It's all coming down to this. Well over a year after beginning its round-the-world trip, Solar Impulse 2 has embarked on the final leg of its journey. The solar-powered aircraft left Cairo early on the morning of July 24th and should reach its original starting point, Abu Dhabi, within 2 to 3 days. This certainly isn't the most arduous part of the adventure (the Pacific crossing was far more challenging). However, it'll likely be the one that everybody remembers -- it'll be the definitive proof that clean energy can be used to accomplish impressive feats.
And this isn't strictly the end. Bertrand PIccard, the pilot on this last stint and the architect of Solar Impulse, stressed to Reuters that the project isn't done once the aircraft touches down. To him, the flight has created an "international community" that will endure after the buzz is over. It's far too soon to say what Solar Impulse's legacy will be, but it'll at least get a page in the history books.