“Dawn Flight Configuration 2”. Licensed under Public Domain via Wikimedia Commons – http://commons.wikimedia.org/wiki/File:Dawn_Flight_Configuration_2.jpg#mediaviewer/File:Dawn_Flight_Configuration_2.jpg
The Dawn Mission is another of these totally crazy ideas that somehow got traction, got funded, got built, got launched, is working as planned, and is still just totally crazy. It’s like some NASA scientists were hanging out drinking with some rocket scientists at Orbital Sciences and they came with this idea to send a rocket ship, using ion-drive thrusters (of course), to orbit not one, but two of the biggest asteroids, Vesta and Ceres in the asteroid belt between the planets Mars and Jupiter.
Here’s the time-line:
- Dec 2003 Mission Cancelled
- Feb 2004 Mission Reinstated
- Oct 2005 Mission placed in “stand-down”
- Mar 2006 Mission Cancelled
- Mar 2006 (later in the month…) Orbital Sciences says they’ll build it on the cheap for the experience – mission back on! (way to go Orbital!)
- Sep 2006 Mission instrumentation payload fully functional
- September 27, 2007: launch
- February 17, 2009: Mars gravity assist
- July 16, 2011: Vesta arrival and capture
- August 11, 2011 – August 31, 2011: Vesta survey orbit
- September 29, 2011 – November 2, 2011: Vesta first high altitude orbit
- December 12, 2011 – May 1, 2012: Vesta low altitude orbit
- June 15, 2012 – July 25, 2012: Vesta second high altitude orbit
- September 5, 2012: Vesta departure
- March–April 2015 : Ceres arrival
- Early 2016: End of primary Ceres operations
Here’s the trajectory:
“Dawn trajectory as of September 2009” by NASA / JPL / courtesy Marc Rayman – http://www.planetary.org/image/dawn_trajectory_20090900.png. Licensed under Public Domain via Wikimedia Commons – http://commons.wikimedia.org/wiki/File:Dawn_trajectory_as_of_September_2009.png#mediaviewer/File:Dawn_trajectory_as_of_September_2009.png
Here’s a cool video with equally cool electric guitar accompaniment:
The motivation, scientifically that is, for sending a space craft to the asteroid belt is to help us understand how the solar system formed and how the planets formed during the early times of the solar system. The conjecture is that the young sun (like 5 or so billion years ago) had no planets – just gas and enormous clouds of junk orbiting the young sun. All this space stuff eventually, somehow (nobody really knows…) coalesced into the planets we have today. Why didn’t the asteroid belt coalesce into another planet? Nobody knows.
So we sent DAWN up to check out these two largish asteroids in the hope we’ll get some better data and maybe more specific ideas about how the planets formed. Oddly enough, we have meteorites on earth that we know came directly from Vesta:
Oh. And DAWN uses an Ion Propulsion Engine to jet around out there. To me, that makes it all worth it!
By NASA (Great Images in NASA Description) [Public domain], <a href=”http://commons.wikimedia.org/wiki/File%3AIon_Engine_Test_Firing_-_GPN-2000-000482.jpg”>via Wikimedia Commons</a>
An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. The term is strictly used to refer to gridded electrostatic ion thrusters, but may often more loosely be applied to all electric propulsion systems that accelerate plasma, since plasma consists of ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and accelerate the ions in the direction of the electric field. Electromagnetic ion thrusters use the Lorentz force to accelerate the ions. In either case, when an ion passes through an electrostatic grid engine, the potential difference of the electric field converts to the ion’s kinetic energy. http://en.wikipedia.org/wiki/Ion_thruster
The fuel for the DAWN mission ion thruster is the noble gas xenon – the heaviest noble gas in fact. Ionizing xenon is like ionizing neon (another noble gas) like in a neon light – but in the case of a thrust engine of this sort, the ionized particles are actually shot out the back of the spacecraft; and while the thrust is low, the velocity of the particles is very high. It’s almost like it’s a light-powered rocket!
The Dawn spacecraft is propelled by three xenonion thrusters that inherited NSTAR engineering technology from the Deep Space 1 spacecraft. They have a specific impulse of 3,100 s and produce a thrust of 90 mN. The whole spacecraft, including the ion propulsion thrusters, is powered by a 10 kW (at 1 au) triple-junctiongallium arsenidephotovoltaic solar array manufactured by Dutch Space. To get to Vesta, Dawn was allocated 275 kg (606 lb) of xenon, with another 110 kg (243 lb) to reach Ceres, out of a total capacity of 425 kg (937 pounds) of on-board propellant. With the propellant it carries, Dawn can perform a velocity change of more than 10 km/s over the course of its mission, far more than any previous spacecraft achieved with onboard propellant after separation from its launch rocket.Dawn is NASA’s first purely exploratory mission to use ion propulsion engines. The spacecraft also has 12 0.9N hydrazine thrusters for attitude control, which can assist in orbital insertion. 
This mission is definitely worth keeping up with. On to Ceres!