Photo album: "Launch of the balloon"

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Continuation of the operations that will end with the launch of the balloon transporting the experiment CITADEL (measurement of the electric field in the ionosphere in Adélie Land). An increase in the wind speed before the launch makes us fear for the worse, i.e. a scratch in the main balloon skin, then a moment of quiet permits the launch without problems.

Jean-Pierre Legrand, near the main balloon which is beginning to inflate. An intermediate strap allows to restrict the inflation to the upper part of the balloon. This tie will be removed just before the launch.

A view of the two balloons on the launch area. The capacity of the main balloon is 4,500 m3 but it will reach this volume only when it is at the altitude of 30 km.

We see, at foreground, on the left, the measurement gondola with its six arms (the lower one is now folded up). It is very fragile because the plates at the extremity of each arm as well as the central part of the module are covered with a very thin layer of carbon which must not get scratched at all. Therefore the measurement gondola will be attached to the auxiliary balloon which will keep it high enough to prevent any contact with the ground during the launch of the main balloon.

At ground-level atmospheric pressure, 80 m3 of helium will be put inside the main balloon. This gas will expend when the atmospheric pressure decreases, during the main balloon climb, until it will occupy its whole volume.

The measurement gondola is ready to be suspended under the auxiliary balloon. The electric field measurement will be done measuring the electric potential difference between every one of the plates attached to the six arms and the central module.

Inflation of the main balloon is going on.

A cable is being attached between the auxiliary balloon and the measurement module, another longer one has already been connected to the main balloon.

Inflation of the main balloon is now finished and the hose has been tied to prevent the helium to escape.

We let the auxiliary balloon rise gently up to when the measurement gondola is high enough above the ground. A few minutes after the launch, a motor will make the gondola to turn slowly on itself around a vertical axis.

When everything is ready for the launch, the wind speed increases suddenly. Jean-Pierre Legrand and Raymond Roger do not free the main balloon because it could be pushed onto the ground and would be definitely damaged.

Taking advantage of a moment of calm, it has been possible to launch the two balloons. The measurement gondola is still carried by the auxiliary balloon. The radar reflector and the technical module are directly appended under the main balloon.

The main balloon rises faster than the auxiliary balloon. As soon as the cable between the measurement gondola and the technical module becomes tight, the auxiliary balloon will break loose automatically.

The auxiliary balloon has just broken loose. It will pursue its ascent till the pressure of the helium inside the balloon will become higher enough than the outside pressure to make it blow up. It will then fall back onto the ground.

Unlike the auxiliary balloon, the main balloon has an aperture at its lower part, this allows the helium in excess to escape. During the flight which can last a few days, helium losses are of two kinds:  - the first one, low enough, is due to the helium molecules that succeed in passing through the balloon skin  - the second one, more important, is due to the dilatation of the gas during the day, under the action of the sun. Some helium escapes, then, through the aperture at the lower part of the balloon.  During the night, the gas cools down and its volume decreases which makes the balloon go down. To compensate this loss of gas, it is necessary to discharge part of the ballast, this action reduces the load carried by the balloon and allows it to rise once more.

Participants to the launch and a few spectators congratulate each other for its success. We recognise on the photo, at left, leaning on the blue box, Roger Raymond, a little farther on the right smiling, Gérard Gogly, then still farther on the right, in profile, with the Inca cap, Jean-Jacques Berthelier.

Jean-Pierre Legrand takes a last look at the balloon slowly disappearing to the sight. A little farther on the right, partly hidden, Jean-Jacques Berthelier is speaking with a member of the French Polar Expeditions. The meteorological radar will follow the balloon during its ascent and will give information on the direction to point the receiving antenna to get the data transmitted by the measurement gondola.

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