Dawn Spacecraft Begins Approach to Dwarf Planet Ceres
 
Dec 30, 2014:   NASA's Dawn spacecraft has entered an approach phase in
which it will continue to close in on Ceres, a Texas-sized dwarf planet
never before visited by a spacecraft. Dawn launched in 2007 and is
scheduled to enter Ceres orbit in March 2015.
 
"Ceres is almost a complete mystery to us," said Christopher
Russell, principal investigator for the Dawn mission, based at the
University of California, Los Angeles. "Ceres has no meteorites linked
to it to help reveal its secrets. All we can predict with confidence is
that we will be surprised."
 
https://www.youtube.com/watch?v=5OFgJwdZxRc
 
Ion propulsion isn't something found only in science fiction. Ion engines
are real, and they drive NASA's Dawn spacecraft en route to dwarf planet
Ceres. To learn more, play this episode of Crazy Engineering
 
The next couple of months promise continually improving views of Ceres,
prior to Dawn's arrival. By the end of January, the spacecraft's images and
other data will be the best ever taken of the dwarf planet.
 
Dawn recently emerged from solar conjunction, in which the spacecraft is on
the opposite side of the sun, limiting communication with antennas on
Earth. Now that Dawn can reliably communicate with Earth again, mission
controllers have programmed the maneuvers necessary for the next stage of
the rendezvous, which they label the Ceres approach phase. Dawn is
currently 400,000 miles (640,000 kilometers) from Ceres, approaching it at
around 450 miles per hour (725 kilometers per hour).
 
The spacecraft's arrival at Ceres will mark the first time that a
spacecraft has ever orbited two solar system targets. Dawn previously
explored the protoplanet Vesta for 14 months, from 2011 to 2012, capturing
detailed images and data about that body.
 
The two planetary bodies are thought to be different in a few important
ways. Ceres may have formed later than Vesta, and with a cooler interior.
Current evidence suggests that Vesta only retained a small amount of water
because it formed earlier, when radioactive material was more abundant,
which would have produced more heat. Ceres, in contrast, has a thick ice
mantle and may even have an ocean beneath its icy crust.
 
Ceres, with an average diameter of 590 miles (950 kilometers), is also the
largest body in the asteroid belt, the strip of solar system real estate
between Mars and Jupiter. By comparison, Vesta has an average diameter of
326 miles (525 kilometers), and is the second most massive body in the
belt.
 
The spacecraft uses ion propulsion to traverse space far more efficiently
than if it used chemical propulsion. In an ion propulsion engine, an
electrical charge is applied to xenon gas, and charged metal grids
accelerate the xenon particles out of the thruster. These particles push
back on the thruster as they exit, creating a reaction force that propels
the spacecraft. Dawn has now completed five years of accumulated thrust
time, far more than any other spacecraft.
 
"Orbiting both Vesta and Ceres would be truly impossible with
conventional propulsion. Thanks to ion propulsion, we're about to make
history as the first spaceship ever to orbit two unexplored alien
worlds," said Marc Rayman, Dawn's chief engineer and mission director,
based at NASA's Jet Propulsion Laboratory in Pasadena, California.
 
Credits:
Production editor: Dr. Tony Phillips | Credit: Science{at}NASA
 
More information:
 
The Dawn mission to Vesta and Ceres is managed by JPL, a division of the
California Institute of Technology in Pasadena, for NASA's Science Mission
Directorate, Washington. UCLA is responsible for overall Dawn mission
science.
 
More information about Dawn: http://dawn.jpl.nasa.gov
 
 
Regards,
 
Roger

--- D'Bridge 3.99