T-minus 15 minutes and counting. The NuSTAR spacecraft has switched to internal power for launch. WATCH LIVE:

T-minus 20 minutes and counting. Although the countdown is managed by the ground-based team, the aircraft crew actually pushes the button to launch Pegasus on its journey into space.

The circuitry for the release system has been armed by the launch panel operator aboard the aircraft. Later, a switch will be flipped in the cockpit by the co-pilot. This switch, located on the right-hand portion of the center console between the captain and pilot, "enables" the release to be become active.

In the final seconds of the countdown the Orbital Sciences launch conductor on the ground will call out "drop on my mark...3, 2, 1, drop." At that point, the co-pilot will push a button next to the enable switch, releasing the Pegasus rocket and NuSTAR to fall away from the L-1011 aircraft. See a photo of the drop button taken during a tour of the L-1011.

"It takes a couple seconds and then it releases," Capt. Bill Weaver explained during a previous interview. "There is no doubt about it that the rocket has released. There is a tremendous reaction throughout the airplane. It weighs 52,000 pounds, so we experience an instantaneous weight loss of 52,000 pounds and the center of gravity shifts aft 10 percent, so the nose comes up in a pretty pronounced fashion, which is good because we like that for separation.


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[link to www.spaceflightnow.com]