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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Absolute Position Encoders With Vertical Image Binning

Improved optoelectronic patternrecognition encoders that measure rotary and linear 1-dimensional positions at conversion rates (numbers of readings per unit time) exceeding 20 kHz have been invented. Heretofore, optoelectronic pattern-recognition absoluteposition encoders have been limited to conversion rates <15 Hz -- too low for emerging industrial applications in which conversion rates ranging from 1 kHz to as much as 100 kHz are required. The high conversion rates of the improved encoders are made possible, in part, by use of vertically compressible or binnable (as described below) scale patterns in combination with modified readout sequences of the image sensors [charge-coupled devices (CCDs)] used to read the scale patterns. The modified readout sequences and the processing of the images thus read out are amenable to implementation by use of modern, high-speed, ultra-compact microprocessors and digital signal processors or field-programmable gate arrays. This combination of improvements makes it possible to greatly increase conversion rates through substantial reductions in all three components of conversion time: exposure time, image-readout time, and image-processing time.

Leviton, Douglas B.↗
NASA NTRS2011

Orion Absolute Navigation System Progress and Challenges

The Orion spacecraft is being designed as NASA's next-generation exploration vehicle for crewed missions beyond Low-Earth Orbit. The navigation system for the Orion spacecraft is being designed in a Multi-Organizational Design Environment (MODE) team including contractor and NASA personnel. The system uses an Extended Kalman Filter to process measurements and determine the state. The design of the navigation system has undergone several iterations and modifications since its inception, and continues as a work-in-progress. This paper seeks to benchmark the current state of the design and some of the rationale and analysis behind it. There are specific challenges to address when preparing a timely and effective design for the Exploration Flight Test (EFT-1), while still looking ahead and providing software extensibility for future exploration missions. The primary measurements in a Near-Earth or Mid-Earth environment consist of GPS pseudorange and deltarange, but for future explorations missions the use of star-tracker and optical navigation sources need to be considered. Discussions are presented for state size and composition, processing techniques, and consider states. A presentation is given for the processing technique using the computationally stable and robust UDU formulation with an Agee-Turner Rank-One update. This allows for computational savings when dealing with many parameters which are modeled as slowly varying Gauss-Markov processes. Preliminary analysis shows up to a 50% reduction in computation versus a more traditional formulation. Several state elements are discussed and evaluated, including position, velocity, attitude, clock bias/drift, and GPS measurement biases in addition to bias, scale factor, misalignment, and non-orthogonalities of the accelerometers and gyroscopes. Another consideration is the initialization of the EKF in various scenarios. Scenarios such as single-event upset, ground command, pad alignment, cold start are discussed as are strategies for whole and partial state updates as well as covariance considerations. Strategies are given for dealing with latent measurements and high-rate propagation using multi-rate architecture. The details of the rate groups and the data ow between the elements is discussed and evaluated.

Holt, Greg N.↗
NASA NTRS2011

Precise Absolute Astrometry from the VLBA Imaging and Polarimetry Survey at 5 GHz

We present accurate positions for 857 sources derived from the astrometric analysis of 16 eleven-hour experiments from the Very Long Baseline Array imaging and polarimetry survey at 5 GHz (VIPS). Among the observed sources, positions of 430 objects were not previously determined at milliarcsecond-level accuracy. For 95% of the sources the uncertainty of their positions ranges from 0.3 to 0.9 mas, with a median value of 0.5 mas. This estimate of accuracy is substantiated by the comparison of positions of 386 sources that were previously observed in astrometric programs simultaneously at 2.3/8.6 GHz. Surprisingly, the ionosphere contribution to group delay was adequately modeled with the use of the total electron content maps derived from GPS observations and only marginally affected estimates of source coordinates.

