Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Track”

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.

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

At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Track structure model of cell damage in space flight

The phenomenological track-structure model of cell damage is discussed. A description of the application of the track-structure model with the NASA Langley transport code for laboratory and space radiation is given. Comparisons to experimental results for cell survival during exposure to monoenergetic, heavy-ion beams are made. The model is also applied to predict cell damage rates and relative biological effectiveness for deep-space exposures.

Katz, Robert↗
NASA NTRS1990

Tracking and letter classification under dichoptic and binocular viewing conditions

Subjects were required to fly a simulated helicopter path, while also classifying letter pairs presented intermitently at 5 retinal locations. Binocular and Dichoptic conditions were compared by employing color filters. Tracking under dichoptic conditions was strongly influenced by the absence of a common optical axis. Classification performance also deteriorated and was influenced by the conditions of tracking.

Gopher, Daniel↗
NASA NTRS1992

Comparisons of the NASA ER-2 meteorological measurement system with radar tracking and radiosonde data

Measurements of aircraft longitude, latitude, and velocity, and measurements of atmospheric pressure, temperature, and horizontal wind from the meteorological measurement system (MMS) on board the NASA ER-2 aircraft were compared with independent measurements of these quantities from radiosondes and radar tracking of both the ER-2 and radiosonde balloons. In general, the comparisons were good and within the expected measurement accuracy and natural variability of the meteorological parameters. Radar tracking of the ER-2 resolved the velocity and position drift of the inertial navigation system (INS). The rms errors in the horizontal velocity components of the ER-2, due to INS errors, were found to be 0.5 m/s. The magnitude of the drift in longitude and latitude depends on the sign and magnitude of the corresponding component velocity drift and can be a few hundredths of a degree. The radar altitudes of the ER-2 and radiosondes were used as the basis for comparing measurements of atmospheric pressure, temperature, and horizontal wind from these two platforms. The uncertainty in the MMS horizontal wind measurement is estimated to be +/- 2.5 m/s. The accuracy of the MMS pressure and temperature measurements were inferred to be +/- 0.3 hPa and +/- 0.3 K.

Gaines, Steven E.↗
NASA NTRS1992

Doppler tracking of planetary spacecraft

This article concerns the measurement of Doppler shift on microwave links that connect planetary spacecraft with the Deep Space Network. Such measurements are made by tracking the Doppler effect with phase-locked loop receivers. A description of equipment and techniques as well as a summary of the appropriate mathematical models are given. The two-way Doppler shift is measured by transmitting a highly-stable microwave (uplink) carrier from a ground station, having the spacecraft coherently transpond this carrier, and using a phase-locked loop receiver at the ground station to track the returned (downlink) carrier. The largest sources of measurement error are usually plasma noise and thermal noise. The plasma noise, which may originate in the ionosphere or the solar corona, is discussed; and a technique to partially calibrate its effect, involving the use of two simultaneous downlink carriers that are coherently related, is described. Range measurements employing Doppler rate-aiding are also described.

Kinman, Peter W.↗
NASA NTRS1992

Man-in-the-loop study of filtering in airborne head tracking tasks

A human-factors study is conducted of problems due to vibrations during the use of a helmet-mounted display (HMD) in tracking tasks whose major factors are target motion and head vibration. A method is proposed for improving aiming accuracy in such tracking tasks on the basis of (1) head-motion measurement and (2) the shifting of the reticle in the HMD in ways that inhibit much of the involuntary apparent motion of the reticle, relative to the target, and the nonvoluntary motion of the teleoperated device. The HMD inherently furnishes the visual feedback required by this scheme.

Lifshitz, S.↗
NASA NTRS1991

A precision transportable tracking telemetry system

New mission requirements and the main fetures of a new generation of tracking telemetry system designed to meet these requriements are discussed. The missions include launch vehicle support, sounding rocket mission support, and LEO satellite support, which often require support from remote sites with no existing tracking resources. To meet these requirements, the new system improves on the existing capabilities in three areas: improved RF performance, automation, and target positional accuracy. Initial results of system testing are presented. Without additional adjustment, the new system routinely falls within an absolute accuracy of +/-0.075 degrees, 3 sigma, and on most passes achieves +/-0.05 degrees, 3 sigma.

Morris, R. A.↗
NASA NTRS1992

Early Track NEP system options for SEI missions

A development option for nuclear electric propulsion, the 'Early Track' option, is considered from system and mission application viewpoints. The intent of this development option is to address demanding missions of the future, such as robotic outer planet exploration or the Space Exploration Initiative. The 'Early Track' scheme utilizes existing technologies, such as the SP-100 space reactor and radiator components, as well as subsystems scalable from existing programs, such as 50 to 100 kWe ion thrusters. Up to 1.5 MWe of powder can be generated by the existing 2.4 MWt SP-100 reactor through the use of dynamic Rankine or Brayton power conversion. The performance characteristics of these systems are projected, and assessed for SEI missions currently under consideration.

