[meteorite-list] Dawn Is 'Go' For Asteroid Belt

[Ron Baalke]

09.25.07

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

George Diller
Kennedy Space Center, Fla.
321-867-2468
george.h.diller at nasa.gov

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
david.c.agle at jpl.nasa.gov

RELEASE: 48-07

NASA SPACECRAFT IS A 'GO' FOR ASTEROID BELT

CAPE CANAVERAL, Fla. -- Launch and flight teams are in final 
preparations for the planned Sept. 27 liftoff from Pad 17-B at Cape 
Canaveral Air Force Station, Fla., of NASA's Dawn mission. The Dawn 
spacecraft will venture into the heart of the asteroid belt, where it 
will document in exceptional detail the mammoth rocky asteroid Vesta, 
then the even bigger, icy dwarf planet Ceres.

"If you live in the Bahamas, this is one time you can tell your 
neighbor, with a straight face, that Dawn will rise in the west," 
said Dawn Project Manager Keyur Patel of NASA's Jet Propulsion 
Laboratory in Pasadena, Calif. "Weather permitting, we are go for 
launch Thursday morning, a little after dawn." 

Dawn's Sept. 27 launch window is 7:20 to 7:49 a.m. EDT. At the moment 
of liftoff, the Delta II's first-stage main engine along with six of 
its nine solid-fuel boosters will ignite. The remaining three solids 
are ignited in flight following the burnout of the first six. The 
first-stage main engine will burn for 4.4 minutes. The second stage 
will deposit Dawn in a 185-kilometer-high (100-nautical-mile) 
circular parking orbit in just under nine minutes. At about 56 
minutes after launch, the rocket's third and final stage will ignite 
for approximately 87 seconds. When the third stage burns out, 
actuators and push-off springs on the launch vehicle will separate 
the spacecraft from the third stage. 

"After separation, the spacecraft will go through an automatic 
activating sequence, including stabilizing the spacecraft, activating 
flight systems and deploying Dawn's two massive solar arrays," said 
Patel. "Then and only then will the spacecraft energize its 
transmitter and contact Earth. We expect acquisition of signal to 
occur anywhere from one-and-a-half hours to three-and-a-half hours 
after launch."

The Dawn mission will explore Vesta and Ceres because these two 
asteroid belt behemoths have been witness to so much of our solar 
system's history.

"Visiting both Vesta and Ceres enables a study in extraterrestrial 
contrasts," said Dawn Principal Investigator Christopher Russell of 
the University of California, Los Angeles. "One is rocky and is 
representative of the building blocks that constructed the planets of 
the inner solar system. The other may very well be icy and represents 
the outer planets. Yet, these two very diverse bodies reside in 
essentially the same neighborhood. It is one of the mysteries Dawn 
hopes to solve."

Using the same spacecraft to reconnoiter two different celestial 
targets makes more than fiscal sense. It makes scientific sense. By 
utilizing the same set of instruments at two separate destinations, 
scientists can more accurately formulate comparisons and contrasts. 
Dawn's science instrument suite will measure mass, shape, surface 
topography and tectonic history, elemental and mineral composition, 
as well as seek out water-bearing minerals. In addition, the Dawn 
spacecraft itself and the way it orbits both Vesta and Ceres will be 
used to measure the gravity fields of the celestial bodies.

"Understanding conditions that lead to the formation of planets is a 
goal of NASA's mission of exploration," said David Lindstrom, Dawn 
program scientist at NASA Headquarters in Washington. "The science 
returned from Vesta and Ceres could unlock many of the mysteries of 
the formation of the rocky planets including Earth."

Before all this celestial mystery unlocking can occur, Dawn has to 
reach the asteroid belt and its first target, Vesta. This is a 
four-year process that begins with launch and continues with the 
firing of three of the most efficient engines in NASA's space motor 
inventory: ion propulsion engines. Employing a complex commingling of 
solar-derived electric power and xenon gas, these frugal powerhouses 
must fire for months at a time to propel as well as steer Dawn. Over 
their eight-year, almost 4-billion-mile lifetime, these three ion 
propulsion engines will fire cumulatively for about 50,000 hours 
(over five years) - a record for spacecraft.

The Dawn mission is managed by JPL for NASA's Science Mission 
Directorate in Washington, D.C. JPL is a division of the California 
Institute of Technology in Pasadena. The University of California, 
Los Angeles, is responsible for overall Dawn mission science. Other 
scientific partners include the Los Alamos National Laboratory, New 
Mexico; Max Planck Institute for Solar System Research, Katlenburg, 
Germany; and Italian National Institute of Astrophysics, Rome. 
Orbital Sciences Corporation of Dulles, Va., designed and built the 
Dawn spacecraft.

For more information about Dawn, visit:

http://www.nasa.gov/dawn

For more information about NASA and agency programs on the Internet, 
visit:

http://www.nasa.gov 

Note to Editors: A video file with animation, b-roll and sound bites 
is airing on NASA TV today.

	
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