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3 May: San Francisco - Phoenix

"Payerne (Switzerland), 4th May 2013, 11h00 GMT. Take-off from San Francisco is scheduled in two hours, and everyone is working in silence, focused on his or her task since the early morning. Luc and Wim (the weather team) analyse the last data concerning the situation above California and Arizona, Nik and Yves-André (the air traffic control team) check the waypoints and their contacts along the route currently planned. Stephane and I (the modelling and simulation team) are computing all details of the last update of the route to Phoenix. Our work is decisive: analysing actual constraints coming from the weather forecast and the air traffic control, we process them into our simulation and computing tools so as to find the best flight strategy. This means that we are responsible for defining the best combination of route, flight profile and energy management leading the Solar Impulse to reach safely its destination. For this reason, we directly report to our Flight Director, Ray, giving him our take-off recommendation.

We have to be reactive, and ready to take into account, at any moment of the flight, the smallest change in the situation: weather update, new constraints on the route given by the US air traffic control, information given by the pilot (modification of the altitude due to turbulences, for instance), actual battery level, drift of the plane due to crosswinds…

As usual, during the next 20 hours, we will almost continuously perform simulations, triple check every detail, study telemetry data, record and analyse the key data of the flight, compute the critical parameters and send them to the control monitors for all the mission control centre teams.


Bertrand, the pilot for this flight, appears on our screens, the pressure is now increasing among all the team. The final countdown indicates H-45 minutes before take-off. We know that this first flight will initiate a great new challenge for us, as our airplane has never faced such complex flights before. Mainly because weather in North America is characterised by its ability to change quite fast, with many local microclimates and specificities.

The plane is now on the runway, performing last engine tests. It’s now time for me to go back behind my three screens. And soon, the big solar bird will once again majestically take off, this time in the rising sun of California."

Christophe Béesau

Esperto Altran per Solar Impulse in Advanced Modelling and Simulation