SEARCH · Search NASA

Results for “Positioning”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4

All sources NASA NTRS DOE OSTI

NASA NTRS1991

Apparatus for precision focussing and positioning of a beam waist on a target

The invention relates to optical focussing apparatus and, more particularly, to optical apparatus for focussing a highly collimated Gaussian beam which provides independent and fine control over the focus waist diameter, the focus position both along the beam axis and transverse to the beam, and the focus angle. A beam focussing and positioning apparatus provides focussing and positioning for the waist of a waisted beam at a desired location on a target such as an optical fiber. The apparatus includes a first lens, having a focal plane f sub 1, disposed in the path of an incoming beam and a second lens, having a focal plane f sub 2 and being spaced downstream from the first lens by a distance at least equal to f sub 1 + 10 f sub 2, which cooperates with the first lens to focus the waist of the beam on the target. A rotatable optical device, disposed upstream of the first lens, adjusts the angular orientation of the beam waist. The transverse position of the first lens relative to the axis of the beam is varied to control the transverse position of the beam waist relative to the target (a fiber optic as shown) while the relative axial positions of the lenses are varied to control the diameter of the beam waist and to control the axial position of the beam waist. Mechanical controllers C sub 1, C sub 2, C sub 3, C sub 4, and C sub 5 control the elements of the optical system. How seven adjustments can be made to correctly couple a laser beam into an optical fiber is illustrated. Prior art systems employing optical techniques to couple a laser beam into an optical fiber or other target simply do not provide the seven necessary adjustments. The closest known prior art, a Newport coupler, provides only two of the seven required adjustments.

Lynch, Dana H.↗

NASA NTRS1992

A radio optical reference frame. IV - Additional radio source positions in the Northern Hemisphere

Seventy-seven extragalactic radio sources north of -2 deg declination have been observed using Mark III VLBI during 13 experiments from 1988 October to 1989 November. Radio positions derived from these observations supplement an ongoing project to define and maintain an all-sky radio/optical reference frame of 400 or more extragalactic sources with milliarcsecond (mas) accurate radio and optical positions. Positions for 11 new sources are presented along with improved positions for 54 sources already in the reference-frame catalog. An additional five sources have been determined to be unsuitable reference-frame objects. Observations of seven calibration sources tie the new positions to the existing catalog. The radio positions of the new sources have formal mean errors of about 0.7 mas in each coordinate. Sources for which improved positions are reported now have formal errors not greater than 1 mas, an improvement in some cases by as much as 85 percent. The complementary optical program is addressed briefly.

Fey, A. L.↗

NASA NTRS2001

Video-Based Sensor for Robotic Position and Attitude determination

NASA's Marshall Space Flight Center (MSFC) has, for the last ten years, developed various video-based sensors for use in automated docking systems. The latest generation of sensor will operate at rates of up to 100 Hz, determining the relative position (X, Y, and Z) and attitude (Roll, Pitch, and Yaw) between the sensor and a small 3-dimensional target, making it suitable for applications in robotic sensing. The Advanced Video Guidance Sensor (AVGS) is designed to track multiple targets at different ranges and determine the position and attitude of each one. The previous generation of video sensor, the Video Guidance Sensor (VGS), was flown twice on the Space Shuttle to test its performance on orbit. One of the tests performed was determining the relative positions and attitudes between the VGS and its target, which was moved to various positions using the Remote Manipulator System (RMS). The RMS position data and VGS measured data were analyzed after the flights, with good correlation between the position and attitude data of the two data sets. The test using the RMS gives a good idea of the ability of the use of the AVGS as a sensor for end-effector position and attitude determination.

Howard, Richard T.↗

NASA NTRS2000

Regional ventilation-perfusion distribution is more uniform in the prone position

The arterial blood PO(2) is increased in the prone position in animals and humans because of an improvement in ventilation (VA) and perfusion (Q) matching. However, the mechanism of improved VA/Q is unknown. This experiment measured regional VA/Q heterogeneity and the correlation between VA and Q in supine and prone positions in pigs. Eight ketamine-diazepam-anesthetized, mechanically ventilated pigs were studied in supine and prone positions in random order. Regional VA and Q were measured using fluorescent-labeled aerosols and radioactive-labeled microspheres, respectively. The lungs were dried at total lung capacity and cubed into 603-967 small ( approximately 1.7-cm(3)) pieces. In the prone position the homogeneity of the ventilation distribution increased (P = 0.030) and the correlation between VA and Q increased (correlation coefficient = 0.72 +/- 0.08 and 0.82 +/- 0.06 in supine and prone positions, respectively, P = 0.03). The homogeneity of the VA/Q distribution increased in the prone position (P = 0.028). We conclude that the improvement in VA/Q matching in the prone position is secondary to increased homogeneity of the VA distribution and increased correlation of regional VA and Q.

NASA Program Biomedical Research and Countermeasur↗

NASA NTRS2005

Rapid Centroids and the Refined Position Accuracy of the Swift Gamma-ray Burst Catalogue

The Swift X-ray Telescope autonomously refines the Burst Alert Telescope positions (approx.1-4' uncertainty) to better than 5 arcsec, within 5 seconds of target acquisition by the observatory for typical bursts. The results of the rapid positioning capability of the XRT are presented here for both known sources and newly discovered GRBs, demonstrating the ability to automatically utilize one of two integration times according to the burst brightness, and to correct the position for alignment offsets caused by the fast pointing performance and variable thermal environment of the satellite as measured by the Telescope Alignment Monitor. We present an evaluation of the position accuracy for both the onboard centroiding software and the ground software for the calibration targets and show that a significant improvement in position accuracy is obtained if the boresight detector position is optimized relative to the spacecraft pointing. Finally, we present an updated catalogue of Swift GRB X-ray positions obtained in Photon Counting Mode using the improved, calibrated boresight.

Hill, J. E.↗

NASA NTRS2010

Automatic Mesh Generation of Hybrid Mesh on Valves in Multiple Positions in Feedline Systems

Fluid flow simulations through a valve often require evaluation of the valve in multiple opening positions. A mesh has to be generated for the valve for each position and compounding. The problem is the fact that the valve is typically part of a larger feedline system. In this paper, we propose to develop a system to create meshes for feedline systems with parametrically controlled valve openings. Herein we outline two approaches to generate the meshes for a valve in a feedline system at multiple positions. There are two issues that must be addressed. The first is the creation of the mesh on the valve for multiple positions. The second is the generation of the mesh for the total feedline system including the valve. For generation of the mesh on the valve, we will describe the use of topology matching and mesh generation parameter transfer. For generation of the total feedline system, we will describe two solutions that we have implemented. In both cases the valve is treated as a component in the feedline system. In the first method the geometry of the valve in the feedline system is replaced with a valve at a different opening position. Geometry is created to connect the valve to the feedline system. Then topology for the valve is created and the portion of the topology for the valve is topology matched to the standard valve in a different position. The mesh generation parameters are transferred and then the volume mesh for the whole feedline system is generated. The second method enables the user to generate the volume mesh on the valve in multiple open positions external to the feedline system, to insert it into the volume mesh of the feedline system, and to reduce the amount of computer time required for mesh generation because only two small volume meshes connecting the valve to the feedline mesh need to be updated.

Ross, Douglass H.↗

NASA NTRS2010

Inductive Non-Contact Position Sensor

Optical hardware has been developed to measure the depth of defects in the Space Shuttle Orbiter's windows. In this hardware, a mirror is translated such that its position corresponds to the defect's depth, so the depth measurement problem is transferred to a mirror-position measurement problem. This is preferable because the mirror is internal to the optical system and thus accessible. Based on requirements supplied by the window inspectors, the depth of the defects needs to be measured over a range of 200 microns with a resolution of about 100 nm and an accuracy of about 400 nm. These same requirements then apply to measuring the position of the mirror, and in addition, since this is a scanning system, a response time of about 10 ms is needed. A market search was conducted and no sensor that met these requirements that also fit into the available housing volume (less than one cubic inch) was found, so a novel sensor configuration was constructed to meet the requirements. This new sensor generates a nearly linearly varying magnetic field over a small region of space, which can easily be sampled, resulting in a voltage proportional to position. Experiments were done with a range of inductor values, drive voltages, drive frequencies, and inductor shapes. A rough mathematical model was developed for the device that, in most aspects, describes how it operates and what electrical parameters should be chosen for best performance. The final configuration met all the requirements, yielding a small rugged sensor that was easy to use and had nanometer resolution over more than the 200-micron range required. The inductive position sensor is a compact device (potentially as small as 2 cubic centimeters), which offers nanometer-position resolution over a demonstrated range of nearly 1 mm. One of its advantages is the simplicity of its electrical design. Also, the sensor resolution is nearly uniform across its operational range, which is in contrast to eddy current and capacitive sensors whose sensitivity is dependent upon position.

