Ariane 5 to propel the James Webb telescope into space: an extraordinary mission

The launch of the James-Webb telescope by Ariane 5 is scheduled for this Saturday from the Guyanese space center. Ariane 5 is awaiting take-off that only the weather could disturb.

The Ariane 5 rocket, which is to propel the James Webb 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.

This revolutionary instrument is the result of an international collaboration led by NASA to give humanity a first glimpse of the nascent universe, as it existed when the first galaxies were formed. At $ 9 billion, it is considered by NASA to be the first space observatory of the next decade. It will mainly observe the cosmos in the infrared spectrum. Its instruments are also ideal for researching evidence of potentially life-supporting atmospheres around dozens of newly documented exoplanets – celestial bodies orbiting distant stars – and for observing worlds much closer to us, such as Mars. and Titan, Saturn’s frozen moon. By comparison, Webb is around 100 times more sensitive than its 30-year-old predecessor, the Hubble Space Telescope.

If all goes according to plan, Webb will be freed from Ariadne 5 after a 26 minute trip to space. Over the next month, the telescope will reach its destination in solar orbit, about 1 million kilometers from Earth, about four times as far as the Moon. Webb’s special orbital path will keep it in constant alignment with Earth, while the planet and telescope circle the sun in tandem.

In the meantime, 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 a.m. local time. To attenuate a temperature rising up to 3000 degrees, and especially 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.

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. 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 operations 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.

Meteorological green light

Friday in the day, the rows of tables covered 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. With a countdown, launched from the Jupiter control center, and which must start precisely at 9:57 p.m. In this big « jar », the operations department « Concentrates all the information making it possible to coordinate the launch », 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 the hour H 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 p.m. Friday, the forecast center gave the green light. He will still launch several probe 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, an official saw this attention to heaven as a good sign: « If we’re talking about the weather, it’s because everything has been done well so far, because it’s the last thing to look at before launch ».


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