JESSICA RYE: T-minus 10, nine, eight, seven, six, five, four, three, two, one.
We have ignition and liftoff of the Delta II rocket, carrying THEMIS, NASA's revolutionary journey to study the Northern Lights.
Everything continues to look good with the Delta II rocket with the THEMIS payload on board.
Nine solid rocket strap-on boosters are burning fine and the spacecraft is on its way to its intended target.
VOICE: All solid motors have reached their peak chamber pressure and now beginning to taper off as expected.
T+48 seconds, we've passed "max Q." All solid motors burning symmetrically, now starting their burnout phase. OK.
All solid, all six ground starts are burned out, and we have ignited the air starts and jettisoned the ground start solid motors.
Vehicle transients at solid motor jettison are nominal. Three air start motors picking up, all burning symmetrically.
They've reached their peak chamber pressure, excuse me.
Vehicle now at an altitude of 16 miles, downrange distance 36 miles and velocity of 3,400 miles an hour.
Main engine and burners continue to burn well.
We've just passed T+110 seconds into the mission. First-stage data continues to look good.
Just a few moments away from the second set of solid motors jettisoning. Burned out and jettisoned, the air start solid motors.