Engineering topics

Birkeland, P. W.

Publications and source records attributed to Birkeland, P. W..

5 records

NASA NTRS1983

Venus gravity anomalies and their correlations with topography

This report provides a summary of the high-resolution gravity data obtained from the Pioneer Venus Orbiter radio tracking data. Gravity maps, covering a 70 deg latitude band through 360 deg of longitude, are displayed as line-of-sight and vertical gravity. Topography converted to gravity and Bouguer gravity maps are also shown in both systems. Topography to gravity ratios are made over several regions of the planet. There are markedly different ratios for the Aphrodite area as compared to the Beta and Atla areas.

Sjogren, W. L.↗

NASA NTRS1981

A navigation model for the Venusian atmosphere

A static, exponential atmosphere model for Venus has been developed using period change data from the Pioneer Venus spacecraft. The model was derived from approximately 600 passages of the spacecraft through the upper Venusian atmosphere, or almost three full circulations of the planet. The model reflects several important, known atmospheric features (diurnal bulge, layering, etc.) and confirms several observations of a more sophisticated analysis. Several new phenomena were observed and successfully modeled.

Birkeland, P. W.↗

NASA NTRS1981

Venus gravity fields

Results of Pioneer Venus Orbiter observations concerning the gravity field of Venus are presented. The gravitational data was obtained from reductions of Doppler radio tracking data for the Orbiter, which is in a highly eccentric orbit with periapsis altitude varying from 145 to 180 km and nearly fixed periapsis latitude of 15 deg N. The global gravity field was obtained through the simultaneous estimation of the orbit state parameters and gravity coefficients from long-period variations in orbital element rates. The global field has been described with sixth degree and order spherical harmonic coefficients, which are capable of resolving the three major topographical features on Venus. Local anomalies have been mapped using line-of-sight accelerations derived from the Doppler residuals between 40 deg N and 10 deg S latitude at approximately 300 km spatial resolution. Gravitational data is observed to correspond to topographical data obtained by radar altimeter, with most of the gravitational anomalies about 20-30 milligals. Simulations evaluating the isostatic states of two topographic features indicate that at least partial isostasy prevails, with the possibility of complete compensation.

Sjogren, W. L.↗

NASA NTRS1980

Gravity anomalies on Venus

Doppler radio tracking of the Pioneer Venus orbiter has provided gravity measures over a significant portion of Venus. Feature resolution is approximately 300-1000 km within an area extending from 10 deg S to 40 deg N latitude and from 70 deg W to 130 deg E longitude (approximately equal to 200 deg). Many anomalies were detected, and there is considerable correlation with radar altimetry topography (Pettengill et al., 1980). The amplitudes of the anomalies are relatively mild and similar to those on earth at this resolution. Calculations for isostatic adjustment reveal that significant compensation has occurred.

Sjogren, W. L.↗

NASA NTRS1979

Orbit determination strategy and results for the Pioneer Venus Orbiter mission

This paper examines the orbit of the Pioneer Venus Orbiter as determined from earth based radio data. The basic orbit determination strategy together with its associated accuracy is presented, and the effect of the changing earth-Venus geometry on that accuracy is discussed. Orbital evolution from insertion to the present time is described and related to the primary forces acting on the spacecraft as well as to the weekly periapsis altitude trim maneuvers. Lastly, the technique used for orbit prediction in the presence of the uncertain Venus atmosphere and gravity environment is discussed.

Jacobson, R. A.↗