Petrov, L.↗
NASA NTRS2013

Tuning and Robustness Analysis for the Orion Absolute Navigation System

The Orion Multi-Purpose Crew Vehicle (MPCV) is currently under development as NASA's next-generation spacecraft for exploration missions beyond Low Earth Orbit. The MPCV is set to perform an orbital test flight, termed Exploration Flight Test 1 (EFT-1), some time in late 2014. The navigation system for the Orion spacecraft is being designed in a Multi-Organizational Design Environment (MODE) team including contractor and NASA personnel. The system uses an Extended Kalman Filter to process measurements and determine the state. The design of the navigation system has undergone several iterations and modifications since its inception, and continues as a work-in-progress. This paper seeks to show the efforts made to-date in tuning the filter for the EFT-1 mission and instilling appropriate robustness into the system to meet the requirements of manned space ight. Filter performance is affected by many factors: data rates, sensor measurement errors, tuning, and others. This paper focuses mainly on the error characterization and tuning portion. Traditional efforts at tuning a navigation filter have centered around the observation/measurement noise and Gaussian process noise of the Extended Kalman Filter. While the Orion MODE team must certainly address those factors, the team is also looking at residual edit thresholds and measurement underweighting as tuning tools. Tuning analysis is presented with open loop Monte-Carlo simulation results showing statistical errors bounded by the 3-sigma filter uncertainty covariance. The Orion filter design uses 24 Exponentially Correlated Random Variable (ECRV) parameters to estimate the accel/gyro misalignment and nonorthogonality. By design, the time constant and noise terms of these ECRV parameters were set to manufacturer specifications and not used as tuning parameters. They are included in the filter as a more analytically correct method of modeling uncertainties than ad-hoc tuning of the process noise. Tuning is explored for the powered-flight ascent phase, where measurements are scarce and unmodelled vehicle accelerations dominate. On orbit, there are important trade-off cases between process and measurement noise. On entry, there are considerations about trading performance accuracy for robustness. Process Noise is divided into powered flight and coasting ight and can be adjusted for each phase and mode of the Orion EFT-1 mission. Measurement noise is used for the integrated velocity measurements during pad alignment. It is also used for Global Positioning System (GPS) pseudorange and delta- range measurements during the rest of the flight. The robustness effort has been focused on maintaining filter convergence and performance in the presence of unmodeled error sources. These include unmodeled forces on the vehicle and uncorrected errors on the sensor measurements. Orion uses a single-frequency, non-keyed GPS receiver, so the effects due to signal distortion in Earth's ionosphere and troposphere are present in the raw measurements. Results are presented showing the efforts to compensate for these errors as well as characterize the residual effect for measurement noise tuning. Another robustness tool in use is tuning the residual edit thresholds. The trade-off between noise tuning and edit thresholds is explored in the context of robustness to errors in dynamics models and sensor measurements. Measurement underweighting is also presented as a method of additional robustness when processing highly accurate measurements in the presence of large filter uncertainties.

Holt, Greg N.↗
NASA NTRS2013

Tuning and Robustness Analysis for the Orion Absolute Navigation System

The Orion Multi-Purpose Crew Vehicle (MPCV) is currently under development as NASA's next-generation spacecraft for exploration missions beyond Low Earth Orbit. The MPCV is set to perform an orbital test ight, termed Exploration Flight Test 1 (EFT-1), some time in late 2014. The navigation system for the Orion spacecraft is being designed in a Multi-Organizational Design Environment (MODE) team including contractor and NASA personnel. The system uses an Extended Kalman Filter to process measurements and determine the state. The design of the navigation system has undergone several iterations and modi cations since its inception, and continues as a work-in-progress. This paper seeks to show the e orts made to-date in tuning the lter for the EFT-1 mission and instilling appropriate robustness into the system to meet the requirements of manned space ight. The results generally show Monte Carlo error performance bounded by the lter uncertainty for all phases of ight. Some future items of investigation are presented related to suspected anomalies in the trajectory truth reference le.

Holt, Greg N.↗
NASA NTRS2012

High Precision, Absolute Total Column Ozone Measurements from the Pandora Spectrometer System: Comparisons with Data from a Brewer Double Monochromator and Aura OMI

We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground-based direct-sun irradiance measurements using our recently deployed Pandora single-grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air-shed and development of a ground-based monitoring network for studying small-scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid- to high-latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double-grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15-80), indicating adequate Pandora stray light correction. A small (1-2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura-OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI-measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short-term (hourly) temporal changes in TCO, not possible to capture by sun-synchronous satellites, such as OMI, alone.

Ozone↗
NASA NTRS2013

Absolute Thickness Measurements on Coatings Without Prior Knowledge of Material Properties Using Terahertz Energy

This study investigates the applicability of a novel noncontact single-sided terahertz electromagnetic measurement method for measuring thickness in dielectric coating systems having either dielectric or conductive substrate materials. The method does not require knowledge of the velocity of terahertz waves in the coating material. The dielectric coatings ranged from approximately 300 to 1400 m in thickness. First, the terahertz method was validated on a bulk dielectric sample to determine its ability to precisely measure thickness and density variation. Then, the method was studied on simulated coating systems. One simulated coating consisted of layered thin paper samples of varying thicknesses on a ceramic substrate. Another simulated coating system consisted of adhesive-backed Teflon adhered to conducting and dielectric substrates. Alumina samples that were coated with a ceramic adhesive layer were also investigated. Finally, the method was studied for thickness measurement of actual thermal barrier coatings (TBC) on ceramic substrates. The unique aspects and limitations of this method for thickness measurements are discussed.

