Image: Solar Impulse/Jean Revillard
Next year, a pair of explorers will set off on a round-the-world trip in a plane running entirely off solar energy. Solar Impulse 2 will build on the legacy of its predecessor, which crossed the US, in a mission to spread the word about energy-saving technologies.
The solar-powered plane has had quite a few upgrades to tackle the global trip, which were necessary to allow it to travel over oceans without too much risk of pitching into the depths should the weather change. That’s pretty important, given its low speed: It’ll take several days of non-stop flying to cross the major oceans, so the plane has to be able to keep going without a break.
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The same applies to the pilot. Bertrand Piccard and André Borschberg will share flying duties, but they’ll only be able to swap over when they make a pit stop on dry land. In the air, they’ll be restricted to a single-seater cabin with a week’s supply of food and water and some oxygen tanks.
Solar Impulse 2. Image: Solar Impulse/Jean Revillard
The plane itself is bigger than a Boeing 747 but a lot more slimline with a weight of 2,300 kg—about the same as a single car. We’ve been following the mission for a while, and with test flights for the new plane starting this week, I caught up with Borschberg to find out more about how plane and pilot are primed for the challenge.
MOTHERBOARD: You’ve already crossed the US on solar, and for this world trip you’re using a new plane. What kind of upgrades does Solar Impulse 2 have?
André Borschberg: The first step was in some ways designed to demonstrate that you can fly day and night; it was the first airplane ever built that has an unlimited endurance [in terms of energy]. That’s what made it special, and that’s what we wanted to demonstrate with the first airplane. But it’s not designed to travel over a long duration, for example over the ocean.
That’s what we had to do with the second airplane, so it’s more reliable, because you cannot do any maintenance when you fly for almost a week over the Pacific non-stop. It also has better performance to be able to do that, and to fly in a little bit more difficult weather situations. Thirdly, it has a cockpit to allow the pilot to become sustainable as well—the aircraft is sustainable in terms of energy, and now the weak part of the chain is the human, the pilot. So we had to build a cockpit and environment system for the pilot in order to allow him to be able to fly alone, non-stop, for up to a week’s time.
André Borschberg. Image: Solar Impulse/Jean Revillard
So what specific changes did you make to improve the performance in these areas?
We tried to use lighter materials than what we had in the first one. For example, the lightest single sheet of carbon fibre now is down to 25 grams per square metre, and if you compare that with a sheet of paper that you get from your printer, this is about 80 g per square metre. This is the kind of development we made between the first and the second one, to make it lighter and of course reduce the energy consumption.
That’s the same for motors. A motor for a car, using fuel, has an efficiency of about 30 percent—so about 70 percent is going into heat in the atmosphere. We have an electric motor with an efficiency of 94 percent for the whole system, so only six percent is going into heat in the air. So through these energy savings, that’s how we increase the performance of the airplane.
And as you mentioned, there are issues for a human pilot flying for so many hours. How will you deal with the physical and mental challenges of flying for so long?
Physical and mental preparation: First, we train to sleep and rest for very short periods of time, 20 minutes duration. So these are micro-naps, micro-resting periods that we can do many times during the day or during the night depending on the situation, allowing us to keep control of the airplane but also rest so that we keep concentration.
We also use different techniques; I’ve been doing yoga for many years and I’ve developed a program with a yogi in India for exercises to keep the body in good physical condition and rest the mind at the same time. Also breathing techniques—yoga is fundamentally built around breathing, and I do meditation. These are tools that I’ve developed over time which help me to rest but in a conscious way, and to be able to in fact enjoy this long-duration flight in this very narrow environment.
André Borschberg with Bertrand Piccard. Image: Solar Impulse/Jean Revillard
You’ll be over the ocean for days at a time—how dangerous is it?
Probably the danger fundamentally is lack of energy—to be caught in a weather situation where you cannot get enough energy from the sun and then you cannot go through the night and you’re forced to ditch the airplane. The difficulty is that when you leave the coast of China, you know the weather that you have in China and you have a weather forecast five or six days in advance for the other side of the Pacific in the United States, but of course the weather forecasts in advance are not very accurate.
But to mitigate the risk, we have a team on the ground in the control centre which is made up of specialists: weather specialists and ATC (air traffic control) specialists—because all this has to be coordinated with the other traffic flying around the different places. Using simulation techniques, they’re able to anticipate where the airplane could be in two days, how the weather could look like, and change the flight plan of the airplane early enough.
What is the flight path?
We’re working on it and it’ll be announced later this year, but fundamentally we’ll start somewhere in the Middle East, we’ll fly past India and China, cross the Pacific, cross the States, cross the Atlantic, and back to the point of departure. So that’s the north hemisphere from west to east, and we’ll stop in the major countries so we can change pilots.
All this should take between three and four months, from March to June of next year.
Ultimately, what’s the point of the mission? What do you hope to achieve?
It’s more for inspiration about what we can do, especially with these technologies—technologies that allow us to fly using very little energy; that’s what makes it feasible to fly in the night. What we want to inspire is not only for people to use this technology in airplanes, because it would of course take quite a long time to make commercial aviation totally clean, but to use these technologies also on the ground. Because if we can be energy-efficient in an airplane, we can certainly be more energy-efficient on the ground, in our homes, in transportation, in appliances … That’s the goal of the project: to be an ambassador for these clean technologies.
Image: Solar Impulse/Jean Revillard
So you’re about to start flight tests. What stage are you at and what do you need to do before you start really flying?
Yes, it’s a very exciting moment. To bring a new airplane for the first time in the air is something tremendous in terms of emotion, especially with such a special airplane. This one is bigger than the biggest 747, so it’s really impressive in terms of size, but it’s very light. We have experience with the first one, but still there are a lot of differences.
Currently we are checking everything, repairing everything, so we have no incidents for the first flight and everything works in a smooth way. Then when this first flight is done we’ll explore a bit more what this airplane can do, and prepare and train for the flight next year.
We also have to get authorization from all the different countries. It’s an airplane which is totally different; it flies very high, but it flies very slowly, and we are sensitive to strong winds so we have to be careful. So we’re asking to be treated sometimes in a different way than traditional aviation and this has to be discussed with the authorities. But I have to say, when people understand the goal and what the project is all about, the reception is very positive.
People often talk about the difficulties we have with the environment in a catastrophic way, telling people that if we don’t change we’ll all be dead very soon. This project is more of a positive message, showing what could be done and the way it can be done, and it’s extremely welcomed by the public because of its positive dimension.
