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Antares countdown timeline
Posted: December 16, 2013

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, 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, 30 minutes Management Call to Stations
Orbital management arrives on console in the launch control center.
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. This step narrows the launch window from 15 minutes to 10 minutes.
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 750,000 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 seconds Liftoff
After the engines are confirmed healthy, the hold-down system releases the Antares rocket at liftoff.

Data source: Orbital Sciences Corp.