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Countdown of an Ariane 5 launcher campaign

Countdown of an Ariane 5 campaign

The word countdown covers all final preparation operations for the launcher, satellites and the launch Base which, when correctly performed, lead to ignition of the main cryogenic stage engine and then the 2 booster stages at the given launch time as early as possible in the launch window determined for the satellites. The countdown finishes with a synchronised sequence controlled by the computer at the control console and by the Ariane launcher and which begins at T0 minus 7 minutes.

If for some reason, there is a delay in the countdown and T0 is pushed beyond the launch window, the launch is postponed to D+1 or later depending on the cause of the problem and the solution found.

Each Ariane mission begins in the Launcher Integration Building (BIL). For two weeks, the launcher is carefully assembled directly on its launch platform.

D-22 to D-21	Arrival of the main cryogenic stage and the storable propellant stage at the Launcher Integration Building (BIL).
D-20 to D-19	Arrival of the booster stages (EAP)
D-22 to D-8	The operations at the BIL begin with : integration of the main cryogenic stage, the equipment bay, the storable propellant stage and the booster stages. connecting and tightness tests for the main cryogenic stage and the storable propellant stage. electrical tests synthesis tests preparation for transfer from the BIL to the BAF.
D-8	The launcher is transferred from the BIL to the final assembly building. Once the work in the BIL has been completed, Ariane is transferred on its launch platform to the final assembly building (BAF). The following nine days include the operations listed below :
D-11 to D-8	Arrival of the payload (satellite) at the BAF
D-8 to D-1	The Combined operations plan (POC) is undertaken at the BAF. It includes : integration of payload no. 1 and of the composite purging of pipelines final inspections filling and pressurising (except for the main cryogenic stage) mechanical arming of the payload
D-1	The launcher is transferred from the final assembly building to the launch area.

D-0 Launch countdown

D-0	The launcher is transferred from the final assembly building to the launch zone.
T0-6h	Beginning of countdown
T0-4h30	Beginning of fuelling
T0-1h	Mechanical arming
T0-6'30''	Synchronised sequence The synchronised sequence begins at T0 - 7 min. It is designed to perform the final operations for implementing the launcher and the necessary tests before putting the launcher in its flight configuration. It is entirely automatic and conducted in parallel up to T0 - 4secs. by two identical computers located in the ELA 3 Launch Centre. The computers perform the last electrical activations (starting of the flight program, the servo-motors, switching from ground power supply to flight batteries, etc.) and corresponding checks. The computers initialise the flight configuration for propellant and fluids and the necessary checks as well as the final initialising of ground system configurations, namely : injecting water into the flame chutes and the flame guide (T0 - 30 s.). sucking of the freezing hydrogen from the Vulcain into the flame guide (T0 - 18 s.). ignition of the freezing hydrogen (T0 – 5.5 s.). From T0 – 4 secs., the onboard computer takes over the final ignition operations for the engines and lift-off by : starting the ignition sequence for the Vulcain engine of the first stage at T0 ; checking engine parameters (between T0 + 4.5 s and T0 + 7.3 s); authorising ignition of the booster stages leading to immediate lift-off at T0 + 7.3 s. Any stopping of the synchronised sequence after T0 - 7 min. automatically returns the launcher to its T0 - 7 min. configuration.
T0	Launch