[meteorite-list] Comet Flyby Demonstrates Science On Shoestring Budget

[Ron Baalke]

http://www.spaceflightnow.com/news/n1011/05epoxifuture/

Comet flyby demonstrates science on shoestring budget
BY STEPHEN CLARK 
SPACEFLIGHT NOW
November 5, 2010

Thursday's daring flyby of comet Hartley 2 not only collected a treasure
trove of spectacular imagery, it also served as a model for future
opportunities to reuse old NASA spacecraft for new missions.

The Deep Impact spacecraft's encounter with Hartley 2 at about 1400 GMT
(10 a.m. EDT) went off without a hitch. The car-sized probe hit its
marks, missing its aimpoint by less than one-half of a percent as it
soared by at a distance of approximately 700 kilometers, or 435 miles.

NASA immediately released five up-close shots of the never-before-seen
comet, but the best imagery is still being processed, scientists said in
a press conference Thursday afternoon.

After tense moments during the flyby, the images triggered applause in
the EPOXI control room at the Jet Propulsion Laboratory in Pasadena, Calif.

"I remember in the seconds before the images came down, I thought to
myself, 'This is an exploration moment,'" said Ed Weiler, associate
administrator of NASA's science directorate. "Here we are sitting in
this little building at JPL, and we're going to see something that no
other humans in the history of humankind have seen, the nucleus of
Hartley 2."

The probe's medium-resolution camera snapped the pictures unveiled
Thursday. Researchers must carefully process high-resolution images to
overcome a defect in the on-board instrument.

The imagery revealed a peanut-shaped rocky nucleus spewing water and
other gases into deep space, creating a cloudy coma, or tail, around
Hartley 2's core.

Only the fifth comet ever imaged by a nearby spacecraft, Hartley 2
doesn't fit the mold of other icy bodies closely studied on previous
missions. Its nucleus is barely one mile across -- much smaller than
other surveyed comets -- and it is much more active.

"While it's the smallest (comet), no doubt about it, I think it's
undoubtedly the most interesting," said Jessica Sunshine, deputy
investigator for the EPOXI mission. "And for its size, it is the most
active."

Scientists hope to determine which features of Hartley 2 are left over
from its ancient genesis, separating those characteristics from changes
during the comet's evolution.

According to NASA, the EPOXI mission costs about $42 million from its
inception to the end of operations. That is about one-tenth the cost of
a new Discovery-class science mission, Weiler said.

The low cost makes EPOXI a "darn good bargain," Weiler told reporters
Thursday afternoon.

"I would like to do that again," Weiler said. "We're going to be looking
at other satellites. In these days of hard economic times, this is a
really good deal."

Deep Impact was originally selected as a Discovery mission in 1999.

Discovery-class missions are relatively low-cost science-based projects
geared for solar system exploration.

Deep Impact dropped a high-speed projectile on the surface of comet
Tempel 1 in July 2005, blasting a hole in its nucleus and sending shards
of icy debris into space. After it completed that mission, the
spacecraft was ready for a new assignment.

The agency selected the EPOXI mission to use Deep Impact's twin
telescopes to help search for planets around other stars. At the same
time, navigators charted a course through the inner solar system to
reach Hartley 2, using a series of small engine burns and three gravity
assist flybys of Earth.

Anticipating another possible extension, NASA issued a request for
information in early October, soliciting ideas from scientists for
another reuse of Deep Impact.

According to Weiler, the probe no longer has enough fuel to change its
trajectory and reach other comet. But it does have enough propellant for
other missions.

Weiler identified hunting for asteroids or astronomy research as
potential applications for Deep Impact, which carries two of the most
sensitive telescopes currently in deep space.

The spacecraft still has about 10 pounds of maneuvering fuel, enough to
maintain its orientation in space for roughly 11 years on a science
mission, according to the request for information document released Oct. 5.

"We'll be entertaining those ideas in the next few months," Weiler said.
"What I do know is it doesn't cost a lot to use a satellite a second,
third, or even fourth time."

Tim Larson, the EPOXI project manager at JPL, said the spacecraft will
continue observing Hartley 2 until the end of November, then perform an
instrument calibration. Funding for the EPOXI mission is expected to run
out around the end of 2010, he said.

Stardust, another retired Discovery mission, is also operating in an
extended phase.

The Stardust spacecraft is heading for a Feb. 14 encounter with comet
Tempel 1. The flyby will be the second look at the comet since Deep
Impact blasted a hole in its nucleus in 2005.

During its original mission, Stardust collected dust from comet Wild 2
and dropped a return capsule to Earth with the samples. The Stardust
mothership continued on in space, presenting an opportunity for a new
objective.

NASA also recycled two small probes built to study Earth's magnetic
field and sent the craft to the moon, where they arrived in a
preliminary orbit in August and October. The satellites are in a bonus
phase to observe the solar wind's interaction with the moon.