This jet of air functions like jet force and propels the balloon forwards. Rocket engines function according to the exact same principle: as the fuel burns inside the rocket, the gases produced escape ...

Cubic space isn’t measured because — again, unlike rocket-powered space tourism ventures ... the HALO capsule will be carried under a massive balloon some 140 metres tall.

They experiment with two ways that vehicles may be driven - energy directly applied to the axle with a wind-up rubber band, and energy that is separate from the axle using balloon-powered propulsion.