Dawn Gets Vesta Target Practice

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 C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Feature: 2011-075 March 10, 2011

Dawn Gets Vesta Target Practice

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-075&cid=release_2011-075

There is an old chestnut about a pedestrian who once asked a virtuoso violinist
near Carnegie Hall how to get to the famed concert venue. The virtuoso's answer:
practice!

The same applies to NASA's Dawn mission to the giant asteroid Vesta. In the lead-
up to orbiting the second most massive body in the asteroid belt this coming July,
Dawn mission planners and scientists have been practicing mapping Vesta's
surface, producing still images and a rotating animation that includes the scientists'
best guess to date of what the surface might look like.

The animation and images incorporate the best data on the dimples and bulges of
Vesta from ground-based telescopes and NASA's Hubble Space Telescope. The The
topography is color-coded by altitude. The cratering and small-scale surface
variations are computer-generated, based on the patterns seen on Earth's moon,
an inner solar system object with a surface appearance that may be similar to
Vesta.

"We won't know what Vesta really looks like until Dawn gets there," said Carol
Raymond, Dawn's deputy principal investigator, based at NASA's Jet Propulsion
Laboratory, Pasadena, Calif., who helped orchestrate the activity. "But we needed a
way to make sure our imaging plans would give us the best results possible. The
products have proven that Dawn's mapping techniques will reveal a detailed view
of this world that we've never seen up close before."

Vesta is one of the brightest asteroids in the night sky. Under the right conditions,
Vesta can be seen with binoculars. But the best images so far from ground-based
telescopes and Hubble still show Vesta as a bright, mottled orb. Once in orbit
around Vesta, Dawn will pass about 650 kilometers (400 miles) above the
asteroid's surface, snapping multi-angle images that will allow scientists to produce
topographic maps. Later, Dawn will orbit at a lower altitude of about 200
kilometers (120 miles), getting closer shots of parts of the surface.

The Dawn mission will have the capability to map 80 percent of the asteroid's
surface in the year the spacecraft is in orbit around Vesta. (The north pole will be
dark when Dawn arrives in July 2011 and is expected to be only dimly lit when
Dawn leaves in July 2012.) The mission will map Vesta at a spatial resolution on the
order of the best global topography maps of Earth made by NASA's Shuttle Radar
Topography mission.

Vesta formed very early in the history of the solar system and has one of the oldest
surfaces in the system. Scientists are eager to get their first close-up look so they
can better understand this early chapter.

Starting in August 2009, Dawn's optical navigation lead, Nick Mastrodemos, based
at JPL, developed a computer simulation of the orbits and images to be taken by
the spacecraft. He adapted software developed by Bob Gaskell of the Planetary
Science Institute, Tuscon, Ariz. Mastrodemos created a model using scientists' best
knowledge of Vesta and simulated the pictures that Dawn would take from the
exact distances and geometries in the Dawn science plan.

He sent those images to two teams that use different techniques to derive
topographical heights from imaging. One, led by Thomas Roatsch, was based at the
Institute of Planetary Research of the German Aerospace Center (DLR) in Berlin.
The other, led by Gaskell, was based at the Planetary Science Institute in Tuscon.
(Like the Roatsch team, the Gaskell team did not have prior knowledge of the
model from which the simulated data were created.) The groups sent their digital
terrain models back to JPL, including the video produced by Frank Preusker from
DLR that is based on his full stereo processing.

Mastrodemos compared their products to the original model he made. Both
techniques reproduced the known data set well with only minor differences in
spatial resolution and height accuracy. "Working through this exercise, the mission
planners and the scientists learned that we could improve the overall accuracy of
the topographic reconstruction, using a somewhat different observation
geometry," Mastrodemos said. "Since then, Dawn science planners have worked to
tweak the plans to implement the lessons of the exercise."

The exercise helped both teams get an early start on updating their software and
planning the necessary computer resources. "In order to plan for proper stereo
coverage of an unknown body like Vesta, practice is essential," said Roatsch, who is
responsible for the framing camera team's stereo observation planning.

For now, the Virtual Vesta exercise gives the Dawn science team a fleshed-out
model to consider. But to see whether their educated guesses were right, the team
will have to wait until Dawn arrives at its target in four months.

The Dawn mission to Vesta and Ceres is managed for NASA's Science Mission
Directorate in Washington by JPL, a division of the California Institute of
Technology in Pasadena, and is a project of the Discovery Program managed at
NASA's Marshall Space Flight Center, Huntsville, Ala. UCLA is home of the
mission's principal investigator, Christopher Russell, and is responsible for overall
Dawn mission science. The Dawn framing cameras have been developed and built
under the leadership of the Max Planck Institute for Solar System Research,
Katlenburg-Lindau, Germany, with significant contributions by the German
Aerospace Center (DLR) Institute of Planetary Research, Berlin, and in
coordination with the Institute of Computer and Communication Network
Engineering, Braunschweig. The framing camera project is funded by the Max
Planck Society, DLR and NASA.

To learn more about Dawn and its mission to the asteroid belt, and to see the new
visuals, visit: http://www.nasa.gov/dawn or http://dawn.jpl.nasa.gov .

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