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Dawn will use a revolutionary ion engine reminiscent of Star Trek to reach two asteroids.

By CURTIS KRUEGER
Published June 26, 2007

Workers monitor the Dawn space probe, seen inside a clean-room at the Astrotech satellite processing facility near Cape Canaveral Air Force Station in Titusville. The un-manned science mission, set to launch in July aboard a Delta II rocket from Cape Canaveral, will use an innovative Ion propulsion system to fly between the astroids Vesta and Ceres.
	[Times photo: Stephen J. Coddington]

ADVERTISEMENT [Times photo: Stephen J. Coddington] Times reporter Curtis Krueger dons full clean-room attire prior to entering a spacecraft processing facility at Astrotech Space Operations in Titusville. [Times photo: Stephen J. Coddington] UCLA Professor Christopher T. Russell, principal investigator for the Dawn mission, holds a piece of meteorite from the astroid Vesta, while giving a briefing about Dawn's mission to Vesta and Ceres.

TITUSVILLE - This is a story about a $446-million spacecraft that spews blue flame and uses a Star Trek-type engine to fly from asteroid to asteroid.

It's the kind of tale that used to fill magazines like Astounding Science Fiction, but this story comes from our very near future.

Next week, on July 7, NASA hopes to launch Dawn, the first spacecraft to orbit two planetary bodies after leaving Earth. Its mission is to transmit information that will help scientists better understand how our solar system was formed. Its power comes from a futuristic ion propulsion engine, which devoted Star Trek fans may remember from an episode in the show's third season "Spock's Brain".

Space shuttle astronauts just returned to Earth, and NASA is scrambling to design a new craft that will send humans to the moon, but Dawn is a reminder that robotic vehicles have become some of the solar system's most intrepid explorers. Some say NASA should be launching a lot more unmanned spacecrafts like this one.

"What this mission represents is an exciting venture to a couple of worlds that haven't been explored, " said Louis Friedman, executive director of the nonprofit organization Planetary Society, which supports both human and robotic spaceflight.

* * *

Scientists would love to travel back in time to watch planets forming out of vast fields of spinning gas and dust. Unfortunately, time machines really are science fiction.

But Chris Russell, a professor at the University of California at Los Angeles who is the chief scientist for Dawn, said this mission will give scientists an important glimpse backward.

In the early eons of the solar system, the giant orb that would later be called Jupiter began to form. It was so huge and massive, Russell explained, that its gravity "stirred the pot" and prevented nearby fields of gas and dust from condensing into a planet. Instead, they became smaller balls and crags called asteroids. Russell dubs some of these "baby planets" because they never had the chance to form.

That makes them especially interesting to scientists because they offer a kind of history lesson on what planets looked like in their early stages.

Dawn will fly to the asteroid belt between Mars and Jupiter and study two of the largest "'baby planets, " Vesta and Ceres. Vesta is an especially bright 320-mile-wide asteroid shaped like a partially deflated basketball. Ceres is a 600-mile-wide asteroid that might contain a layer of ice.

* * *

The journey is easier said than done. It would take a huge amount of conventional rocket fuel to fly to one asteroid, slow down to orbit it, and then fly to the next asteroid and slow down to orbit it.

That's why NASA turned to a different technology.

Hold a sheet of notebook paper in your palm. The force that paper puts on your hand is about the same as the thrust generated by an ion propulsion engine.

In space, a tiny bit of thrust goes a long way because the ship is essentially weightless and doesn't encounter any wind resistance.

Ion propulsion works like this:

- The spacecraft shoots electricity into a chamber filled with xenon gas, which gives individual xenon atoms a positive charge.

- Atoms with the same charge repel each other, just as magnets do. All of these positively charged atoms repel each other and spew out of a hole in the chamber, creating thrust.

This technology has been used in satellites and in a spacecraft called Deep Space 1, but this is the first full-fledged science mission to use an ion engine.

The biggest challenge Dawn faces is the need for each of its systems to work together, said project manager Keyur Patel of the Jet Propulsion Laboratory.

After launch, the spacecraft will unfurl 10 folded solar panels. These provide electricity to shoot into the xenon gas. If for some reason they don't work or don't deploy, the ion engine won't work either. "That whole system has to work to get us there, " he said.

Since this mission calls for Dawn to travel from one planetary body to another, Russell was asked if it reminds him of the planetary journeys featured on Star Trek.

"I go back a little before Star Trek to Buck Rogers, " he said. "I remember those early TV episodes where he would be flying through space with flame coming out the back of his small rocket ship and going from one place in the solar system to another. We're very much doing that."

By the numbers

6 Years since NASA first approved the mission.

8 Length of Dawn's journey in years.

11 Days until the launch window opens at 4:09 p.m. on July 7.

$73M How much more the mission cost than originally planned.

$446M Mission's total cost.

More online

http://dawn.jpl.nasa.gov

Ion propulsion

By using electric fields instead of chemical explosions, ion propulsion produces a less powerful but more efficient engine than traditional rocket engines. Dawn will use electricity to charge the gas xenon, or ionize it. The charged atoms repel each other, producing thrust.

[Last modified June 26, 2007, 00:29:50]