[meteorite-list] NASA Excited for Comet-Busting Spacecraft (Deep Impact)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jan 3 01:16:34 2005
Message-ID: <200501030616.WAA19380_at_zagami.jpl.nasa.gov>

http://story.news.yahoo.com/news?tmpl=story&cid=624&ncid=624&e=5&u=/ap/20050101/ap_on_sc/comet_buster

NASA Excited for Comet-Busting Spacecraft
By MARCIA DUNN
Associated Press
January 1, 2005

CAPE CANAVERAL, Fla. - The big, grown-up boys on the NASA
team can hardly wait. Next Fourth of July, they get to bust up a comet,
Hollywood-style.

"Blow things up? I'm there. Yeah, I don't have any issue with that,"
says Richard Grammier, manager of the project for Jet Propulsion
Laboratory. (And, oh yeah, he used to work with explosives in the
military.)

The spacecraft is called Deep Impact just like the 1998 movie about a
comet headed straight for Earth. NASA's goal is to blast a crater into
Comet Tempel 1 and analyze the ice, dust and other primordial stuff
hurled out of the pit.

Mission planners say the energy produced will be like 4.5 tons of TNT
going off - producing a fireworks display for the world's observatories.

Scientists know little about comets and even less about their nuclei, or
cores. They believe that penetrating the interior for observations by
space and ground telescopes is the next best thing to actually landing,
scooping up samples and delivering them to Earth.

"A sample return would be the ultimate, but this is one exciting mission
because for the first time we're actually reaching out and we're going
to create our own crater," says Donald Yeomans, a senior research
scientist at JPL in California - and an adviser on the movie.

"We'll understand how the comet is put together, its density, its
porosity, whether it has a surface crust and underlying ices, whether
it's layered ice, whether it's a wimpy comet or whether it's a rock-hard
ice ball. All of these things will become apparent after we smack it."

Astronomers are counting on Deep Impact to live up to its Hollywood name
on July 4, six months after its mid-January launch.

This is one spacecraft NASA wants to smash and trash.

"It would be like it's standing in the middle of the road and this huge
semi coming down at it at 23,000 mph, you know, just bam!" Grammier says.

If all goes well, Deep Impact will be the first spacecraft to touch the
surface of a comet. NASA's Stardust spacecraft - on its way back to
Earth with dust from Comet Wild 2 - flew through the coma, or dusty gas
cloud.

Deep Impact will have traveled 268 million miles from the time it is
launched aboard an unmanned rocket until it intersects with Comet Tempel
1 just beyond the orbit of Mars, at a point more than 80 million miles
from Earth.

Liftoff is targeted for Jan. 12, two weeks late because of software and
rocket problems. NASA has until Jan. 28 to launch Deep Impact. After
that, Tempel 1 will be beyond rocket reach and scientists will have to
pick another comet and swallow a lengthy delay.

That's what happened to the European Space Agency's Rosetta spacecraft,
which will attempt a controlled landing on a comet, but not until 2014.

Deep Impact, by contrast, will provide "instant gratification," says
Grammier. The entire $330 million mission should be wrapped up a month
after impact.

Comet Tempel 1 is ideal from a scientific and demolition perspective.

It's a typical comet - all the better for scientific analysis ? yet has
a large nucleus and weak coma, all the easier for the impactor to
survive the dusty obstacle course and to nail the nucleus.

Grammier says the latest calculations put the chance of the impactor
missing its target at less than 1 percent. The automatic navigation
software has already been tested in space; this will be a fancier
version of what successfully flew on NASA's Deep Space 1, a testbed
spacecraft launched in 1998, and Stardust, the earlier comet spacecraft.

"We all feel pretty comfortable with that (the odds), but as we've all
said before, we're doing something we haven't done before," Grammier says.

No matter what, fans of the 1998 disaster film can rest easy.
(Coincidentally, the movie and spacecraft people hit on the same name
independent of each another, at about the same time.)

NASA guarantees that no matter how powerful the punch or how big the
crater, Deep Impact will barely alter the comet's orbital path around
the sun and will not - repeat, not - put the comet or any part of it on
a collision course with Earth.

Yeomans calculates that to move Tempel 1 or a piece of it into an
Earth-intersecting orbit, the impactor would have to be 6,000 times more
massive than what will shoot out of the mothership on July 3. The very
next day, the 820-pound impactor will strike at the heart of the comet,
creating one awesome Fourth of July display.

By celestial standards, the crater that is formed - anywhere from the
size of a house to Rome's Coliseum, and from two to 14 stories deep -
should be just a dent. Besides, comets get bombarded with stuff all the
time; they're pockmarked with craters and cliffs.

"You've got an object the size of a bushel basket running into an object
that's 9 miles in length, so we're not going to do any real damage to
the comet," Yeomans says.

Some scientists, however, contend the comet will shatter into several
pieces. Others hypothesize that Deep Impact will create a crater but
shove everything in, with hardly anything or nothing ejected.

"It is the uncertainty in the predictions - or the wide range of
predictions - that make it particularly important to do this
conceptually very simple experiment," says the University of Maryland's
Michael A'Hearn, the mission's chief scientist.

Whatever the outcome, scientists expect to learn something about
deflecting a killer comet - or possibly an asteroid - if one ever
happens Earth's way. Comets, after all, have hit Earth before and are
thought to have brought water with them.

Another practical benefit of the mission: By knowing what's inside
comets, NASA would be better able to use them in the future as watering
holes and fueling stations. Robots or astronauts, for instance, could
break the comet's water down into its basic elements, hydrogen and
oxygen, the ingredients for rocket fuel.

Then there is all the scientific knowledge to be gained from studying
comets, essentially giant dirty snowballs circling the sun.

Formed the same time as the planets 4.5 billion years ago, comets are
considered the leftover building blocks of the solar system. When the
comets periodically swing close by the sun, their surfaces heat up and
change, and so only their interiors preserve cosmic-origin clues.

The impactor - composed mainly of a 317-pound solid copper disk - will
maneuver itself in the oncoming path of the comet and, in essence, get
run over by the comet. The relative speed at the moment of the collision
will be 23,000 mph, enough to vaporize the impactor.

Copper was chosen because, like gold and silver, it does not react with
water and will not taint the observations, and it is much cheaper.

A camera on the impactor will photograph the comet and beam back the
pictures, almost all the way up until the moment of destruction. A pair
of cameras on the mothership - flying by at a safe 300 miles - will
document the actual strike and the ensuing eruption and crater, and send
back all the images.

"We expect to provide great fireworks for all our observatories,"
Grammier says, "and that's exciting to do it on July Fourth."
Received on Mon 03 Jan 2005 01:16:26 AM PST