Just weeks before we paused to celebrate the 40th anniversary of man landing on the Moon, Sir Richard Branson's space-tourism operation, Virgin Galactic, had announced successful passenger rocket tests.

Recent weeks had seen Virgin Galactic announce successful tests of the rocket motor it will use to launch fare-paying passengers out of the Earth’s atmosphere.

The Saturn V spacecraft used to take man to the Moon in July 1969 was fuelled by millions of litres of RP-1 rocket fuel (kerosene), liquid oxygen and liquid hydrogen.

Continuing the involvement of industrial gases in space exploration, the Virgin Galactic rocket is propelled by a hybrid mixture of tyre rubber and nitrous oxide gas, otherwise known as ‘laughing gas’.

The engine, which will boost the company’s SpaceShipTwo rocket planes to heights of 65 miles after releasing from the ‘Virgin MotherShip’ piggyback jets high up into the stratosphere, is now said to have completed the first phase of ground testing in southern California.

The rocket is described as an ‘unusual’ hybrid type, operating between solid and liquid-fuelled designs. It burns solid hydroxy-terminated polybutadiene (HTPB) fuel - possibly with proprietary additives - using liquefied nitrous oxide gas as an oxidiser.

Unlike a normal solid-fuel rocket, the hybrid can be throttled or turned-off by regulating the flow of oxidizer – seen as something of a safety feature.

Branson is thought to be keen to cast the SpaceShipTwo rocket in an environmentally-friendly light.