That always struck me as extremely weird.<p>If it's a useful vehicle, tying it up for years at a stretch seems terribly wasteful. It seems better to use dedicated equipment for the two-year project, and keep the versatile thing free for things that need versatility.<p>All I can think of is that nobody has actually discovered anything well-suited to its strengths, so they keep it in orbit so it doesn't seem to be doing nothing, and a waste of money.<p>Clue?