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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Measurements of X-ray source positions by the scanning modulation collimator on HEAO 1

This paper reports preliminary results on the positions of X-ray sources obtained with the modulation collimator on the first NASA High Energy Astronomy Observatory, HEAO 1. Calibration on Sco X-1 establishes the experiment capabilities to be within 7 sec as limited by aspect errors. For the reported X-ray sources certain ambiguities in their positions are resolved and the previous optical identifications of four sources are confirmed, two of which are X-ray bursters and one of which is the black hole candidate Cir X-1. An accurate position for a new transient source is also presented.

Gursky, H.↗
NASA NTRS1979

The characteristics of a lift cruise fan V/STOL configuration in near proximity to a small deck with finite edge positions

Two V/STOL model configurations utilizing lift-cruise-fans for the propulsion system have been tested in the presence of a small landing platform with finite deck edge positions. Results and analysis of these tests are presented. The model was tested at both static (zero velocity) and forward speed conditions with several heights and deck edge positions. Configurations utilizing three fans and four fans were investigated. Incremental forces and moments induced by the various deck edge positions are analyzed as relating to the model height above the ground and the thrust velocity relationships. The test and analysis show the induced forces to be relatively unaffected by deck edge.

Stewart, V. R.↗
NASA NTRS1980

Blood filling and flow in lungs during change in body position in space

In the horizontal position (supine and lateral), in the upright position (head up and head down) and during change of the cat body position in space, quantitative responses of regional blood volume and blood flow in the lungs (ml/100 cu cm) revealed presence of the gradient in the gravitation direction. Blood volume and blood flow of different lung portions changed qualitatively and quantitatively in different ways. These changes occurred only in the direction producing the equality of regional hydrostatical and hemodynamic loads in the lungs at either horizontal level.

Pogodin, A. S.↗
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 NTRS1980

Improved position and new optical candidate for A0538-66

An analysis of HEAO 1 modulation collimator data leading to an improved position determination and a new optical counterpart candidate for the transient X-ray source A0538-66 is reported. Data obtained during five outbursts, all of which were separated by 16.7 days or a small multiple thereof, indicates that the outbursts, although of varying duration, intensity, and hardness ratio originated from the same source, at a position of 5 h 35 min 42.7 sec RA and 66 deg 53 arcmin 44 arcsec dec. The improved position determination is found to exclude the previously suggested optical counterpart, and a search of archive plates of the Large Magellanic cloud in the refined error regions has lead to the tentative identification of a B-type star with an observed B variability of 1 mag with the X-ray source.

Johnston, M. D.↗
NASA NTRS1981

A magnetospheric signature of some F layer positive storms

Calculations of electron density distributions in the global thermosphere-ionosphere system perturbed by high-latitude thermospheric heating are presented which indicate a link between the heating and magnetospheric plasma disturbances near the equator. The calculations were made using a self-consistent model of the global sunlit thermosphere-ionosphere system describing the evolution of equatorial plasma disturbances. The heat input is found to cause electron density enhancements that propagate along magnetic field lines from the F2 maximum over mid-latitudes to the equator in the magnetosphere and which correspond to the positive phase of an F layer storm. The positive phase is shown to be generated by the induction of equatorward winds that raise the mid-latitude F layer through momentum transfer from neutral atoms to ionospheric ions, which ions pull electrons with them. Model results are used to identify plasma signatures of equatorward winds and an intensified magnetospheric electric field in Explorer 45 and Arial 4 measurements taken during the positive phase of an F layer storm.

Miller, N. J.↗
NASA NTRS1981

Positive cloud-to-ground lightning flashes in severe storms

The occurrence of cloud-to-ground flashes that effectively lower positive charge to earth (+CG flash) over flat terrain has been documented in the mature stage of severe thunderstorms. Of the 31 documented +CG flashes, most had only one return stroke. Zero-to-peak rise times for the strokes averaged 7 microsec. The +CG flashes averaged 520 ms in duration, with 25 percent lasting more than 800 ms. Many of these had field changes suggestive of continuing current. Positive flashes have been observed to emanate from several regions of severe storms: high on the back of the main storm tower, through the wall cloud, and from the downshear anvil. Visually most of these positive flashes have emanated from high in the storm, and acoustic mapping of two shows thunder sources to a height of about 15 km.

