NASA's "Prius of Space" goes 5,500 mph on only 15 gallons of fuel

How fast would a Prius need to be traveling in order to launch itself into orbit? Really, really fast. Although NASA currently has no plans of attaching rockets to a Toyota any time soon (as far as we know), they will soon be sending a hybrid spacecraft into space. The Prius has a gasoline engine and an electric motor. The Dawn spacecraft has a Delta II Heavy rocket and three Solar Electric Propulsion Technology Applications Readiness engines. Put more simply, it has an ion engine. Take a look at this lifter and you've got an idea of the technology being implemented, but on a much larger scale. Using Xenon gas as fuel and electricity for power, the ion engines can provide scant amounts of thrust for 5.5 years of continuous running. Here on earth, these engines would get you exactly nowhere. But, in space, the engines will get the machine traveling at up to 5,500 miles per hour or so. Why's gravity always gotta be holdin' us back?

[Source: NASA via Wired]