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At least 1,423 records · Page 79

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NASA NTRS1990

Array feeds for reflector surface distortion compensation - Concepts and implementation

The development of a compensation algorithm based on the use of array feeds and a focal-plane conjugate field approach is discussed. Results of numerical simuations performed to verify the accuracy of the computer programs are examined, and an experimental study is described. Both the numerical and experimental results show that the array will compensate for the slowly varying surface distortion. In particular, for some typical, slowly varying thermal or gravitational surface distortions, a 19-element array feed can improve the reflector performance considerably. Additionally, it is demonstrated that it will be possible to compensate for the surface distortion without actual knowledge of the distortion itself.

Rahmat-Samii, Yahya↗

NASA NTRS1990

Interagency telemetry arraying for Voyager-Neptune encounter

The reception capability of the Deep Space Network (DSN) has been improved over the years by increasing both the size and number of antennas at each complex to meet spacecraft-support requirements. However, even more aperture was required for the final planetary encounters of the Voyager 2 spacecraft. This need was met by arraying one radio astronomy observatory with the DSN complex in the United States and another with the complex in Australia. Following a review of augmentation for the Uranus encounter, both the preparation at the National Radio Astronomy (NRAO) Very Large Array (VLA) and the Neptune encounter results for the Parkes-Canberra and VLA-Goldstone arrays are presented.

Brown, D. W.↗

NASA NTRS1990

Linear laser diode arrays for improvement in optical disk recording

The development of individually addressable laser diode arrays for multitrack magneto-optic recorders for space stations is discussed. Three multi-element channeled substrate planar (CSP) arrays with output power greater than 30 mW with linear light vs current characteristics and stable single mode spectra were delivered to NASA. These devices have been used to demonstrate for the first time the simultaneous recording of eight data tracks on a 14-inch magneto-optic erasable disk. The yield of these devices is low, mainly due to non-uniformities inherent to the LPE growth that was used to fabricate them. The authors have recently developed the inverted CSP, based on the much more uniform MOCVD growth techniques, and have made low threshold quantum well arrays requiring about three times less current than the CSP to deliver 30 mW CW in a single spatial mode. The inverted CSP is very promising for use in space flight recorder applications.

Alphonse, G. A.↗

NASA NTRS1990

Reduction of solar vector magnetograph data using a microMSP array processor

The processing of raw data obtained by the solar vector magnetograph at NASA-Marshall requires extensive arithmetic operations on large arrays of real numbers. The objectives of this summer faculty fellowship study are to: (1) learn the programming language of the MicroMSP Array Processor and adapt some existing data reduction routines to exploit its capabilities; and (2) identify other applications and/or existing programs which lend themselves to array processor utilization which can be developed by undergraduate student programmers under the provisions of project JOVE.

Kineke, Jack↗

NASA NTRS1991

Performance, size, mass, and cost estimates for projected 1kW EOL Si, InP, and GaAs arrays

One method of evaluating the potential of emerging solar cell and array technologies is to compare their projected capabilities in space flight applications to those of established Si solar cells and arrays. Such an application-oriented comparison provides an integrated view of the elemental comparisons of efficiency, radiation resistance, temperature sensitivity, size, mass, and cost in combination. In addition, the assumptions necessary to make the comparisons provide insights helpful toward determining necessary areas of development or evaluation. Finally, as developments and evaluations progress, the results can be used in more precisely defining the overall potential of the new technologies in comparison to existing technologies. The projected capabilities of Si, InP, and GaAs cells and arrays are compared.

Slifer, Luther W., Jr.↗

NASA NTRS1991

Ka-band MMIC microstrip array for high rate communications

In a recent technology assessment of alternative communication systems for the space exploration initiative (SEI), Ka-band (18 to 40 GHz) communication technology was identified to meet the mission requirements of telecommunication, navigation, and information management. Compared to the lower frequency bands, Ka-band antennas offer higher gain and broader bandwidths; thus, they are more suitable for high data rate communications. Over the years, NASA has played an important role in monolithic microwave integrated circuit (MMIC) phased array technology development, and currently, has an ongoing contract with Texas Instrument (TI) to develop a modular Ka-band MMIC microstrip subarray (NAS3-25718). The TI contract emphasizes MMIC integration technology development and stipulates using existing MMIC devices to minimize the array development cost. The objective of this paper is to present array component technologies and integration techniques used to construct the subarray modules.