Rust, W. D.↗
NASA NTRS1981

Position surveillance using one active ranging satellite and time-of-arrival of a signal from an independent satellite

A satellite-aided mobile communication service was tested for position surveillance, with an automatic responder circuit connected between the vehicle receiver and transmitter, and a receiver coded for signals from another satellite. Using the ATS-6 and GOES satellites, a tone-code ranging transponder was connected between the receiver and transmitter, and a 468 MHz receiver was connected to the responder unit for passive reception of the 100 bit per second timing and data signal. Results showed lines of position derived from the active ranging through ATS-6 to be accurate to approximately 0.1 nautical mile, while the NOAA-GOES signals were accurate to about 1.6 miles. The active ranging bandwidth was 2.44 kHz, and the integration time was 0.1 second, while the limitation on accuracy was the 100 Hz bandwidth. This technique of position surveillance was concluded to be feasible and simple to operate, providing needed, good quality communications to the inland waterways industry.

Anderson, R. E.↗
NASA NTRS1981

Design studies for a technology assessment receiver for global positioning system

The operational conditions of a radio receiver - microprocessor for the global positioning system are studied. Navigation fundamentals and orbit characterization are reviewed. The global positioning system is described with emphasis upon signal structure and satellite positioning. Ranging and receiver processing techniques are discussed.

Painter, J. H.↗
NASA NTRS1982

Navstar/Global Positioning System

The Global Positioning System (GPS) was developed to provide highly precise position, velocity, and time information to users anywhere in the area of the Earth and at any time. The GPS, when fully operational, will consist of 18 satellites in six orbital planes. Any GPS user, by receiving and processing the radio signals from the satellite network can instantaneously determine navigation information to an accuracy of about 15 m in position and 0.1 m/s in velocity. The GPS is compared with other systems such as Loran-C, Omega, TACAN and Transit.

Ananda, M.↗
NASA NTRS1981

Positive ion observations in the middle magnetosphere of Jupiter

The positive ion data gathered by the Voyager Plasma Science experiment in the middle magnetosphere of Jupiter are considered. It is pointed out that the experiment measures positive ions with energies per charge between 10 and 5950 V. The observations are analyzed to derive the mass and charge densities, velocity components, and temperatures of the low-energy plasma population. The reduced data set is discussed in terms of the outstanding questions concerning this plasma population and its dynamics. It is found that on the dayside there exists a transonic to highly supersonic positive ion population which tends to move azimuthally but does not rigidly corotate with the planet.

Mcnutt, R. L., Jr.↗
NASA NTRS1981

An autonomous Nimbus Doppler positioning system

A single-pass Doppler positioning system was developed at the GSFC in support of the Nimbus-6 mission. The system was designed to satisfy the following requirements: compatibility with the PDP 11/70 minicomputer; single-pass recovery of up to 250 positions with a two-sigma accuracy of 5 km; high reliability with a minimum of human interaction; and near real-time responsiveness. The system consists of a numerical integrator which includes only the J2 term (earth flattening) of the earth's gravity field, an editing routine, a first guess algorithm, a least squares position recovery program, and a routine for generating a 95% confidence circle based on a computer covariance matrix. An analysis and quantification of the following error sources that limit system accuracy are presented: orbit error, radial aliasing, computational difficulties with overhead passes, oscillator drift, and ambiguity problems. Results of system reliability tests and sample outputs are included.

Garza-Robles, R.↗
NASA NTRS1983

Aerodynamic investigation of closely coupled lifting surfaces with positive and negative stagger for general aviation applications

Aerodynamic closely coupled lifting surfaces were investigated for both conventional tail aft configurations and canard configurations to determine whether positive stagger or negative stagger had more attractive aerodynamic characteristics. An inviscid multi-element vortex panel program was used in conjunction with a momentum integral boundary layer program to predict two-dimensional aerodynamic characteristics. A multi-element vortex lattice program was used for three-dimensional characteristics. Pressure distributions, transition location, momentum thickness, two- and three-dimensional drag, and boundary layer separation were compared for the positive and negative stagger case. For staggers less than six the results demonstrated that positive stagger configurations are aerodynamically superior.

