Dec 162013
LLNL artwork depicting the hit-to-kill terminal stage of the Brilliant Pebbles, sans the booster drop-stages. It does not seem to have a go-forward thruster; that would seem to have been provided by the boosters. What it does have is a fair amount of divert capability provided by the thrusters mounted at what should be the center of gravity.
While dimensions are unknown with any certainty, this would be a fairly small system. The kill vehicle – which in this case is somewhat difficult to distinguish from the propulsion system – had a mass goal of only 2.5 kilograms (according to THIS), while the booster was to mass about 100 kilograms. THIS source said the vehicles were about one meter long.