Gilland, J. H.↗
NASA NTRS1992

Error analysis of post-processed orbit determination for the Geosat Follow-On altimetric satellite using GPS tracking

A series of covariance analyses is presented for the Navy's Geosat Follow-On (GFO) altimetric satellite using selective availability/anti-spoof (SA/A-S) qualified (dual frequency) and non-SA/A-S qualified (single frequency) GPS receiver configurations. Data obtained indicate that a SA/A-S qualified GPS receiver is capable of meeting the 10 cm GFO post-processed radial orbit accuracy requirement when using reduced dynamic tracking. The non-SA/A-S qualified receiver is also capable of approaching this 10 cm radial uncertainty level if all systematic errors are removed from the C/A pseudorange and reduced dynamic tracking is used again.

Schreiner, William S.↗
NASA NTRS1991

Evaluation of Kapton pyrolysis, arc tracking, and arc propagation on the Space Station Freedom (SSF) solar array flexible current carrier (FCC)

Recent studies involving the use of polyimide Kapton coated wires indicate that if a momentary electrical short circuit occurs between two wires, sufficient heating of the Kapton can occur to themally chlar (pyrolyze) the Kapton. Such charred Kapton has sufficient electricxl conductivity to create an arc which tracks down the wires and possibly propagates to adjoining wires. These studies prompted an invetigation to ascertain the likelihood of Kapton pyrolysis, arc tracking and propagation phenomena, and the magnitude of destruction conceivably inflicted on Space Station Freedom's (SSF's) Flexible Current Carrier (FCC) for the photovoltaic array. The geometric layout of the FCC, having a planar-type orientation as opposed to bundles, may reduce the probability of sustaining an arc. An experimental investigation was conducted to simulate conditions under which an arc can occur on the FCC of the SSF, and the consequences of arc initiation.

Stueber, Thomas J.↗
NASA NTRS1992

Fuzzy logic control for camera tracking system

A concept utilizing fuzzy theory has been developed for a camera tracking system to provide support for proximity operations and traffic management around the Space Station Freedom. Fuzzy sets and fuzzy logic based reasoning are used in a control system which utilizes images from a camera and generates required pan and tilt commands to track and maintain a moving target in the camera's field of view. This control system can be implemented on a fuzzy chip to provide an intelligent sensor for autonomous operations. Capabilities of the control system can be expanded to include approach, handover to other sensors, caution and warning messages.

Lea, Robert N.↗
NASA NTRS1992

Adaptation of multidimensional group particle tracking and particle wall-boundary condition model to the FDNS code

A particulate two-phase flow CFD model was developed based on the FDNS code which is a pressure based predictor plus multi-corrector Navier-Stokes flow solver. Turbulence models with compressibility correction and the wall function models were employed as submodels. A finite-rate chemistry model was used for reacting flow simulation. For particulate two-phase flow simulations, a Eulerian-Lagrangian solution method using an efficient implicit particle trajectory integration scheme was developed in this study. Effects of particle-gas reaction and particle size change to agglomeration or fragmentation were not considered in this investigation. At the onset of the present study, a two-dimensional version of FDNS which had been modified to treat Lagrangian tracking of particles (FDNS-2DEL) had already been written and was operational. The FDNS-2DEL code was too slow for practical use, mainly because it had not been written in a form amenable to vectorization on the Cray, nor was the full three-dimensional form of FDNS utilized. The specific objective of this study was to reorder to calculations into long single arrays for automatic vectorization on the Cray and to implement the full three-dimensional version of FDNS to produce the FDNS-3DEL code. Since the FDNS-2DEL code was slow, a very limited number of test cases had been run with it. This study was also intended to increase the number of cases simulated to verify and improve, as necessary, the particle tracking methodology coded in FDNS.

Chen, Y. S.↗
NASA NTRS1992

Diffraction analysis and evaluation of several focus- and track-error detection schemes for magneto-optical disk systems

A commonly used tracking method on pre-grooved magneto-optical (MO) media is the push-pull technique, and the astigmatic method is a popular focus-error detection approach. These two methods are analyzed using DIFFRACT, a general-purpose scalar diffraction modeling program, to observe the effects on the error signals due to focusing lens misalignment, Seidel aberrations, and optical crosstalk (feedthrough) between the focusing and tracking servos. Using the results of the astigmatic/push-pull system as a basis for comparison, a novel focus/track-error detection technique that utilizes a ring toric lens is evaluated as well as the obscuration method (focus error detection only).

