Eccentric Orbits Around Planetary Moons
Author(s)
Russell, Ryan P.
Brinckerhoff, Adam T.
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Abstract
Eccentric orbits in the third-body perturbed problem are evaluated in the context of
planetary moon missions. All possible motion in the doubly averaged problem is
overviewed and concisely summarized via contour plots. Special attention is paid to the
well known class of orbits that cycle between low and high eccentricity while circulating
in argument of periapse. Applying the doubly averaged assumptions, the maximum
sustainable inclinations and eccentricities for long-term, circulating, ballistic orbits are
found and discussed for the dimensioned systems at Ganymede, Europa, Titan,
Enceladus, and several other planetary moons. The full cycle periods of the circulations
and librations are reduced to quadratures that are functions only of the two integrals of
motion and the moon and orbiter mean motions. In the specific case of Ganymede,
higher fidelity models are considered to analyze the validity of the doubly averaged
assumptions. Families of stable, long-repeat cycle, periodic orbits are demonstrated in
the un-averaged Hill plus non-spherical potential model. Several point designs are
considered in a full ephemeris model, and promising results include long-term ephemeris
stable orbits that enjoy maximum inclinations above 60 degrees. These circulating "ball of-
yarn" orbits cycle between high and low eccentricities while distributing close
approaches throughout all longitudes. Further, these largely non-Keplerian orbits are less
expensive to achieve than low-altitude, circular orbits, and the orbital geometry and
timing are favorable for a variety of both planetary moon and system science.
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Date
2008-01
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