UPDATE (6 p.m. EST): In the hours following the Falcon 9 launch attempt, SpaceX have determined the root cause for the last-second abort was due to the flight computer detecting a slightly high pressure in the engine 5 combustion chamber. SpaceX Communications Director Kirstin Brost Grantham issued the following statement via email:

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

ORIGINAL: It’s 5 a.m. on a Saturday morning and there’s just been what is truly a heart-stopping moment in the launch business — a last-second launch abort.

But this is a SpaceX flight, which often has these automated cutoffs. In the past, the company could do a bit of troubleshooting, reset computers and have another go. But not today, when the launch window was literally one second.

ANALYSIS: A ‘Giant Leap’ for Commercial Space

SpaceX is aiming to put its Dragon cargo capsule into an orbit that crosses paths with the International Space Station. The company also wants to scrimp on fuel so it has some padding in case there is a problem during the rendezvous and test maneuvers that must take place before NASA will approve a docking.

It’s an ambitious mission.

BIG PIC: SpaceX Ready for Historic Mission to Space Station

“The whole Gemini program had test objectives that, in essence, are all being condensed into this one mission,” said Jeff Greason, founder and chief executive of XCOR Aerospace, another company forging a future in the final frontier. “If they get even halfway there, that’s still one for the books.”

SpaceX’s next opportunity for launch is at 3:44 a.m. EDT Tuesday.

Image: Falcon 9 just after launch abort. Credit: SpaceX/NASA