Ballistic missiles are not to be confused with cruise missiles. The former are unmanned projectiles; the latter are pilotless airplanes, either remote controlled or pre-programmed. They fly through the air, and only through the air. The engines of cruise missiles, like those of aircraft, burn oxygen from the air. Like all other kinds of aircraft, cruise missiles are held up by the flow of air over their wings. Their engines work throughout the flight, not just at the beginning. Cruise missiles fly horizontally rather than in arches, reach only about twice the speed of sound, and typically travel from tens to hundreds of miles. More here:
The thing that got me thinking about this was this article:
In an exclusive interview with ABC News' Martha Raddatz, Adm. Timothy Keating, head of the U.S. Pacific Commands, said that the military is prepared to shoot down any North Korean ballistic missile -- if President Obama should give the order.
"If a missile leaves the launch pad we'll be prepared to respond upon direction of the president," Keating told ABC News. "I'm not a betting man but I'd go like 60/40, 70/30 that it will, they will attempt to launch a satellite. There's equipment moving up there that would indicate the preliminary stages of preparation for a launch. So I'd say it's more than less likely." More here: