NASA's Phoenix Mars Probe Set for Saturday Launch

A new NASA probe destined to dig into the arctic northern plains of Mars is on track for its planned Saturday launch, mission managers said Thursday.

Perched atop its 13-story Delta 2 rocket, NASA's Phoenix Mars lander is set to launch towards the red planet at 5:26:34 a.m. EDT (0926:34 GMT) during the first of two possible Saturday attempts from Florida's Cape Canaveral Air Force Station.

"For summer time in Florida, that is about the best time of day you can launch," said U.S. Air Force Delta 2 launch weather officer Joel Tumbiolo in a Thursday briefing at NASA's Kennedy Space Center in Cape Canaveral.

Current weather forecasts offer an 80 percent chance of favorable conditions during Phoenix's first launch opportunity, as well a second window that opens at 6:02:59 a.m. EDT (1002:59 GMT), Tumbiolo added. About the only weather concern is the possibility of thick clouds near the Mars probe's launch site, he added.

The $420 million Phoenix lander carries a mix of new science tools and recycled instruments originally designed for NASA's ill-fated 1999 Mars Polar Lander and the canceled Mars Surveyor 2001 missions. The planned 90-day mission, researchers hope, will unlock secrets hidden within the red planet's subsurface ice and soil near its north pole, and shed light on whether the region could have once been habitable.

"Our instruments are specially designed to find evidence for periodic melting of the ice and to assess whether this large region represents a habitable environment for Martian microbes," Phoenix principal investigator Peter Smith, of the University of Arizona, said of the mission's planned landing zone. ?

Phoenix carries seven primary experiment packages, including an eight-foot (2.4-meter) robotic arm designed to scoop up martian soil and ice like a backhoe. It also carries tiny, deck-mounted ovens and other instruments to sift for signs of organic compounds within the martian soil, as well as a suite of Mars weather monitoring tools.

If all goes well, Phoenix is expected to land on May 25, 2008 in a flat region known as Vastitas Borealis at a northern Mars latitude that is comparable to those of northern Alaska, Greenland or Siberia on Earth, mission managers have said.

Phoenix's descent to the martian surface, which relies on parachutes and a series of pulse rocket thrusters, will mark NASA's first soft landing on Mars since the Viking missions of the 1970s.

NASA launch director Chuck Dovale said engineers are currently analyzing the impact of a dropout in air conditioning around the protective, shroud-like launch fairing enveloping Phoenix atop its Delta 2 rocket, but the glitch is not expected to be a problem for Saturday's planned liftoff.

Originally slated for an Aug. 3 launch, Phoenix's Earth departure was delayed earlier this week after bad weather prevented the second stage fueling of the probe's Delta 2 rocket. NASA has a 22-day launch window to send Phoenix off towards Mars that closes Aug. 24. Beyond that, the space agency would have to wait 26 months - just over two years - for Mars and Earth to once again return to the proper orbital alignment for the mission.

With such a restricted launch window NASA officials have said they would consider delaying the planned Aug. 7 launch of the space shuttle Endeavour from KSC to offer more flight opportunities for Phoenix.

"We have a three-week launch window, which is quite an extensive period," Deborah Bass, NASA's deputy project scientist for Phoenix at JPL, told reporters Wednesday during a series of interviews on NASA TV. "I feel confident that we?ll get off Earth and on towards Mars within that time."

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