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Atlas/SDO launch timeline

T-0:00:02.7 Engine Start
The Russian-designed RD-180 main engine is ignited and undergoes checkout prior to launch.
T+0:00:01.1 Liftoff
The Atlas 5 vehicle, designated AV-021, lifts off and begins a vertical rise away from Complex 41 at Cape Canaveral Air Force Station, Florida.
T+0:01:21 Sound Barrier
Continuing to accelerate away from the planet, the rocket hits Mach 1.0 and breaks through the sound barrier. It will surpass the region of maximum aerodynanmic pressure 92 seconds into flight.
T+0:04:03 Main Engine Cutoff
The RD-180 main engine completes its firing after consuming its kerosene and liquid oxygen fuel supply in the Atlas first stage.
T+0:04:09 Stage Separation
The Common Core Booster first stage of the Atlas 5 rocket separates from the Centaur upper stage. Over the next few seconds, the Centaur engine liquid hydrogen and liquid oxygen systems are readied for ignition.
T+0:04:19 Centaur Ignition 1
The Centaur RL10 engine ignites for the longer of the day's two upper stage firings. This burn will inject the Centaur stage and spacecraft into a parking orbit.
T+0:04:27 Nose Cone Jettison
The payload fairing that protected the SDO spacecraft during launch is separated once heating levels drop to predetermined limits.
T+0:15:17 Centaur Cutoff 1
The Centaur engine shuts down after arriving in a planned parking orbit. The vehicle enters a lengthy coast period before arriving at the required location in space for the second burn.
T+1:42:43 Centaur Ignition 2
The Centaur re-ignites to accelerate the payload out of the temporary parking orbit achieved earlier in the launch sequence.
T+1:45:57 Centaur Cutoff 2
At the conclusion of its second firing, the Centaur will have propelled the SDO spacecraft into the planned geosynchronous transfer orbit featuring a high point of 21,970 statute miles, low point of 1,555 statute miles and inclination of 28.5 degrees.
T+1:48:46 SDO Separation
NASA's Solar Dynamics Observatory to study the varying behavior of the Sun and its influences on Earth is released from the Centaur upper stage to complete the launch.

Data source: United Launch Alliance.