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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Global Precipitation Measurement Mission Launch and Commissioning

During launch and early operation of the Global Precipitation Measurement (GPM) Mission, the Guidance, Navigation and Control (GNC) analysis team encountered four main on orbit anomalies. These include: (1) unexpected shock from Solar Array deployment, (2) momentum buildup from the Magnetic Torquer Bars (MTBs) phasing errors, (3) transition into Safehold due to albedo-induced Course Sun Sensor (CSS) anomaly, and (4) a flight software error that could cause a Safehold transition due to a Star Tracker occultation. This paper will discuss ways GNC engineers identified and tracked down the root causes. Flight data and GNC on board models will be shown to illustrate how each of these anomalies were investigated and mitigated before causing any harm to the spacecraft. On May 29, 2014, GPM was handed over to the Mission Flight Operations Team after a successful commissioning period. Currently, GPM is operating nominally on orbit, collecting meaningful scientific data that will significantly improve our understanding of the Earth's climate and water cycle.

Guidance Navigation and Control↗
NASA NTRS2018

Performance of Variable Coded Modulations over a Nonlinear Channel for VCM Protocol Red Book

This presentation provides a summary of the results obtained from a study which evaluates the performance of variable coded modulations specified in the "Variable Coded Modulation Protocol" CCSDS Red Book, over a nonlinear channel that is currently on the CCSDS Blue Book track. The objectives are to perform simulation that identifies the operating signal-to-noise-power ratio required to achieve a codeword error rate of 1e-4 over the specified nonlinear channel for various modulations (i.e. BPSK, QPSK, 8-PSK) and LDPC coding schemes, and compare against performance over an ideal additive white Gaussian channel. We select a only subset of operating modes to perform the analysis which are based on a number of mitigation techniques to combat the nonlinear distortions. Specifically, transmitter centroidal pre-distortion, phase post-distortion and receiver mean phase estimation are analyzed in this study.

coding↗
NASA NTRS2018

Effects of Time-Varying Relative Spectral Response on the Calibration of MODIS Reflective Solar Bands

Calibration of the on-orbit gain changes of the narrow bandwidth reflective solar bands (RSB) of Terra and Aqua MODIS is usually based on the band center wavelength. The relative spectral response (RSR) of each band is assumed to be constant on orbit and the time dependence of an overall gain factor is calculated. Any on-orbit changes to the RSR of the MODIS bands will introduce some error into the calibration and may also have an impact on the Earth scene radiance retrieval. We consider two different ways to track how the RSR of the MODIS RSB may be changing on orbit, and the effect that these changes will have on the calibration. First, we examine in-band RSR measurements from the spectro-radiometric calibration assembly (SRCA) carried on-board both MODIS instruments. Second, we study the broadband degradation of the MODIS scan mirror and how it may be changing the effective out-of-band response of the RSB. We find that RSR changes have a small effect on the radiance calibrated using the on-board solar diffuser, generally less than 0.5% in all cases at any time in the missions, with bands 1, 8, and 9 impacted the most.

Twedt, Kevin A.↗
NASA NTRS2020

Revisiting OSIRIS-REx Touch-And-Go (TAG) Performance Given the Realities of Asteroid Bennu

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission is a NASA New Frontiers mission that launched in 2016 and rendezvoused with the near-Earth asteroid (101955) Bennu in late 2018. Upon arrival, the surface of Bennu was found to be much rockier than expected. The original Touch-and-Go (TAG) requirement for sample collection was to deliver the spacecraft to a site with a 25-meter radius; however, the largest hazard-free sites are no larger than 8 meters in radius. To accommodate the dearth of safe sample collection sites, the project reevaluated all aspects of flight system performance pertaining to TAG in order to account for the demonstrated performance of the spacecraft and navigation prediction accuracies. More-over, the project has base lined on board natural feature tracking instead of lidar for providing the on board navigation state update during the TAG sequence. This paper summarizes the improvements in error source estimation, enhancements in on board trajectory correction, and results of recent Monte Carlo simulation to en-able sample collection with the given constraints. TAG delivery and on board navigation performance are presented for the final four candidate TAG sites.

Berry, Kevin↗
NASA NTRS2020

Effects of Out-of-Band and Time-Varying Relative Spectral Response on the Calibration of MODIS Reflective Solar Bands

Calibration of the on-orbit gain changes of the narrow bandwidth reflective solar bands (RSB) of Terra and Aqua MODIS is usually based on the band center wavelength. The relative spectral response (RSR) of each band is assumed to be constant on orbit and the time dependence of an overall gain factor is calculated. Any on-orbit changes to the RSR of the MODIS bands will introduce some error into the calibration and may also have an impact on the Earth scene radiance retrieval. We consider two different ways to track how the RSR of the MODIS RSB may be changing on orbit, and the effects that these changes will have on the calibration. First, we study the broadband degradation of the MODIS scan mirror and how it may be changing the effective out-of-band response of the RSB. Second, we examine in-band RSR measurements from the spectro-radiometric calibration assembly (SRCA) carried on-board both MODIS instruments. We find that RSR changes have a relatively small effect on the radiance calibrated using the on-board solar diffuser, generally less than 0.5% for all RSB at any time in the missions, though the effect may be slightly larger for some scan angles. The impact of RSR changes on the Earth scene radiance retrieval is highly dependent on the spectral properties of the scene and could be significantly larger. The bands showing the largest impacts are Terra bands 1, 4, 8, 9, 17, and 19 and Aqua bands 8 and 9.

