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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Perturbations of non-resonant satellite orbits due to a rotating earth

The dominant perturbations of the motion of a satellite near the earth are due to atmospheric drag and the non-symmetrical gravitational field. Atmospheric drag perturbation continually pulls the satellite in and out of the different long period resonant frequencies. The result is that the resonances never become apparent and may be neglected. The tesseral harmonics have no true secular perturbation but the periodicities in the mean motion induce a secular perturbation in the mean anomaly. This secular perturbation may be determined by simply using the average mean motion instead of the osculating mean motion. The Von Ziepel method is used to determine tesseral perturbations. The solution is found first in the singular DS phi elements and then rewritten in the PS phi elements to remove singularities. The notation used in the development is described in the appendix.

Mueller, A.↗
NASA NTRS1981

Prediction of Earth rotation and polar motion

Based on the analysis of the polar motion behavior, the possibility of predicting polar motion up to one year in advance was found. Comparing these predicted polar coordinates with the observed ones (smoothed), the root mean square (rms) of the differences is about 0.02 seconds. The differences of the relative polar motion are much smaller. For any time interval of 20 to 30 days throughout the whole year, the rms of the relative polar motion differences is about 0.01 second. Compared with the best available VLBI results (from 1977 to 1980), the rms of pred. to obs. is 0.013 seconds, and the relative rms (for time intervals less than two months) is 0.008 seconds (here the observed data is unsmoothed). It appears that 80 to 90% of the polar motion is composed of the stable, predictable Chandler and annual terms. The UT1-UTC has more complicated changes than polar motion making it difficult to find a satisfactory method of long term prediction. So far the rms prediction error is 0.0023 s for up to 30 days.

Zhu, S. Y.↗
NASA NTRS1984

An El Nino signal in atmospheric angular momentum and earth rotation

Anomalously high values of atmospheric angular momentum and length of day were observed in late January 1983. This signal in the time series of these two coupled quantities appears to have been a consequence of the equatorial Pacific Ocean warming event of 1982-1983.

Rosen, R. D.↗
NASA NTRS1985

Mantle viscosity, J2 and the nontidal acceleration of Earth rotation

Recent interpretations of laser ranging for the LAGEOS satellite have rather conclusively established that the observed acceleration in the node of its orbit is just that expected to exist as a residual effect of the last deglaciation event which ended about 6000 years ago. The nontidal acceleration of rotation would be rather different than that observed if there were any significant melting of high latitude continental ice masses currently ongoing. The sensitivity of the expected nontidal acceleration to variations of several elements of the radial viscoelastic structure of the planet is explored using a new normal mode method for the computation of viscoelastic relaxation spectra. These calculations establish that the most important sensitivity is to variations in the mantle viscosity profile. Although the predicted nontidal acceleration does depend upon lithospheric thickness and on the elastic component of the radial structure, the dependence on these components of the structure is much weaker than it is upon mantle viscosity. The observed J sub 2 is therefore a particularly useful determinant of radial variations in the latter parameter.

Peltier, W. R.↗
NASA NTRS1986

Meteorological data for earth rotation studies

To assess the level of uncertainty in current calculations of the atmosphere's angular momentum, comparisons are presented of time series of this quantity produced by two operational weather centers. The two series generally agree quite well, although certain differences are evident and discussed here. The effect of neglecting middle and upper stratospheric winds in the production of these series is also considered and shown to be of some consequence on seasonal time scales.

Rosen, Richard D.↗
NASA NTRS1986

The El-Nino, the Southern Oscillation and the earth rotation

The relationship between length of day (LOD) variations and the Southern Oscillation (SO), and with the associated El Nino phenomenon, is studied. Interannual changes in the LOD are shown to be linearly related to a SO sea level pressure index. A possible physical mechanism for this relationship is the thermal winds caused by changes in the equator to pole heat transports associated with El Nino events and the SO.

Eubanks, T. M.↗
NASA NTRS1993

Toward 10(exp 9) GPS geodesy: Vector baselines, Earth rotation and reference frames

The University of Texas Center for Space Research research efforts under NASA Grant No. NAG-1936 from 1 Jan. 1992 - 31 Dec. 1992 were in the following areas: GPS orbit accuracy assessments and efforts to improve the accuracy; analysis of global GPS data collected during the first three months of the IGS campaign, and analysis of regional data. A brief summary of each of the above activities is presented in the following.

Schutz, Bob E.↗
NASA NTRS1994

Towards 10(exp 9) GPS geodesy: Vector baselines, Earth rotation and reference frames

Effort during the period form January 1, 1993 to December 31, 1993 were in the following areas: GPS orbit accuracy assessments and efforts to improve the accuracy; analysis and effects of GPS receiver antenna phase center variation; analysis of global GPS data being collected for the IGS campaign; and analysis of regional (south west Pacific) campaign data. A brief summary of each of the above activities is presented.

Schutz, Bob E.↗
NASA NTRS1991

The rotation of the earth

Earth rotation studies are reviewed for the 1987-1990 time period. It is noted that the emphasis in these studies has shifted from improvements in the observational techniques to interpreting and gaining greater understanding of the variations of the earth rotations. There have been progressive improvements in the accuracy and the temporal resolution of earth rotation measurements.

Herring, Thomas A.↗
NASA NTRS1990

Interannual and decade fluctuations in the earth's rotation

The main findings of a study of earth rotation changes on the longer interannual and decade range of time scales are summarized. The earth rotation data provide important constraints on models of the internal structure and dynamics of the core and lower mantle. Torques at the core-mantle interface are due to time varying fluid motions in the core. A torque of about 0.2 Hadley units is found in the axial component during the 1980 period.

Dickey, Jean O.↗