Selberg, B. P.↗
NASA NTRS1983

A microprocessor-based position control system for a telescope secondary mirror

The pointing requirements for the Shuttle IR Telescope Facility (SIRTF), which consists of an 0.85-m cryogenically cooled IR telescope, call for an image stability of 0.25 arcsec. Attention is presently given to a microprocessor-based position control system developed for the control of the SIRTF secondary mirror, employing a special control law (to minimize energy dissipation), a precision capacitive position sensor, and a specially designed power amplifier/actuator combination. The microprocessor generates the command angular position and rate waveforms in order to maintain a 90 percent dwell time/10 percent transition time ratio independently of chop frequency or amplitude. Performance and test results of a prototype system designed for use with a demonstration model of the SIRTF focal plane fine guidance sensor are presented.

Lorell, K. R.↗
NASA NTRS1984

Arcsecond Positions for Milliarcsecond VLBI Nuclei of Extragalactic Radio Sources, Part 2: 207 Sources

Very long base interferometry measurements of time delay and fringe frequency at 2.29 GHz on baselines of 10,000 km between Deep Space Network stations were used to determine the positions of the milliarcsecond nuclei in 207 extragalactic radio sources. Estimated accuracies generally range from approximately 0.1 to approximately 1.0, in both right ascension and declination, with all sources having uncertainties 4" in both coordinates. The observed sources are part of an all-sky VLBI catalog of milliarcsecond radio sources. Arcsecond positions are now determined for 752 of these sources. Arcsecond positions serve as a useful starting point in the construction of high-precision VLBI reference frames and are also important for unambiguous determination of optical counterparts to compact radio sources.

Morabito, D. D.↗
NASA NTRS1984

Air data position-error calibration using state reconstruction techniques

During the highly maneuverable aircraft technology (HiMAT) flight test program recently completed at NASA Ames Research Center's Dryden Flight Research Facility, numerous problems were experienced in airspeed calibration. This necessitated the use of state reconstruction techniques to arrive at a position-error calibration. For the HiMAT aircraft, most of the calibration effort was expended on flights in which the air data pressure transducers were not performing accurately. Following discovery of this problem, the air data transducers of both aircraft were wrapped in heater blankets to correct the problem. Additional calibration flights were performed, and from the resulting data a satisfactory position-error calibration was obtained. This calibration and data obtained before installation of the heater blankets were used to develop an alternate calibration method. The alternate approach took advantage of high-quality inertial data that was readily available. A linearized Kalman filter (LKF) was used to reconstruct the aircraft's wind-relative trajectory; the trajectory was then used to separate transducer measurement errors from the aircraft position error. This calibration method is accurate and inexpensive. The LKF technique has an inherent advantage of requiring that no flight maneuvers be specially designed for airspeed calibrations. It is of particular use when the measurements of the wind-relative quantities are suspected to have transducer-related errors.

Whitmore, S. A.↗
NASA NTRS1983

Apparatus for continuous, fast, and precise measurements of position and velocity of a small spherical particle

The position and velocity of optically levitated glass spheres (radii 10-20 microns) movng in a gas are measured accurately, rapidly, and continuously using a high-speed rotating polygon mirror. The experimental technique developed here has repeatable position accuracies better than 20 microns. Each measurement takes less than 1 microsec and can be repeated every 100 microsec. The position of the levitated glass spheres can be manipulated accurately by modulating the laser power with an acoustic optic modulator. The technique provides a fast and accurate method to study general particle dynamics in a fluid.

Venkataraman, T. S.↗
NASA NTRS1983

Positional repeatability measurements of stepper motors at cryogenic temperatures

For cryogenically-cooled infrared instruments and telescopes employed in space, reliable and predictable motor operations at 4 K in vacuum are in most cases necessary. For the Shuttle Infrared Telescope Facility (SIRTF), stepper motors may be employed in a number of applications. A test facility was designed and built for measuring stepper motor positional repeatability, in vacuum, over a temperature range from ambient to liquid helium temperature. Tests regarding positional repeatability were conducted at different motor speeds, directions of motor rotation, step sizes, and power conditions. In addition, tests were performed with respect to the ability of the motor to remain in a position with no power applied to the motor.

Pompea, S. M.↗