As we have repeated so often, before every structural test : « If, at 100 % of the intended load, the part breaks, then it must be too fragile; but if it doesn’t break, there’s a good chance it’s too heavy ! ».

This is the philosophy that we have applied since 2007 in optimizing the design of each component. But once the design process was complete, no component has ever again broken … up to now at least… each part proving both strong enough and light enough in weight.

We are always trying to work at the limits of the technologies we are using, and so we have further optimised the design and construction of the airplane’s spinal column, the main wing-spar. A few hours ago, the central section of the main spar of HB-SIB, our second aircraft, failed a torsion test, breaking before it reached the calculated maximum load factor.

It was the very last test, and everyone was getting ready to celebrate passing an important milestone. But the day was to finish in tears and bitter disappointment. More even than for Bertrand and myself, these prototypes are the cherished offspring of the engineers who did the calculations, designed and built them.

This is a major set-back – in fact the first since the Solar Impulse program was launched in 2003. We don’t yet know exactly what happened, what the explanation for the failure is, nor whether it will cause delays to the future operational timetable. The specialists will now have to start examining the matter, but I wanted to make you aware of it immediately.

Great team spirit happening! The only causality thus far is the coffee machine, which has been working non-stop and could really use a 100'000 km check up!

A last burst of energy and inspiration to share with you the last subject on my list I absolutely need to learn a little "endurance" from André.

One of all the many aspects in keeping André sustainable for so long is the cockpit. This week we have been testing a prototype cockpit for the 2^nd airplane. Compared to the 1^st cockpit in HB SIA, this is definitely upgrade from economy to business class!

In collaboration with Lantal, a partner company, a special seat was developed and tested during the simulation. This seat is built with an inflatable pneumatic technology offers several positions (flying, relaxation and resting) and has an integrated toilet. Wow, no morewaiting in line to go to the bathroom!

As to avoid any health issues that can arrive from immobility, André has been pursuing a series of exercises developed by Doctors and Osteopath from Hirslanden. Watching these exercises on our screens from André's on-board cameras, these look really strange and one may wonder what he is really up to ! Actually my theory is that he is using some of those techniques he picked up in India.

Landing expected at 08h00 (UTC+1). Go for it André, less than 90 minutes left.

And for Bertrand, we will see you later this year here in the simulator. But in the meantime we have a few real flightscoming up soon

Steady state is for a human being what sustainability is for humankind. It means that the physiological parameters of the human body have reached an equilibrium that allow them to continue to work the same way for a long period. When you run, a sprint is not a steady state, a jogging is.

In our case, it would be possible to make a sprint where the pilot doesn't eat neither sleeps for 72 hours, but it would be useless as this situation could never be sustained if the flight was to last longer for a reason or another. The pilot would be so tired that he would never be able to land the airplane.

So the goal here is to push the limits for the lack of sleep, the food patterns, the hygiene in the cockpit, the use of the toilets, the shifts of the mission team, but without going too far. Until now, not too far is already quite impressive!

Bertrand (remembering that my first profession was medical doctor)