Inflatable pneumatic modules already used in some spacecraft could be assembled into a 15-kilometre-high tower, say Brendan Quine, Raj Seth and George Zhu at York University in Toronto, Canada, writing in Acta Astronautica (DOI: 10.1016/j.actaastro.2009.02.018). If built from a suitable mountain top it could reach an altitude of around 20 kilometres, where it could be used for atmospheric research, tourism, telecoms or launching spacecraft.
The team envisages assembling the structure from a series of modules constructed from Kevlar-polyethylene composite tubes made rigid by inflating them with a lightweight gas such as helium. To test the idea, they built a 7-metre scale model made up of six modules (see image). Each module was built out of three laminated polyethylene tubes 8 centimetres in diameter, mounted around circular spacers and inflated with air.
To stay upright and withstand winds, full-scale structures would require gyroscopes and active stabilisation systems in each module. The team modelled a 15-kilometre tower made up of 100 modules, each one 150 metres tall and 230 metres in diameter, built from inflatable tubes 2 metres across. Quine estimates it would weigh about 800,000 tonnes when pressurised – around twice the weight of the world’s largest supertanker.
“Twenty kilometres up is about as dark as outer space. You can see about 600 kilometres in any direction,” Quine says. Tourists could get a view almost like that from space, but without the difficulties of coping with zero gravity. He calculates the tower could be extended up to low Earth orbit at 200 kilometres.
The tower does a similar job to the much-vaunted space elevator. But while the elevator envisages using ribbons woven from superstrong nanotubes – a material that is as yet non-existent – the tower would use materials that are already available. And should something go wrong with the tower, failure of a few modules would not cause the whole structure to collapse.
he team envisages assembling the structure from a series of modules constructed from Kevlar-polyethylene