T-0:00:05.0: Ignition sequence start
The RS-68A main engine begins to ignite as the liquid hydrogen fuel valve is opened, creating a large fireball at the base of the rocket. The engine powers up to full throttle for a computer-controlled checkout before liftoff.
The rocket’s two strap-on solid rocket motors are lit, the four hold-down bolts are released and the Delta 4 lifts off from Cape Canaveral’s pad 37B. The pad’s three swing arms retract at T-0 seconds.
T+0:00:43.8: Mach 1 and Max Q
The Delta rocket achieves Mach 1 some 44 seconds into the flight, then passes through the region of maximum dynamic pressure at 57 seconds with both solid motors and the RS-68A liquid hydrogen/liquid oxygen engine continue to fire as the vehicle heads downrange.
T+0:01:40.1: Solid Rocket Booster Separation
Having used up all their solid-propellant and experienced burnout six seconds ago, the two strap-on boosters are jettisoned from the Delta’s first stage. The spent casings fall into the ocean.
T+0:04:05.1: Stage Separation
The Common Booster Core first stage and the attached interstage are separated in one piece from the Delta 4’s upper stage. The upper stage engine’s extendible nozzle drops into position as the first stage separates.
T+0:04:19.6: Upper Stage Ignition No. 1
The upper stage begins its job to place the Geosynchronous Space Situational Awareness Program satellites into space with the first firing by the RL10B-2 liquid hydrogen/liquid oxygen engine.
The Delta 4 rocket flies into a pre-arranged news blackout, conducting its engine firings and maneuvers in secrecy. As such, the timeline beyond the point of payload fairing jettison is not available.
See earlier Delta 375 coverage.
Our Delta archive.
from Spaceflight Now ift.tt/2bp16R0