Youngquist, Robert↗

NASA NTRS2012

Absolute Position of Targets Measured Through a Chamber Window Using Lidar Metrology Systems

Lidar is a useful tool for taking metrology measurements without the need for physical contact with the parts under test. Lidar instruments are aimed at a target using azimuth and elevation stages, then focus a beam of coherent, frequency modulated laser energy onto the target, such as the surface of a mechanical structure. Energy from the reflected beam is mixed with an optical reference signal that travels in a fiber path internal to the instrument, and the range to the target is calculated based on the difference in the frequency of the returned and reference signals. In cases when the parts are in extreme environments, additional steps need to be taken to separate the operator and lidar from that environment. A model has been developed that accurately reduces the lidar data to an absolute position and accounts for the three media in the testbed air, fused silica, and vacuum but the approach can be adapted for any environment or material. The accuracy of laser metrology measurements depends upon knowing the parameters of the media through which the measurement beam travels. Under normal conditions, this means knowledge of the temperature, pressure, and humidity of the air in the measurement volume. In the past, chamber windows have been used to separate the measuring device from the extreme environment within the chamber and still permit optical measurement, but, so far, only relative changes have been diagnosed. The ability to make accurate measurements through a window presents a challenge as there are a number of factors to consider. In the case of the lidar, the window will increase the time-of-flight of the laser beam causing a ranging error, and refract the direction of the beam causing angular positioning errors. In addition, differences in pressure, temperature, and humidity on each side of the window will cause slight atmospheric index changes and induce deformation and a refractive index gradient within the window. Also, since the window is a dispersive media, the effect of both phase and group indices have to be considered. Taking all these factors into account, a method was developed to measure targets through multiple regions of different materials and produce results that are absolute measurements of target position in three-dimensional space, rather than simply relative position. The environment in which the lidar measurements are taken must be broken down into separate regions of interest and each region solved for separately. In this case, there were three regions of interest: air, fused silica, and vacuum. The angular position of the target inside the chamber is solved using only phase index and phase velocity, while the ranging effects due to travel from air to glass to vacuum/air are solved with group index and group velocity. When all parameters are solved simultaneously, an absolute knowledge of the position of each target within an environmental chamber can be derived. Novel features of this innovation include measuring absolute position of targets through multiple dispersive and non-dispersive media, deconstruction of lidar raw data from a commercial off-the-shelf unit into reworkable parameters, and use of group velocities to reduce range data. Measurement of structures within a vacuum chamber or other harsh environment, such as a furnace, may now be measured as easily as if they were in an ambient laboratory. This analysis permits transformation of the raw data into absolute spatial units (e.g., mm). This technique has also been extended to laser tracker, theodolite, and cathetometer measurements through refractive media.

Kubalak, David↗

NASA NTRS2018

Southeast Greenland Winter Precipitation Strongly Linked to the Icelandic Low Position

Greenland's largest precipitation flux occurs in its southeast (SE) region during the winter, controlled primarily by easterly winds and frequent cyclogenesis in the North Atlantic. Several studies have attempted to link SE Greenland precipitation to the North Atlantic Oscillation (NAO) but results are inconsistent. This work uses reanalysis, automatic weather station data, and regional climate model output to show that the east-west position of the Icelandic low is a better predictor of SE Greenland precipitation (average correlation of r equals -0.48 in DJF (December January February)) than climate indices such as the NAO (r equals -0.06 in DJF). In years when the Icelandic low is positioned extremely west, moisture transport increases up to approximately 40 percent (or up to 40 kilograms per meter per second) off the SE Greenland coast compared to when the low is in an extreme east position. Furthermore, in years when the Icelandic low is positioned extremely west, storm track density and intensity increase just off the SE coast of Greenland. Thus, the Icelandic low's longitudinal position dominates SE Greenland ice sheet's wintertime precipitation, a positive term in the ice sheet mass balance. Given SE Greenland's importance in the overall ice sheet mass balance, the position of the Icelandic low is therefore important for making projections of future sea level.

