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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 667 records · Page 37
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NASA NTRSDate not supplied

NOR Flash Memory Scrubbing Application for Boot File Preservation of NASA’s Descent and Landing Computer (DLC)

Progress on NASA’s Safe and Precise Landing Integrated Capabilities Evolution (SPLICE) project continues, specifically with this development of the Descent and Landing Computer (DLC). One of the DLC’s primary contributions as a SPLICE technology is its implementation of algorithms and operation of sensors to autonomously guide a spacecraft in performing more precise and safer landings on celestial bodies such as the Moon and Mars [1]. The second iteration of the DLC is known as the Engineering Test Unit (ETU) and one of its desired functionalities is the ability to preserve the fidelity of the system’s boot file through the use of memory scrubbing [2]. The ETU has two primary boards, one for housing a Multi-Processor System on a Chip (MPSoC) and the other for housing a Xilinx Kintex Ultrascale FPGA*. To emulate a memory scrubbing function implemented on the ETU’s FPGA board, the design and testing of a software application was performed on a Xilinx KCU105 FPGA evaluation board. The memory scrubbing application had to meet certain key criteria such as (1) properly utilize with the flash memory’s Serial Peripheral Interface (SPI) to read, write, and erase flash memory properly, (2) be able to detect arbitrarily large or small amounts of bit-errors, (3) be able to correct all detected errors, and (4) perform memory scrubbing indefinitely and autonomously. A prototype implementation was constructed and tested, demonstrating successful detection and correction of bit errors in multiple configurations. In the form of burst errors or singular bit flips, and in amounts of errors ranging from one to fifteen (per 256 Bytes), the application was successful in preserving memory fidelity.

Flash memory↗
NASA NTRS1973

The application of VLB interferometry to earth measurements

Results of a four-phase development of capability in very long-baseline interferometry (VLBI) at the Smithsonian Astrophysical Observatory (SAO) are summarized. The objectives of the VLBI program at SAO are to: (1) develop the capability to collect, process, and analyze VLBI data; (2) determine experimentally the accuracy now attainable with VLBI and, within the constraints imposed by this accuracy, initiate a program of VLBI observations for geophysical applications; (3) identify all significant error sources and devise means for eliminating or correcting these errors; and (4) develop a long range plan for applying VLBI techniques to a program of earth physics measurements.

Michelini, R. D.↗
NASA NTRS1985

Analysis and quantification of errors in the geometric correction of satellite images

The quantitative use of remote sensing satellite images in many applications requires that the geometric distortion inherent in these images be corrected, or rectified, to a desired map projection. The most widely used technique relies on ground control points to empirically determine a mathematical coordinate transformation to correct the geometry. In this paper, using the method of least squares, expressions for the accuracy of the geometric transformation and of the rectification of the satellite image to a map projection are derived. Explicit relations between the global accuracy of the transformation and the number, location, and local accuracy of the ground control points are obtained. The results are applied to the correction of a Landsat MSS image.

Ford, G. E.↗
NASA NTRS1993

Updating finite element dynamic models using an element-by-element sensitivity methodology

A sensitivity-based methodology for improving the finite element model of a given structure using test modal data and a few sensors is presented. The proposed method searches for both the location and sources of the mass and stiffness errors and does not interfere with the theory behind the finite element model while correcting these errors. The updating algorithm is derived from the unconstrained minimization of the squared L sub 2 norms of the modal dynamic residuals via an iterative two-step staggered procedure. At each iteration, the measured mode shapes are first expanded assuming that the model is error free, then the model parameters are corrected assuming that the expanded mode shapes are exact. The numerical algorithm is implemented in an element-by-element fashion and is capable of 'zooming' on the detected error locations. Several simulation examples which demonstate the potential of the proposed methodology are discussed.

Farhat, Charbel↗
NASA NTRSDate not supplied

The Spectral Information Based Angular Correction Methodology for Satellite Intercalibration Applications

Satellite inter-calibration often requires collocated observations with minimized discrepancies in sun-view angles, observation times, and sensor characteristics. The collocation criteria directly impact achievable inter-calibration accuracy. Addressing potential angular mismatches in inter-calibration samples is critical but not as fully recognized and addressed as spatial-temporal mismatches in many studies. To achieve high-accuracy corrections for errors due to mismatched sun-view geometry angles, an angular correction algorithm has been developed for the Climate Absolute Radiance and Refractivity Observatory Pathfinder (CPF) mission. This algorithm uses spectral correlation relationships to estimate differences in spectral radiances measured at different angles. This methodology can be extended for inter-calibrations between sensors measuring band radiances across a broad spectral region. We demonstrate its application in reducing angular mismatch errors between collocated measurements of multi-spectral imaging sensors, using the inter-calibration between the Moderate Resolution Imaging Spectrometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) as an example. The angular correction allows for more relaxed collocation criteria so that more satellite-based inter-calibration samples can be utilized. Furthermore, implementing the angular correction algorithm improves inter-calibration accuracy in applications where angular mismatch errors have not been explicitly addressed previously.

