PASADENA, Calif. — It's
going to be a nice day on Mars when NASA's Phoenix Mars Lander makes its planned
touchdown in the northern plains of the red planet on Sunday, mission engineers
said Thursday.
"The weather is good
for our landing on Sunday, no dust," said Phoenix principal investigator Peter
Smith of the University of Arizona. "We are ready to explore the northern
plains of Mars."
Now in the homestretch
of its 422
million-mile (679 million-km) trek to Mars, Phoenix is just 77 hours away
from its May 25 landing, mission managers said during a briefing here at NASA's
Jet Propulsion Laboratory (JPL).
Phoenix is slated to
land on the artic plains of the Vastitas Borealis region of Mars, where it will
dig down into the rock-hard layers of water ice thought to lie under the
Martian soil near the planet's north pole.
Mission scientists had
been monitoring a dust storm in the vicinity of Phoenix's planned landing site,
but determined it won't pose a problem during the craft's descent through
the Martian atmosphere, Smith said.
The $420-million
mission launched in August with some of the same instruments originally
designed for its ill-fated predecessor, the Mars Polar Lander that crashed in
1999, and is aimed at testing
the Martian soil and ice to see if it could have created a habitable zone
for primitive life at some point in the past. The probe carries a shovel-tipped
robotic arm, ovens and a wet chemistry lab to study Mars ice samples.
Mission scientists hope
to receive the signal that Phoenix has landed on Sunday at 7:53 p.m. EDT (2353
GMT) - there will be about a 15-minute delay between landing and when the
signal reaches Earth because it must travel the 171 million miles (275 million
km) between the two planets.
But before Phoenix can
begin its science mission, "it has to go through one of the most risky phases
of its landing, the entry descent and landing," said Fuk Li, NASA's Mars
Exploration Program manager at JPL. "It will be a nerve-wracking time on Sunday
for all of us."
While mission
scientists are optimistic about Sunday's
planned landing, they acknowledge that there is no guarantee of success.
Mission engineers are hoping they've worked out all the problems that were
encountered with the lost Mars Polar Lander (MPL) in 1999, which used a similar
landing system to Phoenix, but failed during descent through the Martian
atmosphere.
Mission scientists say
the craft has performed fine so far with all course adjustments and in-flight
testing, even skipping one trajectory correction since it's been flying so
true.
"We've had a very
clean flight to Mars so far," said Ed Sedivy, Phoenix spacecraft manager from
Lockheed Martin Space Systems. "The spacecraft has been very well-behaved."
Phoenix's next
possible maneuver will come on Saturday at 10:46 p.m. EDT (0246 May 25 GMT)
with an opportunity to adjust the adjust the craft's course toward the Martian
arctic by firing its thrusters.
If all goes according
to plan, Phoenix will land somewhere in an elliptical area at 68 degrees north
latitude, 233 degrees east longitude.
To make successful
landing, the spacecraft will have to endure a harrowing
seven-minute descent through the Martian atmosphere, which Li and the other
mission scientists described as the most difficult part of the whole mission.
Friction at the
beginning of its fall will heat the craft's heat shield to a scorching 2,600
degrees Fahrenheit (1,420 degrees Celsius). Phoenix's parachute should deploy once
the probe is at an altitude of about 7.8 miles (12.6 kilometers) above the
Martian surface. During the next three minutes of the fall, the heat shield
will be jettisoned and the legs will extend. Thrusters should kick in when
touchdown is just 40 seconds away to slow the lander into its planned soft
landing.
The last successful
landings on Mars were NASA's two Mars Exploration Rovers Spirit and Opportunity,
but those craft used airbags to cushion their landing, not thrusters. The
thruster technique that Phoenix will use has not been used successfully since NASA's
two Viking missions set down in 1976.
NASA scientists hope
that Phoenix will follow the successes of the two rovers and other successful
missions. If all goes well, "on Sunday, we'll be welcoming to this family a new
family member, the Phoenix Mars Lander," Li said.
NASA's broadcast Phoenix
Mars Lander events live on NASA TV, with the next mission briefing set for 3:00
p.m. EDT (1900 GMT) on Saturday, May 24. Click
here for SPACE.com's Phoenix mission coverage and a link
to NASA TV.
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