It doesn't seem that mysterious. It's almost certainly involved in reconnaissance.

    [T]he military spacecraft was passing over the
    same region on the ground once every four days,
    a pattern he called “a common feature of U.S.
    imaging reconnaissance satellites.”

    In six sightings, the team has found that the
    craft orbits as far north as 40 degrees
    latitude...In moving from as far as 40 degrees
    north latitude to 40 degrees south latitude,
    the military spacecraft passes over many
    global trouble spots, including Iraq, Iran,
    Afghanistan, Pakistan and North Korea.

http://www.nytimes.com/2010/05/23/science/space/23secret.htm...