It's no longer safe to say that the Solar Impulse 2 aircraft will make it around the world before 2015 draws to a close. The crew is now warning that its sun-powered machine won't fly the next leg of its journey (from Hawaii to Arizona) for at least two to three weeks due to severe heat-related battery damage. While that's not the biggest setback the team could face, it could trigger a domino effect. If SI2 doesn't get to the Eastern side of the US in time, it may miss the weather window it needs to get across the Atlantic this year. You'll find out more about the extent of the problem in the next few days, so it should soon be clear whether this is just a momentary obstacle or a serious showstopper.