Current meteoroid models indicate that the moon is struck by a meteoroid with a mass greater than 1 kg (2 lbs) over 260 times per year

This number is very uncertain, however, as observations for objects in this mass range are embarrassingly few -- a single fireball survey conducted by Canadian researchers from 1971 to 1985

Factors of several, higher or lower, are easily possible

Indeed recent lunar observations by a Spanish team seem to indicate that the rate of impacts is about two times higher

This too is quite uncertain, being based on observations of only 3 impacts

Clearly more observations are needed if we are to establish the rate of large meteoroids impacting the moon

Why it is important: U.S. Space Exploration Policy eventually calls for extended astronaut stays on the lunar surface. Spacecraft, vehicles, habitats, and EVA suits must all be designed to withstand the stresses posed by the harsh lunar environment over this period of time

Meteoroids, and the ejecta produced when they create impact craters, are part of this environment