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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
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NASA NTRS1999

Mantle Q at Period 12.4 Hours: New Estimates from Satellite Tracking and Altimetry

The most convincing estimates of mantle Q at periods of many hours have historically come from extrapolating seismic and free-oscillation estimates via some assumed frequency dependence, sometimes contrained by estimates from the Chandler Wobble. At the semidiurnal tidal period, direct estimates of Q have been difficult to obtain because of the dominating signals of the ocean tides, which account for more than 95!k of the tidal energy dissipation. But knowledge of the ocean tides has been rapidly improving, primarily owing to satellite altimetry, and in 1996 we reported (NATURE, 381, 595-7) an estimate of solid-earth tidal energy dissipation and mantle Q based on combining satellite altimeter measurements with tracking observations of tidally induced satellite orbit perturbations. Tidal estimates from both reveal a small systematic difference in the quadrature component of the degree-2, order-2 spherical harmonic coefficients, which we attribute to a small lag in the earth's body tide. The formalism accounts for this lag in both the altimeter and tracking solutions and also accounts for a very small contribution from the lunar atmospheric tide. Since this original report, both altimeter and tracking estimates have improved. Recent solutions for the body-tide lag at the M2 period are 0.20 +/- 0.09 degrees, implying an energy dissipation of 100 +/- 50 gigawatts and a solid-earth Q of 300. Further new solutions will be discussed, as will the prospects for significantly reducing error bars and for obtaining estimates from other tides in the diurnal band.

Ray, Richard D.↗
NASA NTRS1961

ON THE ACCURACY OF MEASUREMENTS MADE UPON FILMS PHOTOGRAPHED BY BAKER-NUNN SATELLITE TRACKING CAMERAS

The photographs taken by the Baker-Nunn cameras of the Smithsonian Astrophysical Observatory were formerly measured with Van Biesbroeck goniometers, but are now measured exclusively with Mann two-screw comparators. Instead of measuring point images, we usually have to measure oblong images, either trails or breaks (the latter produced by interruption of the exposure). We can therefore expect that the accuracy of the determination of their positions is more influenced by the personal errors than it is in conventional astrometry. Approximately 800 measurements were made on 34 images of different length, and, from these, the frequency distribution of settings was determined. Then the relationship between this distribution and the length of the image (trail or break) was examined, and the relationship between the "magnitude error" and the length of image was determined. Measurements were made at different angles formed by the trails and the reticle lines, and it was found that the accuracy was not affected by the angle of the setting. Position determinations have been made using reference stars at different distances. On the basis of these results, we can conclude that the accuracy is neither influenced by the distortion of the emulsion nor by the optical distortion within an area of a diameter of S cm (5°.8). We believe that we are justified in using the linear plate constant method, at least within this area. From numerous double and multiple measurements, the following standard errors were determined for a single position.

ASTROMETRY↗
NASA NTRS1978

Assessment of needs for satellite tracking of birds and suggestions for expediting a program

Equipment development and testing, animal-instrument interphase or attachment methods, and the evaluation of various feasibility-tracking experiments with raptors are described as well as suggestions for expediting a future program. Results of animal-instrument interphases work indicate that large free-flying birds can be successfully instrumented with radio packages comparable in weight to satellite-transmitter packages. The 401 MHz frequency proved satisfactory for a combination of satellite and ground tracking of migrating birds. Tests run for nearly a year with the Nimbus 6 satellite and a miniaturized, one-watt prototype RAMS transmitter produced encouraging results in regard to location accuracy, frequency of contact with satellite and use of whip antennas. A future program is recommended with priority given to development of six operational transmitters for feasibility experiments.

Craighead, F. C., Jr.↗
NASA NTRS1997

Solution of the Angles-Only Satellite Tracking Problem

A single observation station, located at an arbitrary point on the surface of the Earth, can determine only the azimuth and elevation angles of a satellite or ballistic vehicle, and the time at which these observations occur. No information is available about the range or the range-rate of the target. It is shown that five observations of either the elevation or the azimuth, and the time of either set of observations, determine the complete set of orbital elements of the target. The implementation of the theory presented here could provide a great reduction in the hardware costs associated with satellite and reentry vehicle tracking.

Burnes, R. E.↗
NASA NTRS1978

On the determination and investigation of the terrestrial ionospheric refractive indices using GEOS-3/ATS-6 satellite-to-satellite tracking data

An analysis of the shortening and lengthening of the phase of satellite-to-satellite (SST) data that passed within 40-700 km above the earth surface during its ATS-6 to GEOS-3 to ATS-6 path resulted in refractivity vs height profiles. The SST Doppler data were used directly to adjust the GEOS-3 orbit. Perturbations from the moon, sun, and a 15th-order/degree earth gravity field were included in the orbit solution. This orbit was continued through the occulation period and a model ionosphere was estimated by a least-squares adjustment of the Chapman ionosphere parameters from the SST data residuals. The refractivity profile obtained by this model ionosphere was compared to a refractivity profile obtained by a direct integral inversion of the SST data residuals. Systematic differences between the two methods were caused by orbital errors, which propagated into the solution.

