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2003, Advances in Space Research
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10 pages
1 file
Mathematical Problems in Engineering, 2009
The effects of perturbations due to resonant geopotential harmonics on the semimajor axis of GPS satellites are analyzed. For some GPS satellites, secular perturbations of about 4 m/day can be obtained by numerical integration of the Lagrange planetary equations considering in the disturbing potential the main secular resonant coefficients. Amplitudes for long-period terms due to resonant coefficients are also exhibited for some hypothetical satellites orbiting in the neighborhood of the GPS satellites orbits. The results are important to perform orbital maneuvers of GPS satellites such that they stay in their nominal orbits. Also, for the GPS satellites that are not active, the long-period effects due to the resonance must be taken into account in the surveillance of the orbital evolutions of such debris.
Welcome to the Department of Condensed Matter Physics and Materials Science (CMPMS) at TIFR! Research in CMPMS asks questions about the nature of materials that are in the " condensed state " – familiar condensed phases like solids or liquids, but also more exotic phases such as the superconducting phase at low temperatures, magnetically-ordered phases etc. We also work on semiconductors and nanostructured materials, and soft-matter. We study the electronic, physical, mechanical, optical, and chemical properties of materials, in relation to their structure. Our emphasis is on the experimental measurement of various properties using different probes in an attempt to understand the underlying physical behaviour. We fabricate optoelectronic, plasmonic, and superconducting device structures that serve as test sytems to study novel phenomena and also enable real world applications. A K G r o v e r (o n l i e n) K a l o b a r a n M a i t i A r u n K u m a r N i g a m P L P a u l o s e S h r i g a n e s h P r a b h u S R a m a k r i s h n a n P r a t a p R a y c h a u d h u r i E V S a m p a t h k u m a r a n A T h a m i z h a v e l R V i j a y a r a g h a v a n
Advances in Space Research, 2002
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GPS satellite orbits available from the International GNSS Service (IGS) show a consistent radial bias of up to several cm and a particular pattern in the Satellite Laser Ranging (SLR) residuals, which are suggested to be related to radiation pressure mismodeling. In addition, orbit-related frequencies were identified in geodetic time series such as apparent geocenter motion and station displacements derived from GPS tracking data. A potential solution to these discrepancies is the inclusion of Earth radiation pressure (visible and infrared) modeling in the orbit determination process. This is currently not yet considered by all analysis centers contributing to the IGS final orbits. The acceleration, accounting for Earth radiation and satellite models, is introduced in this paper in the computation of a global GPS network (around 200 IGS sites) adopting the analysis strategies from the Center for Orbit Determination in Europe (CODE). Two solutions covering 9 years (2000-2008) with and without Earth radiation pressure were computed and form the basis for this study. In previous studies, it has been shown that Earth radiation pressure has a non-negligible effect on the GPS orbits, mainly in the radial component. In this paper, the effect on the along-track and cross-track components is studied in more detail. Also in this paper, it is shown that Earth radiation pressure leads to a change in the estimates of GPS ground station positions, which is systematic over large regions of the Earth. This observed "deformation" of the Earth is towards North-South and with large scale patterns that repeat six times per GPS draconitic year (350 days),
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