NASA has moved stuff, again. The online version of "Stages to Saturn", "Chariots for Apollo" and probably many others have moved to http://history.nasa.gov (was: http://www.hq.nasa.gov/office/pao/History).
Since the underlying structure of the pages seems to have remained the same, it should be a "simple" find & replace to fix URLs.
Is it possible to mass-edit with a find & replace across all posts?
This post suggests an internal tool exists.