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After its launch, it is only the start of the journey for the James Webb telescope


I’m happy, excited, relieved, but I dread the rest, it’s not over, it’s only the beginning, told theFrance Media Agency Thomas Zurbuchen, head of scientific exploration at NASA, a few minutes after the telescope separated from the upper stage of the Ariane 5 rocket on Saturday.

It was a joy all the greater since in the minutes which followed the separation, carried out after 27 minutes of flight and at an altitude of around 1400 km, the telescope’s solar panels deployed without hindrance, under the thunderous applause from engineers and the public at the Jupiter Control Center in Kourou.

This was the crucial first step, as the telescope cannot function without this source of electricity. And it still has some way to go – 1.5 million kilometers to cover in a month – before reaching the point of Lagrange 2, four times the distance between Earth and the Moon.

To reach this final vantage point, the James Webb made the first – and most important – of three course corrections. The great impetus given to it by the rocket to reach its goal has been knowingly minimized to prevent the instrument, which cannot slow down its course, from exceeding its goal, with no real hope of return.

SuccessNASA tweeted on Saturday night with the announcement that the telescope’s small motors had been running flawlessly for 62 minutes. They will again be called upon for the approach, then for the final injection in orbit around the point of Lagrange 2.

Mr. Zurbuchen’s caution was not feigned, because if NASA is very used to this kind of maneuver, it will attempt a first: deploy a very large instrument in space.

A crucial week ahead

Folded to fit in Ariadne 5’s headdress, like a chrysalis just over four meters in diameter, the craft built by Northrop Grumman must deploy a 6.5 m primary mirror and a 14-meter flexible heat shield. out of 20, the equivalent of a tennis court.

With no hope of rescue if things go wrong, because of the distance.

The coming week will prove to be crucial. About two and a half days after launch and a second course correction, engineers at the telescope’s control center in Baltimore will oversee the release of the two pallets which contain the solar shield.

This stacking of five large sails of a fabric as thin as a hair is the condition sine qua non the proper functioning of the James Webb and its instruments, the working temperature of which requires a minimum cold of -230 ° C.

The rocket takes off from the launch pad.

The Ariane 5 rocket, which carried the James Webb telescope, took off on the morning of December 25, 2021 from the Guyanese space center.

Photo: afp via getty images / JODY AMIET

The telescopic mast – which carries the mirrors, still folded, and the instruments – will then rise to make room for the two pallets to open. Our shield is very similar to a parachute, it must be folded perfectly to deploy perfectly, had explained, before take-off, Crystel Puga, Webb systems engineer at Northrop.

The operation, which consists of unfolding then stretching and finally hanging the five sails, will last several days and start just after the passage of the Moon. It involves 140 canvas release mechanisms, eight small motors, around 400 pulleys and 90 cables.

During the second week after launch, the tripod at the end of which is the secondary mirror, which concentrates the light from the primary mirror before directing it towards a third mirror and the instruments, will unfold in turn, leaving room to the main mirror, folded in three, to open.

If all goes well then, once arrived at the Lagrange 2 point, the adjustment phase, which will take a few months.

It will require in particular the alignment of the 18 hexagons of the primary mirror to make it the equivalent of a uniform surface with a precision of the order of ten thousandth of the thickness of a hair.

And it will also be necessary to calibrate the instruments, which will then be able to reveal things never before seen on the Universe. The first meeting is scheduled for June, six months after takeoff.

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