NASA and university astronomers are eagerly awaiting
the launch of a space probe bound to collide with a comet and give
researchers a glimpse inside the solar system's icy
wanderers.
The Deep Impact mission, now set to launch on Jan.
12, will send two spacecraft on brief spaceflight to Comet Tempel 1,
where an "Impactor" payload will slam into the object while its mothership,
"Flyby," looks on.
The entire mission should last only a few months, but
researchers are hopeful they will finally be able to break through the outer
surface of a comet.
"Only the internal material of a comet is unchanged
from the beginning of the solar system," said Deep Impact principal investigator
Michael A'Hearn, of the University of Maryland, during a press briefing
today at NASA headquarters in Washington D.C. "But there are no data on the
interior, and that's what we're hoping to solve with Deep Impact."
The $330 million mission has been delayed
twice from its original Dec. 30 launch date, first to allow engineers to rerun
ground tests, then once more to replace a launch component. Deep Impact has a
window running through Jan. 28, 2005, during which time the mission can
launch anytime and still make its July 4, 2005 rendezvous
with Comet Tempel 1.
"I have every confidence that we're going to make it
by the 28th," said Deep Impact project manager Rick Grammier, of NASA's Jet
Propulsion Laboratory in Pasadena, California, during the briefing. "We're good
to go."
If successful, Deep Impact will be NASA's second
probe to visit a comet in as many years. On Jan. 2, 2004, the Stardust
spacecraft flew through the comet 81P/Wild 2, taking images and collecting
samples that will be returned to Earth for study in 2006. The European Space
Agency (ESA) also launched its comet probe Rosetta on March 2 to visit comet
67P/Churyumov-Gerasimenko, where it is expected to drop its lander Philae on the
comet's surface in 2014.
A quick comet cruise
Deep Impact is unique among NASA missions in its
brevity. From launch to impact, the mission spans just six months of
spaceflight, giving mission controllers little time to shake out any bugs that
may pop during the cruise.
To that end, spacecraft engineers have been
continually testing their flight hardware and software to ensure the mission
will go smoothly. At least twice during that testing they found need to recheck
their work, hence the launch delays.
"Our checks are in place to detect these things,"
Grammier said. "That's why they're there."
Flyby and Impactor won't be alone on their cruise
either. A host of ground- and space-based telescopes, including the Hubble and
Spitzer space telescopes and the Chandra X-ray observatory, will be watching
Comet Tempel 1 before, during and after Deep Impact's encounter.
"There will be lots of exciting science at many
wavelengths from many observatories around the world," said Deep Impact
co-investigator Karen Meech, of the Institute of Astronomy in Hilo,
Hawaii, during the briefing. "We're hoping to see a change in the comet's
chemistry
Looking inside a comet
Once Deep Impact arrives at Comet Tempel 1, much of
what is expected to occur should do so automatically.
The Flyby mothership is expected to release the
Impactor probe, a 820-pound (372-kilogram) spacecraft with its own camera to
record the impact, in Tempel 1's path.
The comet should then overtake Impactor in a
collision that is anticipated to occur at about 23,000 miles (37,014 kilometers)
an hour. Moments before the crash, Impactor will snap the closest images -
ranging between 20 to 300 kilometers depending on dust levels
- ever obtained of a comet nucleus, while Flyby and Earth instruments
will monitor the collision from afar.
By studying the collision's ejecta and resulting
crater, researchers should be able to determine the physical properties of
Tempel 1 as well as get a front row seat to crater formation.
"It's less than a 1 percent chance of missing the
target," Grammier said. "But we're doing something we haven't done before, so
we're just going to keep testing."
Flyby is equipped with both high and low-resolution
cameras to monitor the collision, researchers said.
"While a technically challenging, this is an utterly
simple experiment," A'Hearn said.
Launch ahead
But before Deep Impact can lay the smackdown on its
cometary target, it has to get off the ground first.
The current Jan. 12 launch target lies near the
middle of the current launch window, and while NASA officials are confident the
mission will fly before Jan. 28, mission planners are making contingency plans.
They have selected a short list naming about six
potential replacement comets that Deep Impact could swing by should it miss its
Comet Tempel 1 window, mission planners said. The earliest available comet
alternate would require a launch in about two months or so after the initial
target, though that comet has a smaller nucleus and sheds a larger amount of
dust which could make spacecraft targeting difficult, they added.
Deep Impact scientists said Tempel 1 need
not be the only comet their mission visits during its lifetime. Although
Impactor will be destroyed in the encounter, Flyby will swing past the
comet and could encounter at least one other icy wanderer should
researchers choose to extend their mission.
"We've identified at least two other comets that
Flyby could visit in an extended mission," A'Hearn said. "But we have not yet
chosen which [comet] we'd propose for that."
advertisement