Lee, R. Q.↗

NASA NTRS1991

Measurement of high-voltage and radiation-damage limitations to advanced solar array performance

A description is given of the reconfigured Photovoltaic Array Space Power (PASP) Plus experiment: its objectives, solar-array complement, and diagnostic sensors. Results from a successful spaceflight will lead to a better understanding of high-voltage and radiation-damage limitations in the operation of new-technology solar arrays.

Guidice, D. A.↗

NASA NTRS1990

Characterization of tapered slot antenna feeds and feed arrays

A class of feed antennas and feed antenna arrays used in the focal plane of paraboloid reflectors and exhibiting higher than normal levels of cross-polarized radiation in the diagonal planes is addressed. A model which allows prediction of element gain and aperture efficiency of the feed/reflector system is presented. The predictions are in good agreement with experimental results. Tapered slot antenna (TSA) elements are used an example of an element of this type. It is shown that TSA arrays used in multibeam systems with small beam spacings are competitive in terms of aperture efficiency with other, more standard types of arrays incorporating waveguide type elements.

Kim, Young-Sik↗

NASA NTRS1991

An experimental SMI adaptive antenna array simulator for weak interfering signals

An experimental sample matrix inversion (SMI) adaptive antenna array for suppressing weak interfering signals is described. The experimental adaptive array uses a modified SMI algorithm to increase the interference suppression. In the modified SMI algorithm, the sample covariance matrix is redefined to reduce the effect of thermal noise on the weights of an adaptive array. This is accomplished by subtracting a fraction of the smallest eigenvalue of the original covariance matrix from its diagonal entries. The test results obtained using the experimental system are compared with theoretical results. The two show a good agreement.

Dilsavor, Ronald S.↗

NASA NTRS1990

Pupil geometry and pupil re-imaging in telescope arrays

This paper considers the issues of lateral and longitudinal pupil geometry in ground-based telescope arrays, such as IOTA. In particular, it is considered whether or not pupil re-imaging is required before beam combination. By considering the paths of rays through the system, an expression is derived for the optical path errors in the combined wavefront as a function of array dimensions, telescope magnification factor, viewing angle, and field-of-view. By examining this expression for the two cases of pupil-plane and image-plane combination, operational limits can be found for any array. As a particular example, it is shown that for IOTA no pupil re-imaging optics will be needed.

Traub, Wesley A.↗

NASA NTRS1990

256 x 256 PACE-1 PV HgCdTe focal plane arrays for medium and short wavelength infrared applications

The development of two 256 by 256 hybrid HgCdTe focal plane array (FPA) families is described, and their performance is discussed. The hybrid FPAs employ a PV HgCdTe detector array and custom Si CMOS readouts. The PACE-1 process was used to fabricate the detectors, whereby the liquid phase epitaxial growth of HgCdTe occurs on sapphire substrates buffered by a layer of CdTe. The performance characteristics of the detector arrays are given. A tactical 256 by 256 CMOS readout is tested, in which a high functional yield was achieved. Updated test results are given for a 256 by 256 readout circuit developed for use in an orbital replacement instrument for the Hubble Space Telescope. The characterizations of several MWIR and SWIR FPAs were thorough and shown to be reliable. The pixel yield, maximum FPA responsivity nonuniformity, and SWIR FPA read noise for the tests are given. The high contrast and insignificant fixed pattern noise of the imagery from the MWIR 256 by 256 FPA are emphasized. These qualities were obtained when the device was operating at 80 k and utilizing f/2 optics with an 8-in. focal length and a 4.4 micron high pass filter.

Kozlowski, L. J.↗

NASA NTRS1991

Digital array scanned interferometers for astronomy

Investigations are reported of digital array scanned interferometers (DASI) with silicon CCD array detectors to define the operational capabilities of a mapping (polarimetric) spectrometer for astronomical applications based on these instruments. For spectral mapping, spatially resolved spectra using a cylindrical lens to image in the interferometers's redundant coordinate are given. The signal-to-noise characteristics of the Fourier transformed data are demonstrated with regard to the effects of a rectangular sampling function, spectral multiplexing and the pixel-to-pixel variation of the CCD array. These data indicate that DASIs can offer simple, versatile (polarization) mapping spectrometers suitable for spectral mapping observations from the ultraviolet to the infrared of extended sources at variable spatial resolution, particularly where long term stable operation is essential, as for spacecraft instruments.

