Space Probe Dawn Delayed Until Thursday
“Dawn will be history’s first mission to go out into the solar system, orbit and explore a distant body, and then go on to a totally different celestial body and explore that one,” said Dawn project manager Keyur Patel of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “To do all that you need a spacecraft with a lot under the hood.”
Originally set to launch on Wednesday, September 26, 2007, as the launch period opens for the space probe Dawn, at the last minute it was postponed to September 27, 2007, due to bad weather. Dawn’s launch window will remain open until October 15 if bad weather continues, presently at a 24-hour postponement, or if needed a 48-hour postponement.
With an eight-year mission ahead of the Dawn spacecraft, NASA states the goal of this Delta II craft is to “characterize the conditions and processes of the solar system’s earliest epoch 4.5 billion years ago by investigating in detail the massive asteroid Vesta and the dwarf planet Ceres. To do so, Dawn will be recognized as the first mission to enter space and orbit two different planets at two different times for one mission, in two different celestial bodies.
The engine of the space probe Dawn is what NASA calls “Solar Electric Propulsion Technology Applications Readiness”—or ion propulsion. Running on electricity, it is fitted with 54-feet of an electrical production of solar array. The gas is four times heavier than air, considered the propellant of choice for asteroid explorers, as it is an inert, colorless gas.
Each of the ion engines weighs 20 pounds, about the size of a basketball says NASA, and is capable of shooting a blue beam of rocket exhaust at 89,000 mph. Made with a magnitude higher than chemical rockets, it can reduce the mass of fuel onboard a spacecraft up to 90 percent.
NASA has the fuel figured to the penny, “At first glance, Dawn’s full throttle, pedal-to-the-metal, performance is a not-so-inspiring 0-to-60 mph in 4 days. But consider this - because of its incredible efficiency, it expends only 40 ounces of xenon propellant during that time. And then take into consideration that after those four days of full-throttle thrusting, it will do another four days - and then another four. By the end of 12 days the spacecraft will have increased its velocity by over 180 miles per hour, with more days and weeks and months of continuous thrusting to come. After a year Dawn’s ion propulsion system will have increased the spacecraft’s speed by 5,500 mph while consuming the equivalent of only 15 gallons of fuel. By the end of its mission Dawn will have accumulated more than 5 years of total thrust time, giving it an effective change in speed of about 23,000 mph.” (NASA, Mission Pages, Dawn-20070913)
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