The Falcon 9 rocket began the initiation sequence for launch and then cutoff at the last second. Smoke appeared at the base of the rocket before the flight was terminated at 4:55 a.m. EDT. There was an abort on Engine No. 5 due to excessively high chamber pressure. The computer apparently saw a parameter it didn’t like on that engine and aborted the launch sequence.
The next possible launch date is on Tuesday, May 22 at 3:44 a.m. EDT.