ULA scrubs Delta IV launch with NROL-47

About five and a half seconds before liftoff, Delta 379 will light its RS-68A engine. Once the count reaches zero, the two booster rockets will ignite, and the Delta IV will begin its ascent towards orbit. The rocket will take about fifty seconds to reach a speed of Mach 1 – the speed of sound – and will pass through the area of maximum dynamic pressure (Max-Q) about twelve seconds later.

Delta at Twitter: