spacetoday.net: First GRAIL spacecraft enters orbit

Posted: Sat, Dec 31, 2011, 10:21 PM ET (0321 GMT)
GRAIL orbit insertion illustration (NASA)

The first of NASA's twin lunar spacecraft entered orbit around the Moon on Saturday. The Gravity Recovery And Interior Laboratory (GRAIL) A spacecraft fired its engine at 4:21 pm EST (2121 GMT) Saturday for 39 minutes, slowing the spacecraft down enough to enter orbit. Project officials confirmed later Saturday the spacecraft was in its planned orbit of 90 by 8.363 kilometers. GRAIL-A will be joined on Sunday by its twin, GRAIL-B, whose orbit insertion burn is planned for 5:05 pm EST (2205 GMT). 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 map the Moon's gravity.