Radial Orbit Error from Gravity Field Covariances
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## Radial Orbit Error from Gravity Field Covariances to 70x70

The radial orbit error was computed for circular orbits at the altitudes of
525 and 830 km, using linear orbit perturbation theory and the gravity
field error covariances [Rosborough
, 1986]
from JGM2, JGM3, and EGM96, as a function of satellite inclination.
Orbit perturbations longer than ten days were excluded, and the analysis
does not include the long period perturbations due to the odd zonals.
The structure of the radial error vs inclination shows the weakness of JGM2/JGM3
at the low inclinations (i <35 degrees). The poor behavior at these low
inclinations is a consequence of the dearth of tracking data from satellites
at such inclinations in JGM2 and JGM3. In EGM96, significant new data
from the EUVE satellite (i=28.5 degres, mean altitude=525 km) was included.

EGM96 also shows an improvement at the polar inclinations (i=82 to 93 degrees)
which may be attributed in part to the addition of tracking data from the
Hilat and Radcal spacecraft.

**References:**

Kaula, W. M., *Theory of satellite geodesy*,
Blaisdell Publishing Co., Waltham, MA 1966.

Rosborough, G. W.,
*Satellite orbit perturbations due to the geopotential *,
Center for Space Research, The University of Texas at Austin, January 1986.

## Radial orbit error at 525 km altitude

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## Radial orbit error at 830 km altitude

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## Radial orbit error at 830 km altitude at polar inclinations

The Hilat and Radcal data benefit the EGM96 solution by reducing the
predicted radial orbit error in this altitude and inclination band by
up to 20 cm.

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## Radial orbit error at 1336 km altitude

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Send questions or comments to:

Frank.G.Lemoine@nasa.gov or Douglas.Chinn@nasa.gov.

Last revised December 22, 2004 16:25 UTC.