MODIS↗
NASA NTRS1988

A model study of potential sampling errors due to data scatter around expendable bathythermograph transects in the tropical Pacific

A linear multiple vertical-mode model described by McPhaden et al. (1988) is used to examine potential errors due to data scatter around expendable bathythermograph (XBT) transects in the tropical Pacific. Two methods of sampling are compared. In the first, the model was sampled along approximately straight lines of grid points corresponding to the mean positions of XBT tracks in the eastern, central, and western Pacific; in the second, the model was sampled again at the dates and locations of actual XTB casts for 1979-1983. The model indicates that the data scattered zonally around XBT transects in general can lead to about 2 dyn cm error in dynamic height in composite sections of XBT data. Errors larger than 2 dyn cm occurred in regions where XBT sample spacing in the zonal direction was insufficient to resolve Rossby wave variations in the model.

Mcphaden, Michael J.↗
NASA NTRS1990

High-accuracy, high-resolution gravity profiles from 2 years of the Geosat Exact Repeat Mission

Satellite altimeter data from the first 44 repeat cycles (2 years) of the Geosat Exact Repeat Mission (EWRM) were averaged to improve accuracy, resolution and coverage of the marine gravity field. Individual 17-day repeat cycles were first edited and differentiated, resulting in the along-track vertical deflection (i.e., gravity disturbance). To increase the signal-to-noise ratio, 44 of these cycles were then averaged to form a single highly accurate vertical deflection profile. The largest contribution to the vertical deflection error is short-wavelength altimeter noise and longer-wavelength oceanographic variability; the combined noise level is typically 6 microrad. Both types of noise are reduced by averaging many repeat cycles. Over most ocean areas the uncertainty of the average profile is less than 1 microrad which corresponds to 1 mgal of along-track gravity disturbance. However, in areas of seasonal ice coverage, its uncertainty can exceed 5 microrad. To assess the resolution of individual and average Geosat gravity profiles, the cross-spectral analysis technique was applied to repeat profiles. Individual Geosat repeat cycles are coherent (greater than 0.5) for wavelengths greater than about 30 km and become increasingly incoherent at shorter wavelengths.

Sandwell, David T.↗
DOE OSTI2015

Magellan adaptive optics first-light observations of the exoplanet β PIC b. II. 3–5 μm direct imaging with MagAO+Clio, and the empirical bolometric luminosity of a self-luminous giant planet

Young giant exoplanets are a unique laboratory for understanding cool, low-gravity atmospheres. A quintessential example is the massive extrasolar planet β Pic b, which is 9 AU from and embedded in the debris disk of the young nearby A6V star β Pictoris. We observed the system with first light of the Magellan Adaptive Optics (MagAO) system. In Paper I we presented the first CCD detection of this planet with MagAO+VisAO. Here we present four MagAO+Clio images of β Pic b at 3.1 μm, 3.3 μm, L′, and M{sup ′}, including the first observation in the fundamental CH{sub 4} band. To remove systematic errors from the spectral energy distribution (SED), we re-calibrate the literature photometry and combine it with our own data, for a total of 22 independent measurements at 16 passbands from 0.99 to 4.8 μm. Atmosphere models demonstrate the planet is cloudy but are degenerate in effective temperature and radius. The measured SED now covers >80% of the planet’s energy, so we approach the bolometric luminosity empirically. We calculate the luminosity by extending the measured SED with a blackbody and integrating to find log(L{sub bol}/L{sub ⊙}) = −3.78±0.03. From our bolometric luminosity and an age of 23 ± 3 Myr, hot-start evolutionary tracks give a mass of 12.7 ± 0.3 M{sub Jup}, radius of 1.45 ± 0.02 R{sub Jup}, and T{sub eff} of 1708 ± 23 K (model-dependent errors not included). Our empirically determined luminosity is in agreement with values from atmospheric models (typically −3.8 dex), but brighter than values from the field-dwarf bolometric correction (typically −3.9 dex), illustrating the limitations in comparing young exoplanets to old brown dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2020

