Thanks for submitting this now rather than 15 minutes from now! Moments like these are historic, and it's wonderful to experience this in realtime rather than watching a replay. T minus 10min. Go SpaceX! EDIT: It's impressive they were able to abort safely after ignition. That's historically rare, isn't it?
Aborting after ignition is only possible with liquid engines. The F9 in particular is designed to light and stabilize all nine engines before removing the restraints holding the rocket down - this gives them very robust abort capabilities. And since the engines are designed for multiple lights, they can even retry it without needing refurbishment.
The wiki page is a pretty interesting read: http://en.wikipedia.org/wiki/Mercury-Redstone_1#Test_backgro...