CAPE CANAVERAL, FL - APRIL 29:  A SpaceX rocket sits on launch pad 39A as it is prepared for the NROL-76 launch on April 29, 2017 in Cape Canaveral, Florida.   SpaceX will attempt to deliver a  classified payload to orbit and liftoff is scheduled for tomorrow at 7 a.m. ET from Kennedy Space Center.  (Photo by Joe Raedle/Getty Images)