Arctic↗

NASA NTRS1995

Precise Kinematic Positioning with Simultaneous GPS Pseudorange and Carrier Phase Measurements

This paper investigates three precise kinematic positioning techniques with simultaneous GPS pseudorange and carrier phase measurements. These techniques are simple, efficient, and well suited for real-time positioning applications. A simulation/covariance analysis is carried out comparing the relative performance of these techniques. The analysis indicates that GPS carrier phase measurements significantly strengthen kinematic positioning. When wide-area differential GPS for reducing SA clock errors and GPS ephemeris errors is available, a low Earth orbiting satellite can be positioned to 0.5-0.8 m in accuracy (3-D RSS). The accuracy is superior to positioning with pseudorange measurements alone by a factor of 2 to 3. Relative positioning performance and complexity between the three techniques are compared.

['Kinematic↗

NASA NTRSDate not supplied

Lunar Surface Position Determination using Perceived Signal Strength

The purpose of this project is to evaluate the feasibility of transmitters and receivers on the lunar surface for Position Determination (PD) without any form of lunar Global Positioning System (GPS). The early Artemis program may lack GPS satellites orbiting the Moon, and it is critical that activities with the lander, rover, and crew EVA identify their position on the lunar surface at all times. This project creates a prototype system that trilaterates user position based upon the perceived signal from at least 3 nearby transmission towers, called “Lunar Access Points”. The application of perceived signal strength for surface PD has historically been used in terrestrial systems such as Long Range Navigation (LORAN), which was popular with the maritime industry prior to the Global Positioning System (GPS). The ease of installing such a local system for early Artemis missions provides a critical resource until satellite-based position determination systems are deployed. A surface-based PD can also be used in GPS-denied environments such as deep craters or lava tubes where satellite visibility is compromised. By demonstrating the basic capability of surface PD, this student team has learned about issues with power, distance, thermal, dust, radiation, data processing, and communication problems applicable to the lunar surface. This knowledge can feed into future NASA requirements to improve the capability of a LunaNET implementation for the Artemis program. This project follows 10 years of successful collaboration between NASA JSC/ARES, Texas Space, Technology, Applications and Research (T STAR) and Texas A&M University in a Public, Private, Academic (PPA) Partnership. NASA funds T STAR to mentor undergraduate Capstone teams in the College of Engineering Department to design, built, and test prototypes meeting NASA requirements. TAMU faculty lead the student teams in their academic class, and NASA Subject Matter Experts (SMEs) provide T STAR and students insight on requirements evolution, prior design projects, and future development goals.

Position Determination↗

NASA NTRS1979

Experimental determination of position-estimate accuracy using back-azimuth signals from a microwave landing system

Flight tests using the Boeing 737 airplane to obtain position estimates with back azimuth signals from a microwave landing system (MLS) are discussed. The equations and logic used to generate a navigation position estimate in the MLS back azimuth signal environment are described. The error in the navigation position estimate is determined. A summary of the Boeing 737 position estimate update process is described. The navigation position estimate error calculated flight data and radar tracking information is analyzed. The position estimate error data using the MLS inputs are compared with error data obtained during dual distance measuring equipment updates.

Knox, C. E.↗

NASA NTRS1980

Unidentified galactic X-ray sources positioned with the HEAO-1 scanning modulation collimator

Observations made with the HEAO-1 scanning modulation collimator are used to determine the positions of 16 unidentified X-ray sources at low galactic latitudes. Positions were obtained to within 10-30 arcsec in one dimension from two four-grid collimator observations made at six-month intervals. Positions determined in addition for eight sources identified with optical objects verify the method employed. Of the unidentified sources, the positional uncertainties of ten are reduced by factors of two to eight, the precise X-ray positions (within 10 arcsec) obtained by lunar occultation experiments are confirmed for three and multiple precise positions (within 20 arcsec) which reduce the previous location uncertainties by factors of greater than 100 are obtained for the remaining three.

