The bit about the spaceship 'falling' bears some similarity to the slingshot effect that we already use with interplanetary launches. Of course, to keep it going, you'd basically have to have a portable gravitational well - perhaps even a portable black hole - to let you go where you wanted to, instead of just where the gravity well happened to be.
I haven't seen anything as specific as what NotoriousBEN describes, though.
EDIT: I should really learn to Google before hitting 'Post'. Is this
what you're talking about BEN?