[meteorite-list] Dawn Gets Vesta Target Practice

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 10 Mar 2011 14:46:12 -0800 (PST)
Message-ID: <201103102246.p2AMkCbG020756_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2011-075

Dawn Gets Vesta Target Practice
Jet Propulsion Laboratory
March 10, 2011

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

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook at jpl.nasa.gov

2011-075
Received on Thu 10 Mar 2011 05:46:12 PM PST