Terrain Relative Navigation for Guided Descent on Titan

Titan’s dense atmosphere, low gravity, and high winds at high altitudes create descent times of >90 minutes with standard entry/descent/landing (EDL) architectures and result in large unguided landing ellipses, with 99% values of 110x110 km and 149x72 km in recent Titan lander proposals. Enabling precision landing on Titan could increase science return for the types of missions proposed to date and make additional types of landing sites accessible, opening up new possibilities for science investigations. Precision landing on Titan has unique challenges, because the hazy atmosphere makes it difficult to see the surface and because it requires guided descent with divert ranges that are one to two orders of magnitude larger than needed for other target bodies, i.e. up to on the order of 100 km. It is conceivable that such a divert capability could be provided economically by a parafoil or other steerable aerodynamic decelerator deployed several 10s of km above the surface. The long descent times lead to large inertial navigation errors, hence a need for terrain relative navigation (TRN). This would require a TRN capability that can operate at such altitudes, despite challenges of seeing the surface sufficiently clearly and of depending on map products that are two orders of magnitude lower in spatial resolution than those for Mars and airless bodies. We then develop algorithms for map matching and feature tracking with descent images and test these with synthetic images created from Cassini/Huygens data sets and our radiative transfer model. We also introduce new possibilities for TRN based on the potential to discriminate some specific types of terrain onboard in descent imagery, such as lake vs adjacent ground and dune vs interdune. We use sensor measurement noise models in simulations of state estimation with an extended Kalman filter that includes coordinates of a set of tracked features in the state vector. Case studies were done for two notional landing sites, one in a site with only dry ground and one in a Titan lake district. In both cases, the filter error model shows 3 position error at touchdown on the order of 2 km. More work is needed to validate these results with higher fidelity camera models and larger data sets, but this is very promising.

Matthies, Larry↗
NASA NTRS1990

Algorithm For Control Of Large Antenna

Alternative position-error feedback modes provided. Modern control theory basis for computer algorithm used to control two-axis positioning of large antenna. Algorithm - incorporated into software of real-time control computer - enables rapid intertarget positioning as well as precise tracking (using one of two optional position-feedback modes) without need of human operator intervention. Control system for one axis of two-axis azimuth/elevation control system embodied mostly in software based on advanced control theory. System has linear properties of classical linear feedback controller. Performance described by bandwidth and linear error coefficients.

Hill, Robert E.↗
NASA NTRS1996

A Real-Time Position-Locating Algorithm for CCD-Based Sunspot Tracking

NASA Marshall Space Flight Center's (MSFC) EXperimental Vector Magnetograph (EXVM) polarimeter measures the sun's vector magnetic field. These measurements are taken to improve understanding of the sun's magnetic field in the hopes to better predict solar flares. Part of the procedure for the EXVM requires image motion stabilization over a period of a few minutes. A high speed tracker can be used to reduce image motion produced by wind loading on the EXVM, fluctuations in the atmosphere and other vibrations. The tracker consists of two elements, an image motion detector and a control system. The image motion detector determines the image movement from one frame to the next and sends an error signal to the control system. For the ground based application to reduce image motion due to atmospheric fluctuations requires an error determination at the rate of at least 100 hz. It would be desirable to have an error determination rate of 1 kHz to assure that higher rate image motion is reduced and to increase the control system stability. Two algorithms are presented that are typically used for tracking. These algorithms are examined for their applicability for tracking sunspots, specifically their accuracy if only one column and one row of CCD pixels are used. To examine the accuracy of this method two techniques are used. One involves moving a sunspot image a known distance with computer software, then applying the particular algorithm to see how accurately it determines this movement. The second technique involves using a rate table to control the object motion, then applying the algorithms to see how accurately each determines the actual motion. Results from these two techniques are presented.

Taylor, Jaime R.↗
NASA NTRS1990

Orbiter-orbiter and orbiter-lander tracking using same-beam interferometry

Two spacecraft orbiting Mars may be tracked simultaneously by a single earth-based antenna. Same-beam interferometric techniques, using two widely separated antennas, produce a spacecraft-spacecraft measurement in the plane of the sky, complementary to the line-of-sight Doppler information. This paper presents an overview of the same-beam interferometric measurement technique, a measurement error analysis, and examples of the application of same-beam interferometry to orbit determination. For the case of Mars Observer and the Soviet Mars '94 mission, orbit determination improvement up to an order of magnitude is found. Relative tracking between a Mars orbiter and a lander fixed on the surface of Mars is also studied. The lander location may be determined to a few meters, while the orbiter ephemeris may be determined with accuracy similar to the orbiter-orbiter case.