Liu, A. S.↗
NASA NTRS1983

Second Shuttle Join NASA's STS Fleet: Challenger Launches First New Tracking Satellite

NASA made a major stride in readying a second delivery vehicle for its Space Transportation System (STS) fleet with the perfect landing of Shuttle Orbiter Challenger at Edwards Air Force Base, California, April 9, 1983. Besides being the first flight test of Challenger's performance, the mission marked the orbiting of the first spacecraft in NASA's new Tracking and Data Relay Satellite System (TDRSS). The new family of orbiting space communications platforms is essential to serve future Shuttle missions. Although the Inertial Upper Stage (IUS) second stage engine firing failed to place TDRS in its final 35,888 kilometer (22,300 mile) geosynchronous orbit, its release from the orbiter cargo bay went as planned. Launch officials were confident they can achieve its planned orbit in a matter of weeks.

Source record↗
NASA NTRS1966

Tracking

Satellite tracking and data acquisition networks for space exploration

SATELLITE TRACKING↗
NASA NTRS1977

Real time control of satellite tracking station operation for millimeter wave experiments and associated data processing

Real time control, data collection, and data reduction of an earth-satellite millimeter wave system are discussed. Experiment control and data processing requirements are considered with attention to signal data acquisition, weather data acquisition, support and control functions, task classifications, the fundamental data acquisition procedure, and the computer-experiment interface. The general analysis is applied to a description of the Communications Technology Satellite system and its hardware.

Kauffman, S. R.↗
NASA NTRS1986

Near-optimal strategies for sub-decimeter satellite tracking with GPS

Decimeter tracking of low Earth orbiters using differential Global Positioning System (GPS) techniques is discussed. A precisely known global network of GPS ground receivers and a receiver aboard the user satellite are needed, and all techniques simultaneously estimate the user and GPS satellite orbits. Strategies include a purely geometric, a fully dynamic, and a hybrid strategy. The last combines dynamic GPS solutions with a geometric user solution. Two powerful extensions of the hybrid strategy show the most promise. The first uses an optimized synthesis of dynamics and geometry in the user solution, while the second uses a gravity adjustment method to exploit data from repeat ground tracks. These techniques promise to deliver subdecimeter accuracy down to the lowest satellite altitudes.

Yunck, Thomas P.↗
NASA NTRS1974

Direct recovery of mean gravity anomalies from satellite to satellite tracking

The direct recovery was investigated of mean gravity anomalies from summed range rate observations, the signal path being ground station to a geosynchronous relay satellite to a close satellite significantly perturbed by the short wave features of the earth's gravitational field. To ensure realistic observations, these were simulated with the nominal orbital elements for the relay satellite corresponding to ATS-6, and for two different close satellites (one at about 250 km height, and the other at about 900 km height) corresponding to the nominal values for GEOS-C. The earth's gravitational field was represented by a reference set of potential coefficients up to degree and order 12, considered as known values, and by residual gravity anomalies obtained by subtracting the anomalies, implied by the potential coefficients, from their terrestrial estimates. It was found that gravity anomalies could be recovered from strong signal without using any a-priori terrestrial information, i.e. considering their initial values as zero and also assigning them a zero weight matrix. While recovering them from weak signal, it was necessary to use the a-priori estimate of the standard deviation of the anomalies to form their a-priori diagonal weight matrix.

Hajela, D. P.↗
NASA NTRSDate not supplied

Satellite Tracking of Shallow Cumulus during CAMP2Ex: The Aerosol and Organization Connection

Shallow moist convection is ubiquitous throughout the tropics and represents a key player in boundary layer processes. Shallow clouds come in many forms, from scattered, short-lived cumulus to organized features that include cold pool boundaries and lines reaching O(100 km) scale lasting several hours. In this study, we explore how cloud morphology and environmental aerosol affect shallow cumulus lifecycle properties. Measuring such influences requires a broad, detailed view of these cloud fields as they grow and decay. Geostationary satellites provide a means to follow the clouds with enhanced spatiotemporal sampling from space. We apply a cloud-tracking tool to study lifecycle properties of shallow cumulus sampled during the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) field campaign of 2019. The mission conducted airborne and shipborne operations over the West Pacific Ocean, in tandem with Rapid Scan imagery from the Advanced Himawari Imager (AHI) on the Japan Meteorological Agency’s (JMA) Himawari-8 satellite. We segment shallow cumulus on AHI 0.5-km visible reflectance during the daylit hours of several research flights that exhibited ideal atmospheric conditions for tracking. We collect the resulting cloud tracks by regions containing airborne sampling of the cloud environments and by two specific segmentation techniques: one optimized for small, disorganized cumulus and the other for larger, organized clouds using suitable thresholds for reflectance and blurring. We present an analysis of cloud lifecycle properties using our dual segmentation approach for various sampled environments of CAMP2Ex. A total of 7 research flights (RFs) exhibited ideal conditions for generating cloud-track ensembles under similar thermodynamic and kinematic profiles but with varying aerosol load. We consider lifetime, track-achieved metrics, and ensemble-fitted growth rates to evaluate the aerosol effect. Cloud elongation, a factor in cloud morphology, is also considered for any potential influence in observed shifts in growth rates. The results suggest that aerosol affects cloud lifecycles more significantly for clouds with larger areas and independent of the elongation factor.

