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NASA's twin spacecraft on final approach for lunar orbit

12-29-2011 09:29 BJT

WASHINGTON, Dec. 28 (Xinhua) -- NASA's twin spacecraft to study the moon from crust to core are nearing their New Year's Eve and New Year's Day main-engine burns to place the duo in lunar orbit, the U.S. space agency announced Wednesday.

Named Gravity Recovery And Interior Laboratory (GRAIL), the spacecraft are scheduled to be placed in orbit beginning at 4:21 p. m. EST (2121 GMT) for GRAIL-A on Dec. 31, and 5:05 p.m. EST (2205 GMT) on Jan. 1 for GRAIL-B.

"Our team may not get to partake in a traditional New Year's celebration, but I expect seeing our two spacecraft safely in lunar orbit should give us all the excitement and feeling of euphoria anyone in this line of work would ever need," said David Lehman, project manager for GRAIL at NASA's Jet Propulsion Laboratory.

The distance from Earth to the moon is approximately 250,000 miles (402,336 kilometers). NASA's Apollo crews took about three days to travel to the moon. Launched from Cape Canaveral Air Force Station Sept. 10, the GRAIL spacecraft are taking about 30 times that long and covering more than 2.5 million miles (4 million kilometers) to get there.

This low-energy, long-duration trajectory has given mission planners and controllers more time to assess the spacecraft's health. The path also allowed a vital component of the spacecraft' s single science instrument, the Ultra Stable Oscillator, to be continuously powered for several months. This will allow it to reach a stable operating temperature long before it begins making science measurements in lunar orbit.

"This mission will rewrite the textbooks on the evolution of the moon," said Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology. "Our two spacecraft are operating so well during their journey that we have performed a full test of our science instrument and confirmed the performance required to meet our science objectives."

As of Dec. 28, GRAIL-A is 65,860 miles (106,000 kilometers) from the moon and closing at a speed of 745 mph (1,200 kph). GRAIL- B is 79,540 miles (128,000 kilometers) from the moon and closing at a speed of 763 mph (1,228 kph).

Editor:Zhang Hao |Source: Xinhua

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