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NASA NTRS2016

Mach Cutoff Analysis and Results from NASA's Farfield Investigation of No-Boom Thresholds

In support of the ongoing effort by the National Aeronautics and Space Administration (NASA) to bring supersonic commercial travel to the public, the NASA Armstrong Flight Research Center and the NASA Langley Research Center, in partnership with other industry organizations and academia, conducted a flight research experiment to analyze acoustic propagation in the Mach cutoff shadow zone. The effort was conducted in the fall of 2012 and named the Farfield Investigation of No-boom Thresholds (FaINT). The test helped to build a dataset that will go toward further understanding of the unique acoustic propagation characteristics below Mach cutoff altitude. FaINT was able to correlate sonic boom noise levels measured below cutoff altitude with precise airplane flight conditions, potentially increasing the accuracy over previous studies. A NASA F-18B airplane made supersonic passes such that its Mach cutoff caustic would be at varying distances above a linear 60-microphone, 7375-ft (2247.9 m) long array. A TG-14 motor glider equipped with a microphone on its wing-tip also attempted to capture the same sonic boom waves above ground, but below the Mach cutoff altitude. This paper identified an appropriate metric for sonic boom waveforms in the Mach cutoff shadow zone called Perceived Sound Exposure Level; derived an empirical relationship between Mach cutoff flight conditions and noise levels in the shadow zone; validated a safe cutoff altitude theory presented by previous studies; analyzed the sensitivity of flight below Mach cutoff to unsteady atmospheric conditions and realistic aircraft perturbations; and demonstrated the ability to record sonic boom measurements over 5000 ft (1524.0 m) above ground level, but below Mach cutoff altitude.

flight research↗

NASA NTRSDate not supplied

Development and Airborne Demonstration of the Concurrent Artificially-Intelligent Spectrometry and Adaptive Lidar System: Advancing Lidar Capabilities for the STV Observing System

We report on the design, build and planned airborne demonstration of a spaceflight-prototype Concurrent Artificially-intelligent Spectrometry and Adaptive Lidar System (CASALS). The CASALS lidar is an Adaptive Wavelength Scanning Lidar (AWSL) operating in push broom mode. The demonstration has three major goals: advance the Technical Readiness Level of the AWSL hardware, validate its measurement performance and mature algorithms and methods needed for the Surface Topography and Vegetation (STV) observing system. AWSL acquires parallel tracks of surface heights by rapidly steering a laser beam across a swath. A 1040nm-centered laser is tuned across 30nm and carved into 2-ns pulses, the pulse energy is fiber amplified and the pulses are dispersed cross-track using a non-mechanical wavelength-to-angle grating. For the spaceflight system the beam will be pointable to 1200 10m footprints across a 7km swath. For the airborne demonstration there will be 256 0.7m footprints across a 110m swath. In both cases the footprints overlap across- and along-track for uniform target illumination. For the airborne demonstration a steering mirror will increase the accessible swath width to 4km. At the receiver, solar radiation is filtered with a narrow-slit grating-spectrometer and the footprints are imaged onto a linear-mode, photon-sensitive HgCdTe APD-array. The received pulses are time-division-multiplexed to a few high-speed analog-to-digital converters to record waveforms. Spaceflight and airborne CASALS are designed to nominally detect 20 photons per pulse and, by averaging 27 overlapping footprints, achieve 2cm flat target range precision and high-quality vegetation structure waveforms The AWSL will be flown in the summer of 2024, along with a Headwall VNIR-SWIR hyperspectral sensor imaging a 4km wide swath, at NEON eddy covariance flux towers in the U.S. mid-Atlantic where high resolution hyperspectral and lidar data, acquired annually, are available for validation.

Guangning Yang↗

NASA NTRS1983

Direct and implicit optical matrix-vector algorithms

New direct and implicit algorithms for optical matrix-vector and systolic array processors are considered. Direct rather than indirect algorithms to solve linear systems and implicit rather than explicit solutions to solve second-order partial differential equations are discussed. In many cases, such approaches more properly utilize the advantageous features of optical systolic array processors. The matrix-decomposition operation (rather than solution of the simplified matrix-vector equation that results) is recognized as the computationally burdensome aspect of such problems that should be computed on an optical system. The Householder QR matrix-decomposition algorithm is considered as a specific example of a direct solution. Extensions to eigenvalue computation and formation of matrices of special structure are also noted.

