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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Detection and Prevention of Arrhythmias During Space Flight

Objectives of this research include:determine if orthogonal lead sets can; determine if orthogonal lead sets can correct artifactual ECG changes caused by correct artifactual ECG changes caused by microgravity- induced alterations in cardiac position; determine if markers of susceptibility to SCD (TWA and QT restitution) can be reliably measured during space flight; determine the effects of continuous microgravity on markers of susceptibility to SCD.

Pillai, Dilip↗
NASA NTRS1979

Experiments for improved positioning by means of integrated Doppler satellite observations and the NNSS broadcast ephemeris

A study to improve position determination using broadcast ephemeris in Doppler data reduction is presented. The uncertainty of the broadcast ephemeris was assessed, and sample autocovariances were computed for acceleration, velocity, and position considering the state disturbance as a signal. An experiment was made in which three stations coobserved 12 passes, and the removal of the radial bias resulted in a chord distance which was in better agreement with the ground survey. In the second experiment, the station positions of the first test simulated the range observations, and the autocovariance function of the acceleration signal in the Cartesian coordinate system was used in an adaptive filtering procedure to improve the state of the satellite in one pass.

Arur, M. G.↗
NASA NTRS1990

Optical neural network system for pose determination of spinning satellites

An optical neural network architecture and algorithm based on a Hopfield optimization network are presented for multitarget tracking. This tracker utilizes a neuron for every possible target track, and a quadratic energy function of neural activities which is minimized using gradient descent neural evolution. The neural net tracker is demonstrated as part of a system for determining position and orientation (pose) of spinning satellites with respect to a robotic spacecraft. The input to the system is time sequence video from a single camera. Novelty detection and filtering are utilized to locate and segment novel regions from the input images. The neural net multitarget tracker determines the correspondences (or tracks) of the novel regions as a function of time, and hence the paths of object (satellite) parts. The path traced out by a given part or region is approximately elliptical in image space, and the position, shape and orientation of the ellipse are functions of the satellite geometry and its pose. Having a geometric model of the satellite, and the elliptical path of a part in image space, the three-dimensional pose of the satellite is determined. Digital simulation results using this algorithm are presented for various satellite poses and lighting conditions.

Lee, Andrew↗
NASA NTRS2008

Gamma Ray Burst Discoveries by the Swift Mission

With 3 years of on-orbit operations (launched in Nov 2004), Swift has detected over 300 gammaray bursts (GRBs). The unique combination of quick and accurate position determinations by the BAT instrument, fast autonomous spacecraft slewing, and multi-band instrumentation (XRT and UVOT) has allowed Swift to accumulate a long list of discoveries about GRBs. These positions are also available to the ground follow-up community (via TDRSS and GCN) within 15-30 sec. A summary of these discoveries will be given (e.g. long and short GRB host associations, SN associations, flaring and on-going activity in the central engine). The Swift spacecraft and instruments are in fine working order with no signs of performance degradation. With an expected orbital lifetime well past 2020, the overlap with GLAST (launch in mid-2008) will yield greater than 30 GRBs/year with observations by both missions. This will provide an unprecedented wavelength coverage from optical to 100 GeV. The coordination of pointing Swift with GLAST will be described.

Barthelmy, Scott↗
NASA NTRS1979

The potential for astrometry in the infrared

Using a 10-micron heterodyne interferometer, it proved possible to obtain measurements of the star alpha-Orionis, which exhibit phase coherence over a period of at least 1000 seconds and which are equivalent to a positional determination of 60 milliarcsecond accuracy every 5 seconds of integration. A feature of the IR interferometer that makes it an attractive instrument for astrometry is its capability of measuring the relative positions of stars with a precision independent of how widely the stars are separated, or the amount of time that elapses between measurements.

