Twin Gravity Spacecraft Set to Enter Lunar Orbit   
       
   Dec. 30, 2011: NASA's twin GRAIL spacecraft, on a mission to study the moon's   
   gravitational field, are nearing their New Year's Eve and New Year's Day   
   main-engine burns to place the duo in lunar orbit.   
       
   Named Gravity Recovery And Interior Laboratory (GRAIL), the spacecraft are   
   scheduled to be placed into orbit beginning at 1:21 p.m. PST (4:21 p.m. EST)   
   for GRAIL-A on Dec. 31, and 2:05 p.m. PST (5:05 p.m. EST) 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 we need," said David Lehman, project manager for GRAIL at   
   NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.   
       
   http://www.nasa.gov/mission_pages/grail/main/index.html   
       
   An artist's concept of the GRAIL spacecraft in action. [more]   
       
   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, 2011, 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 (MIT) in Cambridge. "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."   
       
   During their final approaches to the moon, both orbiters move toward it from   
   the south, flying nearly over the lunar south pole. The lunar orbit insertion   
   burn for GRAIL-A will take approximately 40 minutes and change the   
   spacecraft's velocity by about 427 mph (688 kph). GRAIL-B's insertion burn 25   
   hours later will last about 39 minutes and is expected to change the probe's   
   velocity by 430 mph (691 kph).   
       
   iPhone APP only.   
       
   Click to download the GRAIL mission iPhone appThe insertion maneuvers will   
   place each orbiter into a near-polar, elliptical orbit with a period of 11.5   
   hours. Over the following weeks, the GRAIL team will execute a series of burns   
   with each spacecraft to reduce their orbital period from 11.5 hours down to   
   just under two hours. At the start of the science phase in March 2012, the two   
   GRAILs will be in a near-polar, near-circular orbit with an altitude of about   
   34 miles (55 kilometers).   
       
   When science collection begins, the spacecraft will transmit radio signals   
   precisely defining the distance between them as they orbit the moon. As they   
   fly over areas of greater and lesser gravity, caused both by visible features   
   such as mountains and craters and by masses hidden beneath the lunar surface.   
   they will move slightly toward and away from each other. An instrument aboard   
   each spacecraft will measure the changes in their relative velocity very   
   precisely, and scientists will translate this information into a   
   high-resolution map of the Moon's gravitational field. The data will allow   
   mission scientists to understand what goes on below the surface. This   
   information will increase our knowledge of how Earth and its rocky neighbors   
   in the inner solar system developed into the diverse worlds we see today.   
       
   For more information about GRAIL, visit: http://www.nasa.gov/grail   
       
       
   Production Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Lunar GRAIL -- Science@NASA   
       
   Bizarre Lunar Orbits -- Science@NASA   
       
   A New Paradigm for Lunar Orbits -- Science@NASA   
       
   GRAIL Home Page   
       
   Credits: JPL manages the GRAIL mission. MIT is home to the mission's principal   
   investigator, Maria Zuber. The GRAIL mission is part of the Discovery Program   
   managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed   
   Martin Space Systems in Denver built the spacecraft   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.71   
    * Origin: NCS BBS (1:3828/7)