The solar-powered plane will take off from Abu Dhabi and head east, first to Oman, and then to India.
Over the next five months, Solar Impulse 2 will skip from continent to continent, crossing both the Pacific and Atlantic oceans in the process.
Swiss adventurers Bertrand Piccard and Andre Borschberg will share the pilot duties in the single-seater vehicle.
They will stop off at various locations to rest and to carry out maintenance, and also to spread a campaigning message about clean technologies.
Andre Borschberg will start the journey with a takeoff from the Emirate’s international airport at about 06:30 local time.
The project has already set a number of world records for solar-powered flight, including making a high-profile transit of the US in 2013.
The round-the-world venture is altogether more dramatic and daunting, and has required the construction of an even bigger plane than the prototype, Solar Impulse-1.
This new model has a wingspan of 72m, which is wider than a 747 jumbo jet. And yet, it weighs only 2.3 tonnes.
Its light weight will be critical to its success.
Solar Impulse 2 has 17,000 solar cells that line the top of the wings, and the energy-dense lithium-ion batteries will use to sustain night-time flying.
Operating through darkness will be particularly important when the men have to cross the Pacific and the Atlantic.
The slow speed of their prop-driven plane means these legs will take several days and nights of non-stop flying to complete.
Bertrand Piccard and Andre Borschberg – whoever is at the controls – will have to stay alert for nearly all of the time they are airborne.
They will be permitted only catnaps of up to 20 minutes – in the same way a single-handed, round-the-world yachtsman would catch small periods of sleep.
They will also have to endure the physical discomfort of being confined in a cockpit that measures just 3.8 cubic meters in volume – not a lot bigger than a public telephone box.
Flight simulators have helped the pilots to prepare, and each man has developed his own regimen to cope.
Andre Borschberg will use yoga to try to stay fresh. Bertrand Piccard is using self-hypnosis techniques.
The support team is well drilled. While the mission will be run out of a control room in Monaco, a group of engineers will follow the plane around the globe. They have a mobile hangar to house the plane when it is not in the air.
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