Twin Grail Spacecraft To Enter Moon's Orbit Over Weekend, NASA Says
LOS ANGELES -- The moon has come a long way since Galileo first peered at it through a telescope. Unmanned probes have circled around it and landed on its surface. Twelve American astronauts have walked on it. And lunar rocks and soil have been hauled back from it.
Despite being well studied, Earth's closest neighbor remains an enigma.
Over the New Year's weekend, a pair of spacecraft the size of washing machines are set to enter orbit around it in the latest lunar mission. Their job is to measure the uneven gravity field and determine what lies beneath – straight down to the core.
Since rocketing from the Florida coast in September, the near-identical Grail spacecraft have been independently traveling to their destination and will arrive 24 hours apart. Their paths are right on target that engineers recently decided not to tweak their positions.
"Both spacecraft have performed essentially flawlessly since launch, but one can never take anything for granted in this business," said mission chief scientist Maria Zuber of the Massachusetts Institute of Technology.
The nail-biting part is yet to come. On New Year's Eve, one of the Grail probes – short for Gravity Recovery and Interior Laboratory – will fire its engine to slow down so that it could be captured into orbit. This move will be repeated by the other the following day.
Engineers said the chances of the probes overshooting are slim since their trajectories have been precise. Getting struck by a cosmic ray may prevent the completion of the engine burn and they won't get boosted into the right orbit.
"I know I'm going to be nervous. I'm definitely a worrywart," said project manager David Lehman of NASA's Jet Propulsion Laboratory, which manages the $496 million, three-month mission.
Once in orbit, the spacecraft will spend the next two months flying in formation and chasing one another around the moon until they are about 35 miles above the surface with an average separation of 124 miles. Data collection won't begin until March.
Previous missions have attempted to measure lunar gravity with mixed success. Grail is the first mission dedicated to this goal.
As the probes circle the moon, regional changes in the lunar gravity field will cause them to speed up or slow down. This in turn will change the distance between them. Radio signals transmitted by the spacecraft will measure the slight distance gaps, allowing researchers to map the underlying gravity field.
Using the gravity information, scientists can deduce what's below or at the lunar surface such as mountains and craters and may help explain why the far side of the moon is more rugged than the side that faces Earth.
The probes are officially known as Grail-A and Grail-B. Several months ago, NASA hosted a contest inviting schools and students to submit new names. The probes will be christened with the winning names after the second orbit insertion, Zuber said.
Besides the one instrument on board, each spacecraft also carries a camera for educational purposes. Run by a company founded by Sally Ride, the first American woman in space, middle school students from participating schools can choose their own lunar targets to image during the mission.
A trip to the moon is typically relatively quick. It took Apollo astronauts three days to get there. Since Grail was launched from a relatively small rocket to save on costs, the journey took 3 1/2 months.
Scientists expect the mission to yield a bounty of new information about the moon, but don't count on the U.S. sending astronauts back anytime soon. The Constellation program was canceled last year by President Barack Obama, who favors landing on an asteroid as a stepping stone to Mars.
___Check out NASA's biggest discoveries of 2011.
Entire Sun Imaged
In February, <a href="http://www.nasa.gov/mission_pages/stereo/main/index.html" target="_hplink">NASA's STEREO probes</a>, two observatories that were launched in 2006 to survey the sun, reached opposite ends of the sun and thus, were able to give scientists (and the rest of us!) a never-before-seen view of the far side of the star at the center of our universe. The composite image above was captured on June 1, 2011, <a href="http://www.nasa.gov/mission_pages/stereo/news/farside-060111.html" target="_hplink">and according to NASA</a>, "is the first complete image of the solar far side, the half of the sun invisible from Earth." <a href="http://www.huffingtonpost.com/2011/02/07/nasa-stereo-sun-images-video_n_819510.html" target="_hplink">Click here for more</a> on the STEREO probes.
