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)