Reid, C. A.↗

NASA NTRS1988

Local position control: A new concept for control of manipulators

Resolved motion rate control is currently one of the most frequently used methods of manipulator control. It is currently used in the Space Shuttle remote manipulator system (RMS) and in prosthetic devices. Position control is predominately used in locating the end-effector of an industrial manipulator along a path with prescribed timing. In industrial applications, resolved motion rate control is inappropriate since position error accumulates. This is due to velocity being the control variable. In some applications this property is an advantage rather than a disadvantage. It may be more important for motion to end as soon as the input command is removed rather than reduce the position error to zero. Local position control is a new concept for manipulator control which retains the important properties of resolved motion rate control, but reduces the drift. Local position control can be considered to be a generalization of resolved position and resolved rate control. It places both control schemes on a common mathematical basis.

Kelly, Frederick A.↗

NASA NTRS1991

A radio optical reference frame. II - Additional radio and optical source positions in the Northern Hemisphere

VLBI observations from 12 sessions have been made of a total of 103 sources north of -2 deg declination. These data give the first extension to the radio/optical reference frame catalog already defined by the data in the NASA Crustal Dynamics Project database prior to July 1988. The new observations add 53 new sources to the radio reference frame catalog, improve the positions of 29 from the previous version, and show another seven sources to be unsuitable reference frame objects. Observations of 14 calibration sources tie the new positions to the existing catalog. The formal mean errors for the radio positions of the additional sources are about 0.8 mas in each coordinate. Optical positions for eight sources have been measured in the FK5 system, bringing the total number of sources in the catalog with accurate positions for their optical counterparts to 36. The new optical positions have an accuracy of about 50 mas.

Russell, J. L.↗

NASA NTRS1992

Accurate radio and optical positions for southern radio sources

Accurate radio positions with a precision of about 0.01 arcsec are reported for eight compact extragalactic radio sources south of -45-deg declination. The radio positions were determined using VLBI at 8.4 GHz on the 9589 km Tidbinbilla (Australia) to Hartebeesthoek (South Africa) baseline. The sources were selected from the Parkes Catalogue to be strong, flat-spectrum radio sources with bright optical QSO counterparts. Optical positions of the QSOs were also measured from the ESO B Sky Survey plates with respect to stars from the Perth 70 Catalogue, to an accuracy of about 0.19 arcsec rms. These radio and optical positions are as precise as any presently available in the far southern sky. A comparison of the radio and optical positions confirms the estimated optical position errors and shows that there is overall agreement at the 0.1-arcsec level between the radio and Perth 70 optical reference frames in the far south.

Harvey, Bruce R.↗

NASA NTRS1992

SHAPES - Spatial, high-accuracy, position-encoding sensor

Future space systems will require control sensors capable of real-time measurements of position coordinates of many structural locations. Applications for such a sensor include figure and vibration control, rendezvous and docking, and structure assembly verification. The paper discusses an experimental study of SHAPES (spatial, high-accuracy, position-encoding sensor), a 3D position sensor that provides range and two angular positions of laser-illuminated retroreflector targets that mark the locations to be measured. Simultaneous range measurements to multiple targets by a time-of-flight corelation of short laser pulses are made with a CCD-equipped streak tube. Angular positions are measured with a CCD camera. Position measurements of 24 targets with sub-millimeter range accuracy at a 10 Hz update rate have been demonstrated.

Nerheim, Noble M.↗

NASA NTRS1992

A radio optical reference frame. III - Additional radio and optical positions in the Southern Hemisphere

Radio and optical positions are presented for southern hemisphere extragalactic sources from the Parkes 2.7 GHz survey. Sixty-one sources were observed with Mark III VLBI at 8.4 GHz between Tidbinbilla, Australia, and Hartebeesthoek, South Africa. The results presented are part of the effort to establish a global reference frame of 400 extragalactic radio sources. Radio positions with about 10 milliarcsec errors have been estimated for 39 sources not previously in the present radio reference frame catalog, and provisional positions were obtained for two additional sources, bringing the total number of catalog sources to 276. The principal source of error is the uncalibrated ionosphere. Of the remaining sources five were completely undetected, six were either too faint or too resolved, and nine had previous catalog positions. Optical positions on the FK5 system have also been measured for four southern sources using prime focus plates from the Anglo-Australian 4 m telescope with an accuracy of 0.06 arcsec. This raises to 40 the number of radio sources with accurately measured positions for their optical counterparts.

Russell, J. L.↗