Storey, J. W. V.↗
NASA NTRS1974

A comprehensive experimental program for investigation of various Omega operational modes with selected data analysis results

The investigations considered are concerned with a better definition of the achievable accuracy and propagation characteristics of Omega and the provision of data which could be used for an analysis to study the potential application of Omega position determination to support other NASA projects. The data collection program is considered along with the experimental equipment employed. Attention is given to the design of the receiving station, aspects of data processing, position measurement errors, differential errors, problems of lane decision, and the definition of the update rate.

Lytle, C. D.↗
NASA NTRS1986

Sagittarius A(asterisk) and the positions of infrared sources in the galactic center

Observations of the central region of the Galaxy have been made with the University of Rochester 32 x 32 element InSb array camera in the 1-5 micron wavelength range. The 2.2-micron images have been used to determine positions of infrared features in comparison with that of the galactic center compact radio source Sgr A(asterisk). No infrared source lies precisely at the Sgr A(asterisk) position in the images. However, the infrared source closest to the Sgr A(asterisk) position is a previously little studied source directly south of IRS 7 that was called IRS 16NW and not the often referred to IRS 16C. IRS 16NW is coincident with one of the very red objects seen in various 1-micron images of this region.

Forrest, W. J.↗
NASA NTRS1993

Tectonic deformation in southern California

Our objectives were to use modem geodetic data, especially those derived from space techniques like Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and the Global Positioning System (GPS) to infer crustal deformation in southern California and relate it to plate tectonics and earthquake hazard. To do this, we needed to collect some original data, write computer programs to determine positions of survey markers from geodetic observables, interpret time dependent positions in terms of velocity and earthquake caused episodic displacements, and construct a model to explain these velocities and displacements in terms of fault slip and plate movements.

Jackson, David D.↗
NASA NTRS1975

Entopistic scintillators

Trajectories of cosmic rays through a balloon-borne experiment will be determined by pulse height analyzing the signals from each of the two or more phototubes coupled to each scintillator. Thin or tapered scintillators produce sufficiently strong gradients of phototube signal with respect to scintillation position that position uncertainties of about 1 cm can be achieved over 1-sq-m areas. Calculations and some test results for entopistic, or position determining, scintillators are presented.

Arens, J. F.↗
NASA NTRS1975

Evaluation of several navigation algorithms for application to general aviation

Using data obtained in flight, three position determining algorithms for use by general aviation aircraft were evaluated representing increasing software requirements. These were a DME only, DME/air data and blended DME/air data. Although each step represented additional software with resultant increase in position accuracy, all could be performed on a programmable electronic desk calculator. Results from the computation of aircraft position using the three algorithms are presented. The algorithms employed can be extended to accept VOR, TACAN bearing, ADF, or other NAVAID Data. To obtain the flight data an experimental system was configured and flown on a general aviation aircraft. Principal hardware elements (all with low-cost potential) were a programmable calculator, a single DME receiver (multiplexed for multiple DME use) and a low-cost air speed sensor (shed-vortex principle). The flight test demonstrated satisfactory performance of these principal elements.

Conrad, B.↗
NASA NTRS1979

Satellite interferometer as an advanced navigation/communication system

An orthogonal system of interferometry baselines aboard a geostationary satellite is proposed to be used for navigation, surveillance, and traffic control. Position determination is based on the relationship between the measured phase differences, the known and unknown transmitter locations, and other systematic error model parameters using a generalized least-squares estimation procedure. It is shown that position accuracy is critically dependent on the baseline length and on the magnitude of the random component of the measuring errors. Several trade-offs with respect to the system accuracies, the number of users, data rates, hardware costs, etc., are examined. Simultaneous use of the same channels for navigation and data transfer is found feasible and five candidate or 'strawman' interferometer system proposals are presented. It is concluded that the system's performance is excellent in comparison with present or planned systems, and that it is viable in meeting potential user's requirements.