Casasent, D.↗

NASA NTRS2000

Focal plane scanner with reciprocating spatial window

A focal plane scanner having a front objective lens, a spatial window for selectively passing a portion of the image therethrough, and a CCD array for receiving the passed portion of the image. All embodiments have a common feature whereby the spatial window and CCD array are mounted for simultaneous relative reciprocating movement with respect to the front objective lens, and the spatial window is mounted within the focal plane of the front objective. In a first embodiment, the spatial window is a slit and the CCD array is one-dimensional, and successive rows of the image in the focal plane of the front objective lens are passed to the CCD array by an image relay lens interposed between the slit and the CCD array. In a second embodiment, the spatial window is a slit, the CCD array is two-dimensional, and a prism-grating-prism optical spectrometer is interposed between the slit and the CCD array so as to cause the scanned row to be split into a plurality of spectral separations onto the CCD array. In a third embodiment, the CCD array is two-dimensional and the spatial window is a rectangular linear variable filter (LVF) window, so as to cause the scanned rows impinging on the LVF to be bandpass filtered into spectral components onto the CCD array through an image relay lens interposed between the LVF and the CCD array.

Mao, Chengye↗

NASA NTRS1985

Circuit transients due to negative bias arcs on a high-voltage solar array in low Earth orbit

Arcing to negatively biased, exposed solar cell interconnects on solar arrays placed in plasma environments was established. Arcing, however, may cause damaging interference with the operation of electrical power systems in spacecraft planned to be driven with high-voltage solar arrays. An analytical model was developed to estimate the effects of netagive bias arcs on solar array power system performance. Solar cell characteristics, plasma interactions, and power system features are modeled by a linear, lumped element transient circuit, and the time domain equations are solved. Numerical results for solar array common mode and load voltage transients are calculated for typical conditions. Acceptable load transients are found for a range of arc current amplitudes and time constants.

Metz, R. N.↗

NASA NTRS1994

The JPL deep-well mid-infrared array camera

We describe the development of a mid-infrared camera intended for use at the Palomar 5-m telescope and at the NASA Infrared Telescope Facility. The camera is based on Rockwell's HF-16 128x128 Si:As blocked impurity band (BIB) array. This array is unusual in that it has a well depth of approximately 30 million electrons; this will allow the use of traditional broadband astronomical filters (N and Q) while keeping a reasonable field-of-view. Measured array performance indicates that it has a read noise of 1100 electrons and shows non-linearities of less than 1% up to 65% of full well. In this paper, we discuss the array and its operating characteristics, and we give a brief overview of the camera design.

Ressler, Michael E.↗

NASA NTRS1981

Efficient structures for geosynchronous spacecraft solar arrays. Phase 1, 2 and 3

Structural concepts for deploying and supporting lightweight solar-array blankets for geosynchronous electrical power are evaluated. It is recommended that the STACBEAM solar-array system should be the object of further study and detailed evaluation. The STACBEAM system provides high stiffness at low mass, and with the use of a low mass deployment mechanism, full structural properties can be maintained throughout deployment. The stowed volume of the STACBEAM is acceptably small, and its linear deployment characteristic allows periodic attachments to the solar-array blanket to be established in the stowed configuration and maintained during deployment.

Adams, L. R.↗

NASA NTRS1993

Order-sorting filter transmittance measured with an array detector

The simultaneous measurement of the spectrally and spatially variant transmittance of a linear variable order-sorting filter in a manner that closely resembles its conditions of actual use is described. The transmittance of a prototype order-sorting filter was measured in the 400- to 880-nm wavelength region by illuminating it with the output beam of a spectrophotometer while the filter was attached to the front of a 30 x 32 pixel silicon array detector. The filter was designed to be used in the output beam of a grating spectrometer to prevent the dispersal of higher diffracted orders onto an array detector. Areas of the filter that were spatially matched to the corresponding detector pixel column had measured peak transmittances of about 90 percent that were uniform to within +/- 1.5 percent along a given column. Transmittances for incident wavelengths shorter than the desired bandpass, corresponding to the order overlap region, were measured in the 0.003 range. Line spread function measurements made with the array detector indicated no significant beam spreading caused by inserting the filter into the beam.

