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Climatological study

Starting from 1994, a certain amount of round the world simulations have been carried out on a climatological basis, meaning with winds observed around the globe on previous years. These studies figured out following facts:

  • The best season is winter, from November to February in the northern hemisphere.
  • 35 degrees is the latitude that presents the best regularity in the wind speed and the lowest risk in terms of adverse meteorological elements (rain, thunderstorms, turbulence). The term of subtropical jet stream is often used to characterise the winds at these latitudes.
  • It must be possible to fly up to 10000 metres (30000 feet) in order to have a good chance to close the loop.
  • It must be possible to often change the altitude in order to keep a suitable direction.
  • The minimal duration of the tour is of about 10 days. Practically one must count with 15 to 20 days.

The design of the gondola and envelopes of the Bretling Orbiter 1, 2 et 3 has been conceived taking into account these constraints.

Example of a round the world in 10 days
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Example of a round the world in 20 days
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Choosing the start window

The first task of the forecaster is to find a good start window from Château d'Oex. Following conditions must be fulfilled:

  • No precipitation.
  • Very little wind during the whole time of the inflation.
  • A north-westerly to northerly wind in altitude allows to drive the balloon quickly to a latitude close to 35 degrees.
    A first alert is given 4 to 5 days in advance. It will be confirmed or cancelled until the final green light.

Example of a 10 day forecast for the region of Château d'Oex
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Example of a local wind forecast on Switzerland
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Real time routing

Once the balloon is launched, a permanent meteorological support is established at the control centre of the International Airport of Geneva. On a regular basis, the pilots are provided with advice on the best altitude to hold in order to go as fast as possible in direction of the East. To do so, we use the forecast winds at several altitudes my the numerical model of the Centre for Medium-range Weather Forecasts. The further computation of a trajectory takes into account both the spatial and temporal changes in the wind.

Example of a wind forecast at 9000 metres
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Example of a trajectory
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The wind is not the only actor in the game. The other meteorological parameters present often a danger for the crew:

  • Turbulence shakes the balloon.
  • Humidity, clouds, precipitation, icing bring weight to the envelope and so decrease the flight autonomy.
  • Thunderstorms produce strong vertical currents that can tear up the envelope.

MeteoSwiss possesses a long a long experience in forecasting these phenomena for the regular flights and the private pilots leaving Switzerland for a variety of countries. This time again, for the Breitling Orbiter 3 project, the skill of our aeronautical briefing will be used in order to ensure the safety of Tony and Bertrand.

Example of a significant weather chart for the use of regular pilots
mentioning the areas of turbulence, icing and thunderstorms
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Jet streams
The concept
Contents The itinerary
The concept

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