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NASA to place twin probes in Moon orbit as you snog beneath mistletoe

Formation-flying washing machines in spaaaace! Excellent

NASA has announced that it expects to place two formation-flying space probes into orbit around the Moon on New Year's Eve and New Year's Day. The Gravity Recovery And Interior Laboratory (GRAIL) spacecraft are intended to map the lunar gravitational field with unprecedented accuracy, giving the boffinry community many useful facts about our largest natural satellite.

GRAIL-A and GRAIL-B lifted off from Cape Canaveral back on September 10. Normally a journey by rocket to the Moon requires only a few days (as was the case with the manned Apollo missions of yesteryear) but the GRAILs have taken an unusual and prolonged path, both because of the particular orbits in which they need to be inserted and in order to let their highly sensitive instrument packages completely stabilise in space conditions before approaching the target.

Originally the trip to the Moon was projected with no more accuracy than "about 3 to 4 months", but now NASA has gone firm and told the world that GRAIL-A will arrive in lunar orbit at 1:21 p.m. PST (2100 GMT) on Saturday December 31, and GRAIL-B on Sunday January 1 2012 at 2:05 p.m. PST (2200 GMT).

The space agency also informs us that:

The two GRAIL spacecraft are near-twins, each about the size of a washing machine, with minor differences resulting from the need for one specific spacecraft (GRAIL-A) to follow the other (GRAIL-B) as they circle the Moon.

The science payload on each spacecraft is the Lunar Gravity Ranging System, which will measure changes in the distance between the two spacecraft down to a few microns - about the diameter of a red blood cell.

The GRAILs also carry cameras for the MoonKAM project, an educational outreach effort which will allow students and schoolchildren to download lunar imagery directly. ®

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