WASHINGTON (AFP) - NASA said all systems were "go" and the weather forecast was good for Saturday's launch of space probe Phoenix on its nine-month journey to Mars, where it will dig for clues to past and present life.
The Phoenix Mars Lander is scheduled for blastoff from Cape Canaveral, Florida with a first attempt at 5:36 am (0936 GMT) and a second attempt, should it be needed, at 6:02 am (1002 GMT).
NASA's Launch Director Chuck Dovale said the launch team was ready to go and the weather forecast called for scattered clouds, light winds and good visibility.
"We have worked for four years to get to this point, so we are all very excited," said Phoenix project manager Barry Goldstein at NASA's Jet Propulsion Laboratory in Pasadena, California.
Phoenix was originally scheduled to launch on Friday, but postponed 24 hours after bad weather Tuesday prevented fueling of the two-stage Delta II rocket that will propel Phoenix into space.
The space probe's full launch window for its 680 million kilometer (422 million mile), 420 million dollar mission to Mars extends until August 24.
If Saturday's launch goes off as scheduled, Phoenix should land on Mars in late May 2008 -- a later launch would put it on Mars in June 2008.
NASA hopes to land the probe on flat ground with few or no rocks at a Martian latitude equivalent to northern Alaska on Earth.
Phoenix is likely to face Martian temperatures that range from minus 73 degrees Celsius (minus 99 degrees Fahrenheit) to minus 33 C (minus 91 F).
Once it lands safely on the Martian surface, the probe will deploy a set of research tools never before used on the planet.
The solar-powered craft is equipped with a 2.35 meter (7.5 foot) robotic arm that will enter vertically into the soil, aiming to strike the icy crust that is believed to lie within a few inches of the surface.
The Phoenix's robotic arm will lift soil samples to two instruments on its deck. One instrument will check for water and carbon-based chemicals, considered essential building blocks for life, while the other will analyze the soil chemistry.
Many scientists see signs of ancient rivers and oceans on the arid and sterile surface of Mars, and believe the planet may once have harbored some forms of life.
In 2002, the NASA probe Mars Odyssey detected huge quantities of hydrogen on the Martian surface, a likely sign there could be ice at a depth of less than one meter (three feet).
Unlike NASA rovers Spirit and Opportunity, which have been rolling across the Martian landscape since 2004 powered by their solar batteries, Phoenix will stay in one place on the Martian ground.
And unlike the rovers, which made a bouncy landing on Mars inside huge air bags, Phoenix is programmed to carry out a soft touchdown.
As with previous missions, Phoenix will deploy a heat shield to slow its high-speed entry into the Martian atmosphere. It will then open a supersonic parachute that will cut its speed to about 217 kilometers (135 miles) per hour.
The lander then separates from the parachute and fires pulsed descent rocket engines to slow the craft to about nine kilometers per hour (5.5 miles per hour) before landing on its three legs.
Fifteen minutes after landing, the probe's solar panels will deploy and power up its instruments.
The Phoenix Mars Lander measures 5.5 by 1.5 meters (18 by 5 feet) and carries 55 kilograms (121 pounds) of scientific equipment.