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[b]Countdown highlights[/b] [b]T-7 hours[/b] [list][*]First weather balloon is launched to collect atmospheric thermal properties[/list] [b]T-4 hours, 30 minutes[/b] [list][*]Technicians remove the external environmental control systems that provide cool airflow to the vehicle [*]Onboard navigation unit begins system alignment [*]Additional subsystems complete testing and remain powered on [*]First stage avionics module access platform is retracted[/list] [b]T-3 hours, 30 minutes[/b] [list][*]Six additional weather balloons begin to launch to evaluate if the conditions are suitable for flight[/list] [b]T-3 hours[/b] [list][*]Fault tolerant inertial navigation unit completes alignment and begins navigation testing[/list] [b]T-2 hours, 30 minutes[/b] [list][*]C-band beacon transponder is powered up and tested with the range [*]Range safety system verification walk down is completed [*]Auxiliary power unit is verified for system health[/list] [b]T-2 hours[/b] [list][*]Vehicle stabilization system is retracted and secured [*]Ground control station system begins monitoring for commands from the Launch Control Center [*]Sound suppression water control is transferred to the ground control station [*]Video, operational flight instrumentation and developmental flight instrumentation are checked[/list] [b]T-1 hour, 45 minutes[/b] [list][*]Safety personnel begin the process of securing launch pad[/list] [b]T-1 hour, 15 minutes[/b] [list][*]Ground command, control and communication initiates launch commit criteria monitoring [*]Developmental flight instrumentation covers are removed [*]Fault tolerant inertial navigation unit executes final alignment after the vehicle stabilization system is retracted[/list] [b]T-1 hour[/b] [list][*]All personnel depart Launch Pad 39B for the safe haven [*]Range verifies all "go/no-go" interfaces T-43 minutes [*]Flight termination system is activated and set to safe[/list] [b]T-30 minutes[/b] [list][*]Developmental flight instrumentation, with the exception of cameras, are powered on and recording T-4 minutes, built-in hold [*]Enter 20-minute built-in hold (Vehicle can remain in this hold status for up to four hours.) [*]Six video cameras and low-power transmitters are powered up [*]Telemetry is verified, and readiness for launch is established [*]Range safety issues cleared for launch [*]Countdown clock initiates automated count[/list] [b]T-3 minutes, 55 seconds[/b] [list][*]Sound suppression system is verified for pressure, water tank level and power [*]Flight termination system and solid rocket motor ignition are set to arm [*]Power to avionics cooling fans is terminated [*]Onboard data recorder begins taking data[/list] [b]T-1 minute, 40 seconds[/b] [list][*]Flight control system is enabled and prepared for flight [*]Inertial measurement subsystem executes final alignment[/list] [b]T-1 minute, 20 seconds[/b] [list][*]Flight control system receives the start count [*]Signal is sent to the operational flight instrumentation and developmental flight instrumentation data streams to synchronize[/list] [b]T-35 seconds[/b] [list][*]Flight control system transfers from alignment to navigation mode [*]Inertial and navigation data are verified for accuracy [*]Auxiliary power unit start sequence is initiated[/list] [b]T-21 seconds[/b] [list][*]Reusable solid rocket motor thrust vector control gimbal test performed by rocking and tilting each axis approximately 1.5 degrees[/list] [b]T-16 seconds[/b] [list][*]Ground control station issues commands for sound suppression, opening the valves to flood the mobile launch platform with water (At its peak, water will flow at a rate of 900,000 gallons per minute.)[/list][b]T-0, liftoff[/b] [list][*]Reusable solid rocket motors ignite, and hold-down bolts fire[/list]
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