SCIENCE: NASA setting off on first-ever collision course with comet

[conjur]

http://www.usatoday.com/tech/s...-12-comet-window_x.htm

CAPE CANAVERAL ? For the first time ever, NASA is setting off on a collision course with a comet, in hopes of blasting a huge hole in the celestial snowball and gazing upon the original ingredients of the solar system preserved inside.
It all begins with a planned Wednesday launch of Deep Impact, a copper-fortified, comet-busting spacecraft.

NASA has a single second ? at precisely eight seconds past 1:47 p.m. ? to send Deep Impact on a 268 million-mile, six-month voyage to Comet Tempel 1. Good weather is forecast, cheering scientists who are up against a firm two-week deadline for launching the probe.

Scientists have no idea what Comet Tempel 1 looks like. They don't know whether the spacecraft will have to punch through a crust as hard as a concrete sidewalk or as flimsy as corn flakes.

All they know with certainty is that the nucleus, or core, of the comet is three times as long as it is wide, and that they must crash into the sunlit side to capture pictures of the resulting crater and all the ice, dust and other primordial matter shooting out of the hole July 4.

Uncertainty over the comet's shape "has caused us some concern about, can we hit the comet," said Jay Melosh, a planetary geologist at the University of Arizona. Officially, NASA puts the odds of a bull's-eye at better than 99%.

"We hope we'll make a crater ... perhaps 300 feet in diameter, 100 feet deep, that we'll get through that crust and reveal the interior of the comet," Melosh said Tuesday. "But we don't know what comets are made of. We don't know how strong they are."

This $330 million mission should provide those answers, along with clues to the origin of the solar system 4{ billion years ago.

Because of the relative speed at the moment of impact ? 23,000 mph ? no explosives are needed for the job. The force of the smashup will be the equivalent of 4½ tons of TNT going off.

"The amount of energy of the spacecraft is about 10 times larger than an equivalent mass of TNT hitting the comet so we could pack it with explosives, it wouldn't make much of a difference," Melosh said. "Just by colliding with it, we're going to blast a big hole."

Deep Impact actually consists of two spacecraft, the SUV-sized mothership and the TV-sized impactor that will spring free one day before the Fourth of July strike. The mothership is equipped with the largest telescope ever destined for deep space, to record the impact from a safe 300 miles away. Ground observatories also will record the event, as well as amateur astronomers.

Both craft are shielded to protect against all the dust coming off the comet. Once on its own, the impactor will have to maneuver through this cloud of fine but potentially damaging particles to get out ahead of the comet and be run over by it.

Those last 24 hours will be the most perilous part of the journey.

"The last 20 minutes is when I'm going to really bite my fingernails," Melosh said.

"I'd even go with the last one minute," said the University of Maryland's Michael A'Hearn, the principal scientist.

The impactor will vaporize instantly when it hits, as will its small payload, a compact disc containing more than 500,000 names of people who wanted to vicariously tag along.

I wonder if Bruce Willis' name is on that CD.

 

[EXman]

That was Aramageddon... this is Deep impact the spacecraft so there will be Damn that movie sucked! I saw this and thought woo hoo the world is gonna end!

 

[umbrella39]

Anyone else get a little cynical when we start trying to impact comets/asteroids? Hmm, wonder how long before the one that is on a collision course with Earth gets here then?

 

[conehead433]

It would be ironic if the collision caused the comet to move off course and then be on a collision path with Earth.

 

[conjur]

Originally posted by: conehead433
It would be ironic if the collision caused the comet to move off course and then be on a collision path with Earth.

http://deepimpact.jpl.nasa.gov/faq3.html#q1

Q: Will the Impactor knock Tempel 1 out of its orbit, change its orbit or cause any debris to hit the earth?

No, the Impactor will not knock Tempel 1 out of it's orbit. However, the impact will cause a slight change in the comet's orbit, but that change is so small that it won't be noticed. A good analogy is to imagine a small pebble hitting an 18-wheeler truck.

Over time, the changes we introduce might become noticeable except for the fact that this comet also has close approaches to the planet Jupiter which exerts gravitational forces that change Tempel 1's orbit more than the impact. Dr. Don Yeomans has written a detailed history about Tempel 1's orbit.

Finally, any material knocked off of Tempel 1 will continue along the comet's orbit. Tempel 1 has an orbit that is larger than Earth's so the two orbits do not cross. So debris from Tempel 1 will not hit Earth.

 

[kage69]

Copper fortified? Anyone know what this is in reference to?

 

[conjur]

Originally posted by: kage69
Copper fortified? Anyone know what this is in reference to?

http://deepimpact.jpl.nasa.gov/faq2.html#q2
Q: Why is the impactor made of copper?

Copper was chosen because it will cause the least interference with the measurements that will be made during the impact, will not leave a residue that would confuse potential future measurements, and can be made into a structurally strong impactor. In particular, all the inner shells of electrons for copper are completely filled. This means that it reacts very slowly with other elements, such as with the oxygen in cometary water, and it will end up producing relatively few bright emission lines in the spectrum of the vaporized materials. Other materials such as aluminum would produce far more and stronger emission lines (mostly due to aluminum oxides). There are only a few materials that satisfy this criterion and copper is the least expensive of them that is structurally sound. The material used to make the impactor is actually a copper alloy with about 3% beryllium to make the copper more stiff.

 

[kage69]

Sounds cool, thx!