Image caption Engineers have some final work to do to get MSL's rocket ready for launch

Nasa is in final preparations for the launch of its latest rover mission to the Red Planet.

The Mars Science Laboratory (MSL) is the biggest, most capable robot ever built to land on another planet.

It is expected to lift off from Cape Canaveral Air Force Station, Florida, on Saturday.

Lift-off is actually a day later than originally planned, to give engineers time to replace a problem battery in the spacecraft's Atlas rocket.

The one-hour-and-43-minute launch window will now open at 10:02 local time (15:02 GMT). MSL's cruise to Mars should take eight-and-a-half months.

The rover will aim to touch down in an equatorial depression called Gale Crater, where it will use its suite of 10 instruments to assess whether the Red Planet has ever been habitable.

It is not a life-detection mission as such; the $2.5bn robot cannot identify microbes or even microbial fossils. But it can assess whether ancient conditions could have ever supported organisms.

This means Gale must show evidence for the past presence of water, a source of energy with which lifeforms could have metabolised, and a source of organic compounds with which those organisms could have built their structures.

Gale has been chosen as the landing site because satellite imagery has suggested it may well be one of the best places on Mars to look for these biological preconditions.

Jonathan.Amos-INTERNET@bbc.co.uk