[meteorite-list] Dawn Will Show How Different Two Asteroids Can Be

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:54 2005
Message-ID: <200503072102.j27L28S19505_at_zagami.jpl.nasa.gov>

http://www.universetoday.com/am/publish/dawn_two_asteroids.html

Dawn Will Show How Different Two Asteroids Can Be
Fraser Cain
Universe Today
March 7, 2005

Summary - (Mar 7, 2005) It's called Dawn, and in a little more than a
year, this spacecraft will blast off from Florida, bound for two
separate asteroids: Vesta and Ceres. Visiting the two most massive
asteroids in our Solar System will be an ambitious undertaking; maybe
one of the most difficult and dangerous orbital missions attempted. Dawn
will bring a suite of scientific instruments to these two asteroids and
serve as a time machine to help scientists understand what our Solar
System looked like 4.6 billion years ago.

Full Story - Although they're both enormous asteroids, protoplanets really,
and lie within the asteroid belt between Mars and Jupiter, Vesta and Ceres
couldn't be more different.

Vesta formed closer to the Sun, and probably shares many features of the
inner planets. Scientists believe it formed in a hot, dry environment
and will probably have layers of volcanic flows and a solid metallic
core. But even the best photos from Hubble show a blurry gray world,
bringing more questions than answers. It's the brightest asteroid in the
Solar System, measuring 530 km (329 miles) across. You can even see it
with the unaided eye; in fact, it's the only main belt asteroid you can
see. Traveling to Vesta could be a little dangerous. "We know very
little about Vesta's internal structure," explained Chief Engineer Dr.
Marc Rayman, "it has an unpredictable and possibly very irregular
gravity field."

Just a little further out - across an invisible line that separates the
inner rocky planets from the outer planets - is Ceres; the largest
asteroid in the Solar System, measuring 957 km (595 miles) across.
Unlike Vesta, Ceres is believed to have formed in a cool, wet
environment, and in the presence of water. This water is probably still
there, in the form of ice caps, a thin water vapour atmosphere, or even
as a liquid underneath the surface.

While most of the objects in the asteroid belt are pulverized chunks of
rock, accumulations of material from different bodies, Vesta and Ceres
remain largely unchanged from when they first formed 4.6 billion years
ago. Revelations about the early history of the Solar System could be
written on their surfaces.

The $370 million US spacecraft is scheduled for liftoff in June, 2006.
After 4 or 5 years of travel time (depending on whether or not it'll be
making a flyby of Mars first) Dawn will arrive at Vesta in 2010 or 2011,
studying it for almost a year before flying off to rendezvous with Ceres
three years later. It has a suite of scientific instruments on board to
study the two asteroids in great detail: their mass, volume, spin rate,
chemical and elemental composition, and gravity. Oh, and it'll be taking
pretty pictures too.

Dawn will be the first spacecraft ever to orbit two separate objects in
the solar system (and no, orbiting the Earth doesn't count here). A feat
that wouldn't even be possible without its ion engine. A very similar
engine helped Deep Space 1 set speed and duration records, and served as
a model for Dawn's development. It uses solar electricity to ionize
xenon atoms and then hurl them out the back of the spacecraft. The
thrust is tiny but fuel efficient, and the engine can keep running for
months or even years providing a tremendous velocity.

And an ion engine gives controllers flexibility. "It gives us a very
long launch window. We're launching in June 2006 because that's when the
spacecraft will be ready. But we could still make it in November or even
after that," said Dr. Rayman. So far, though, the project is right on
schedule. The completed spacecraft shipped this week from NASA's Jet
Propulsion Laboratory to Orbital Sciences for the next stage of assembly
and testing.

If you're interested in finding out more about this mission, stay tuned.
Dr. Rayman is planning on keeping the world well informed, through the
Internet. He learned how important this can be while working on Deep
Space 1, taking the unusual step - at the time - of maintaining a web
log to describe his experiences working with the spacecraft. "I was in
the airport when I realized that we needed to get the word out. I
dictated my first entry over the phone," recalled Dr. Rayman. Rayman
continued maintaining his popular DS1 blog, giving armchair mission
controllers a unique insight into the day-to-day challenges and
decisions that go into managing a spacecraft half a solar system away.

Expect more of the same with Dawn. "These missions belong to more than
just NASA, or the United States. They're humanity's emissaries to the
cosmos, and we want everyone to come along for the ride," explained
Rayman. But this time, he'll get started earlier, bringing an Internet
audience into the development stages as well as post-launch.

Official Dawn Mission Page <http://dawn.jpl.nasa.gov/>
Received on Mon 07 Mar 2005 04:02:08 PM PST