Keith's note: Comcast has decided to block customer access to *.NASA.gov due, I am told, to an issue involving how NASA maintains its DNS records. Why these geniuses at Comcast chose the SOPA/PIPA protest day to do this is curious to say the least. Right now, if you are a Comcast customer, you are being purposefully denied access to one part of your government's services.
Keith's update: I have confirmed this via IT professionals at NASA and in several places across the U.S. that Comcast DNS is broken - but only for NASA.gov, it would seem.
Keith's update: Alan Boyle from MSNBC tweeted some good advice - change your DNS setting to Google's Public DNS. Info here.
Keith's update: Everything works again. Apparently NASA provided an update key for DNS and the new key did not match the Comcast key. So Comcast simply cut off DNS access for all of its customers to everything at NASA.gov. The old key has been sent by NASA and everything works again - so far.