Posted: Fri, Dec 30, 2011, 6:40 AM ET (1140 GMT)
Two NASA spacecraft launched in December are ready to enter lunar orbit this weekend, project officials confirmed this week. The twin Gravity Recovery And Interior Laboratory (GRAIL) spacecraft will fire thrusters to go into orbit around the Moon, with GRAIL-A arriving at 4:21 pm EST (2121 GMT) Saturday and GRAIL-B at 5:05 pm EST (2205 GMT) Sunday. The two spacecraft, launched together on a Delta 2 in September, will use radio signals transmitted between each other to determine their separation distance, which in turn will be used to measure the Moon's gravity map. The spacecraft also carry cameras that will be used for educational purposes.

Related Links:

•  SPACE.com article
•  AP article
•  Florida Today article
•  Spaceflight Now article
•  NASA press release