This
story was updated at 3:55 EDT.
PASADENA, Calif. – The big day has finally
arrived: After 10 months of spaceflight, NASA's Phoenix Mars Lander is headed
for its long-awaited attempt to touch down in the arctic region of the red
planet later today.
"We've bet the whole farm on this safe
landing," said Phoenix principal investigator Peter Smith of the University of
Arizona in a Saturday briefing here at NASA's Jet Propulsion Laboratory (JPL).
"We can't do our science without the safe landing."
The $420-million Phoenix mission, which
launched in August, is expected
to dig down into the rock-hard layers of water ice thought to lie under the
Martian soil in the planet's northern polar region. It carries a robotic arm,
ovens and wet chemistry lab to test the soil and ice to see if the region could
have once been a habitable zone for microbial life.
The craft has performed beautifully so far,
with all systems checking out throughout the 422 million-mile (679 million-km)
trip to Mars, mission scientists have said. "Now what we need is a successful
entry, descent and landing," said Doug McCuistion,
director of the Mars Exploration program for NASA.
Phoenix is slated to land on the Vastitas Borealis plains of Mars later today, with
mission scientists expecting to receive the first signal that Phoenix has
landed at 7:53 p.m. EDT (2353 GMT). (The signal should arrive at Earth about 15
minutes after leaving Mars due to the 171 million miles (275 million km)
between the red planet and Earth.) The spacecraft currently has about 30,000
miles (50,000 km) left to travel, Smith said, adding that from the spacecraft,
Mars would look about 10 times the size of a full moon.
If all goes well, Phoenix will touchdown
under its own rockets to mark NASA's first powered landing on Mars since the
agency's two Viking probes landed in 1976. The last spacecraft to attempt a
powered landing - the ill-fated Mars Polar Lander (MPL) - crashed before
reaching the surface of the planet's southern polar region in 1999.
Phoenix mission engineers believe they have
worked out all the problems that plagued MPL and are hoping the system is all
set to guide the craft safely to the surface. If successful, the spacecraft
would join NASA's Spirit and Opportunity rovers, which used airbags to land in
2004 and are currently roaming the planet's equatorial regions.
NASA will broadcast Phoenix's approach and
landing attempt live on NASA TV from the JPL control room here, with
commentary set to begin at 6:30 p.m. EDT (2200 GMT).
Fiery descent ahead
By the time Phoenix arrived at Mars this
morning, it was travelling at 6,100 mph (9,800 kph),
the Mars Reconnaissance Orbiter, Mars Odyssey Orbiter and the ESA's Mars
Express will be in
position to observe its landing attempt and relay information back to
Earth.
To make a successful landing, the craft must
execute a complicated series of actions in a very short amount of time; it will
take just seven
terrifying minutes for the spacecraft to plummet through the Martian
atmosphere, mission managers have said.
"It's not going to be an easy one," said
Phoenix mission manager Joe Guinn of JPL. But he added, "I think we're actually
in fairly good shape."
Mission scientists decided to forgo an
opportunity to adjust the craft's trajectory late Saturday and again this
morning because Phoenix remains on course toward its target landing ellipse: a
50-mile (80-km) long drop zone that sits in a broad, shallow valley. Controllers
have sent Phoenix its last instructions before landing, so "the rest of the day
is just watching and waiting," Smith said.
All that watching and waiting, "means I'm a
heck of a lot more tense today," said Barry Goldstein, Phoenix project manager
of JPL.
Mars' gravity has started to accelerate the
craft, which will eventually enter the Martian atmosphere at 12,600 mph (20,300
kph) as it approaches the planet. "Today our
spacecraft is starting to feel the pull of Martian gravity," Smith said at
press briefing today at JPL. "I understand this well; I've been feeling the
pull of Martian gravity for 15 years"
Phoenix should separate from its cruise stage
at about 7:39 p.m. EDT (2339 GMT) tonight, after which there will be a
three-second communication blackout before the craft's UHF radio antenna is
supposed to kick in. Goldstein has said that milestone is the one that worries
him most. If communications aren't restored between Phoenix and Earth and the lander fails, scientists won't be able to glean any data to
tell what went wrong, he added.
Smith agreed: "If you see me
freak out, it's because we've lost the signal and we don't know what that means."
The spacecraft is then supposed to turn and
enter the atmosphere, its heat shield guarding it from the superhot plasma
created by friction as the craft falls. (This plasma could cause another
blackout period by interfering with the UHF antenna.) This stage will reduce
Phoenix's speed by 90 percent until it's falling at 1.5 times the speed of sound.
Phoenix is then supposed to deploy its orange
and white parachute, which will slow the craft to about 1,100 mph (TK kph), jettison its heat shield and stick out its landing
legs. Shortly after, its radar system should activate, providing the craft with
its first measurement of where the ground is.
Once that occurs, Phoenix should
separate from its back shell at 7:50:15 p.m. EDT (2350:15 GMT), "and then
shortly after that, the fireworks, literally, will begin," Goldstein said, as
the craft fires up its thrusters to further slow its descent and guide it to a
three-point landing.
Smith and Goldstein will be with other
mission scientists in mission control, monitoring the radio signal sent from
Phoenix to Mars Odyssey Orbiter that could give them and idea of how things are
going.
The first images from the spacecraft on Mars
could be received as soon as a few hours after landing, but only after
Phoenix's vital solar arrays deploy to begin generating power for its planned
six-month mission. Without the solar panels, Phoenix only has about 31 hours of
battery power on which to live.
"This is truly the defining moment of this
mission," McCuistion said of today's landing attempt.
NASA's next Phoenix mission briefing
will be broadcast live on NASA TV at 12:00 a.m. EDT (0400 GMT) on Monday, May
26 Click
here for SPACE.com's Phoenix mission coverage and
a link
to NASA TV.
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