Gopalapillai, G. S.↗
NASA NTRS1974

Astrometric observations of Saturn's satellites from McDonald Observatory, 1972

Observations of Saturn's satellites were reduced by means of secondary reference stars obtained by reduction of Palomar Sky Survey (PSS) plates. This involved the use of 39 SAO stars and plate overlap technique to determine the coordinates of 59 fainter stars in the satellite field. Fourteen plate constants were determined for each of the two PSS plates. Comparison of two plate measurement and reduction techniques on the satellite measurements demonstrate the existence of a serious background gradient effect and the utility of microdensitometry to eliminate this error source in positional determinations of close satellites.

Abbot, R. I.↗
NASA NTRS2011

Robust Control Algorithm for a Two Cart System and an Inverted Pendulum

The Rectilinear Control System can be used to simulate a launch vehicle during liftoff. Several control schemes have been developed that can control different dynamic models of the rectilinear plant. A robust control algorithm was developed that can control a pendulum to maintain an inverted position. A fluid slosh tank will be attached to the pendulum in order to test robustness in the presence of unknown slosh characteristics. The rectilinear plant consists of a DC motor and three carts mounted in series. Each cart s weight can be adjusted with brass masses and the carts can be coupled with springs. The pendulum is mounted on the first cart and an adjustable air damper can be attached to the third cart if desired. Each cart and the pendulum have a quadrature encoder to determine position. Full state feedback was implemented in order to develop the control algorithm along with a state estimator to determine the velocity states of the system. A MATLAB program was used to convert the state space matrices from continuous time to discrete time. This program also used a desired phase margin and damping ratio to determine the feedback gain matrix that would be used in the LabVIEW program. This experiment will allow engineers to gain a better understanding of liquid propellant slosh dynamics, therefore enabling them to develop more robust control algorithms for launch vehicle systems

Wilson, Chris L.↗
NASA NTRS1975

Astrometric observations of Saturn's satellites from McDonald Observatory, 1972

Observations of Saturn's satellites have been reduced by means of secondary reference stars obtained by reduction of Palomar Sky Survey plates. This involved the use of 29 SAO stars and plate overlap technique to determine the coordinates of 59 fainter stars in the satellite field. Fourteen plate constants were determined for each of the two PSS plates. Comparison of two plate measurement and reduction techniques on the satellite measures appears to demonstrate the existence of a serious background gradient effect and the utility of microdensitometry to eliminate this error source in positional determinations of close satellites.

Abbot, R. I.↗
NASA NTRS2002

The SIM astronmetric grid

The Space Interferometry Mission (SIM) is fundamentally a one-dimensional instrument with a 15-degree field-of-regard. Mission objectives require a global reference grid of thousands of well-understood stars with positions known to 4 microarcseconds which will be used to establish the instrument baseline vector during scientific observations. This accuracy will be achieved by frequently observing a set of stars throughout the mission and performing a global fit of the observations to determine position, proper motion and parallax for each star. Each star will be observed approximately 200 times with about 6.5 stars per single instrument field on the sky. We describe the nature of the reference grid, the candidate objects, and the results of simulations demonstrating grid performance, including estimates of the grid robustness when including effects such as instrument drift and possible contamination of the grid star sample by undetected binaries.

SIM grid astrometry Space Interferometry Mission S↗
NASA NTRS1985

Theoretical prediction of stationary positions in the rectangular chamber during asymmetric electroosmotic flow

Most microscopic cell electrophoretic work depends on the theortical prediction of stationary positions by Smoluchowski and Komagata. Their theoretical solutions are based on the assumption that the electroosmotic flow in a chamber is symmetric. Because experiences with the rectangular chamber indicate that symmetric flow occurs during less than 8% of the experiments, the existing theory for stationary position determination is expanded to include the more general case of asymmetric flow. Smoluchowski's equation for symmetric electroosmotic flow in a rectangular chamber having a width much smaller than its height or length is examined. Smoluchowski's approach is used to approximate stationary positions in rectangular chambers with height/width ratios greater than 40. Support for the theoretical prediction of stationary positions using is given by three types of experimental evidence.

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