More than a year ago, one of the pioneering exploration projects of our times began, when two Swiss pilots set off to circumnavigate the globe in their Solar Impulse 2 plane using nothing but solar power.

Now, this mission is almost at its conclusion, with the final leg from Cairo in Egypt to Abu Dhabi in the United Arab Emirates set to take place in the next few days. Provisionally, the single-seater plane is scheduled to touch down in Abu Dhabi at sunrise (local time) on Tuesday, July 19, following a 40-hour flight from Seville, Spain.

Depending on weather, the flight may be delayed by 24 hours, but it cannot be delayed further for political reasons, a spokesperson from Solar Impulse told IFLScience.

Both pilots, André Borschberg and Bertrand Piccard, readily admit that they do not expect solar power to become the future of aviation. But, rather, the mission is intended to show the capabilities of solar power. Solar Impulse 2, which has a wingspan of 72 meters (236 feet), uses 17,000 solar cells on its wings to power its propellers, with an average speed of a modest 75 kilometers per hour (47 miles per hour).

During the mission, the pilots have taken turns to fly each leg, with the longest trip from Nagoya (Japan) to Kalaeloa, Hawaii (US), taking almost five days. Borschberg flew the penultimate leg from Seville to Cairo, and Piccard will do the final leg to Abu Dhabi, which will land in the evening US time.

"All the partners of Solar Impulse knew it would be a difficult challenge, but they wanted to try and make it possible," Piccard said in a tweet.

Since the journey began on March 9, 2015, Solar Impulse 2 has made 16 stops around the world, including India, China, Japan, and the US. Its final stop sees it return to the location where it all started, completing the first round-the-world flight by a solar-powered plane.

To keep the weight as low as possible (Solar Impulse 2 is as wide as a jumbo jet, but as light as a car), the pilots have had to go without many comforts on each flight. The cockpit has no air conditioning or heating, and only a very basic autopilot system. As each pilot flies alone, the only sleep they get is short 20-minute catnaps while in the air. To go to the toilet, there’s a rather unsavory hole in their seat.

It's all set to be a rather exciting ending to the mission. You'll be able to watch a live cockpit stream of Solar Impulse 2's final flight on their website. And we may have something exciting in store for you, too...

^{Old meets new as Solar Impulse 2 flies over the pyramids in Egypt on its way to Cairo on July 13, 2016. Solar Impulse}