QUESTION:
Where in the Saturnian ring-plane does the Saturn Orbit Injection 
occur? Where does the first ring plane passage occur? Inside the B 
ring? The Voyagers survived their ring plane passage, but they did it 
outside the dense A, B, and C rings. I vaguely remember reading 1/6 
Rs (saturnian radii) and thought "whoa: there's bound to be more ring 
particles there, and the craft is approaching with a relative 
velocity of kilometers per second?!".

The follow-on question is: is the craft shielded in anyway to protect 
it against small impactors during the SOI maneuver?

ANSWER from Jim Frautnick on January 12, 2000:
Cassini will approach from under the rings and then do an ascending ring
plan crossing between the F & G rings, quite a ways from the dense rings.
The descending crossing, about 3.76 hours later will also be between the F
& G rings.   Even though we are crossing in a ring gap, there are still
many more particles in the ring plane than we experience during the cruise
to Saturn.  There is only the thermal blankets and spacecraft structure as
protection against particles.  Cassini will orient the spacecraft so as to
keep the optical instruments away from incoming particles during ring plane
crossings.

The SOI maneuver will begin about 15 minutes after the initial ring
crossing and will last about 95 minutes, ending at closest approach.  At
closest approach Cassini will be out of the ring plane by about 11 degrees.