.4 mm x 0.4 mm) for larger than previously thought possible. Step-free surface areas were then extended by growth fo thin lateral cantilevers from the mesa tops. These lateral cantilevers enabled substrate defects to be reduced and relocated in homoepitaxial films in a manner not possible with off-axis SiC growth. Finally, growth of vastly improved 3C-SiC heterofilms was achieved on 4H/6H-SiC mesas using the recently develop step-free surface heteroepitaxy process. These epitaxial growth developments should enable improved homojunction and heterojunction silicon carbide prototype devices.

Neudeck, Philip G.↗
NASA NTRS1996

Programmable Multiresolution CMOS Active Pixel Sensor

CMOS active pixel sensors (APS) allow the flexibility of placing signal processing circuitry on the imaging focal plane. The multiresolution CMOS APS can perform block averaging on-chip to eliminate the off-chip software intensive image processing. This 128 x 128 APS array can be read out at any user-defined resolution by configuring a set of digital shift registers. The resolution frame rate is 30 Hz with higher rates for all other image resolutions.

APS↗
NASA NTRS1979

New dominance characteristics for the multivariable Nyquist array method

Three new dominance characteristics are introduced to the multivariable Nyquist array methods. The first characteristic utilizes a conformal mapping procedure to establish a new set of bands in the 'image' plane to assist in feedback gain selection and stability assessment. The second characteristic uses the 'image' band concept to provide a theoretical foundation for finite frequency dominance considerations, thus removing the restrictive requirement of dominance for all s on the Nyquist D contour. The third characteristic provides for the sharing of system dominance among the feedback control loops. The dominance sharing concept may be used to establish dominance and/or to improve the dominance condition in prespecified feedback loops.

Leininger, G. G.↗
NASA NTRS1980

Solar power satellite offshore rectenna study

Offshore rectennas are feasible and cost competitive with land rectennas but the type of rectenna suitable for offshore use is quite different from that specified in the present reference system. A nonground plane design minimizes the weight and greatly reduces the number of costly support towers. This perferred design is an antenna array consisting of individually encapsulated dipoles with reflectors or tagis supported on feed wires. Such a 5 GW rectenna could be built at a 50 m water depth site to withstand hurricane, winter storm, and icing conditions for a one time cost of $5.7 billion. Subsequent units would be about 1.3 less expensive. More benign and more shallow water sites would result in substantially lower costs. The major advantage of an offshore rectenna is the removal of microwave radiation from populated areas.

Source record↗
NASA NTRS1977

A system definition study for the Advanced Meteorological Temperature Sounder (AMTS)

The functional requirements of Exhibit A (11) were used as the baseline for the conceptual design of a fixed grating out of plane multidetector spectrometer for the Space Shuttle application. Because the grating instrument would be large and the 28 element detector array would be difficult to cool radiatively from a free flying spacecraft and because increasing the spectral resolution of the grating instrument would be difficult in an instrument of reasonable size, a parallel study of a Nichelson interferometer spectrometer was undertaken. This type of instrument offers compact size, fewer detectors to cool, and the possibility of increased spectral resolution. The design and performance parameters of both the grating and interferometer approaches are described. The tradeoffs involved in comparing the two systems for sounding applications are discussed.

Source record↗
NASA NTRS1984

Solar reflection from interacting and shadowing cloud elements

An attempt is made to relate the reflection from a broken cloud field to that from a plane parallel cloud of the same optical properties by using Monte Carlo simulations for a very simple model of an array of regularly spaced, infinitely long bar clouds. Reflection from the array is represented by an effective cloud fraction, and it is shown that for many cases this may be obtained by treating the cloud elements to be noninteracting azimuthally symmetric reflectors. The effective cloud fraction is a function of solar zenith angle, the aspect ratio of the individual cloud elements, and the normal or zenith cloud fraction of the array. Model computations for reflection from an array of randomly distributed identical cylinders are also presented as an example of a possible application of this technique.

HARSHVARDHAN↗