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NASA launches twin probes to measure lunar gravity

English.news.cn   2011-09-10 21:19:27 FeedbackPrintRSS

WASHINGTON, Sept. 10 (Xinhua) -- The U.S. space agency NASA launched a new, nearly-half-billion-U.S.-dollar lunar mission on Saturday morning that will enable scientists to better understand the moon's gravitational field and the lunar interior -- from crust to core.

Near-identical twins Grail-A and Grail-B -- short for Gravity Recovery and Interior Laboratory -- blast off at 9:08 a.m. EDT (1308 GMT) aboard a Delta II heavy rocket from Cape Canaveral Air Force Station in central Florida.

"We are on our way, and early indications show everything is looking good," said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory in Pasadena, California. "We will know more about GRAIL's status in a few hours, after an opportunity to analyze telemetry and poll our mission controllers."

Mission controllers will await communication in approximately 90 minutes from the lunar duo indicating they have achieved proper orientation and deployed their solar arrays.

Although launched together, the two washing machine-sized spacecraft will separate an hour into the flight and travel independently to the moon. The 496-million-dollar spacecraft will take a long, looping trip via the sun-Earth Lagrange Point 1, a gravitationally stable spot between our planet and the sun. This route is energy-efficient, helping keep the mission's costs down, researchers said.

They will journey to the moon for three and a half months, entering a polar lunar orbit one after the other around New Year's Day. During NASA's Apollo missions, astronauts reached the moon just three days after blasting off.

The pair will settle into polar orbits just 34 miles above the lunar surface and essentially chase each around the moon for nearly three months. The distance between the two probes will range from 40 miles to 140 miles.

In lunar orbit, the spacecraft will transmit radio signals precisely defining the distance between them. Regional gravitational differences on the moon are expected to expand and contract that distance. GRAIL scientists will use these accurate measurements to define the moon's gravity field. The data will allow mission scientists to understand what goes on below the surface of our natural satellite, how it formed and how it evolved over time.

Knowing more about the moon's history should also help scientists understand how other big rocky bodies, such as Earth and Mars, form and behave, researchers said.

"GRAIL will unlock lunar mysteries and help us understand how the moon, Earth and other rocky planets evolved as well," said Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology.

The orbiting probes also will help pinpoint the best landing sites for future explorers, whether human or mechanical.

The mission is relatively short in duration -- just 90 days once the two spacecraft reach orbit. It is the first lunar mission devoted to studying the insides of the moon.

GRAIL's first launch attempt Thursday was scuttled by high winds. The flight initially was rescheduled for Friday, but engineers wanted more time to review technical data after the Delta 2 rocket was drained of fuel following Thursday's scrub.

Since the Space Age began in 1957, 110 missions have targeted the moon, 12 men have walked on its surface during six landings, and 842 pounds of rock and soil have been brought back to Earth and are still being analyzed.

Three spacecraft currently are orbiting the moon and making science observations. A plan to return U.S. astronauts to the moon was nixed in favor of an asteroid and Mars.

By the time their science mission ends in late spring next year, Grail-A and Grail-B will plunge into the moon. Scientific analysis of their data is expected to continue for a year.

After GRAIL, NASA plans to launch its Mars Science Laboratory, or Curiosity, in November on a nearly two-year journey to the red planet. It will land at the foot of a layered mountain inside the planet's Gale crater.

Editor: yan
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