Dawn at Vesta II 
LAUNCH CONTROL: 13, 12, green status board!
When we think of rocket power, we think of something like the booster that launched the Dawn mission in 2007.
CONTROL: 3, 2, main engine start, 1, zero, and liftoff of the Delta II rocket with Dawn, using ion propulsion to reach the catalysts of our solar system....
The booster's engines produced a million pounds of thrust at launch. And in just minutes, they pushed Dawn fast enough to escape Earth's gravity and head toward the asteroid Vesta.
But the boost wasn't enough, so Dawn used its own engines to add the extra kick -- ion engines. Combined, the three engines generate no more than one ounce of thrust. But they operated for years without stopping, so their kick added up. Dawn's lead scientist, Christopher Russell, explains:
RUSSELL: Take an ordinary sheet of paper -- an eight-and-a-half-by-eleven sheet of paper, and then hold it in your hand. And the force of gravity on that paper is the same as the thrust on our thrusters. So it's very, very light. But you keep doing that for a long time and it changes the velocity of the spacecraft a lot.
The ion thrusters use solar power to give an electric charge to their xenon fuel. Magnets then shoot the xenon out at high speed. The thrusters produce more than 10 times as much thrust per pound of fuel as chemical rockets.
On Saturday, they'll help Dawn settle into orbit around Vesta. And a year later, Dawn will leave Vesta and head toward a second asteroid -- with the gentle nudge of ion power.
More about Dawn tomorrow.
Script by Damond Benningfield, Copyright 2011