A solar-powered plane that is to be flown to the edge of space has been officially unveiled today. The SolarStratos plane is powered by 22 sq m (237 sq ft) of solar panels and will be flown to an altitude of 25,000 m (82,000 ft) to demonstrate and explore the potential of the technology.
"Our goal is to demonstrate that current technology offers us the possibility to achieve above and beyond what fossil fuels offer," says project founder and pilot Raphaël Domjan in a press release. "Electric and solar vehicles are amongst the major challenges of the 21st century. Our aircraft can fly at an altitude of 25,000 m and this opens the door to the possibility of electric and solar commercial aviation, close to space."
The solar-electric plane is said to have an environmental footprint that is equivalent to that of an electric car and is aimed at offering an alternative to using large quantities of energy or helium as a means of reaching the stratosphere. It is 8.5-m (27.9-ft) long, has a wingspan of 24.8 m (81.4 ft) and weighs in at just 450 kg (992 lb).
The solar panel array charges a 20 kWh lithium-ion battery, which powers a 32-kW electric motor that in turn drives a 2.2-m (7.2-ft) propeller. SolarStratos says it is able to fly continuously for over 24 hours, which is more than enough to cover the expected two-and-a-half hours it will take to reach space, 15 minutes cruising at peak altitude and three hours to return to the Earth.
The project began in 2014, after Domjan had the idea during the solar-powered boat crossing of the Atlantic on his PlanetSolar round-the-world journey. Beyond the project's demonstrative and exploratory tech goals, it is hoped that it will inspire people and to help uncover new scientific knowledge.
The SolarStratos plane and operational hangar were unveiled at an event in Payerne, Switzerland, to around 300 guests, including ambassadors, partners, government representatives and members of the media.
The project is currently in the development phase, but the first roll tests, touch-and-go landings and test flights are due to take place in January next year. All being well, medium-altitude flights will follow later in the year and initial stratospheric flights in 2018. The mission itself is also scheduled for 2018.
Source: SolarStratos
82000ft = 164 minutes of descent at a "standard" 500ft/min descent. So 2.7 - 3 hours just sounds like a ballpark figure for flight planning.
Ascent in 2.5 hours = 546.67ft/min
That is likely the AC's max climb rate (at somewhere between 45-60kt)
In an aircraft designed for lift and efficiency, if you push the nose down gravity takes over and the speed will quickly exceed "normal operating speed", with no speed brakes the only way to control this is by pushing down more gently (lower descent rate). Nothing to do with "fighting those lift generating forces" while maintaining control. Well, exceeding Vne, or Vturb can have significant "controlled flight" consequences, under extreme circumstances.