10 March 2015
Last updated at 08:13
Solar Impulse heads out over the Arabian Sea
Solar Impulse is back in the air on the second leg of its historic attempt to fly around the world.
After the briefest of lay-overs, the prop-driven plane took off from Muscat in Oman at 06.35 (02:35 GMT).
It is heading across the Arabian Sea to Ahmedabad in India.
Project chairman, Bertrand Piccard, is now at the controls, having taken over from Andre Borschberg, who flew the first leg on Monday from Abu Dhabi to Muscat.
The second leg will cover about 1,465km (791 nautical miles), and should take about 16 hours. Live coverage of Tuesday’s leg is being relayed on the internet.
It is expected to take five months in total for the single-seater Solar Impulse vehicle to cross the continents, passing over both the Pacific and Atlantic oceans in the process.
The Solar Impulse project has already set a number of world records for solar-powered flight, including making a high-profile transit of the US in 2013.
But 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.
So, too, will the performance of the 17,000 solar cells that line the top of the wings, and the energy-dense lithium-ion batteries it 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.
Piccard and Borschberg – they take it in turns to fly solo – will have to stay alert for nearly all of the time they are airborne.
They will be permitted only catnaps of up to 20 mins – 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 metres in volume – not a lot bigger than a public telephone box.
Andre Borschberg is a trained engineer and former air-force pilot, he has built a career as an entrepreneur in internet technologies.
Bertrand Piccard is well known for his ballooning exploits. Along with Brian Jones, he completed the first non-stop, circumnavigation of the world in 1999, using the Breitling Orbiter 3 balloon. The Piccard name has become synonymous with pushing boundaries.
Bertrand’s father, Jacques Piccard, was the first to reach the deepest place in the ocean (a feat achieved with Don Walsh in the Trieste bathyscaphe in 1960). And his grandfather, Auguste Piccard, was the first person to take a balloon into the stratosphere, in 1931.
A solar revolution – by Roger Harrabin, BBC environment analyst
It’s a deep-breath moment in the history of technology as Solar Impulse soars to the skies.
Because, pinch yourself, solar power is predicted to become the dominant source of electricity globally by 2050.
The price of solar electric panels fell 70% in recent years and costs are expected to halve again this decade.
And Deutsche Bank forecasts that, based on current fossil fuel prices, solar will produce power as cheaply as gas in two thirds of the world before 2020.
In the UK the solar industry thinks it can compete with wind within 18 months and with gas in the near future. In the US, solar jobs already outnumber coal jobs.
The solar revolution was sparked by government subsidies, which attracted venture capitalists to fund innovation and created a huge market that Chinese manufacturers are battling to exploit.
The solar boom is a huge help in the battle against climate change, but scientists warn it’s not nearly enough. And we must find ways of storing that mighty but capricious power, and making it work with the grid.