[meteorite-list] NASA Dawn Spacecraft Reaches Milestone Approaching Vesta

[Ron Baalke]

May 03, 2011

Dwayne C. Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Jia-Rui Cook 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-0850 
jccook at jpl.nasa.gov   


RELEASE: 11-133

NASA DAWN SPACECRAFT REACHES MILESTONE APPROACHING ASTEROID

Dwayne C. Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Jia-Rui Cook 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-0850 
jccook at jpl.nasa.gov 

WASHINGTON -- NASA's Dawn spacecraft has reached its official approach 
phase to the asteroid Vesta and will begin using cameras for the 
first time to aid navigation for an expected July 16 orbital 
encounter. The large asteroid is known as a protoplanet - a celestial 
body that almost formed into a planet. 

At the start of this three-month final approach to this massive body 
in the asteroid belt, Dawn is 752,000 miles (1.21 million kilometers) 
from Vesta, or about three times the distance between the Earth and 
the moon. During the approach phase, the spacecraft's main activity 
will be thrusting with a special, hyper-efficient ion engine that 
uses electricity to ionize and accelerate xenon to generate thrust. 
The 12-inch-wide ion thrusters provide less thrust than conventional 
engines, but will provide propulsion for years during the mission and 
provide far greater capability to change velocity. 

"We feel a little like Columbus approaching the shores of the New 
World," said Christopher Russell, Dawn principal investigator, based 
at the University of California in Los Angeles (UCLA). "The Dawn team 
can't wait to start mapping this Terra Incognita." 

Dawn previously navigated by measuring the radio signal between the 
spacecraft and Earth, and used other methods that did not involve 
Vesta. But as the spacecraft closes in on its target, navigation 
requires more precise measurements. By analyzing where Vesta appears 
relative to stars, navigators will pin down its location and enable 
engineers to refine the spacecraft's trajectory. Using its ion engine 
to match Vesta's orbit around the sun, the spacecraft will spiral 
gently into orbit around the asteroid. When Dawn gets approximately 
9,900 miles (16,000 kilometers) from Vesta, the asteroid's gravity 
will capture the spacecraft in orbit. 

"After more than three and a half years of interplanetary travel, we 
are finally closing in on our first destination," said Marc Rayman, 
Dawn's chief engineer, at NASA's Jet Propulsion Laboratory (JPL) in 
Pasadena, Calif. "We're not there yet, but Dawn will soon bring into 
focus an entire world that has been, for most of the two centuries 
scientists have been studying it, little more than a pinpoint of 
light." 

Scientists will search the framing camera images for possible moons 
around Vesta. None of the images from ground-based and Earth-orbiting 
telescopes have seen any moons, but Dawn will give scientists much 
more detailed images to determine whether small objects have gone 
undiscovered. 

The gamma ray and neutron detector instrument also will gather 
information on cosmic rays during the approach phase, providing a 
baseline for comparison when Dawn is much closer to Vesta. 
Simultaneously, Dawn's visible and infrared mapping spectrometer will 
take early measurements to ensure it is calibrated and ready when the 
spacecraft enters orbit around Vesta. 

Dawn's odyssey, which will take it on a 3-billion-mile journey, began 
on Sept. 27, 2007, with its launch from Cape Canaveral Air Force 
Station in Florida. It will stay in orbit around Vesta for one year. 
After another long cruise phase, Dawn will arrive at its second 
destination, an even more massive body in the asteroid belt called 
Ceres, in 2015. 

These two icons of the asteroid belt will help scientists unlock the 
secrets of our solar system's early history. The mission will compare 
and contrast the two giant asteroids, which were shaped by different 
forces. Dawn's science instrument suite will measure surface 
composition, topography and texture. In addition, the Dawn spacecraft 
will measure the tug of gravity from Vesta and Ceres to learn more 
about their internal structures. 

The Dawn mission to Vesta and Ceres is managed by JPL for NASA's 
Science Mission Directorate (SMD) in Washington. Dawn is a project of 
SMD's Discovery Program, which is managed by NASA's Marshall Space 
Flight Center in Huntsville, Ala. UCLA is responsible for overall 
Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed 
and built the Dawn spacecraft. The framing cameras have been 
developed and built under the leadership of the Max Planck Institute 
for Solar System Research in Katlenburg-Lindau in Germany, with 
significant contributions by the German Aerospace Center (DLR) 
Institute of Planetary Research in Berlin, and in coordination with 
the Institute of Computer and Communication Network Engineering in 
Braunschweig. The framing camera project is funded by NASA, the Max 
Planck Society and DLR. 

For more information about Dawn, visit: 

http://www.nasa.gov/dawn   
	
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