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This is the ascent timeline to be followed by the United Launch Alliance Delta 4 rocket in launching the Air Force’s GPS 2F-9 navigation satellite on March 25 at 2:36 p.m. EDT.

T-0:00:05.0: Ignition sequence start



The RS-68 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.

T+0:00:00.0: 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+0:00:48.4: Mach 1 and Max Q



The Delta rocket achieves Mach 1 some 48 seconds into the flight, then passes through the region of maximum dynamic pressure at 61 seconds with both solid motors and the RS-68 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+0:04:08.1: Main Engine Cutoff

The liquid hydrogen-fueled RS-68 rocket engine throttles down to its minimum power level and then shuts down to finish the first stage burn.

T+0:04:15.1: 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+0:04:29.6: Upper Stage Ignition No. 1

The upper stage begins its job to place the GPS 2F-9 satellite into space with the first of two firings by the RL10B-2 liquid hydrogen/liquid oxygen engine.

T+0:04:40.1: Jettison payload fairing

The four-meter diameter composite payload fairing that protected the GPS 2F-9 cargo atop the Delta 4 during the atmospheric ascent is no longer needed, allowing it to be jettisoned in two halves.

T+0:15:30.9: Upper stage shutdown

The RL10 upper stage engine shuts down to complete its first firing of the launch. The rocket and attached satellite reach an intermediate transfer orbit where it coasts for the next three hours.

T+3:02:00.1: Restart upper stage

The upper stage reaches the proper point in space and reignites the the RL10 engine to circularize the orbit.

T+3:03:46.2: Upper stage shutdown

The powered phase of the Delta 4’s mission to reach the GPS constellation concludes. The targeted circular orbit is 11,047 nautical miles with an inclination of 55 degrees.

T+3:14:27.6: Separate spacecraft

The GPS 2F-9 satellite is released into space from the Delta 4 rocket to upgrade the orbiting navigation network.