Cloud Tracking↗
NASA NTRS1991

Improved accuracies for satellite tracking

A charge coupled device (CCD) camera on an optical telescope which follows the stars can be used to provide high accuracy comparisons between the line of sight to a satellite, over a large range of satellite altitudes, and lines of sight to nearby stars. The CCD camera can be rotated so the motion of the satellite is down columns of the CCD chip, and charge can be moved from row to row of the chip at a rate which matches the motion of the optical image of the satellite across the chip. Measurement of satellite and star images, together with accurate timing of charge motion, provides accurate comparisons of lines of sight. Given lines of sight to stars near the satellite, the satellite line of sight may be determined. Initial experiments with this technique, using an 18 cm telescope, have produced TDRS-4 observations which have an rms error of 0.5 arc second, 100 m at synchronous altitude. Use of a mosaic of CCD chips, each having its own rate of charge motion, in the focal place of a telescope would allow point images of a geosynchronous satellite and of stars to be formed simultaneously in the same telescope. The line of sight of such a satellite could be measured relative to nearby star lines of sight with an accuracy of approximately 0.03 arc second. Development of a star catalog with 0.04 arc second rms accuracy and perhaps ten stars per square degree would allow determination of satellite lines of sight with 0.05 arc second rms absolute accuracy, corresponding to 10 m at synchronous altitude. Multiple station time transfers through a communications satellite can provide accurate distances from the satellite to the ground stations. Such observations can, if calibrated for delays, determine satellite orbits to an accuracy approaching 10 m rms.

Kammeyer, P. C.↗
NASA NTRS1986

Strategies for sub-decimeter satellite tracking with GPS

Decimeter tracking of low earth orbiters can be achieved with a variety of differential GPS techniques. A precisely known global network of GPS ground receivers and a receiver aboard the user satellite are needed, and all techniques must simultaneously estimate the user and GPS satellite orbits. Three basic strategies include a purely geometric, a fully dynamic, and a hybrid strategy, the last of which combines dynamic GPS solutions with a geometric user solution. Two powerful extensions of the hybrid strategy show the most promise. The first uses a quasi-optimal synthesis of dynamics and geometry in the user solution, while the second uses a novel gravity adjustment method to exploit data from repeat ground tracks in a computationally efficient way. The best of these techniques promise to deliver sub-decimeter accuracy down to the lowest possible orbits.

Yunck, Thomas P.↗
NASA NTRS1987

NORAD satellite tracking

NORAD routinely tracks about 6000 orbiting objects. During the last 30 days of orbital time, prior to reentry, special perturbations are used in the orbital update procedure. Besides routine orbit determination, NORAD does special tasks such as predicting satellite orbit conjunctions within 20 km, ephimerides of weather satellites, satellite decay predictions and other studies. Since their mission is operational, they do not store the data from their analyses. The ballistic coefficient is not known for most of the orbiting objects. If a ballistic coefficient were derived that was consistent with one density model, it might give erroneous results if used with a different density model. Given the ballistic coefficient, density values could, in principle, be obtained from their tracking data. The densities would represent an integrated mean over the orbital path near perigee. They would be model dependent and would not necessarily represent the real density. In summary, the primary need is for reliable forecasts of solar flux (F10.7) and geomagnetic activity (Ap) in the 1 to 4 week time scale. Forecasts over longer time spans would also be useful for special projects.

Liu, Joseph J. F.↗
NASA NTRS1976

Design, fabrication and systems integration of a satellite tracked, free-drifting ocean data buoy

Engineering details are presented of a small free-drifting buoy configuration designed for use in the study of continental shelf water circulation patterns in the Chesapeake Bight of the Western North Atlantic Ocean. The buoy incoporated French instrumentation and was interrogated by the French EOLE satellite to provide position and four channels of temperature data. The buoy design included a variable depth drogue and a power supply sufficient for six weeks of continuous operations. Proof tests of the configuration indicated an adequate design and subsequent field experiments verified the proper functioning of the system.

Wallace, J. W.↗