Delta IV Heavy Countdown Timeline

Time (L-) Event
05:15:00 Countdown Clock Initialization
HOLDING Countdown Initiation
HOLDING Countdown Briefing
05:00:00 Redundant Inertial Flight Control Assembly Activation
04:50:00 Launch Area Clear
04:35:00 Go/No GO for Propellant Loading
04:30:00 Cryogenic Tanking begins
04:30:00 Common Booster Core LH2 Tank Chilldown
04:10:00 Common Booster Core LH2 Loading in Slow Fill
04:00:00 CBC LH2 Load Transitions to Fast Fill
04:00:00 Common Booster Core LOX Tank Chilldown
03:50:00 Common Booster Core LOX Loading in Slow Fill
03:45:00 CBC LOX Load Transition to Fast Fill
03:35:00 C-Band Beacon Checkouts, GPS Verifications
03:25:00 Delta Cryogenic Upper Stage LH2 Tank Chilldown
03:25:00 Guidance System Activation
03:10:00 CBC LH2 Topping – Fill & Drain Valve Checks
03:05:00 DCSS LH2 Loading
02:55:00 CBC LOX Topping – Fill & Drain Valve Checks
02:45:00 Delta Cryogenic Upper Stage LOX Tank Chilldown
02:45:00 Launch Weather Briefing
02:35:00 DCSS LOX Loading
02:00:00 DCSS LH2 Topping
01:35:00 DCSS LOX Topping
01:25:00 Radio/Telemetry Link Checks, FTS Checks
01:10:00 Command Receiver Decoder Testing
01:00:00 Flight Termination System Testing complete
00:50:00 RS-68 Engine Spin Start Pressurization
00:50:00 RS-68 Gimbal Steering Checks
00:25:00 Weather Briefing
00:08:00 Launch Pad Ordnance Armed
T-4 Minutes Weather Update
HOLDING Spacecraft to internal power
HOLDING Final Status Polls
HOLDING Launch Director GO/no GO; Range Clear
00:04:00 Delta IV to internal Power
00:04:00 Arm Safe and Arm Switches
00:04:00 DCSS Tank Propellant Securing
00:03:30 Transfer to Internal complete
00:03:30 Common Booster Core Propellant Tank Securing
00:03:15 CBC Pre-Press
00:03:00 Common Booster Core LOX secure at Flight Level
00:03:00 Common Booster Core LH2 secure at Flight Level
00:03:00 Vehicle Ordnance Arming
00:03:00 CBC LOX at Flight Level and Flight Pressure
00:02:00 Master Script Running
00:02:00 Second Stage LOX Securing
00:02:00 Hydraulic System to Flight Pressure
00:01:45 CBC LH2 at Flight Level and Flight Pressure
00:01:30 Second Stage LOX secured at Flight Level
00:01:20 Second Stage LH2 Securing
00:01:20 LOX Ground Support Equipment secured
00:01:00 Range Verification
00:00:50 Second Stage LH2 secure at Flight Level
00:00:45 Launch Enable
00:00:45 Main Power Off
00:00:25 Green Board
00:00:15 Launch Vehicle Igniters armed
00:00:14 Radially Outward Firing Initiators Ignition
00:00:10 Terminal Countdown Sequencer in Control
00:00:07 Starboard RS-68 Main LH2 Valve Open
0:00:05.5 Center & Port RS-68 LH2 Valve Open
0:00:03.5 Starboard RS-68 LOX Valve Open
0:00:02.0 Center & Port RS-68 LOX Valve Open
0:00:02.0 RS-68 Main Engines to Full Thrust Level – 102%
0:00:00.04 Launch Commit
0:00:00.00 Hold-Down Release
0:00:00.00 LIFTOFF