Bernacki, Bruce E.↗
NASA NTRS1991

Reusable Reentry Satellite (RRS): Telemetry, Tracking, and Command (TT/C) Coverage Tradeoff Study

The Reusable Reentry Satellite (RRS) Telemetry, Tracking & Command (TT&C) Coverage Tradeoff Study described herein was performed during Part 1 of the RRS Phase B contract. This report is one of several that describes the results of various trade studies performed to arrive at a recommended design for the RRS satellite system. The overall RRS Phase B Study objective is to design a relatively inexpensive satellite to access space for extended periods of time, with eventual recovery of experiments on Earth. The RRS will be capable of: (1) being launched by a variety of expendable launch vehicles; (2) operating in low earth orbit as a free flying unmanned laboratory; and (3) executing an independent atmospheric reentry and soft landing. The RRS will be designed to be refurbished and reused up to three times a year for a period of 10 years. The expected principal use for such a system is research on the effects of variable gravity (0 to 1.5 g) and radiation on small animals, plants, lower life forms, tissue samples, and materials processes. This Summary Report provides a description of the RRS Telemetry, Tracking & Command Analysis performed to study the ground station coverage available to meet RRS requirements. Concepts were considered that used off-the-shelf technology, had generous margins of capability, and high reliability, were easily maintained, cost effective, and were compatible with existing support networks. From this study, a recommended RRS TT&C configuration will be developed.

Source record↗
NASA NTRS1993

A ground track control algorithm for the Topographic Mapping Laser Altimeter (TMLA)

The results of an analysis of an algorithm that will provide autonomous onboard orbit control using orbits determined with Global Positioning System (GPS) data. The algorithm uses the GPS data to (1) compute the ground track error relative to a fixed longitude grid, and (2) determine the altitude adjustment required to correct the longitude error. A program was written on a personal computer (PC) to test the concept for numerous altitudes and values of solar flux using a simplified orbit model including only the J sub 2 zonal harmonic and simple orbit decay computations. The algorithm was then implemented in a precision orbit propagation program having a full range of perturbations. The analysis showed that, even with all perturbations (including actual time histories of solar flux variation), the algorithm could effectively control the spacecraft ground track and yield more than 99 percent Earth coverage in the time required to complete one coverage cycle on the fixed grid (220 to 230 days depending on altitude and overlap allowance).

Blaes, V.↗
NASA NTRS1992

The determination of a one year mean sea surface height track from Geosat altimeter data and ocean variability implications

Results are presented for determinations of mean sea surface along a reference Geosat altimeter tracking, using Geosat data from the first year of the exact repeat mission (ERM) and improved orbits. The results were used to study the time variability of the ocean surface, and a map was constructed of the major current structure. The data included 21 complete and one incomplete ERMs, with the sea surface heights being referenced to the single reference track through the application of geoid gradient corrections. This Geosat surface can be used as a reference surface to which other altimeter data could be incorporated; the data could then be used for the recovery of geoid undulations and gravity anomalies in the ocean areas.

Wang, Yan M.↗
NASA NTRS1992

Quadratic stabilization and tracking - Applications to the benchmark problem

Recent results regarding quadratic stabilization and disturbance attenuation are applied to the benchmark problem. The authors investigate the minimum achievable levels of disturbance attenuation for different disturbance inputs and controlled outputs. They then design a feedforward tracking controller which tracks step inputs while maintaining the disturbance attenuation properties of the regulator.

Schmitendorf, W. E.↗
NASA NTRS1991

Particle image velocimetry for the Surface Tension Driven Convection Experiment using a particle displacement tracking technique

The Surface Tension Driven Convection Experiment (STDCE) is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for 1992. One of the components of data collected during the experiment is a video record of the flow field. This qualitative data is then quantified using an all electronic, two-dimensional particle image velocimetry technique called particle displacement tracking (PDT) which uses a simple space domain particle tracking algorithm. The PDT system is successful in producing velocity vector fields from the raw video data. Application of the PDT technique to a sample data set yielded 1606 vectors in 30 seconds of processing time. A bottom viewing optical arrangement is used to image the illuminated plane, which causes keystone distortion in the final recorded image. A coordinate transformation was incorporated into the system software to correct this viewing angle distortion. PDT processing produced 1.8 percent false identifications, due to random particle locations. A highly successful routine for removing the false identifications was also incorporated, reducing the number of false identifications to 0.2 percent.

Wernet, Mark P.↗
NASA NTRS1991

Space-based millimeter-wave debris tracking radar

NORAD system currently tracks and predicts orbits of space objects of 80 mm or larger in diameter. The small debris of less than 80 mm, traveling at high speed, could cause damage to Space Station or space vehicles. To overcome this problem, a 35 GHz space-based millimeter-wave radar system is proposed to track the particles ranging in size from 4 mm to 80 mm up to a range of 25 Km. The system requires a large phased array which should be developed in monolithic circuits for cost reduction.

Chang, Kai↗