TO ARRIVE AT ITS DESTINATION IN 2015
Prompts Launch Delay for NASA's Asteroid Probe
By Tariq Malik
posted: 5 July 2007
1:13 p.m. ET
NASA's beleaguered Dawn asteroid probe will have to wait at least one more day to launch after lightning prevented workers from fueling the spacecraft's rocket Thursday.
Initially targeted for a Saturday afternoon liftoff, Dawn is now set to launch from Florida's Cape Canaveral Air Force Station on Sunday, July 8 at 4:04 p.m. EDT (2004 GMT). Current forecasts predict a 60 percent chance that poor weather will prevent the weekend space shot.
A lightning advisory prevented launch pad workers from fueling the second stage of Dawn's Delta 2 booster, NASA spokesperson D.C. Agle told SPACE.com from the agency's Kennedy Space Center spaceport in Cape Canaveral. The United Launch Alliance rocket's payload fairing was also too warm to begin loading the Delta 2 with the super-chilled oxidizer for its propellant, NASA officials said, adding that fueling operations should resume by Friday.
The delay is the latest in a series of difficulties for NASA while preparing Dawn for its $449 million mission to study the asteroids Vesta and Ceres.
In recent weeks, the mission managers have repaired last-minute damage to the spacecraft's solar arrays, weathered the late delivery of rocket parts that delayed Dawn's planned June 20 liftoff, and wrestled with a malfunctioning crane while assembling the probe's Delta 2 booster. Mission managers also needed more time to study the impact of higher than expected loads on parts of the Delta 2's solid rocket motors and substitute a launch tracking ship with an aircraft.
The Dawn spacecraft, too, has traveled a rocky road to the launch pad. NASA initially canceled the asteroid-bound mission in March 2006 due to cost overruns and technical challenges with the probe's xenon-powered ion engine. But the space agency reinstated the mission a few weeks later after an in-depth study into those hurdles.
Researchers hope the 2,684-pound (1,217-kilogram) Dawn spacecraft will answer questions on the formation of Vesta, which sports signs of lava flows on its surface, and potentially water ice-harboring Ceres. The probe is due to swing by Vesta in October 2011 and then rendezvous with Ceres in February 2015.
NASA's window to launch Dawn closes on July 11, when the space agency will shift over to prelaunch preparations for the Mars Phoenix lander and the shuttle Endeavour. Phoenix is slated to launch on Aug. 3 and be followed by Endeavour's STS-118 mission to the International Space Station on Aug. 7.
If Dawn misses its July launch window, it would be delayed until later this fall and cost an extra $25 million due to the need to replace the spacecraft's Delta 2 rocket's second stage, mission managers have said.
(LOS ANGELES) — NASA this weekend is set to launch a spacecraft that will journey to the asteroid belt that lies between Mars and Jupiter, a mission that involves a rendezvous with two of the solar system's largest asteroids.
Seeking clues about the birth of the solar system, the Dawn spacecraft will first encounter Vesta, the smaller of the two bodies, four years from now. In 2015, it will meet up with Ceres, which carries the status of both asteroid and, like Pluto, dwarf planet.
"We're trying to go back in time as well as to go out there in space," said planetary scientist Christopher Russell of University of California, Los Angeles, who is heading up the mission.
Weather permitting, Dawn is set to blast off Sunday afternoon from Cape Canaveral, Fla., on a Delta II rocket. The launch caps a tumultuous effort in which the $344 million mission was killed last year because of cost overruns and technical problems.
Ultimately, though, the Jet Propulsion Laboratory in Pasadena, which manages the spacecraft, appealed to NASA Administrator Michael Griffin and got the project revived.
Adding to the drama, Ceres briefly flirted with planethood during last summer's scientific debate about whether Pluto is a planet. Both Pluto and Ceres were finally classified dwarf planets.
Vesta and Ceres are believed to have evolved in different parts of the solar system more than 4.5 billion years ago around the same time as the formation of the rocky planets including Mercury, Venus, Earth and Mars. Scientists believe the asteroids' growth was stunted by Jupiter's gravitational pull and never had the chance to become full-fledged planets.
