But some are also thought to harbour water ice, which could be used as a raw material for the manufacture of rocket propellant or even breathable air.

BBC: New venture 'to mine asteroids'

After setting a record mission rate of seven flights in 2009, launch attempts in the early months of this year experienced a series of frustrating postponements as engineers grappled with a faulty pressure regulator on the rocket's propellant system.

BBC: Ariane rocket completes flawless satellite launch

Yet the ability to stir up that kind of excitement, among consumers, at least, is the propellant in Apple's rocket.

FORBES: Chief Executive Steve Jobs