[meteorite-list] How Capt. Kirk Changed the World (Dawn)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 5 May 2010 15:58:01 -0700 (PDT)
Message-ID: <201005052258.o45Mw1us011856_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2010/04may_dawn/

How Capt. Kirk Changed the World
NASA Science News

May 4, 2010: "Standard orbit, Mr. Sulu." Captain Kirk barks out the
order with such confidence. He knows the USS Enterprise can slip in and
out of planetary orbits with ease. But it's only easy in the realm of
science fiction. In the real world, such maneuvers have been impossible
--until now.

Enter Dawn, NASA's cutting edge mission to the asteroid belt.

Powered with a futuristic sounding new technology called "ion
propulsion," this spacecraft will perform space moves rivaling those of
the Enterprise.

At this very moment, Dawn is slowly climbing away from the sun, beyond
Mars, on its way to its first destination, asteroid Vesta. Dawn will
enter "standard orbit" around this rocky world for a year, exploring its
mysteries.

Then Dawn will do something unprecedented in real-world spaceflight:
exit the orbit of one distant body, and fly to and orbit another. The
second destination is asteroid Ceres.

"Dawn will be the first spacecraft ever built to orbit two target bodies
after leaving Earth," says Marc Rayman, Dawn chief engineer at NASA's
Jet Propulsion Laboratory. "There's not even a concept for doing such a
mission with conventional propulsion systems. The spacecraft would have
to carry so much fuel, it would be too heavy to launch."

Instead, Dawn relies on ion propulsion, which doesn't require a huge
spacecraft. Rayman first heard the term years ago while watching -- you
guessed it -- Star Trek.

Using solar arrays spanning 65 feet, Dawn collects power from the sun to
ionize atoms of xenon. These ions are expelled by a strong electric
field out the back of the spacecraft, producing a gentle thrust. The
weightless and frictionless conditions of space flight allow this
gossamer force effect to build up, so the spacecraft gains speed slowly
and continuously.

"Dawn isn't exactly a hot rod," says Rayman. "It would take 4 days to go
from 0 to 60. But it ultimately achieves fantastically high velocity
while consuming very little propellant. It uses only a kilogram of xenon
every 4 days."

Typically, conventional rockets thrust for a few minutes at most before
they run out of fuel, then they coast to their destination. Dawn???s
engines, on the other hand, are almost constantly active.

"Dawn will thrust for 5 1/2 years!" says Rayman. "It's already been
thrusting for 591 days. That's 62% of the time it's been in space."

This means Dawn must be very fuel efficient. "A typical Mars orbiter
could consume more than 600 pounds of propellants to enter orbit around
the red planet," says Rayman. "With its ion propulsion system, Dawn
could do it with less than 60 pounds of xenon."

Add all of these advantages together and you get a spacecraft that can
accomplish -- well -- the impossible.

"Dawn is taking us, in the truest sense, up close to two distant, alien,
unexplored worlds."

Its destinations -- Ceres and Vesta -- are two of the biggest asteroids
in the solar system. Indeed, Ceres is so big, it is actually classified
as a dwarf planet, and Vesta is not far behind. Yet to date they've been
studied only from a great distance, so they're virtually unknown. What
is known is that they're not alike.

"Vesta is more like the rocky bodies of the inner solar system, one of
which is right under our feet," explains Rayman. "And Ceres is more like
the icy moons of the outer solar system. Scientists think it may even
have a subsurface ocean of liquid water!"

Dawn's instruments
will collect data and images to uncover the secrets these two bodies
conceal and perhaps reveal why they're so different from one another
even though they inhabit such similar regions of the solar system.

"This mission will help us understand what the conditions were when
Vesta and Ceres formed at the dawn of the solar system. It will fit more
pieces in the grand puzzle of how our solar system formed and evolved ???
and perhaps how others do as well."

Executing new cosmic maneuvers, exploring alien worlds, answering
profound questions -- Dawn has it all. But Rayman thinks the most
compelling aspect of missions like Dawn may be that we are, in a sense,
going along for a deep-space ride.

"Dawn is taking us all on a virtual trip through the cosmos. It's not
just a mission by the JPL team, or by NASA, or by the U.S and its
partner countries. It's a mission of humankind -- something that
represents all of us who share a spirit of adventure and curiosity, a
passion for exploration. It's an extension of ourselves into the universe."

As one Star Trek crew member with particularly pointy ears would say --
"Fascinating."


Author: Dauna Coulter
Editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Wed 05 May 2010 06:58:01 PM PDT