Heaney, James B.↗

NASA NTRS2004

A Planar Two-Dimensional Superconducting Bolometer Array for the Green Bank Telescope

In order to provide high sensitivity rapid imaging at 3.3mm (90GHz) for the Green Bank Telescope - the world's largest steerable aperture - a camera is being built by the University of Pennsylvania, NASA/GSFC, and NRAO. The heart of this camera is an 8x8 close-packed, Nyquist-sampled detector array. We have designed and are fabricating a functional superconducting bolometer array system using a monolithic planar architecture. Read out by SQUID multiplexers, the superconducting transition edge sensors will provide fast, linear, sensitive response for high performance imaging. This will provide the first ever superconducting bolometer array on a facility instrument.

Benford, Dominic↗

NASA NTRS2012

Mathematical Simulation for Integrated Linear Fresnel Spectrometer Chip

A miniaturized solid-state optical spectrometer chip was designed with a linear gradient-gap Fresnel grating which was mounted perpendicularly to a sensor array surface and simulated for its performance and functionality. Unlike common spectrometers which are based on Fraunhoffer diffraction with a regular periodic line grating, the new linear gradient grating Fresnel spectrometer chip can be miniaturized to a much smaller form-factor into the Fresnel regime exceeding the limit of conventional spectrometers. This mathematical calculation shows that building a tiny motionless multi-pixel microspectrometer chip which is smaller than 1 cubic millimter of optical path volume is possible. The new Fresnel spectrometer chip is proportional to the energy scale (hc/lambda), while the conventional spectrometers are proportional to the wavelength scale (lambda). We report the theoretical optical working principle and new data collection algorithm of the new Fresnel spectrometer to build a compact integrated optical chip.

Park, Yeonjoon↗

NASA NTRS1989

Contamination effects of GPS Navstar solar array performance

The solar arrays on Navstars 1 to 6 have been limiting the electrical power capabilities in the extended life (beyond the 5 year design life). The departure from predicted performance consists of an extra 2.5 percent per year degradation beyond the radiation model estimates. This degradation is unusual in showing a linear rather than exponential decay with time. The performance of the arrays on these satellites has been examined in order to predict future behavior and to make refined projections on the Navstar 7 to 11 solar arrays. Evidence obtained from flight experiments on Navstar 5 and 6, and from laboratory experiments, suggests that contamination of the solar arrays while on orbit may be responsible. The evidence for photo-induced contamination of spacecraft surfaces is presented, and the effect on solar array output in the case of the GPS satellites is shown to be consistent with the observed anomalies.

Marvin, Dean C.↗

NASA NTRS1975

Improved circularly polarized antenna

Antenna includes two sets of linearly polarized elements. Each set contains slots in parallel array. Sets are mutually orthogonal and are driven in phase quadrature. By changing lengths of slots or their separations, antenna beamwidth can be changed over wide range. Similar results are achieved with dipole configuration.

Van Atta, L. C.↗

NASA NTRS1982

SEASAT SAR performance evaluation study

The performance of the SEASAT synthetic aperture radar (SAR) sensor was evaluated using data processed by the MDA digital processor. Two particular aspects are considered the location accuracy of image data, and the calibration of the measured backscatter amplitude of a set of corner reflectors. The image location accuracy was assessed by selecting identifiable targets in several scenes, converting their image location to UTM coordinates, and comparing the results to map sheets. The error standard deviation is measured to be approximately 30 meters. The amplitude was calibrated by measuring the responses of the Goldstone corner reflector array and comparing the results to theoretical values. A linear regression of the measured against theoretical values results in a slope of 0.954 with a correlation coefficient of 0.970.

Source record↗

NASA NTRS1981

A failure mechanism in adaptive arrays

The steady-state behavior of an adaptive array is considered and the degradation of its output SNR in the presence of jammers is analyzed. It is shown that for given incident powers (of jammers and signal), there are geometric configurations of the sources exciting the array for which the SNR degradation is much more pronounced than for other configurations. This result is proved for the case where the thermal noise power of each array receiver is negligible compared to the total power intercepted by the array from each jammer. The result is general, being valid for an array of n arbitrary antennae in an arbitrary three-dimensional configuration. It is stated in terms of linear dependence relationships among the n-dimensional vectors that describe the effects of the sources on the array.

