A few days ago on my facebook page I discussed the Dawn mission that is currently being undertaken. Dawn is a spacecraft that is exploring several large Asteroids in the Asteroid Belt between Mars and Jupiter.
The image shown above is the asteroid Vesta which has a diameter of about 350 miles. Below is a movie showing a full rotation of the asteroid.
This is not a recent mission as it has taken many years to reach the first of two destinations. Dawn was launched in September 2007, arrived at Mars in February 2009 for a "gravity assist" maneuver to speed up it's velocity (a sort of slingshot effect around the planet). It arrived at Vesta in July 2011, spent a year orbiting the asteroid, and recently departed this past July on to it's next destination the "minor planet" Ceres. Ceres is large (a diameter of 600 miles, about as big as Texas). It is an interesting destination because it is thought to contain large amounts of frozen water, and possibly a thin atmosphere.
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| Path of Dawn Spacecraft |
In addition to the exploration aspects of the mission another interesting aspect of Dawn is the innovation of the spacecraft itself. Most rockets and spacecraft use liquid fuels to create power and acceleration (the Apollo missions used this type of rocket). A combination of hydrogen and oxygen is combined so that the spacecraft "burns" fuel and in an action/reaction type of deal, creates acceleration. Dawn uses a different type of engine, an ION engine. The principals of an ION engine is that it accelerates atoms and shoots them out the nozzle to create thrust.
ION engines have pluses and minuses. The pluses are that it is very fuel efficient, it needs much less fuel than a traditional liquid fuel engine. This means for the same weight of fuel, you can operate the engine for longer periods of time and have longer missions. The minus is that acceleration is very slow. It would take an ION engine about 4 days to go from 0 to 60 miles per hour. However, in space, once you are traveling at a certain speed, you will stay at that speed (nothing in space to slow you down). The Dawn spacecraft can continue to fire it's engine for days, weeks or months at a time and slowly build up speed, essentially being able to move faster than any conventional hydrogen/oxygen engine. In theory, if you had an infinite amount of fuel this type of engine could eventually accelerate close to the speed of light, although it would take slightly over 122,000 years to reach that speed (LOL). This type of technology was used successfully on the Deep Space 1 mission
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| Dawn is an Ion Powered Rocket |
Why bother studying asteroids. Fair questions. Well one theory is that an asteroid large enough impacting the earth could have severe and possible fatal consequences for the entire planet. We need to understand the threat. In order to understand the threat we need close observations of these types of objects.
It is estimated that about 10% of all the meteorites that fall to earth are from an impact of the asteroid Vesta. I don't know who is doing the estimation and how "they" know this, but I present it to you and you can take it for what it is worth. Meteorites of all sizes fall upon the earth all the time. Some are specs of dust and burn up harmlessly in the atmosphere as streaks. Other large one fall to the ground. Some even larger will make craters, like Meteor Crater in Arizona.
It may seem unlikely but meteors also fall on other planets and the moon and our space program even have pictures of these events and objects from other places than the earth. We have recorded impacts of meteors on the moon in the past several years.
However the most fascinating (for me at least) is the fact that the twin Mars rovers Spirit and Opportunity discovered intact meteorites on the surface of Mars. The first one discovered, shown in the pictures below was discovered shortly after the rovers arrived on Mars in 2004. Opportunity when inspecting it's discarded heat shield used during the entry into martian atmosphere, observed a strange rock in the background. Upon closer examination both photographically and spectrally using on board instruments, it was determined to be a meteorite.
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| Heat Shield Rock - A Meteorite on Mars |
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| Closeup of Heat Shield Rock |
As it turns out, meteorites are pretty common on Mars as the twin rovers over the next 8 years discovered at least a half a dozen other ones.
The universe is a fun place with lots of discoveries yet to be found. You never know what lies around the next bend.
We will examine the Mars Rovers and other space program topics in future posts.
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