The weather conditions on Mars are expected to be favorable when NASA's $2.5 billion Mars Science Laboratory attempts its risky landing on August 6, the US space agency said Saturday.

"Mars is playing nice and we are going to get good conditions for Sunday," said MSL deputy project scientist Ashwin Vasavada at a new briefing ahead of the landing set for 0531 GMT on Monday (10:31 pm on Sunday Pacific time).

A dust storm spotted days ago near the landing site has dissipated into a "fairly harmless cloud of dust," he said.

"That dust cloud probably will not reach Gale Crater by the time we land," he said, adding that it was not "expected to affect entry, descent and landing in any meaningful way."

The robotic rover is carrying a complex chemistry toolkit for analyzing rocks and soil in the hunt for signs of past life on the Red Planet.

The six-wheeled vehicle is the size of a small car and is due to be lowered onto the surface in a high-drama operation that includes spacecraft separation, parachute dropdown, a rocket-powered sky crane and a tethered soft landing.