PASADENA -- With a little
more than two days left in its six-month journey, managers for NASA's Deep
Impact mission said the spacecraft is on course to make its historic encounter
with a comet late Sunday evening.
The mission is slated to
crash an 820-pound (371-kilogram) Impactor probe into Comet Tempel 1 and record
the event via a Flyby mothership. The impact is expected to take place at 1:52
a.m. EDT (0552 GMT) on July 4.
"I'm pleased to report that
both the Flyby and the Impactor spacecraft are ready for encounter operations,"
Dave Spencer, Deep Impact's mission manager at NASA's Jet Propulsion Laboratory
(JPL), announced today at a mission briefing.
The announcement follows
several major mission milestones that were achieved over the past two weeks.
On June 23, the spacecraft successfully
completed its third trajectory correction. The burn of the spacecraft's engines
changed Deep Impact's speed by 13 miles per hour (about 21 kilometers per hour).
Another trajectory correction for final targeting before Impactor release is
scheduled for 8:00 p.m. EDT July 2 (5:00 p.m. PDT).
Mission planners separated
the spacecraft's flight operations into six mission phases; launch,
commissioning, cruise, approach, encounter and playback. The five-day encounter
phase incorporates the final approach to the comet and transmission to Earth of
collected data.
Fresh comet science
Although Deep Impact is
still about 1.7 million miles (2.7 million kilometers) from Tempel 1, it is
already giving astronomers an eyeful. Onboard cameras have picked up several outbursts
of material jetting out of the comet, most recently on June 30, and allowed
researchers a chance front row seat to the phenomenon.
"We've known for a long time
that comets have outbursts, but we don't know what drives them," said Michael
A'Hearn, Deep Impact's principal investigator at the University of Maryland,
during the briefing. "We are getting great science now."
One such outburst was so
strong it nearly doubled the amount of water in hazy cloud, called a coma,
surrounding Tempel 1's nucleus, mission scientists said. In addition to water,
Deep Impact's onboard spectrometer has also picked up traces of complex
hydrocarbons, carbon dioxide and carbon monoxide, they added.
Deep Impact researchers said
that past probes to comet Halley in 1986, comet Borrelly
in 2001 and comet Wild-2
in 2004 recorded images at resolutions that ranged between 328 feet (100
meters) - or just over an entire football field - and about 75 feet (about 23
meters).
"Our spacecraft is going to
resolve items about the size of the football," said Don Yeomans,
co-investigator for Deep Impact at JPL. "So that's good."
But it's the main event
astronomers are waiting for. Mission scientists hope Deep Impact's Impactor
probe will punch through Tempel 1's outer surface and reveal inner material
that has lain unchanged since the formation of our solar system.
"Literally, these materials
have not seen the light of day in 4.6 billion years," said Jessica Sunshine, a
mission co-investigator at Science Applications
International Corp. (SAIC).
Impactor separation
On late Saturday evening, 24
hours prior to its estimated collision with Tempel 1, the Impactor will
separate from the Flyby mothership and begin its final approach on the comet.
The mothership will then adjust its course to monitor the Impactor's mission,
Spencer explained.
"Twelve minutes later the flyby
spacecraft--now flying on its own--will turn and perform its largest maneuver of
the entire mission," Spencer said. "It will slow itself down by about 220 miles
per hour relative to the Impactor ... this slowdown will allow it to witness the
impact events itself and subsequent crater formation for about 13 minutes after
impact."
Should something go wrong and the Flyby craft fail to break away from Tempel 1 after Impactor's release, there is a contingency plan to ram both vehicles into the comet's surface, Spencer added.
During the entire encounter, both the
Impactor and Flyby will use medium and high resolution imagers and an infrared
spectrometer to collect and send to Earth pictures and spectra of the event.
The plan is not without
technological and environmental risks: Following impact and the initial
observations, the Flyby spacecraft will adjust its position, using its shielded
solar array to protect its major hardware from any debris thrown up from the
comet's surface by the collision. During this time the mission team will be
working at full speed to download as much information as possible from the
spacecraft, systems engineer Jennifer Rocca said.
"We will try our best to
transmit the highest priority images from both Flyby and Impactor before Flyby
reaches its closest approach to the comet," Rocca explained. "This allows us to
capture our very best data even if Flyby suffers damage as it flies close to
Tempel 1."
The spacecraft will be
assisted with information gathered by a variety of spaceborne science platforms
including the Hubble and Spitzer space telescopes, the Chandra X-ray
Observatory, the Swift and Submillimeter Wave Astronomy satellites, the
European Space Agency's XMM-Newton X-ray observatory and the Rosetta
spacecraft. Observatories on Earth will view the impact and its aftermath.
All information transmitted
from Deep Impact will be collected on Earth for mission managers through NASA's
Deep Space Network (DSN). The DSN consists of three deep-space communications
facilities placed approximately 120 degrees apart around the globe: one at
Goldstone, in California's Mojave Desert; a station outside Madrid, Spain; and
the last near Canberra, Australia.
"Our antenna coverage for
our short encounter event is absolutely critical," said Rocca. "So we planned
our impact to occur in an area of overlap between a 70-meter antenna at
Goldstone and a similar one in Australia."
SPACE.com Staff Writer Tariq Malik contributed to this story from New York City.
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