Wan Wu↗
NASA NTRS1973

Digital rectification of ERTS multispectral imagery

Rectified ERTS multispectral imagery have been produced utilizing all digital techniques, as the first step toward producing precision corrected imagery. Errors arising from attitude and ephemeris sources have been corrected, and the resultant image is represented in a meter/meter mapping utilizing an intensity resampling technique. Early results from available data indicate negligible degradation of the photometric and resolution properties of the source data as a consequence of the geometric correction process. Work utilizing ground control points to produce precision rectified imagery, and including photometric corrections resulting from available sensor calibration data, is currently in progress.

Rifman, S. S.↗
NASA NTRS1981

Ionospheric propagation correction modeling for satellite altimeters

The theoretical basis and avaliable accuracy verifications were reviewed and compared for ionospheric correction procedures based on a global ionsopheric model driven by solar flux, and a technique in which measured electron content (using Faraday rotation measurements) for one path is mapped into corrections for a hemisphere. For these two techniques, RMS errors for correcting satellite altimeters data (at 14 GHz) are estimated to be 12 cm and 3 cm, respectively. On the basis of global accuracy and reliability after implementation, the solar flux model is recommended.

Nesterczuk, G.↗
NASA NTRS1996

Correction of WindScat Scatterometric Measurements by Combining with AMSR Radiometric Data

The Seawinds scatterometer on the advanced Earth observing satellite-2 (ADEOS-2) will determine surface wind vectors by measuring the radar cross section. Multiple measurements will be made at different points in a wind-vector cell. When dense clouds and rain are present, the signal will be attenuated, thereby giving erroneous results for the wind. This report describes algorithms to use with the advanced mechanically scanned radiometer (AMSR) scanning radiometer on ADEOS-2 to correct for the attenuation. One can determine attenuation from a radiometer measurement based on the excess brightness temperature measured. This is the difference between the total measured brightness temperature and the contribution from surface emission. A major problem that the algorithm must address is determining the surface contribution. Two basic approaches were developed for this, one using the scattering coefficient measured along with the brightness temperature, and the other using the brightness temperature alone. For both methods, best results will occur if the wind from the preceding wind-vector cell can be used as an input to the algorithm. In the method based on the scattering coefficient, we need the wind direction from the preceding cell. In the method using brightness temperature alone, we need the wind speed from the preceding cell. If neither is available, the algorithm can work, but the corrections will be less accurate. Both correction methods require iterative solutions. Simulations show that the algorithms make significant improvements in the measured scattering coefficient and thus is the retrieved wind vector. For stratiform rains, the errors without correction can be quite large, so the correction makes a major improvement. For systems of separated convective cells, the initial error is smaller and the correction, although about the same percentage, has a smaller effect.

Song, S.↗
NASA NTRS1994

Partial pressure analysis in space testing

For vacuum-system or test-article analysis it is often desirable to know the species and partial pressures of the vacuum gases. Residual gas or Partial Pressure Analyzers (PPA's) are commonly used for this purpose. These are mass spectrometer-type instruments, most commonly employing quadrupole filters. These instruments can be extremely useful, but they should be used with caution. Depending on the instrument design, calibration procedures, and conditions of use, measurements made with these instruments can be accurate to within a few percent, or in error by two or more orders of magnitude. Significant sources of error can include relative gas sensitivities that differ from handbook values by an order of magnitude, changes in sensitivity with pressure by as much as two orders of magnitude, changes in sensitivity with time after exposure to chemically active gases, and the dependence of the sensitivity for one gas on the pressures of other gases. However, for most instruments, these errors can be greatly reduced with proper operating procedures and conditions of use. In this paper, data are presented illustrating performance characteristics for different instruments and gases, operating parameters are recommended to minimize some errors, and calibrations procedures are described that can detect and/or correct other errors.

Tilford, Charles R.↗
NASA NTRS2004

Ensemble Data Mining Methods

Ensemble Data Mining Methods, also known as Committee Methods or Model Combiners, are machine learning methods that leverage the power of multiple models to achieve better prediction accuracy than any of the individual models could on their own. The basic goal when designing an ensemble is the same as when establishing a committee of people: each member of the committee should be as competent as possible, but the members should be complementary to one another. If the members are not complementary, Le., if they always agree, then the committee is unnecessary---any one member is sufficient. If the members are complementary, then when one or a few members make an error, the probability is high that the remaining members can correct this error. Research in ensemble methods has largely revolved around designing ensembles consisting of competent yet complementary models.

