Two thoughts, one good, one not so good.

First the good. This is not an unusual event for SpaceX. They have had a number of previous aborts at launch, with both Falcon 1 and Falcon 9, initiated by computer. What has been very encouraging about all these events is they have always been able to make the rocket safe and recover to launch another time. And that recovery has always been breathtakingly fast, sometimes taking just a few minutes.

This pattern of last second scrubs however suggests something more worrisome. I wonder if we might be seeing a design issue with Falcon 9’s first stage, which uses nine Merlin engines. When they first announced this configuration — chosen to save money as they would not have to design and build a new more powerful engine — my first thought was that it was going to be very complicated pumping fuel and oxidizer to all those engines simultaneously and with precision. One of the reasons the Soviet Union’s N1 rocket failed was it’s first stage had 30 engines, requiring an incredibly complex fuel system. I worry that Falcon 9’s first stage carries with it this same problem. It seems to me, for example, that most of the past launch aborts occurred because of fuel pressure anomalies detected by the control computer.

Having said this, I must add that I am speculating, and really have no idea what the issue is. According to this report, the problem might have less to do with pressure issues and more to do with a fundamental issue with the engine itself. That in itself will be unfortunate, because if SpaceX has to swap out an engine it is going to be very difficult to get this rocket off the ground before May 29. After that date the next launch window will not be until after mid June.