Um, eh? (Orbital Mechanics for Dummies)

Randy said:
>This is actually one of the flaws in orbitally dropped munitions (like
>Thor from Renegade Legion).  It takes just as much work to drop
something
>from orbit as it takes to get it up there (aside from the fact that on
the
>way down you can use atmospheric drag to do some of the work).

???? 

Okay, I'm an idiot. Let's start by assuming I know very little. 

I'm in orbit (ignore drag). I launch a Thor Javelin by applying thrust
directly towards planetary centre of mass. What will happen to my
projectile? With thrust applied, it should move away from the
satellite.... and then what? 

PS - won't gravity play into the picture? I understood orbit was
achieved by balancing gravity with centripetal (or was that
centrifugal... never get those two straight) force?

I'm thinking (ignoring atmospheric drag) that it can't take as much
energy to leave orbit to return to the surface as it does to get up
there... because gravity is applying a force to your object. But I may
be not accounting for the centripetal force.

PS - Someone want to do something really interesting? After developing a
gravity based mechanic for FT, then come up with an algorithm to
calculate a method of entering orbit. Orbiting seems to be uber hard in