Oza, Nikunj C.↗
NASA NTRS2004

What is data assimilation really solving, and how is the calculation actually done?

Data assimilation is a procedure in which observations are combined with models. The observations correct model errors on the one hand, and the models extrapolate the data information in space, time, and among different properties on the other. The result of assimilation is generally a more complete and more accurate description of the state of the modeled system than those obtained by either observations or model simulations alone. However, data assimilation is not a panacea for correcting every model error or for compensating all deficiencies of observations.

smoother↗
NASA NTRS1991

Correction of magnetooptic device phase errors in optical correlators through filter design modifications

We address the problem of optical phase errors in an optical correlator introduced by the input and filter plane spatial light modulators. Specifically, we study a laboratory correlator with magnetooptic spatial light modulator (MOSLM) devices. We measure and characterize the phase errors, analyze their effects on the correlation process, and discuss a means of correction through a design modification of the binary phase-only optical filter function. The phase correction technique is found to produce correlation results close to those of an error-free correlator.

Downie, John D.↗
NASA NTRS2010

Self-Nulling Beam Combiner Using No External Phase Inverter

A self-nulling beam combiner is proposed that completely eliminates the phase inversion subsystem from the nulling interferometer, and instead uses the intrinsic phase shifts in the beam splitters. Simplifying the flight instrument in this way will be a valuable enhancement of mission reliability. The tighter tolerances on R = T (R being reflection and T being transmission coefficients) required by the self-nulling configuration actually impose no new constraints on the architecture, as two adaptive nullers must be situated between beam splitters to correct small errors in the coatings. The new feature is exploiting the natural phase shifts in beam combiners to achieve the 180 phase inversion necessary for nulling. The advantage over prior art is that an entire subsystem, the field-flipping optics, can be eliminated. For ultimate simplicity in the flight instrument, one might fabricate coatings to very high tolerances and dispense with the adaptive nullers altogether, with all their moving parts, along with the field flipper subsystem. A single adaptive nuller upstream of the beam combiner may be required to correct beam train errors (systematic noise), but in some circumstances phase chopping reduces these errors substantially, and there may be ways to further reduce the chop residuals. Though such coatings are beyond the current state of the art, the mechanical simplicity and robustness of a flight system without field flipper or adaptive nullers would perhaps justify considerable effort on coating fabrication.

Bloemhof, Eric E.↗
NASA NTRS1979

Optimizing multislot feeds for reflecting antennas

Multislot feed corrects phase errors in reflecting antennas. Variables are reduced by considering symmetry and corrective effect of each phase mode. Overall computation concerning calculation of correct phase angles while optimizing main beam efficiency is simplified by analysis used parabolic torus reflector aboard Space Shuttle.

Waineo, D. K.↗
NASA NTRS1971

Optimum impulsive midcourse guidance with control dependent errors.

The problem of determining the optimum guidance policy for an interplanetary spacecraft is treated as a stochastic optimal control problem. An algorithm for computing the optimum velocity correction and the optimum execution time (with allowance for correction-dependent errors) is derived in the case of a single midcourse correction. The performance index was chosen to be an upper bound for the probability that the mission fails, and it is defined as a function of the maximum allowable velocity correction and the maximum allowable deviation of the terminal state. Numerical results obtained for a Jupiter fly-by mission indicate that the execution errors have a significant influence on the performance index, but an acceptably small upper bound on the probability of mission failure can be obtained for sufficiently small execution errors.

Tapley, B. D.↗
NASA NTRS2015

Preliminary Analysis of Effect of Random Segment Errors on Coronagraph Performance

Are we alone in the Universe is probably the most compelling science question of our generation. To answer it requires a large aperture telescope with extreme wavefront stability. To image and characterize Earth-like planets requires the ability to block 10(exp 10) of the host stars light with a 10(exp -11) stability. For an internal coronagraph, this requires correcting wavefront errors and keeping that correction stable to a few picometers rms for the duration of the science observation. This requirement places severe specifications upon the performance of the observatory, telescope and primary mirror. A key task of the AMTD project (initiated in FY12) is to define telescope level specifications traceable to science requirements and flow those specifications to the primary mirror. From a systems perspective, probably the most important question is: What is the telescope wavefront stability specification? Previously, we suggested this specification should be 10 picometers per 10 minutes; considered issues of how this specification relates to architecture, i.e. monolithic or segmented primary mirror; and asked whether it was better to have few or many segmented. This paper reviews the 10 picometers per 10 minutes specification; provides analysis related to the application of this specification to segmented apertures; and suggests that a 3 or 4 ring segmented aperture is more sensitive to segment rigid body motion that an aperture with fewer or more segments.

Stahl, Mark T.↗