How the Dawn mission works
By Marshall Brain
http://www.JewishWorldReview.com | (MCT) If everything goes as planned, NASA will launch an incredibly interesting mission on June 30. It is called the Dawn mission, and its goal is to visit and map out the two largest asteroids in the asteroid belt.
The first asteroid on the menu is Vesta. At 321 miles long, it is the second largest asteroid. For comparison, the earth's moon is about 2,100 miles in diameter. On a planetary scale, Vesta is tiny. But in terms of asteroids, it is huge. Like most asteroids, Vesta is a big, rocky, irregularly shaped lump.
The second asteroid is named Ceres. This asteroid is so big that it actually looks spherical like a planet, but at 600 miles in diameter it is much smaller than a normal planet. The most interesting thing about Ceres is its similarities to Earth. Scientists believe Ceres has an iron core and possibly lots of fresh water (in the form of ice) stored underneath the surface.
One unusual part of the Dawn mission is the engine that the spacecraft uses. Instead of using big, fiery chemical rockets to blast from one asteroid to another, Dawn is using a Xenon ion drive powered by huge, 10,000-watt solar panels. The ion drive uses electrical fields to turn Xenon atoms into ions. Then the engine shoots the ions out of the nozzle at 78,000 miles per hour. The total thrust that this engine produces is very small (it would take four days for the spacecraft to accelerate from zero to 60 using this propulsion system), but the engine can fire for months when it needs to. The Dawn spacecraft will be the fastest ship NASA has ever built and will also be the first to orbit one body, then move to a second body and orbit it.
Here is how the mission will unfold. A Delta 2 rocket will take the Dawn spacecraft out of earth's orbit. Then the ion engine will fire and send the spacecraft toward Mars. Dawn will slingshot past Mars in March of 2009, arriving at Vesta in October of 2011. In April 2012 the spacecraft will fire its ion drive again to leave Vesta and arrive at Ceres in February of 2015, having traveled a total of three billion miles.
The goals of the mission are to map the two asteroids using an optical camera and then use two different kinds of spectrometers to see what the asteroids are made of. The first spectrometer is like a super-specialized camera. It has only one pixel of resolution, but can deliver very precise color readings from this pixel by looking at visible and infrared light. With this data, scientists can identify different minerals seen on the surface of the asteroid. The second spectrometer is the gamma ray and neutron spectrometer. It can see the gamma rays and neutrons that the asteroids emit. This instrument can detect things like hydrogen, carbon, oxygen and nitrogen, along with radioactive elements.
To send all of its data and images back to earth, Dawn uses a 100-watt radio and a 5-foot diameter dish antenna. Back here on earth, gigantic dish antennas up to 200 feet in diameter pick up the faint signals so that computers can decode them.
One of the things that NASA scientists hope to discover is why one asteroid looks like a lump while the other is a nice, spherical, planet-like object. What would cause the two asteroids to be so different? Using the data that Dawn gathers, scientists may be able to discover the reason. Another goal is to understand exactly what elements make up these asteroids. The thought is that asteroids can tell us what the earth might have looked like when it first formed, and with this information we can learn more about the origins of the earth, Venus and Mars. We may also learn a great deal about the beginnings of our solar system.
Because of the long timeline for the mission, we won't hear much about Dawn after its launch. Then, four years from now, it will be in the news again as images start streaming back from Vesta and we learn new things about the asteroid belt. Then things will get quiet again for 3 more years until, once again, images start arriving from Ceres. It is a very long mission, and one that will reveal many new things about our solar system's origins.
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