Ariane 5 ready for take off, only the weather can still interfere


The countdown has begun. The Ariane 5 rocket, which is to propel the James Webb space telescope into space on Saturday, was waiting on its launch pad for the start of the final count on Friday, which only capricious weather could still interrupt. If all goes well the European launcher must start from 9.20 am Saturday morning (1.20 pm Paris time).

In the middle of a vast expanse surrounded by barbed wire and the Guyanese jungle, the white rocket is erected on its launching table, a large mobile steel structure, itself crowned by four immense lightning rod towers. So far, only the rain and the wind especially, have played tricks on the machine, forcing a postponement of the date.

An imposing water tower nearby must supply the « deluge », at 30 tonnes of water per second, which will be triggered under the engines when they are ignited, scheduled for 9.20 am. To attenuate a temperature rising up to 3,000 degrees, and above all to drown the shock of the acoustic wave of take-off, which could damage the on-board electrical components. At around 180 decibels, this is the loudest noise a man-made machine can make.

210 tons of hydrogen and liquid oxygen

Two long silver pipes connect the top of the mast of the table to the Ariane 5 fairing, which houses the telescope. They guarantee it an air conditioning of cold and dry air, to preserve it from the ambient air, hot and humid. The minimum for the most sophisticated observation machine ever sent into space.

A little below, two bright yellow arms carry the fuel supply lines for the upper stage, the lower stage being fed directly from the table. Still empty, the rocket’s tanks will accommodate a total of 210 tonnes of hydrogen and liquid oxygen. These propellants wait wisely in tanks placed at a good distance. Because it is their mixture, highly combustible, which will allow take-off.

“When the filling maneuvers will start at H-7 am, no one will be able to stay on the site anymore,” explains Jean-Marc Durand, deputy director of Arianespace Guyane. The rocket will remain alone, all the controls, including those for filling fuel, then arriving from the launch center, located 2.3 km away. It is from the bunker part of this building, – closed 45 minutes before takeoff – that the site manager and his teams will give their commands to the launcher, such as filling the tanks, and receive all the parameters.

Friday in the day, the rows of tables clad with screens in the center were still empty, « because the sequence will start late », specifies Jérôme Rives, director of the Ariane 5 program at Arianespace. It will even be scratched all night from Friday to Saturday.

Automatic take-off

With a countdown, launched from the Jupiter control center, and which must start precisely at 9:57 p.m. In this large « jar », the operations department « concentrates all the information enabling the launch to be coordinated », explains Jean-Luc Mestre, deputy director of operations.

If no red comes from those in charge of the telescope, the space base, the launcher or the weather forecast, the director of operations will launch the synchronized sequence at H minus seven minutes. At that moment all the operations will switch to automatic mode, piloted by the control center and rocket computers.

At H hour the Ariane 5 Vulcain engine will start, but it is only seven seconds later that the two powder engines will ignite which will allow the rocket to tear itself from the ground. All this pretty ballet will only be possible if the weather is playing the game, under an overcast and windy sky.

At 1:00 p.m. Friday, the forecast center gave the green light. He will still launch several weather balloons in the air to refine his forecasts by the launch, including the last less than three hours before. In the Jupiter center on Friday, a manager saw this attention to the sky as a good sign: “if we talk about the weather, it’s because everything has been done well so far, because it’s the last thing to look at before the launch ”.

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