I just read that when Cassini makes it's first close pass of Saturn's F-ring on December 4, it will be the 183rd time the engine fires. I googled Cassini's engine and found this site which has a cool 3D WebGL(?) model of Cassini's engine(s) that you can rotate with your cursor.
I show a screen shot below. The accompanying text says:
The main engine is used for spacecraft velocity and trajectory correction changes. To be on the safe side, there are two identical main engines: One is in use and the other is a backup. There are also 16 monopropellant hydrazine thrusters of which eight are prime and eight are backups. The thrusters are used for attitude control and also for small velocity-change maneuvers.
Bipropellant system- Nitrogen Tetroxide (NTO)/Monomethylhydrazine (MMH) Main (445 Newton) engine for propulsive maneuvers – Burns can be blow-down or pressurized (with Helium)
Engines are protected from micrometeoroid particles by articulating cover
Redundant main engine (never used in flight)
The two engine nozzles in the 3D model appear to be slightly angled so that they are both axial with the spacecraft center of mass, but the view is not orthographic and the shapes of the nozzles themselves are highly distorted.
In reality, are the two nozzles really oriented so that their axes both intercept the spacecraft center of mass? THough there are thrusters, it seems like you'd want to at least try to minimize the torque of the laterally offset engine(s).
aboveL Screenshot of this 3D interactive model of Cassini's engines.