Messenger Reaches Mercury
While it's not a "discovery," <em>per se</em>, it's a milestone that will no doubt lead to many new findings about the smallest and innermost planet in our solar system. In March, after a 6 1/2-year, 4.9 billion mile journey, <a href="http://www.huffingtonpost.com/2011/03/18/nasa-messenger-mercury_n_837503.html" target="_hplink">NASA's Messenger spacecraft reached Mercury's orbit</a>. Messenger, the first spacecraft to orbit Mercury, <a href="http://messenger.jhuapl.edu/mer_orbit.html" target="_hplink">orbits the planet</a> every 12 hours. In November, <a href="http://www.nasa.gov/mission_pages/messenger/media/MissionExtends.html" target="_hplink">NASA announced that the spacecraft's mission</a>, which was supposed to end on March 17, 2012, would be extended for an additional year.
Pluto's Tiny Moon
In July, NASA said that its Hubble Space Telescope <a href="http://www.huffingtonpost.com/2011/07/20/new-pluto-moon-hubble-space-telescope_n_904578.html" target="_hplink">discovered an eight to 21-mile-wide moon</a> circling the dwarf planet.
Black Hole Eats A Star
In March, <a href="http://www.huffingtonpost.com/2011/04/07/nasa-cosmic-blast_n_846333.html" target="_hplink">NASA's Swift satellite saw an unusually long explosion of gamma-rays</a>. After studying the X-rays, <a href="http://www.huffingtonpost.com/2011/08/25/black-hole-eats-star-video_n_937150.html" target="_hplink">scientists found that they came from</a> a black hole that had become reenergized when it devoured a star. <a href="http://www.nasa.gov/home/hqnews/2011/aug/HQ_11-271_Swift_Black_Hole.html" target="_hplink">From NASA</a>: <blockquote>Astronomers soon realized the source, known as Swift J1644+57, was the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth. </blockquote>
Huge Mountain Discovered On Asteroid
<a href="http://www.nasa.gov/mission_pages/dawn/main/index.html" target="_hplink">NASA's Dawn</a>, an ion-propelled spacecraft that traveled 1.7 billion miles before reaching the asteroid Vesta in July, sent back images in October revealing that <a href="http://www.huffingtonpost.com/2011/10/05/vesta-mountain-dawn-nasa_n_996282.html" target="_hplink">Vesta is home to a mountain larger than any mountain</a> on Earth. In December, NASA released new images that Dawn took when it was orbiting only 130 miles above the asteroid, the closest it will get to Vesta. Dawn will continue to image Vesta until next summer, when it will make its way to Ceres, a bigger asteroid.
'Star Wars'-Like Planet
<a href="http://www.huffingtonpost.com/2011/09/15/kepler-16b-planet-two-suns_n_964799.html" target="_hplink">NASA's Kepler spacecraft found a planet</a> that orbits two suns, driving fans of the "Star Wars" franchise <a href="http://blog.moviefone.com/2011/09/16/astronomers-discover-real-life-tatooine-star-wars/" target="_hplink">to call it a real-life Tatooine</a>. Astronomers announced Kepler-16b, which is the first circumbinary planet -- meaning it orbits two stars -- in September. <a href="http://www.huffingtonpost.com/2011/09/15/kepler-16b-planet-two-suns_n_964799.html" target="_hplink">Click here for more</a> on Kepler-16b.
'Habitable Zone' Planet Found
Scientists in early December <a href="http://www.huffingtonpost.com/2011/12/05/kepler-22b-new-planet-discovered-habitable-zone_n_1129591.html" target="_hplink">announced the discovery of Kepler-22b</a>, a planet with a temperature of around 72 degrees that's in the so-called <a href="http://en.wikipedia.org/wiki/Habitable_zone" target="_hplink">"Goldilocks," or habitable zone</a>. While the temperature of the 600-light-year away planet could sustain water, it has a radius of 2.4 times that of Earth's, so <a href="http://www.huffingtonpost.com/huff-wires/20111206/us-sci-alien-planet/" target="_hplink">it's probably too big</a> to harbor life.
