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oxygen

Next, engineers will perform several tests of the Delta II. In mid-June, as a leak check, the first stage will be loaded with liquid oxygen during a simulated countdown. The next day, a simulated flight test will be performed, simulating the vehicle's post-liftoff flight events without fuel aboard. The electrical and mechanical systems of the entire Delta II will be exerc

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ised during this test. Once the Dawn payload is atop the launch vehicle, a final major test will be conducted: an integrated test of the Delta II and Dawn working together. This will be a combined minus and plus count, simulating all events as they will occur on launch day, but without propellants aboard the vehicle.

model

The rocket that will launch Dawn is a Delta II 7925-H manufactured by the United Launch Alliance; it is a heavier-lift model of the standard Delta II that uses larger solid rocket boosters. The first stage is scheduled to be erected on Pad 17-B in late May. Then the nine strap-on solid rocket boosters will be raised and attached. The second stage, which burns hypergolic p

ropellants, will be hoisted atop the first stage in the first week of June. The fairing which surrounds the spacecraft will then be hoisted into the clean room of the mobile service tower.

Technicians

Now that Dawn has arrived at Astrotech near NASA's Kennedy Space Center, final prelaunch processing will begin. Technicians will install the spacecraft's batteries, check out the control thrusters and test the spacecraft's instruments. In late April, Dawn's large solar arrays will be attached and then deployed for testing. In early May, a compatibility test will b

e performed with the Deep Space Network used for tracking and communications. Dawn will then be loaded with fuel to be used for spacecraft control during the mission. Finally, in mid-May, the spacecraft will undergo spin-balance testing. Dawn will then be mated to the upper stage booster and installed into a spacecraft transportation canister for the trip to Cape Canaveral Air Force Station. This is currently scheduled for June 19, when it will be mated to the Delta II rocket at Pad 17-B.

Pasadena

"Dawn only has two more trips to make," said Dawn project manager Keyur Patel of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "One will be in mid-June when it makes the 15-mile journey from the processing facility to the launch pad. The second will be when Dawn rises to begin its eight-year, 3.2-billion-mile odyssey into the heart of the asteroid belt."

two

Dawn's 4.8-billion-kilometer (3-billion-mile) odyssey includes orbiting Vesta and the dwarf planet Ceres in 2015. These two giants of the asteroid belt have been witness to much of our solar system's history. By using Dawn's instruments to study both objects for several months, scientists can more accurately compare and contrast the two. Dawn's s

cience instrument suite will measure geology, elemental and mineral composition, shape, surface topography, geomorphology and tectonic history, and will also seek water-bearing minerals. In addition, the Dawn spacecraft's orbital characteristics around Vesta and Ceres will be used to measure the celestial bodies' masses and gravity fields.

spacecraft

Further observations were planned during the flyby, but fault detection software canceled the data collection and put the spacecraft into safe mode, a limited-activity precautionary status. The cause was determined to be an inappropriate software response to an expected temporary loss of valid data from the spacecraft's star tracker in the vicinity of Mars, and engin

eers were able to restore the spacecraft to normal operations within 48 hours.

provide

Dawn's navigators placed the spacecraft on a close approach trajectory with Mars so the planet's gravitational influence would provide a kick to the spacecraft's velocity. If Dawn had to perform these orbital adjustments on its own, with no Mars gravitational deflection, the spacecraft would have had to fire up its engines and change velocity by more than 9,330 ki

lometers per hour (5,800 miles per hour).

Washington

The Dawn mission to asteroid Vesta and dwarf planet Ceres is managed by JPL, for NASA's Science Mission Directorate, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. The University of California, Los Angeles, is responsible for overall Dawn mission science. Other scientific partners include: Los Alamos National L

aboratory, New Mexico; Max Planck Institute for Solar System Research, Katlenburg, Germany; and Italian National Institute of Astrophysics, Rome. Orbital Sciences Corporation of Dulles, Va., designed and built the Dawn spacecraft.

four

Before all this celestial mystery unlocking can occur, Dawn has to reach the asteroid belt and its first target – Vesta. This is a four-year process that begins with launch and continues with the firing of three of the most efficient engines in NASA's space motor inventory - ion propulsion engines. Employing a complex commingling of solar-derived electric power an

d xenon gas, these frugal powerhouses must fire for months at a time to propel as well as steer Dawn. Over their eight-year, almost 4-billion-mile lifetime, these three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) - a record for spacecraft.

