Abstract
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Abstract
N A T I O N A L L A B O R A T O R Y
Abstract
Background and Research Objectives
Background and Research Objectives
In previous work we undertook a theoretical effort to model the spin dynamics of a LAGEOS-type satellite. It is the knowledge of the state of spin axis of the satellite that allows one to minimize the consequence of the thermal rocketing effect on the rate of nodal precession. In particular, we integrated the spin dynamics equations numerically. These equations included the eddy-current interaction within the satellite with a perfect dipole field. Furthermore, the satellite was assumed to be a perfect sphere of brass (a fair approximation), and its orbit was assumed to be spherical and not precessing. Using this model we were able to qualitatively analyze the spin dynamics through its spin-orbit resonance phase and onto its tidal-locking phase.
Importance to LANL's Science and Technology Base and National R&D

Needs
The geodynamic data we obtain from LAGEOS-I and -11 is used to determine Universal Time (UT-1) and polar wobble (xp,yp). This data is crucial for real-time *Principal Investigator, E-mail: warn @lanl.gov navigational systems. The analysis of the surface forces on the LAGEOS satellite has solved anomalous orbital dynamics paradoxes in LAGEOS (e.g. the 1-mm delay of LAGEOS's orbit is a result of thermal rocketing).
Needs
The goal of the LAGEOS-3 mission is to measure the frame-dragging effect predicted by Einstein's theory of gravity. This effect provides the key mechanism of astrophysical jet alignment in AGNs (Bardeen-Petterson effect).
Scientific Approach and Accomplishments
A new set of observational measurements between 1988 and 1996 were made available in a joint effort with Professor Curie of the University of Maryland. These measurements made it possible to test our enhanced theoretical model w i t h experimental data. Enhancing our model involved four tasks: 1) the dipole field.
Scientific Approach and Accomplishments
Creating a more realistic model of the Earth's magnetic field by including the tilt of 2) due to the oblateness of the Earth.
Scientific Approach and Accomplishments
Including the tidal precession of the line of nodes of the satellite's orbit (-126O/yr)
3)
This requires one to relate the Euler angles and their time rate of change to R.A and DEC.
3)
Starting the calculation using data points from our effort with Professor Cume.
4)
satellite geometry. For example, the eddy currents will be greatly reduced due the 426 cylindrical holes drilled into the aluminum shell of the satellite.
4)
Provide a qualitative argument transcribing the numerical results to the actual These modifications were made and the code results were compared with the glint measurements of Professor Currie in the recent RAU Colloquium 165 on the "Dynamics of Natural & Artificial Celestial Bodies" held in Poznar, Poland. A manuscript comparing the data with observations is currently in preparation. The code results were consistent with the observations made at the University of Maryland. In particular, the drift of the spin axes of LAGEOS-1 toward the North Pole was c o m t l y modeled for the first time. In addition, our code predicts a spin-orbit resonance phase that can dramatically affect the orientation of the satellite.
4)
Our enhanced code is more advanced than any other in the field. It will serve as the new spin-dynamics model for future LAGEOS satellite missions.

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