Nasa are making final preparations for the most dangerous moments of the biggest Mars mission in recent years.

On August 6, if all goes well, the 900kg Mars Space Laboratory, a huge robotic geologist, will arrive on the surface of the planet.

The rover, also known as Curiosity, will spend up to two years surveying the surface around Mount Sharp and analysing samples to try and ascertain whether the planet harbours the tell-tale signs that life once existed there.

The landing will use an innovative robotic crane system to overcome the enormous re-entry speed and poor slowing properties of the Martian atmosphere.

The crane fires rockets to slow the rover's descent, before lowering it the last few metres to the surface on a cable.

Mars Program Director Doug McCuistion admits the landing is not without its risks: "Is it crazy? Well, not so much. Once you get comfortable, once you understand it, it's not a crazy concept. It works.

"Is it risky? Landing on Mars is always risky. There are hundreds of discreet events that occur from release of the cruise stage to parachute deployments to heat shield deployments. All of these are unique and any one could cause problems."

He went on: "We go from 13000 miles an hour to zero in seven minutes. That's quite a challenge in itself. And then there's the unknown. There's Mars.

"Mars throws things at you. Dust storms, atmospheric density changes, wind. So it's a very unique and a very challenging environment."