The most expensive and ambitious mission to Mars remains on course for a spectacular landing on the red planet on Monday morning.
Scientists and engineers will be watching anxiously from 154m miles away as the Curiosity rover plunges through the thin atmosphere of Mars on its final approach.
The planned descent of the spacecraft - slowing from 13,000mph to a complete stop on the surface - has been dubbed "seven minutes of terror".
Nasa is already trying to manage expectations, aware even the tiniest factor could mean failure for the £1.6bn project.
Dr Tom Jones, an astronaut on the Space Shuttle programme, told Sky News: "I would say this is the most difficult spacecraft landing sequence since the days of the moon landings on Apollo."
Because it takes 14 minutes for radio signals to reach earth from Mars, there will be an agonising wait before we know whether Curiosity has survived the landing.
The Mini-sized spacecraft will zig-zag to slow itself down during descent before unfurling a parachute while travelling at 900mph.
The rover will fire up its rocket-powered backpack to slow it down a mile from the surface of Mars, until it hovers.
Cables will then unspool from the backpack and slowly lower the rover, ensuring the rocket engines do not get so close that they churn up dust.
Once the rover senses touchdown, the cords will be cut – but the whole operation could be de-railed by a sudden guest of wind or a freak storm.
Former Nasa Mars chief Scott Hubbard said: "You've done everything that you can think of to ensure mission success, but Mars can still throw you a curve."
The future of Mars exploration is hanging on the outcome of the project to determine whether the environment was once suitable for microbes to live.
Previous missions have found signs that water once flowed and Curiosity will drill into rocks and soil in search of carbon and other elements during its two-year mission.
President Obama has called on Nasa to put a man on Mars by the 2030s and experts say the Curiosity project is a small step towards that ambition.
Dr Jones said: "It is actually a bridge towards the idea of humans getting there. This large, one-ton rover is closer in size to the spacecraft that will carry humans there.
"It seems it has got a magical place in our imagination, its got that ruddy appearance, that orange star in the sky, its got a mythological significance and because of its earth-like qualities and because life might have existed there, we are very curious."
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