Image: Artist's concept of the two GRAIL spacecraft orbiting the moon
Lockheed Martin
Artist's concept of the two Gravity Recovery and Interior Laboratory (GRAIL) spacecraft orbiting the moon. NASA will launch the twin probes on Sept. 8, 2011, to study the moon's gravitational field in unprecedented detail.
By
updated 9/5/2011 12:58:03 PM ET 2011-09-05T16:58:03

NASA is gearing up for this week's launch of twin lunar orbiters built to map the gravity of Earth's moon in unprecedented detail.

The twin GRAILl lunar probes are slated to blast off from Florida's Cape Canaveral Air Force Station on Thursday. The mission has two instantaneous (one-second) launch windows on that date, one at 8:37 a.m. EDT and another at 9:16 a.m. EDT (1237 and 1316 GMT), NASA officials said.

The two unmanned spacecraft should reach the moon around New Year's Day, at which point they'll begin probing the moon's composition from crust to core. GRAIL's observations should help scientists better understand how the moon formed and evolved, researchers said.

The mission "will reveal clues not only into the history of the moon and Earth, but will provide important data for future lunar exploration," said GRAIL principal investigator Maria Zuber of MIT in a statement. [ Photos From NASA's Moon Gravity Mission ]

A long trip to the moon
Once launched, the twin probes will embark on a circuitous, 3 1/2-month trip to the moon via the sun-Earth Lagrange Point 1, a gravitationally stable spot between our planet and the sun. This route is energy-efficient and thus helps keep the $496 million mission's costs down, researchers said.

When they arrive at Earth's nearest neighbor, the two GRAIL (Gravity Recovery And Interior Laboratory) spacecraft will settle into polar orbits just 34 miles (55 kilometers) above the lunar surface. [ Video: Grail's Mission to Map Moon Gravity ]

They'll essentially chase each around the moon, keeping close tabs on the distance between them. This distance will change slightly as they travel, owing to regional differences in the moon's gravitational field.

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By analyzing these distance variations, researchers will be able to determine the lunar gravity field in great detail. And this information, in turn, will yield insights into the moon's structure and evolutionary history.

Knowing how the moon formed and changed over billions of years should also give scientists a better understanding of the inner solar system's other big, rocky bodies — Mercury, Venus, Earth and Mars — researchers said.

GRAIL launch Tweetup
NASA personnel won't be the only ones who get to watch GRAIL launch on Sept. 8. The space agency has invited 150 of its Twitter followers to the event as well.

These lucky 150, selected from more than 800 people who registered, will be treated to a two-day event that culminates with GRAIL's launch aboard a Delta 2 rocket on Sept. 8. They will share their experiences, in short bursts of 140 characters or less.

If the launch doesn't go off on Sept. 8, GRAIL will have plenty of other chances. The mission's launch period lasts until Oct. 19.

You can follow SPACE.com senior writer Mike Wall on Twitter:@michaeldwall. Follow SPACE.com for the latest in space science and exploration news on Twitter@Spacedotcomand onFacebook.

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Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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