Images by the Hubble Space Telescope show Vesta and Ceres as geologically diverse.
Mysteries abound: Why are Vesta and Ceres so different? How do size and water affect planet formation? What does the evolution of the asteroids say about Earth's formation?
Vesta, which measures 326 miles across, is dry and pocked with a deep impact crater in its southern hemisphere. By contrast, Ceres, about twice as large as Vesta, has a dusty surface covered by what appears to be an ice shell and may even contain water inside.
When Dawn reaches each asteroid, first Vesta in 2011, it will orbit each body, photographing the surface and studying the asteroid's interior makeup, density and magnetism. Pictures and data will be sent back to Earth.
Dawn will be powered by ion propulsion instead of conventional rocket fuel, making it more fuel-efficient and allowing it to cruise between the asteroids and lower itself to about 125 miles above the surface to study them in depth.
Although previous spacecraft have explored smaller asteroids, researchers hope Dawn will shed light on the solar system's origins.
"If you want to understand the Earth, it's important to understand how it came to be and that's where asteroids come in. They're the building blocks," said Jay Melosh, a planetary geologist at the University of Arizona who has no role of the Dawn mission.
Asteroid Probe Set for Monday Launch
By Tariq Malik
posted: 6 July 2007
3:43 p.m. ET
NASA is hoping for a Monday liftoff for the Dawn spacecraft, a probe bound to visit the two largest asteroids in the solar system.
Dawn is now set to ride a United Launch Alliance Delta 2 rocket into space July 9 at 3:56 p.m. EDT (1956 GMT) after new issues scrapped plans for a Sunday liftoff.
Mechanical difficulties with a telemetry relay aircraft, combined with the unavailability of a tracking ship and an unfavorable weather forecast for rocket fueling, delayed plans for a Sunday launch, NASA officials said. Weather forecasts for Monday improve to a 60 percent chance of favorable liftoff conditions, they added.
Dawn's planned Monday launch will kick off an eight-year trip to Vesta and Ceres, the two largest space rocks in the Asteroid Belt that rings the Sun between the planets Mars and Jupiter. The $449 million mission will mark NASA's first to orbit two different planetary bodies, and will study space rocks that formed about 4.6 billion years ago while the solar system was still young.
"What's exciting to me is that this is comparative planetology at its best," said David Lindstrom, NASA's Dawn program scientist, during a Friday briefing. "We truly are going back in time; back to the dawn of the solar system."
Powered by an ion drive, Dawn is due to enter orbit around Vesta in October 2011 and use three onboard instruments to study the space rock's surface before heading off towards a February 2015 orbital rendezvous with Ceres.
Vesta is a dense body scarred by an ancient impact that, researchers believe, sent a myriad of small meteorites falling to Earth. Ceres, with its spherical shape and a diameter about 600 miles (almost 1,000 kilometers) wide, is so large it is considered to be a dwarf planet and may sport a subterranean cache of ice or water, mission scientists added.
Examining the differences between dense, bright Vesta and the dimmer, less-dense Ceres may yield new answers for researchers studying the formation of planets, NASA officials said.
Dawn's ability to shift from one target to another hinges on its three xenon ion-driven thrusters, which allow the probe to maneuver with less propellant than that required for chemical-based rockets.
"We couldn't do this mission without the ion drive," said Mark Sykes, a Dawn mission co-investigator from the Planetary Science Institute at the University of Arizona. "It's an extremely flexible way of moving around the solar system."
NASA now has until July 19, a window eight days longer than first announced, to launch Dawn before standing down to allow preparations for the planned Aug. 3 liftoff of Phoenix, the space agency's next Mars lander mission.
"We're kind of just threading the needle with these two launches," Kurt Lindstrom, NASA's Dawn program executive, told SPACE.com.
The next opportunity to launch the mission arises this fall. By the end of October the distance between Vesta and Ceres - which are currently relatively close to one another - will begin increasing, mission managers said, adding that the two space rocks will near each other again in 15 years.
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