Smith, Wm. Hayden↗

NASA NTRS1991

Ka-band MMIC microstrip array for high rate communications

Lee, R. Q.↗

NASA NTRS1991

Design of an inflatable, optically controlled and fed, phased array antenna

Initial studies on the antenna requirements of the Space Exploration Initiative (SEI) system architecture have indicated the need for large, lightweight antennas. This paper discusses the design of a modular, inflatable, optically controlled and fed phased array antenna suitable for SEI aplications. When high gain antennas are required for space applications, large aperture mesh or collapsible solid antenna reflectors are considered. However, these designs are generally not lightweight, and have complicated deployment mechanisms. Alternatively, the modular, inflatable antenna design discussed here is a lightweight, modular design that incorporates a simple deployment scheme, and after deployment, can be rigidized to enhance its structural integrity. Further, the design features the fiberoptic distribution of both RF and control signals to individual microwave integrated circuit/reflector modules in each of the inflatable, phased array antenna cells. The result of combining these two technologies is a modular, phased array antenna design that is both mechanically and electrically agile and robust.

Kunath, Richard R.↗

NASA NTRS1992

Arraying Techniques In The Deep Space Network

Report discusses performances of number of techniques for combining radio signals received at several antennas to increase signal-to-noise ratio of specified weak signal bearing digital data via phase modulation. Techniques studied: symbol-stream combining, baseband combining, carrier arraying, and full-spectrum combining. Basic idea to synthesize effect of larger antenna or, equivalently, array of antennas. Called "arraying", techniques used in Space Network to extend range of reception of signals from spacecraft traveling beyond distant planets.

Mileant, Alexander↗

NASA NTRS1991

The structure and development of streamwise vortex arrays embedded in a turbulent boundary layer

An investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer was conducted. The vortices were generated by a single spanwise row of rectangular vortex generator blades. A single embedded vortex was examined, as well as arrays of embedded counter rotating vortices produced by equally spaced vortex generators. Measurements of the secondary velocity field in the crossplane provided the basis for characterization of vortex structure. Vortex structure was characterized by four descriptors. The center of each vortex core was located at the spanwise and normal position of peak streamwise vorticity. Vortex concentration was characterized by the magnitude of the peak streamwise vorticity, and the vortex strength by its circulation. Measurements of the secondary velocity field were conducted at two crossplane locations to examine the streamwise development of the vortex arrays. Large initial spacings of the vortex generators produced pairs of strong vortices which tended to move away from the wall region while smaller spacings produced tight arrays of weak vortices close to the wall. A model of vortex interaction and development is constructed using the experimental results. The model is based on the structure of the Oseen Vortex. Vortex trajectories are modelled by including the convective effects of neighbors.

Wendt, Bruce J.↗

NASA NTRS1992

Method and apparatus for phasing segmented mirror arrays

A method and an apparatus are disclosed for edge phasing an array of segments in a segmented primary telescope mirror using white light from a far field source and starting with the inner edge of each segment in the first ring of segments. The segments are individually phased for zero piston and tilt error with respect to the edge of a reference surface in the open center position of the telescope mirror. After edge phasing of all segments in the telescope mirror array is completed, full surface phasing can be achieved by using a conventional Shack-Hartmann technique followed by finding the RMS best fit for each segment of the mirror array.

Manhart, Paul K.↗

NASA NTRS1992

Ka-band feed arrays for spacecraft reflector antennas with limited scan capability: An overview

JPL and NASA are in the process of developing ground and spacecraft antenna systems at Ka-band frequencies for future deep space applications. The use of Ka-band (32-GHz down) communication will result in smaller ground and spacecraft antennas and associated equipment, and will provide larger bandwidths necessary for very high data rate communication and radio navigation. In this article, the use of a small phased array as a feed for a reflector antenna system with limited scan capability is addressed. Different feed and antenna configurations, as well as array architectures, are examined. Some theoretical and experimental parameters of a particular breadboard feed array developed by JPL and the University of Massachusetts are presented. Guidelines for the future direction of this effort are provided.

Jamnejad, V.↗