Water from asteroids could be broken down in space to liquid oxygen and liquid hydrogen for rocket fuel.

BBC: Plans for asteroid mining emerge

Liquid-fuelled rocket engines work by mixing the fuel (in this case kerosene) with liquid oxygen at high pressure.

ECONOMIST: On a rotor-blade and a prayer | The

The term hybrid is used because this type of rocket motor uses neither all-liquid fuel nor all-solid fuel, but a combination of both.

BBC: Hybrid success for British rocket