Dawn asteroid probe back
on the launch pad again
BY JUSTIN RAY
Posted: September 11, 2007
"From here, the only way to go is up," said Keyur Patel, Dawn project manager at the Jet Propulsion Laboratory. "We are looking forward to putting some space between Dawn and Mother Earth and making some space history."
The eight-year, 3.2-billion-mile mission is scheduled for liftoff from Florida's east-central coast on Wednesday, September 26 at 7:25 a.m. EDT. The morning's available launch period will extend to 7:54 a.m.
After being grounded earlier this summer by an assortment of factors, Dawn was pulled off its United Launch Alliance Delta 2-Heavy rocket at Cape Canaveral's pad 17B two months ago. The spacecraft was placed in protective storage while engineers proceeded to launch the Mars-bound Phoenix lander atop another Delta rocket from neighboring pad 17A in early August.
Rocket-related delays, troubles arranging downrange tracking assets to monitor the launch and a rapidly closing launch window in July forced NASA officials to make the unusual decision of postponing the Dawn liftoff after the satellite was already on the pad. Senior agency managers opted to go with the Phoenix launch first, putting Dawn second in NASA's launch lineup.
See our story from July that recounts the issues prompting the unusual delay.
The Delta 2-Heavy to launch Dawn is a three-stage rocket, with a kerosene-fueled first stage, nine strap-on solid boosters, a hydrazine second stage and solid-fuel third stage. The 12-story vehicle is the most powerful version of the venerable Delta 2 family, owing its extra thrust to slightly larger strap-on boosters.
The Heavy has flown three times, successfully lofting the Mars rover Opportunity, Spitzer Space Telescope and the MESSENGER orbiter now en route to Mercury.
Key testing and final preparations for the launch are planned over the next two weeks. The flight program verification, a readiness test between the Dawn spacecraft and the Delta rocket to simulate launch events, is scheduled for Thursday. Installation of the rocket's nose cone to shroud Dawn during ascent through the atmosphere is planned for next Wednesday, September 19.
Also next week, another Delta 2 rocket is targeted for liftoff from California's Vandenberg Air Force Base carrying a sophisticated commercial Earth-imaging satellite. Our coverage of that launch will be available here.
Dawn's launch window to begin its journey into the asteroid belt will feature daily liftoff opportunities between September 26 and October 15.
Scientists want up-close studies of Vesta and Ceres to learn more about the processes and conditions during the solar system's formation four-and-a-half-billion years ago. The spacecraft will orbit at increasingly lower altitudes above the two diverse objects during multi-month visits to determine the composition, internal structure and evolutionary history of the bodies.
"Dawn is also a journey back in time," says Chris Russell, the scientist leading the mission. "Ceres and Vesta have been altered much less than other bodies. The Earth is changing all the time; the Earth hides its history, but we believe that Ceres and Vesta, formed more than 4.6 billion years ago, have preserved their early record. They're revealing information that was frozen into their ancient surfaces."
Vesta is believed to be solid rock. The oval-shaped object has an average diameter of approximately 320 miles. But Ceres could harbor water or ice beneath its rocky crust. The "baby planet" has an average diameter of about 600 miles.
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