Biggest Black Holes Ever Discovered
Astronomers announced in early December that <a href="http://www.huffingtonpost.com/2011/12/05/black-hole-scientists-discover-huge_n_1129727.html" target="_hplink">they had found the biggest black holes to date</a>. The massive black holes, which are 10 billion times the size of the sun, are located over 300 million light years away.
Europa's 'Great Lakes'
Scientists had long-thought that a large body of water existed under the surface of Europa, Jupiter's moon, but it was thought to be tens of miles below an icy crust. In November, though, astronomers analyzing data from <a href="http://solarsystem.nasa.gov/galileo/" target="_hplink">NASA's Galileo spacecraft</a> found evidence that suggests blocks of ice interact with water below the surface, which could mean that nutrients and energy are moving between the underground ocean and icy shell. <a href="http://www.ig.utexas.edu/people/staff/britneys/" target="_hplink">Britney Schmidt</a>, the lead author of the study, <a href="http://www.nature.com/nature/journal/v479/n7374/full/nature10608.html" target="_hplink">which appeared in the journal Nature</a>, said that the interaction "could make Europa and its ocean more habitable for life." <a href="http://www.huffingtonpost.com/2011/11/17/europa-water-jupiter-moon-photo-video_n_1099463.html#s480278&title=Europa" target="_hplink">Click here to read more</a> about water on Europa.
'Bubbles' At The Edge Of Solar System
NASA's Voyager probes -- launched over 30 years ago -- found huge magnetic "bubbles" at the edge of the solar system. "The sun's magnetic field extends all the way to the edge of the solar system," astronomer Merav Opher of Boston University <a href="http://www.nasa.gov/mission_pages/voyager/heliosphere-surprise.html" target="_hplink">said in a NASA statement</a>. "Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are, the folds of the skirt bunch up." Voyager 1 and Voyager 2 were launched in 1977. Voyager 1 is currently 11 billion miles away and may exit our solar system within the next few years.
Gypsum On Mars
In December, scientists announced that NASA's <a href="http://www.huffingtonpost.com/2011/12/08/mars-water-opportunity-rover-gypsum_n_1136483.html" target="_hplink">Mars Rover Opportunity may have found gypsum </a>that had been deposited by water. "This tells a slam-dunk story that water flowed through underground fractures in the rock," <a href="http://astro.cornell.edu/people/facstaff-detail.php?pers_id=112" target="_hplink">Steve Squyres</a>, a planetary scientist at Cornell University and the principal investigator for Opportunity <a href="http://www.nasa.gov/mission_pages/mer/news/mer20111207.html" target="_hplink">said in a NASA statement</a>. NASA's Curiosity Rover <a href="http://www.huffingtonpost.com/2011/11/26/nasa-mars-curiosity-launc_n_1113995.html" target="_hplink">is en route to the Red Planet</a> and will arrive in August 2012.
Earth-Size Planets Discovered
Weeks after <a href="http://www.huffingtonpost.com/2011/12/05/kepler-22b-new-planet-discovered-habitable-zone_n_1129591.html" target="_hplink">the announcement of Kepler-22b</a>, scientists said that <a href="http://www.huffingtonpost.com/2011/12/20/new-planets-kepler-exoplanets_n_1161213.html" target="_hplink">they'd discovered Kepler-20e and Kepler-20f</a>, two planets that are about the size of Earth. While the planets are too close to their sun-like star to harbor life as we know it, the discovery proved that the Kepler spacecraft was capable of spotting planets that are Earth-size, and brings us one step closer to finding a true Earth twin. <a href="http://www.huffingtonpost.com/2011/12/20/new-planets-kepler-exoplanets_n_1161213.html" target="_hplink">Click here for more</a> on the new planets.
Charles Camarda: NASA Innovation