In an email update, SpaceX reports that they have found the cause of the Falcon 9 launch abort this morning.
During rigorous inspections of the engine, SpaceX engineers discovered a faulty check valve on the Merlin engine. We are now in the process of replacing the failed valve. Those repairs should be complete tonight. We will continue to review data on Sunday. If things look good, we will be ready to attempt to launch on Tuesday, May 22nd at 3:44 AM Eastern.
If this is true, than this entire exercise is an unqualified success and illustrates a certain robustness to SpaceX’s engineering on Falcon 9. Their control computer during the launch process spotted the problem before it caused a complete loss of the vehicle and payload. They can now locate the problem, fix it, and proceed with launch.