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@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   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)