Consider a typical space shuttle launch. The orbiter is so huge that only enormous engines can break it free from Earth's gravity. Big engines, in turn, demand a lot of fuel. So technicians bolt an extra tank and two booster rockets to the orbiter, point the whole contrivance straight up, and fire the engines. Whoosh! A lot of noise, a lot of flame, enough smoke and steam to suffocate a small city, and the rocket just sort of sits there for a second or two, looking as if it might fall over instead of shoot into space. Of course, this usually works out fine. But once those engines ignite, there's no stopping the bullet if something goes wrong.
Courtesy: NASA/SPL/Photo Researchers
Now consider an alternative scenario. Suppose a force other than a rocket engine could accelerate the shuttle sideways along the ground until it reaches, say, 400 miles per hour ...
