Burns, J.A., R.A. Kolvoord and D.P. Hamilton 1989. An assessment of
potential hazards to the Cassini spacecraft from debris along
satellite orbits. In Cassini Mission Proposal
Information Package (JPL PD 699-11) 13, 6-1
to 6-23.
The Cassini spacecraft, which is to orbit Saturn for almost four years
during the early part of the next century, is designed to be captured
when its engines fire deep within the planet's magnetosphere. Many of
the spacecraft's subsequent traverses through the planet's equatorial
plane will occur close to satellite orbit paths in order to permit
various high-resolution observations of the satellites. In addition,
early in the mission the spacecraft will fly along a low inclination
path passing over many satellite orbits. Questions have arisen over
the years as to whether the regions near satellites are likely to be
unusually safe (the simple argument going that the satellites
themselves have swept such regions clear) or abnormally hazardous (the
point being that, at least for an isolated three-body system, orbits
in this locale are the only ones that can possible be stable).
We provide here a preliminary discussion of the likely risk to be
faced by a spacecraft passing near the satellite orbits. We start by
summarizing the evidence for material in orbit near the satellites;
this includes direct observations of co-orbiting moons and dust as
well as indirect clues for debris clouds as inferred from charged
particle absorption signatures. Following this precis, we consider two
different approaches to the problem. First, we recall theoretical
results form the classical circular restricted three-body problem as
to the circumstances under which orbits are stable versus when they
are chaotic; we then illustrate these orbital classes by a numerical
simulation that is generalized by showing how it scales for the
relevant Saturnian satellites. Second, using arguments coming from
theoretical studies of magnetospheric absorption by rings and
satellites, we are able to place some very weak constraints on the
nature of the material that is thought to be responsible for the
observed depletion of charged particles.
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