[FPSPACE] Dawn Journal for July 28, 2009

[LARRY KLAES]

Dawn Journal

 

July 28, 2009

 

Dear Indawnfautigables,

 

Shhhh! Dawn is in “quiet cruise,” and we do not want to disturb it. The indefatigable spacecraft is devoting most of its time to thrusting with its ion propulsion system, applying a gentle but persistent pressure to its trajectory around the Sun. With patience, it will reshape its orbit to match those of the mysterious and intriguing protoplanets Vesta and Ceres. In order to conduct its detailed explorations of each of these exotic worlds, Dawn will accompany them around the Sun, visiting with Vesta in 2011–2012 and rendezvousing with Ceres in 2015.
 
Today Dawn is 220 million kilometers (137 million miles) from the star at the solar system’s center. We can express this more conveniently by recalling the ruler so often used in describing interplanetary distances, the astronomical unit (AU). The average distance between Earth and the Sun, nearly 150 million kilometers (93 million miles), is defined to be 1 AU. (For comparison, Mars, whose orbit is not as circular as Earth’s, travels between about 1.38 AU and 1.67 AU.) Today Dawn is 1.47 AU from the star at the solar system’s center.
 
If the spacecraft stopped thrusting now, well, gosh, that would be a disappointment! But let’s calm down and think about it anyway. Its momentum would keep it going around the Sun in an elliptical orbit that ranged from about 1.38 AU to 1.84 AU. Vesta, the first stop on Dawn’s solar system itinerary, lives between 2.15 AU and 2.57 AU. Dawn has a lot of work left to do! 


Full journal entry here:

 

http://dawn.jpl.nasa.gov/mission/journal_7_28_09.asp

 

 
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