Folkner, W. M.↗
NASA NTRS1998

Automated Track Recognition and Event Reconstruction in Nuclear Emulsion

The major advantages of nuclear emulsion for detecting charged particles are its submicron position resolution and sensitivity to minimum ionizing particles. These must be balanced, however, against the difficult manual microscope measurement by skilled observers required for the analysis. We have developed an automated system to acquire and analyze the microscope images from emulsion chambers. Each emulsion plate is analyzed independently, allowing coincidence techniques to be used in order to reject back- ground and estimate error rates. The system has been used to analyze a sample of high-multiplicity Pb-Pb interactions (charged particle multiplicities approx. 1100) produced by the 158 GeV/c per nucleon Pb-208 beam at CERN. Automatically reconstructed track lists agree with our best manual measurements to 3%. We describe the image analysis and track reconstruction techniques, and discuss the measurement and reconstruction uncertainties.

Deines-Jones, P.↗
DOE OSTI2022

Field quality of the 4.5 m-long MQXFA pre-series magnets for the HL-LHC Upgrade as observed during magnet assembly

We report that the U.S. High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) is developing MQXFA magnets, a series of 4.5 m long 150 mm aperture high-field Nb 3 Sn quadrupole magnets for the HL-LHC upgrade at CERN. Five pre-series magnets, MQXFA03 through MQXFA07, have been developed. During the magnet assembly stage, we perform magnetic measurements on the coil-pack sub-assembly and magnets after loading to track the field quality for two purposes. First, it serves as a quality assurance tool to check if the magnetic field quality is on track to meet the acceptance criteria. Magnetic measurements are used to understand if magnetic shims are needed to compensate low-order field errors and to meet the field quality targets. Second, the measurements during the assembly stage can also help understand the field quality, especially the geometric field errors, for Nb 3 Sn accelerator magnets. Here we summarize the measurement results of the pre-series MQXFA magnets, including the magnetic axis and twist angle. The results will provide useful feedback for the series production of Nb 3 Sn magnets and on the optimization of field quality of accelerator magnets based on the wind-and-react Nb 3 Sn technology.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Theoretical Control-Centric Modeling for Precision Model-Based Sliding Mode Control of a Hydraulic Artificial Muscle Actuator

Artificial muscles (AMs) typically rely on pneumatic sources of fluid power. The use of hydraulics can increase the power and force to weight and volume ratios of AM actuators. This paper develops a control-centric third-order single-input single-output (SISO) lumped-parameter dynamic model and sliding mode position controller based on Filippov's principle of equivalent dynamics for a braided hydraulic artificial muscle (HAM) actuator. The model predicts the nonlinear behavior of the HAM free contraction and captures the fluid and actuator nonlinear dynamic interactions in addition to the braid deformation. Model simulations are compared to experimental results for quasi-static pressurization, isometric pressurization, and open-loop square wave commands at 0.25, 0.5, and 1 Hz. Experiments of sine wave tracking at 0.25, 0.5, and 1 Hz and continuous square wave tracking at 0.067 Hz are conducted using a sliding mode controller (SMC) derived from the model. The SMC achieves a steady-state error of 6 μm at multiple setpoints within the actuator's 17 mm stroke. Compared to a proportional-integral-derivative (PID) controller, the SMC root-mean-square (RMS) error, mean error, and absolute maximum error are reduced on average by 53%, 61%, and 44%, respectively, demonstrating the benefit of model-based approaches for controlling HAMs.

42 ENGINEERING↗
NASA NTRS1972

Utilization of a CRT display light pen in the design of feedback control systems

A hierarchical structure of the interlinked programs was developed to provide a flexible computer-aided design tool. A graphical input technique and a data structure are considered which provide the capability of entering the control system model description into the computer in block diagram form. An information storage and retrieval system was developed to keep track of the system description, and analysis and simulation results, and to provide them to the correct routines for further manipulation or display. Error analysis and diagnostic capabilities are discussed, and a technique was developed to reduce a transfer function to a set of nested integrals suitable for digital simulation. A general, automated block diagram reduction procedure was set up to prepare the system description for the analysis routines.

Thompson, J. G.↗
NASA NTRS1973

Orbit determination by range-only data.

The determination of satellite orbits for use in geodesy using range-only data has been examined. A recently developed recursive algorithm for rectification of the nominal orbit after processing each observation has been tested. It is shown that when a synchronous satellite is tracked simultaneously with a subsynchronous geodetic target satellite, the orbits of each may be readily determined by processing the range information. Random data errors and satellite perturbations are included in the examples presented.

Duong, N.↗
NASA NTRS1975

A Study of Synchronization Techniques for Optical Communication Systems

The study of synchronization techniques and related topics in the design of high data rate, deep space, optical communication systems was reported. Data cover: (1) effects of timing errors in narrow pulsed digital optical systems, (2) accuracy of microwave timing systems operating in low powered optical systems, (3) development of improved tracking systems for the optical channel and determination of their tracking performance, (4) development of usable photodetector mathematical models for application to analysis and performance design in communication receivers, and (5) study application of multi-level block encoding to optical transmission of digital data.

Gagliardi, R. M.↗