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Solar Impulse 2 Comes Out of Hibernation

Solar Impulse 2 at Kalaeloa Airport

Solar Impulse 2 is a solar-powered airplane currently in the midst of a flight around the world. The journey began at Abu Dhabi in the UAE on March 9, 2015, and was expected to conclude before the days got shorter towards autumn (the aircraft needs long periods of daylight to charge up its batteries so it can continue to fly at night). However, weather delays plagued the team for months in Asia, and when the plane finally made it to Hawaii the batteries had been damaged by heat and required repairs that couldn't be completed before the days got too short. Thus the project went into hibernation until spring, with the aircraft parked in a hangar at Kalaeloa Airport on the west end of the island of Oahu. I was present to welcome Solar Impulse 2 as it landed on July 3, 2015, and visited again with my family a few days later. Then as the project got back into gear to prepare for resumption of the journey, supporters were invited to a special open house (er, hangar) on March 26, 2016, with a public open house to follow on April 2. Above is my old friend, stretching across the vastness of the hangar with a wingspan greater than that of a 747.

Close up of nacelle

I did not see any visual evidence of the battery repairs, and redesign of the thermal control system, that had occurred over the winter. Each engine nacelle, containing a motor, a battery pack, and the power control electronics for a subset of the solar cells, was being cooled in the warm hangar by external air conditioners; however, the manifold to which the green-wrapped tube is attached is only in place for the air conditioners on the ground and is not part of a new "ram air" system for use in flight or anything. All the changes were internal; the only alterations of the exterior of the aircraft that I could see were the additions of some new sponsors' logos.

Tail and rear of fuselage

Prominent among the new logos was that of Covestro, which was just added as a co-sponsor and partner. This is the tail and aft fuselage of Solar Impulse 2; in this light it is easy to see the structural ribs through the thin, translucent skin. If you look closely at the previous photo of the nacelle, you can see that the wing surface and propellor spinner are also translucent; paint, except for markings and logos, is dispensed with in order to reduce weight. I recall that several hundred pounds were saved on the Space Shuttle external tank after the first couple of missions by not painting it white; I don't know how much weight was saved here, but every bit counts when capabilities are being stretched as they are for this journey.

Solar Impulse 2 from the gallery

It was too crowded at my last visit for the stairs to the gallery above the hangar floor to be opened up, but for this supporters-only event they did allow us to go up and get a view over the top of the aircraft. From this vantage point you can see the dark-colored solar cells covering the tops of the wings, the fuselage, and the horizontal stabilizer. I learned that these cells were made by SunPower, who also made the photovoltaic panels installed on our house; of course, the ones flying around the world are thinner, lighter, and doubtless more expensive than the ones we bought, and also about 40% more efficient at converting sunlight to electricity. All part of making a round-the-world flight possible!

The current plan is for Bertrand Piccard, one of the two alternating pilots of Solar Impulse 2 on the round-the-world flight, to take off on April 15th, 2016; I certainly hope I can return here to witness that! The destination on the North American mainland is still to be confirmed; the plan is to land at Phoenix, Arizona, but it may be necessary to go instead to Los Angeles or San Francisco, California, or possibly far to the north at Vancouver, British Columbia. Test flights have already begun; I spoke with some visitors who live within sight of the airport (I had to come from the other end of the island), and they told me of watching the slow, nearly silent takeoffs and landings.

I'd like to thank Paige Kassalen for briefing me on the status of the aircraft and the journey. She has had a pretty interesting journey herself: she graduated last year from Virginia Tech with a degree in electrical engineering and went to work for Covestro, who assigned her a few months ago to accompany Solar Impulse 2 as part of the ground crew for the continuation of the round-the-world flight. Pretty cool way to start one's career, I must say!

Aircraft at the Udvar-Hazy Center

As it happens, I was in Virginia myself last month for a scientific meeting, and I had a few hours to myself at Dulles Airport before my departing flight, so I took the bus to the nearby Udvar-Hazy Center, a vast annex of the Smithsonian Air and Space Museum. The collection includes many firsts, fastests, highests, and farthests in the history of aviation; in the foreground here you can see the Spirit of Texas, the first helicopter to fly around the world (in 1982), and high above is the Virgin Atlantic Global Flyer, which made the first solo nonstop flight around the world (in 2005). The helicopter had extra fuel tanks to extend its range between stops, but the Global Flyer was mostly fuel, 2915 gallons of it or 83% of its gross takeoff weight, to enable multi-day flights.

Pathfinder Plus

Solar Impulse 2 carries no fuel, so the limits to the duration of its flights are set by the (very durable!) human pilots. This photo shows a prototype pilotless solar aircraft, the Pathfinder Plus, that explored the possibility of unlimited-endurance flight in the 1990s. (AeroVironment is also well known in the field of alternative-fueled ground transportation, notably through their involvement with the General Motors Impact prototype that led to the EV1 production electric car.)

Breitling Orbiter 3 gondola

And here is a sight familiar to Bertrand Piccard: the gondola of the Breitling Orbiter 3, in which he and Brian Jones completed the first nonstop balloon flight around the world in 1999. Looking at this and the other historic aircraft and spacecraft present, it occurred to me that there can't be that many other museums around the world that are large enough to house a wingspan greater than that of a 747. Perhaps in a few years I will be able to visit Solar Impulse 2 here, when I again have some time to kill at Dulles!

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new 30 March 2016, updated 21 April 2016