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Antares countdown timeline
Posted: July 7, 2014

NOTE: All times approximate

L-minus 8 hours, 15 minutes Call to Stations
The launch team reports to the control center at NASA's Wallops Flight Facility.
L-minus 7 hours, 45 minutes Begin Launch Checklist
The launch team conducts voice checks over radio loops and begins setup of the Range support systems.
L-minus 6 hours, 30 minutes Clear the Pad
Workers evacuate the launch pad.
L-minus 6 hours, 5 minutes Poll to Initiate Loading Sequencer Timeline
The launch team conducts a "go/no go" poll to initiate the loading sequencer timeline.
L-minus 6 hours Initiate Orbital Commodities Control System Sequencer
The Orbital Commodities Control System sequencer begins operating and warm helium charging begins on the Antares rocket's first stage.
L-minus 5 hours, 55 minutes Vehicle Power-Up
The Antares launch vehicle is powered on using an external power source to begin systems testing.
L-minus 4 hours, 55 minutes Poll to Initiate Pre-Launch Processing
The launch team is polled for a "go" to begin the pre-launch processing sequence.
L-minus 3 hours, 40 minutes Begin First Hold
The countdown pauses for 15 minutes to allow Orbital management to arrive on console and begin monitoring the launch preparations.
L-minus 3 hours, 50 minutes Management Call to Stations
Orbital management arrives on console in the launch control center.
L-minus 3 hours, 30 minutes RF Transmitter Checks
The launch team tests the Antares rocket's radio transmitter, which will be the communications link between the vehicle and the ground during flight.
L-minus 3 hours, 25 minutes Resume Countdown
The countdown resumes after a 15-minute hold.
L-minus 3 hours, 20 minutes Poll to Initiate LOX Chilldown
The launch team is a polled for a "go" to begin chilldown of the Liquid Oxygen Loading System (LOLS), which conditions the ground and vehicle propellant lines for loading of the cryogenic propellant, which is stored at a temperature of approximately minus 298 degrees Fahrenheit.
L-minus 3 hours, 15 minutes Begin Liquid Oxygen Chilldown
The liquid oxygen chilldown sequence begins.
L-minus 2 hours, 48 minutes FTS Testing
The Antares flight termination system, which would destroy the rocket if it flew off course during launch, is tested to ensure it is ready for launch.
L-minus 2 hours, 24 minutes Enable Ordnance
The Antares rocket's pyrotechnic charges, which are used to separate the rocket's stages and other components in flight, are set to enable.
L-minus 1 hour, 45 minutes 15-minute Hold
The countdown holds for 15 minutes.
L-minus 1 hour, 30 minutes Resume Countdown and Begin Propellant Loading
Liquid propellants are pumped into the Antares first stage through the base of the rocket. The 12.8-foot-diameter first stage, fabricated in Ukraine, holds about 21,000 gallons of RP-1 kerosene and about 41,000 gallons of liquid oxygen. The Antares second stage is fueled by solid propellants, which were loaded when the stage was fabricated.
L-minus 30 minutes Start of Engine Low-Flow Chilldown
The chilldown sequence for the Antares rocket's two AJ26 main engines begins to prepare the engines for ignition.
L-minus 15 minutes Transfer Cygnus to Internal Power
The Cygnus spacecraft is transitioned from a ground power source to internal battery power.
L-minus 11 minutes Arm TEL for Rapid Retract
The Antares rocket's Transporter-Erector-Launcher is armed for rapid retract.
L-minus 10 minutes Start of Engine Medium-Flow Chilldown
The chilldown sequence is transitioned to a medium flow.
L-minus 5 minutes Transfer Avionics to Internal Power
The Antares rocket's avionics are switched to run off of an internal battery.
L-minus 3 minutes, 30 seconds Initiate Terminal Countdown
The final three-and-a-half minutes of the countdown are run off a computer autosequence.
L-minus 2 minutes Pressurize Propellant Tanks
The Antares rocket's first stage propellant tanks are pressurized for launch.
L-minus 15 seconds Main Engine Slew Test
The Antares rocket's AJ26 first stage engines are slewed in a preflight steering check to ensure the gimbal system is ready for flight. The engines can gimbal up to 6 degrees from center to steer the rocket.
L-minus 5 seconds TEL Retraction
The rocket's umbilical tower, which is also used to transport and erect the vehicle at the launch pad, is retracted away from the launch vehicle.
L-minus 0 seconds Main Engine Ignition
The two AJ26 main engines ignite with the help of a start cartridge before ramping up to a combined thrust level of approximately 730,000 pounds.
T+plus 1.5 seconds Engine Health Check Complete
A computer-controlled health check of the performance of the AJ26 engines is completed before liftoff.
T+plus 2.1 seconds Liftoff
After the engines are confirmed healthy, the hold-down system releases the Antares rocket at liftoff.

Data source: Orbital Sciences Corp.