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Dawn


Dawn Journals: Dawn Project System Engineer Marc Rayman is contributing updates on the status of Dawn to The Planetary Society Weblog!

Aug. 28, 2008: Some explanations of orbital dynamics
Jul. 27, 2008: We crave power!
Jun. 26, 2008: Cruising past Mars' orbit
May 29, 2008: Dawn Journal
Apr. 22, 2008: Software updates
Mar. 30, 2008: One AU from Earth
Mar. 3, 2008: Backup camera checks out
Jan. 31, 2008: Safely cruising
Dec. 17, 2007: Checkout complete, interplanetary cruise underway
Oct. 26, 2007: Testing, Testing, Testing
Nov. 14, 2007: Halfway through checkout
Oct. 9, 2007: Firing Up the Ion Propulsion System
Sep. 21, 2007: Awaiting launch II
September 14, 2007: What to expect after the launch II
September 5, 2007: Dawn prepares to launch II
Jul. 17, 2007: More than one way to leave the launch pad
Jul. 6, 2007: More bad weather - Awaiting launch
Jun. 26, 2007: What to expect after the launch
Jun. 12, 2007: Readying the rocket
Jun. 4, 2007: Dawn prepares for launch

Between the orbits of Mars and Jupiter circles the main asteroid belt, remnants of the formation of the solar system, millions of rocky bodies with orbits too disturbed by the gravitational pull of Jupiter for them to coalesce into a single planet. Among these are a few big ones, protoplanets that started down the road to terrestrial planethood but failed to thrive. Ceres and Vesta are the most massive of the minor planets, and the Dawn mission aims to visit them both to discover what clues they may hold to how our solar system, and particularly the terrestrial planets (Mercury, Venus, Earth, and Mars), formed.

Ceres and Vesta could hardly be more different. Ceres is a spherical, ice-rich world, similar (perhaps) to the icy moons of the outer solar system. Vesta is probably all rock and metal, and is so battered by past collisions with other asteroids that its shape is noticeably lumpy. Both bodies likely formed only 5 to 10 million years after the birth of the solar system, unlike Mars and Earth, which took much longer (30 and 50 million years, respectively). Although both formed in a relatively short period of time, Ceres was left with primordial water, while Vesta was not. The water at Ceres prevented it from developing the internal volcanic activity that developed on drier Vesta. Ceres' water almost certainly melted into a global subsurface ocean, and there may yet be liquid water beneath its icy crust.

Dawn will journey to Vesta and then Ceres under the power of an ion engine, technology it inherits from the successful Deep Space 1 technology development spacecraft. The ion engine gives the spacecraft a leisurely cruise. The low speed of the spacecraft relative to the objects in the asteroid belt will enable it to enter orbit at the two worlds, becoming the first spacecraft to enter orbit around two different planetary bodies. Instead of a flyby mission lasting only hours, Dawn's survey of Vesta and Ceres will include many months spent at each. It will initially enter a high-altitude orbit at Ceres, and then shift its orbit downward twice to obtain closer and closer views, and repeat the same sequence as at Vesta. It should obtain photographic and mineralogic maps of the entire surface of each world. Sensitive tracking of the spacecraft as it orbits the minor planets will lead to models of their topography and gravity and a better understanding of their internal structure.

Dawn Facts
Launch: September 27, 2007 at 11:34 UTC
Mars flyby: February 2009
Vesta rendezvous: October 2011 - May 2012
Ceres rendezvous: February 2015 - July 2015