.

Using the same spacecraft to reconnoiter two different celestial targets makes more than fiscal sense. It makes scientific sense. By utilizing the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn's science instrument suite will measure mass, shape, surface topography and

tectonic history, elemental and mineral composition, as well as seek out water-bearing minerals. In addition, the Dawn spacecraft itself and the way it orbits both Vesta and Ceres will be used to measure the celestial bodies' gravity fields.

.

Russell

"Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Dawn Principal Investigator Christopher Russell of the University of California, Los Angeles. "One is rocky and is representative of the building blocks that constructed the planets of the inner solar system. The other may very well be icy and represents the outer planets. Yet, these tw

o very diverse bodies reside in essentially the same neighborhood. It is one of the mysteries Dawn hopes to solve."

activating

"After separation, the spacecraft will go through an automatic activating sequence, including stabilizing the spacecraft, activating flight systems and deploying Dawn's two massive solar arrays," said Patel. "Then and only then will the spacecraft energize its transmitter and contact Earth. We expect acquisition of signal to occur anywhere from one-and-a-half hours to t

hree-and-a-half hours after launch."

said

"If you live in the Bahamas this is one time you can tell your neighbor, with a straight face, that Dawn will rise in the west," said Dawn Project Manager Keyur Patel of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Weather permitting, we are go for launch Thursday morning -- a little after dawn."

moment

Dawn's Sept. 27 launch window is 7:20 to 7:49 a.m. Eastern Daylight Time (4:20 to 4:49 a.m. Pacific Daylight Time). At the moment of liftoff, the Delta II's first-stage main engine along with six of its nine solid-fuel boosters will ignite. The remaining three solids are ignited in flight following the burnout of the first six. The first-stage main engine will bur

n for 4.4 minutes. The second stage will deposit Dawn in a 185-kilometer-high (100- nautical-mile) circular parking orbit in just under nine minutes. At about 56 minutes after launch, the rocket's third and final stage will ignite for approximately 87 seconds. When the third stage burns out, actuators and push-off springs on the launch vehicle will separate the spacecraft from the third stage.

Piazzi

Besides being the largest asteroid, Ceres also was the first asteroid to be discovered. Sicilian astronomer Father Giuseppe Piazzi spotted the object in 1801. Piazzi was looking for suspected planets in a large gap between the orbits of Mars and Jupiter. As more such objects were found in the same region, they became known as "asteroids" or "minor planets."

that

The astronomers suspect that water ice may be buried under the asteroid's crust because the density of Ceres is less than that of the Earth's crust, and because the surface bears spectral evidence of water-bearing minerals. They estimate that if Ceres were composed of 25 percent water, it may have more water than all the fresh water on Earth. Cere

s' water, unlike Earth's, would be in the form of water ice and located in the mantle, which wraps around the asteroid's solid core.

to

The astronomers used Hubble's Advanced Camera for Surveys to study Ceres for nine hours, the time it takes the asteroid to complete a rotation. Hubble snapped 267 images of Ceres. From those snapshots, the astronomers determined that the asteroid has a nearly round body. The diameter at its equator is wider than at its poles. Computer models sho

w that a nearly round object like Ceres has a differentiated interior, with denser material at the core and lighter minerals near the surface. All terrestrial planets have differentiated interiors. Asteroids much smaller than Ceres have not been found to have such interiors.

of

Ceres is approximately 580 miles (930 kilometers) across, about the size of Texas. It resides with tens of thousands of other asteroids in the main asteroid belt. Located between Mars and Jupiter, the asteroid belt probably represents primitive pieces of the solar system that never managed to accumulate into a genuine planet. Ceres comprises 25 percent of

the asteroid belt's total mass. However, Pluto, our solar system's smallest planet, is 14 times more massive than Ceres.