Nondestructive evaluation↗
NASA NTRS2014

Orion Exploration Flight Test-l (EFT -1) Absolute Navigation Design

Scheduled to launch in September 2014 atop a Delta IV Heavy from the Kennedy Space Center, the Orion Multi-Purpose-Crew-Vehicle (MPCV's) maiden flight dubbed "Exploration Flight Test -1" (EFT-1) intends to stress the system by placing the uncrewed vehicle on a high-energy parabolic trajectory replicating conditions similar to those that would be experienced when returning from an asteroid or a lunar mission. Unique challenges associated with designing the navigation system for EFT-1 are presented in the narrative with an emphasis on how redundancy and robustness influenced the architecture. Two Inertial Measurement Units (IMUs), one GPS receiver and three barometric altimeters (BALTs) comprise the navigation sensor suite. The sensor data is multiplexed using conventional integration techniques and the state estimate is refined by the GPS pseudorange and deltarange measurements in an Extended Kalman Filter (EKF) that employs the UDUT decomposition approach. The design is substantiated by simulation results to show the expected performance.

Sud, Jastesh↗
NASA NTRS2014

Relationship Between LIBS Ablation and Pit Volume for Geologic Samples: Applications for the In Situ Absolute Geochronology

These first results demonstrate that LIBS spectra can be an interesting tool to estimate the ablated volume. When the ablated volume is bigger than 9.10(exp 6) cubic micrometers, this method has less than 10% of uncertainties. Far enough to be directly implemented in the KArLE experiment protocol. Nevertheless, depending on the samples and their mean grain size, the difficulty to have homogeneous spectra will increase with the ablated volume. Several K-Ar dating studies based on this approach will be implemented. After that, the results will be shown and discussed.

Devismes, Damien↗
NASA NTRS1996

High Angular Sensitivity, Absolute Rotary Encoding Device with Polygonal Mirror and Stand-Alone Diffraction Gratings

A device for position encoding of a rotating shaft in which a polygonal mirror having a number of facets is mounted to the shaft and a monochromatic light beam is directed towards the facets. The facets of the polygonal mirror direct the light beam to a stand-alone low line density diffraction grating to diffract the monochromatic light beam into a number of diffracted light beams such that a number of light spots are created on a linear array detector. An analog-to-digital converter is connected to the linear array detector for reading the position of the spots on the linear array detector means. A microprocessor with memory is connected to the analog-to-digital converter to hold and manipulate the data provided by the analog-to-digital converter on the position of the spots and to compute the position of the shaft based upon the data from the analog-lo-digital converter.

Leviton, Douglas B.↗
NASA NTRS2016

Absolute Navigation Performance of the Orion Exploration Fight Test 1

Launched in December 2014 atop a Delta IV Heavy from the Kennedy Space Center, the Orion vehicle's Exploration Flight Test-1 (EFT-1) successfully completed the objective to stress the system by placing the un-crewed vehicle on a high-energy parabolic trajectory replicating conditions similar to those that would be experienced when returning from an asteroid or a lunar mission. Unique challenges associated with designing the navigation system for EFT-1 are presented with an emphasis on how redundancy and robustness influenced the architecture. Two Inertial Measurement Units (IMUs), one GPS receiver and three barometric altimeters (BALTs) comprise the navigation sensor suite. The sensor data is multiplexed using conventional integration techniques and the state estimate is refined by the GPS pseudorange and deltarange measurements in an Extended Kalman Filter (EKF) that employs UDU factorization. The performance of the navigation system during flight is presented to substantiate the design.

Zanetti, Renato↗
NASA NTRS2019

Method for the Absolute Calibration of the Location and Orientation of Large-Format Detectors Using Laser Radar

A method of mapping pixel locations of a detector array includes measuring a location on the detector array, initiating a frame readout of the detector array, measuring a location of one or more metrology targets on the detector array, analyzing the frame readout to identify a pixel at the location on the detector array, and defining a location of the identified pixel with respect to the location of the one or more metrology targets. Subsequent measurement of the metrology targets alone by another metrology system allows one to infer the six degree of freedom alignment of the detector array in space.

Coulter, Phillip↗
NASA NTRS2019

Goddard Laser for Absolute Measurement of Radiance

High accuracy achieved with temperature stabilized unfiltered trap detectors illuminated by monochromatic light. Tunable lasers and optical parametric oscillators provide orders of magnitude higher spectral radiance than blackbody or other broadband sources; calibrate at high signal levels.

McAndrew, Brendan↗