NASA's twin GRAIL spacecraft are scheduled to drop themselves into lunar orbit this weekend after a voyage that started last September. The long trip gave mission managers time to thoroughly check out the two identical craft. By contrast, of course, Apollo capsules reached the Moon in two or three days.
The GRAIL spacecraft are designed to fly in the same orbit and study the Moon in microwave. The object is to map the lunar gravitational field in unprecedented detail. Doing that, scientists expect to learn much about the composition, internal structure, and evolution of the Moon.