With a mixture of tense nerves and confidence, NASA counted down to the landing of its largest ever robotic rover on Mars, where it will search for signs that life may once have existed.

The $2.5 billion Mars Science Laboratory, featuring a car-sized rover called Curiosity, is expected to land on Mars at 0531 GMT on Monday (10:31 pm Sunday on the US West Coast).

However, success is anything but certain with this first-of-its-kind attempt to drop a six-wheeled chemistry lab by rocket-powered sky crane on an alien planet. NASA's more recent rover dropoffs were done with the help of airbags.

"We are rationally confident, emotionally terrified and ready for EDL," said NASA engineer Adam Steltzner, leader of the US space agency team tasked with entry, descent and landing (EDL), a process NASA has called "Seven Minutes of Terror."

In these final moments, the spacecraft should accelerate with the pull of gravity as it nears Mars' atmosphere, making a fiery entry at a speed of 13,200 miles (21,240 kilometers) per hour and then slowing down with the help of a supersonic parachute.
After that, an elaborate sky crane powered by rocket blasters kicks in, and the rover is due to be lowered down by nylon tethers, hopefully landing upright on all six wheels.

"Excitement is building while the team is diligently monitoring the spacecraft," said mission manager Brian Portock. "It's natural to get anxious before a big event, but we believe we are very well prepared."

Scientists do not expect Curiosity to find aliens or living creatures. Rather they hope to use it to analyze soil and rocks for signs that the building blocks of life are present and may have supported life in the past.

The project also aims to study the Martian environment to prepare for a possible human mission there in the coming years.