Scientists are
priming two spacecraft to slam into the moon's South Pole to see if the lunar
double whammy reveals hidden water ice.
The
Earth-on-moon violence may raise eyebrows, but NASA's history shows that such
missions can yield extremely useful scientific observations.
"I
think that people are apprehensive about it because it seems violent or crude,
but it's very economical," said Tony Colaprete, the principal investigator
for the mission at NASA's Ames Research Center in Moffett Field, Calif.
NASA's
previous Lunar Prospector mission detected large amounts of hydrogen at the
moon's poles before crashing itself into a crater at the lunar South Pole. Now
the much larger Lunar
Crater and Observation Sensing Satellite (LCROSS) mission, set for a
February 2009 moon crash, will take aim and discover whether some of that
hydrogen is locked away in the form of frozen water.
LCROSS will
piggyback on the Lunar
Reconnaissance Orbiter (LRO) mission for an Oct. 28 launch atop an Atlas 5
rocket equipped with a Centaur upper stage. While the launch will ferry LRO to
the moon in about four days, LCROSS is in for a three-month journey to reach
its proper moon smashing position. Once within range, the Centaur upper stage
doubles as the main 4,400 pound (2,000 kg) impactor spacecraft for LCROSS.
The smaller
Shepherding Spacecraft will guide Centaur towards its target crater, before
dropping back to watch - and later fly through - the plume of moon dust and
debris kicked up by Centaur's impact. The shepherding vehicle is packed with a
light photometer, a visible light camera and four infrared cameras to study the
Centaur's lunar plume before it turns itself into a second impactor and strikes
a different crater about four minutes later.
"This
payload delivery represents a new way of doing business for the center and the
agency in general," said Daniel Andrews, LCROSS project manager at Ames,
in a statement. "LCROSS primarily is using commercial-off-the-shelf instruments
on this mission to meet the mission's accelerated development schedule and cost
restraints."
Figuring
out the final destinations for the $79 million LCROSS mission is "like trying
to drive to San Francisco and not knowing where it is on the map,"
Colaprete said. He and other mission scientists hope to use observations from
LRO and the Japanese Kaguya (Selene) lunar orbiter to map crater locations
before LCROSS dives in.
"Nobody
has ever been to the poles of the moon, and there are very unique craters -
similar to Mercury - where sunlight doesn't reach the bottom," Colaprete
said. Earth-based radar has also helped illuminate some permanently shadowed
craters. By the time LCROSS arrives, it can zero in on its 19 mile (30 km) wide
targets within 328 feet (100 meters).
Scientists
want the impactor spacecraft to hit smooth, flat areas away from large rocks,
which would ideally allow the impact plume to rise up out of the crater shadows
into sunlight. That in turn lets LRO and Earth-based telescopes see the
results.
"By
understanding what's in these craters, we're examining a fossil record of the
early solar system and would occurred at Earth 3 billion years ago,"
Colaprete said. LCROSS is currently aiming at target craters Faustini and Shoemaker,
which Colaprete likened to "fantastic time capsules" at 3 billion and
3.5 billion years old.
LCROSS researchers
anticipate a more than a 90 percent chance that the impactors will find some
form of hydrogen at the poles. The off-chance exists that the impactors will
hit a newer crater that lacks water - yet scientists can learn about the
distribution of hydrogen either way.
"We
take [what we learn] to the next step, whether it's rovers or more
impactors," Colaprete said.
This comes
as the latest mission to apply brute force to science.
The Deep
Impact mission made history in 2005 by sending a probe crashing into comet
Tempel 1. Besides Lunar Prospector's grazing strike on the moon in 1999, the
European Space Agency's Smart-1
satellite dove more recently into the lunar surface in 2006.
LCROSS will
take a much more head-on approach than either Lunar Prospector or Smart-1,
slamming into the moon's craters at a steep angle while traveling with greater
mass at 1.6 miles per second (2.5 km/s). The overall energy of the impact will
equal 100
times that of Lunar Prospector and kick up 1,102 tons of debris and dust.
"It's
a cost-effective, relatively low-risk way of doing initial exploration,"
Colaprete said, comparing the mission's approach to mountain prospectors who
used crude sticks of dynamite to blow up gully walls and sift for gold.
Scientists are discussing similar missions for exploring asteroids and planets such
as Mars.
Nevertheless,
Colaprete said they "may want to touch the moon a bit more softly"
after LCROSS has its day.
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