Zohar, S.↗

NASA NTRS1989

Digital optical spark chambers

The authors constructed and tested a prototype digital readout system for optical spark chambers using a linear, solid-state charge-coupled-device detector array. Position resolution of 0.013 mm (sigma) over a 25-cm field of view has been demonstrated. It is concluded that this technique should permit the construction of economical, lightweight and low-power trajectory hodoscopes for use in cosmic-ray instrumentation on balloons and in spacecraft.

Evenson, Paul↗

NASA NTRS1991

The Small Explorer power system electronics

The power system electronics for the NASA Goddard Space Flight Center Small Explorer Satellites are intended to satisfy various planned missions. The selected topology is a direct energy transfer (DET) system with the battery connected directly to the bus. The shunt control technique is a linear sequential full shunt which provides a simple solar array interface and can support both 3 axis stabilized and spinner satellites. In addition, it can meet stringent electromagnetic interference requirements which are expected on some Small Explorer Missions. The Power Systems Electronics (PSE) performs battery charge control using both temperature compensated charge/discharge ratio ampere hour integration and voltage-temperature control. The PSE includes all the circuits needed to perform telemetry and command functions using an optical MIL-STD-1773 interface.

Dakermanji, G.↗

NASA NTRS1994

BMDO photovoltaics program overview

This is an overview of the Ballistic Missile Defense Organization (BMDO) Photovoltaic Program. Areas discussed are: (1) BMDO advanced Solar Array program; (2) Brilliant Eyes type satellites; (3) Electric propulsion; (4) Contractor Solar arrays; (5) Iofee Concentrator and Cell development; (6) Entech linear mini-dome concentrator; and (7) Flight test update/plans.

Caveny, Leonard H.↗

NASA NTRS1994

A Navier-Strokes Chimera Code on the Connection Machine CM-5: Design and Performance

We have implemented a three-dimensional compressible Navier-Stokes code on the Connection Machine CM-5. The code is set up for implicit time-stepping on single or multiple structured grids. For multiple grids and geometrically complex problems, we follow the 'chimera' approach, where flow data on one zone is interpolated onto another in the region of overlap. We will describe our design philosophy and give some timing results for the current code. A parallel machine like the CM-5 is well-suited for finite-difference methods on structured grids. The regular pattern of connections of a structured mesh maps well onto the architecture of the machine. So the first design choice, finite differences on a structured mesh, is natural. We use centered differences in space, with added artificial dissipation terms. When numerically solving the Navier-Stokes equations, there are liable to be some mesh cells near a solid body that are small in at least one direction. This mesh cell geometry can impose a very severe CFL (Courant-Friedrichs-Lewy) condition on the time step for explicit time-stepping methods. Thus, though explicit time-stepping is well-suited to the architecture of the machine, we have adopted implicit time-stepping. We have further taken the approximate factorization approach. This creates the need to solve large banded linear systems and creates the first possible barrier to an efficient algorithm. To overcome this first possible barrier we have considered two options. The first is just to solve the banded linear systems with data spread over the whole machine, using whatever fast method is available. This option is adequate for solving scalar tridiagonal systems, but for scalar pentadiagonal or block tridiagonal systems it is somewhat slower than desired. The second option is to 'transpose' the flow and geometry variables as part of the time-stepping process: Start with x-lines of data in-processor. Form explicit terms in x, then transpose so y-lines of data are in-processor. Form explicit terms in y, then transpose so z-lines are in processor. Form explicit terms in z, then solve linear systems in the z-direction. Transpose to the y-direction, then solve linear systems in the y-direction. Finally transpose to the x direction and solve linear systems in the x-direction. This strategy avoids inter-processor communication when differencing and solving linear systems, but requires a large amount of communication when doing the transposes. The transpose method is more efficient than the non-transpose strategy when dealing with scalar pentadiagonal or block tridiagonal systems. For handling geometrically complex problems the chimera strategy was adopted. For multiple zone cases we compute on each zone sequentially (using the whole parallel machine), then send the chimera interpolation data to a distributed data structure (array) laid out over the whole machine. This information transfer implies an irregular communication pattern, and is the second possible barrier to an efficient algorithm. We have implemented these ideas on the CM-5 using CMF (Connection Machine Fortran), a data parallel language which combines elements of Fortran 90 and certain extensions, and which bears a strong similarity to High Performance Fortran. We make use of the Connection Machine Scientific Software Library (CMSSL) for the linear solver and array transpose operations.

Jespersen, Dennis C.↗