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)
|
