NASA Spacecraft to Enter Asteroid's Orbit on July 15

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

Jia-Rui Cook/Priscilla Vega 818-354-0850/4-1357
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov/priscilla.r.vega@jpl.nasa.gov

Dwayne C. Brown 202-358-1726
NASA Headquarters, Washington July 14, 2011
dwayne.c.brown@nasa.gov

News release: 2011-208

NASA Spacecraft to Enter Asteroid's Orbit on July 15

PASADENA, Calif. -- On July 15, NASA's Dawn spacecraft will begin a prolonged encounter with
the asteroid Vesta, making the mission the first to enter orbit around a main-belt asteroid.

The main asteroid belt lies between the orbits of Mars and Jupiter. Dawn will study Vesta for one
year, and observations will help scientists understand the earliest chapter of our solar system's
history.

As the spacecraft approaches Vesta, surface details are coming into focus, as seen in a recent image
taken from a distance of about 26,000 miles (41,000 kilometers). The image is available at:
http://www.nasa.gov/mission_pages/dawn/multimedia/dawn-image-070911.html .

Engineers expect the spacecraft to be captured into orbit at approximately 10 p.m. PDT Friday, July
15 (1 a.m. EDT Saturday, July 16). They expect to hear from the spacecraft and confirm that it
performed as planned during a scheduled communications pass that starts at approximately 11:30
p.m. PDT on Saturday, July 16 (2:30 a.m. EDT Sunday, July 17). When Vesta captures Dawn into its
orbit, engineers estimate there will be approximately 9,900 miles (16,000 kilometers) between them.
At that point, the spacecraft and asteroid will be approximately 117 million miles (188 million
kilometers) from Earth.

"It has taken nearly four years to get to this point," said Robert Mase, Dawn project manager at
NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Our latest tests and check-outs show that
Dawn is right on target and performing normally."

Engineers have been subtly shaping Dawn's trajectory for years to match Vesta's orbit around the sun.
Unlike other missions, where dramatic propulsive burns put spacecraft into orbit around a planet,
Dawn will ease up next to Vesta. Then the asteroid's gravity will capture the spacecraft into orbit.
However, until Dawn nears Vesta and makes accurate measurements, the asteroid's mass and gravity
will only be estimates. So the Dawn team will need a few days to refine the exact moment of orbit
capture.

Launched in September 2007, Dawn will depart for its second destination, the dwarf planet Ceres, in
July 2012. The spacecraft will be the first to orbit two bodies in our solar system.

Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in
Washington. Dawn is a project of the directorate'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 spacecraft. The German
Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and
the Italian National Astrophysical Institute are part of the mission team.

For a current image of Vesta and more information about the Dawn mission, visit:
http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov .You also can follow the mission on Twitter
at: http://www.twitter.com/nasa_dawn .

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