It’s swollen! Make reusable balloons capable of going into the stratosphere, approximately 25 kilometers above sea level. At this height, in the pressurized pod, tourists will have the impression of floating in the black of space and will see the curvature of the Earth in almost absolute silence. This is the technological challenge that the Toulouse start-up Zephalto and its 25 employees must meet to make balloon excursions at very high altitude affordable. To start, it will cost 170,000 euros to complete a five-hour flight (i.e. an hour and a half of ascent and the same amount of descent and two hours of parking at very high altitude).
A bit like Space Thanks to their reuse and a sufficient volume of activity, “the price could be divided by 10 in the long term”aims Vincent Farret from Asties, founder of Zephalto.
The development of the reusable envelope is the main technological challenge. Current stratospheric balloons are not intended to be reused. At the end of the mission, their envelopes tear at altitude and let their cargo escape under parachute.
The challenge is all the greater as these envelopes reach incredible dimensions. Once inflated with hydrogen, the envelope will represent a volume of approximately 120,000 cubic meters. “The facade of Notre-Dame could fit inside”, explains Vincent Farret from Asties. They therefore have nothing to do with hot air balloons… Even if they are reusable. Due to their dimensions, stratospheric balloons would be too heavy if they were made of a comparable material. They must also be airtight unlike hot air balloons which are porous.
Combine lightness, resistance and flexibility
Finally, they must also be extremely flexible: their volume will be multiplied by 40, from 3,000 to 140,000 cubic meters between low and very high altitudes! Enough to add up the constraints. “It’s difficult to find a material that combines all the required qualities: lightness, waterproofness and flexibility,” explains the manager, an engineer by training and former air traffic controller.
And to make the stratospheric balloon envelopes traditionally made of polyethylene reusable, the Zéphalto teams assembled them with another material that is more resistant and barely heavier, but with similar qualities. Thanks to the five flights already carried out with prototypes, Zephalto has evolved the composition of this material, jealously kept secret, several times to optimize it. The objective is to reuse the same envelope several dozen times.
The company indicates that it has filed its own patents without wanting to specify in which field. As part of its developments, Zephalto has also benefited from technology transfers from CNES (national center for space studies), an expert in the field of stratospheric balloons. To be sure to control the manufacturing processes, Zephalto plans to invest in its own balloon manufacturing factory. The start-up plans to raise 16 million euros thanks in particular to the help of the real estate and investment group Magellim.
Up to 60 flights per year
Another factor which will allow prices to be lowered: mass production and launch rates. Ultimately, the Toulouse start-up hopes to deploy eight bases around the world, each capable of operating around 60 balloon flights per year. Zephalto designed and tested an altitude regulator to allow the balloon to make flights for several weeks in a row by maintaining it at the desired altitude despite temperature variations between day and night. “The device will act as a float to compensate for variations in gas pressure and temperature”explains Vincent Farretd’Asties.
The balloon won’t just carry space tourists. It will also be able to carry equipment such as telecommunications relays or instruments allowing Earth observation for companies, scientific organizations and even armies. Zephalto’s bet is still ongoing. Last October, Vincent Farret from Asties and his co-pilot made a trip to an altitude of 6 kilometers. Zephalto hopes to carry out its first flights at very high altitude by the end of 2025 and carry tourists the following year.
Source: www.usinenouvelle.com
