NASA’s image of the day is the Dawn spacecraft launching via a Delta II rocket. It’s heading to two asteroids: Ceres (actually a dwarf planet) and Vesta. The journey will take several years. In March 2009, Dawn will slingshot around Mars to arrive at Vesta in September of 2011, where it will stay for about seven months. After that it will head to the dwarf planet Ceres, a journey of three more years, arriving in February of 2015. Five months later, the primary mission will end.
The Dawn spacecraft will be using an ion propulsion system. This allows the spacecraft to travel with much less weight. An electrical charge is used to accelerate Xenon atoms at rates 10 times faster than chemical fuels. Because the force it takes to accelerate something depends on its mass (F = ma), the lighter (less massive) a spacecraft is, the less it takes to move it. Petroleum is heavy, so using it for a spacecraft really doesn’t work very well, but it is used for launch vehicles like the Delta II rocket. The petroleum used is known as RP-1 (Refined Petroleum) and is mixed with liquid oxygen. The ion propulsion drive is fuel efficient but not exactly speedy. No one is going to brag about 0 to 60 mph in 4 days. The bonus is, the spacecraft only uses 10 ounces of fuel per day at full burn. At that rate, Dawn can go about 1500 days, but it won’t need to be at full burn every day.
