[meteorite-list] Deep Impact's Flyby Craft Ready For Course Correction Today

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jul 20 12:45:26 2005
Message-ID: <200507201644.j6KGiVA25189_at_zagami.jpl.nasa.gov>

http://space.com/missionlaunches/050720_flyby_update.html

Deep Impact's Flyby Craft Ready For Course Correction Today
By Leonard David
space.com
20 July 2005

BOULDER, Colorado - The Flyby spacecraft used in NASA's Deep Impact
mission to comet Tempel 1 is to be powered into a new trajectory today - a
maneuver that could allow it to explore yet another comet in years to come.

The two-part "crash and dash" Deep Impact spacecraft made use of a
now-destroyed Impactor that collided with the city-sized Tempel 1, as
well as a Flyby vehicle that monitoring the powerful collision from a
distance.

Engineers here at Ball Aerospace & Technologies Corporation, designers
and builders of the $333 million dual-element Deep Impact mission are
delighted with the overall health of their Flyby vehicle. It watched the
washing machine-sized Impactor as it collided with the target on July 4
at 1:52 a.m. EDT (0552 GMT).

Future missions

The smashing success of the mission resulted in a spewing up of material
far away from Tempel 1's nucleus - the central portion of the head of a
comet.

"We are very pleased by how well the Flyby survived its pass through the
comet's coma and tail," said Monte Henderson, Deputy Director of
Programs in Civil Space Systems for Ball Aerospace.

Today's trajectory correction maneuver - or TCM in spacecraft operations
lingo - "will put the Flyby spacecraft in an orbit path that allows us to
contact it at any time. This provides NASA time to investigate
opportunities to utilize the Deep Impact spacecraft for future
missions," Henderson told SPACE.com.

Gravity and cash assist

The trajectory change will place the spacecraft on an Earth-return
heading, arriving in late 2007 or early 2008, said Donald Yeomans,
Supervisor of the Solar System Dynamics Group at the Jet Propulsion
Laboratory (JPL) in Pasadena, California. The Deep Impact project is
managed by JPL.

"That will allow a gravity assist to comet Boethin in late 2008. Then we
will have to submit - and win - a Discovery proposal for the extended
mission funds," Yeomans added.

NASA's Discovery-class missions carry out highly-focused science tasks
within stringent cost and schedule limitations.

In a historical collision of space and time, the July 20th maneuver of
the Flyby spacecraft falls on the same day 36 years ago that Apollo 11
astronauts - Neil Armstrong and Buzz Aldrin - touched down on the Moon.

Extended mission benefits

There are benefits to an extended mission proposal for Deep Impact, said
Michael A'Hearn, an astronomer at the University of Maryland in College
Park, Maryland. He is the principal investigator for the Deep Impact
mission.

"Deep Impact's prime mission will have taught us something about the
relationship between interior composition and surface composition,"
A'Hearn explained.

But there are also things scientists didn't have time to do during the
encounter.

"Our spectrometer [onboard the Flyby spacecraft] is really outstanding
and the encounter with comet Boethin should allow us to operate it at an
even colder temperature, despite being closer to the Sun, than was the
case for Tempel 1," A'Hearn said.

Without an impact event to follow, A'Hearn continued, scientists can use
the Flyby craft as it slips by Boethin to map in detail the composition
of the comet's inner coma. Doing so will help relate the composition at
the surface of the comet to what is observed at different scales from
Earth and Earth orbit.

Boethin and the jets

There are big differences among cometary nuclei, A'Hearn noted, and a
crucial reason for trying to visit more comets.

"Furthermore, in the absence of an impact event," A'Hearn told
SPACE.com, "we can concentrate our imaging on questions like relating
jets in the coma to the surface and making sure that we get stereoscopic
imaging of the jets."

Those jets are made of gas and dust that can rocket from a comet's surface.

"These are all questions that we tried to address in the prime mission,
but because the prime mission was the impact, that event took up most of
our data volume when near the comet. A second flyby without the impact
would allow us to focus on these goals that got pushed aside to
emphasize the impact," A'Hearn concluded.

Deep pool of data

Meanwhile, as the Flyby spacecraft is being re-targeted to perhaps a
future comet encounter, scientists are delving into Impactor results.

Pete Schultz, Deep Impact scientist from Brown University in Providence,
Rhode Island, said the team is "jumping into the pool of data
headfirst...and this is a deep pool."

"We know that the impact was oblique and that the actual crater was
obscured by debris," Schultz said. "Lots of data to look at," he told
SPACE.com.

Extensive studies of cratering using oblique impacts into highly porous
materials will certainly help in the interpretations, Schultz noted.
"But there is so much in the data, both from the [dual Deep Impact]
spacecrafts and the Earth-based data. We really are just getting
started. We know that there was hot gas and dust ejected by the impact,"
he said.

But where's the crater?

JPL's Yeomans said the detection of the crater as seen through the dust
curtain, the material tossed off the comet due to the Impactor, is still
ongoing. The dust excavated from the comet's surface has been
characterized as extremely fine, more like talcum powder than beach sand.

Images taken by the Flyby spacecraft are being tweaked to perhaps reveal
the crater caused by the Impactor.

"Personally, I don't understand the fuss over whether the crater will be
visible. Even without the crater size, the well-observed dust curtain
expansion rate will likely provide the comet's local gravity (mass) and
this mass, coupled with the shape model (volume) will allow a
determination of the bulk density (mass/volume)," Yeomans explained.

"Even without the crater size," Yeomans concluded, "we're already trying
to drink from the fire hose of data."
Received on Wed 20 Jul 2005 12:44:31 PM PDT