From SpaceX:

SpaceX’s Falcon 9 rocket and Dragon spacecraft were set to liftoff from Launch Complex 40 at the Cape Canaveral Air Force Station, Florida, for their fifth official Commercial Resupply (CRS) mission to the orbiting lab.

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Launch Update:

During the terminal count engineers observed drift on one of the two thrust vector actuators on the second stage that would likely have caused an automatic abort. Engineers called a hold in order to take a closer look. SpaceX is scrubbed for today and we are now targeting launch on Jan. 9th at 5:09am ET.

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The SpaceX launches are streamed live on Livestream. Very cool!

73, Eric W3DQ Washington, DC