NASA's Dawn Spirals Down to Lowest Orbit

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

News release: 2011-384 Dec. 12, 2011

NASA's Dawn Spirals Down to Lowest Orbit

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-384&cid=release_2011-384

PASADENA, Calif. – NASA's Dawn spacecraft successfully maneuvered into its closest
orbit around the giant asteroid Vesta today, beginning a new phase of science
observations. The spacecraft is now circling Vesta at an altitude averaging about 130
miles (210 kilometers) in the phase of the mission known as low altitude mapping orbit.

"Dawn has performed some complicated and beautiful choreography in order to reach
this lowest orbit," said Marc Rayman, Dawn chief engineer and mission manager based
at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We are in an excellent position
to learn much more about the secrets of Vesta's surface and interior."

Launched in 2007, Dawn has been in orbit around Vesta, the second most massive object
in the asteroid belt between Mars and Jupiter, since July 15. The team plans to acquire
data in the low orbit for at least 10 weeks.

Dawn's framing camera and visible and infrared mapping spectrometer instruments will
image portions of the surface at greater resolution than obtained at higher altitudes. But
the primary goal of the low orbit is to collect data for the gamma ray and neutron detector
(GRaND) and the gravity experiment. GRaND will be looking for the by-products of
cosmic rays reflected off Vesta to reveal the identities of many kinds of atoms in the
surface of Vesta. The instrument is most effective at this low altitude.

Close proximity to Vesta also enables ultrasensitive measurements of its gravitational
field. These measurements will tell scientists about the way masses are arranged in the
giant asteroid's interior.

"Dawn's visit to Vesta has been eye-opening so far, showing us troughs and peaks that
telescopes only hinted at," said Christopher Russell, Dawn's principal investigator, based
at UCLA. "It whets the appetite for a day when human explorers can see the wonders of
asteroids for themselves."

After the science collection is complete at the low altitude mapping orbit, Dawn will
spiral out and conduct another science campaign at the high altitude mapping orbit
altitude (420 miles, or 680 kilometers), when the sun will have risen higher in the
northern regions. Dawn plans to leave Vesta in July 2012 and arrive at its second
destination, the dwarf planet Ceres, in February 2015.

Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission
Directorate in Washington. JPL is a division of the California Institute of Technology in
Pasadena. Dawn is a project of the directorate's Discovery Program, managed by NASA's
Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn
mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft.
The German Aerospace Center, the Max Planck Institute for Solar System Research, the
Italian Space Agency and the Italian National Astrophysical Institute are international
partners on the mission team.

More information about the Dawn mission is online at: http://www.nasa.gov/dawn .

To follow the mission on Twitter, visit: http://www.twitter.com/NASA_Dawn .

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