SpaceX Dragon to the ISS

That was quick! Swap out the part, and ready to fly again!

Yeah. They've shown quick turnaround like this before, with the cracked nozzle. They found the crack, decided that the engine would work well enough with a couple of inches less nozzle, grabbed an angle grinder and cut off the cracked bit. And then successfully launched the rocket. No management meetings, lengthy discussions or piles of paperwork, but just a couple engineers who know their stuff figuring out the simplest solution and applying it. And the vehicle has enough margin that they can do these things too. So now they just swap the part, test that it works, and then launch. Kind of like what an aeroplane mechanic at an airline would do I imagine. Very promising.

Of course, to achieve reusability with quick turnaround they'll have to make it so that these things only happen very rarely, but then they've just started production. No doubt it will improve once the production line gets settled down and they've built a couple hundred Merlins.

If the Livestream picture at SpaceflightNow is for real, it looks like they haven't even rolled back to the hangar.

So, would they do another test firing in this situation, before the launch window? Is it surprising that the original test firing didn't discover this issue?

I doubt they will do another test firing. I think the test firing at the cape is done to see if the complete, integrated vehicle works as intended, which has already been shown. If engine problems continue, than they can (and I say will) catch them during the next hold down before the launch.

Personally I don't find it surprising that this issue has not been discovered during the static test fire. I was wondering the same thing at first, but if you think about it, there is a reason why it is so hard to make rocket engines reusable. In my opinion, the valve simply failed after the static fire, possibly in the middle of the ignition process. Maybe it had been "weakened" in some way and could not handle another run, who knows.
In engineering there is this saying, that you do not learn anything from a successful test. You have to test something until it fails to learn how much it can handle.

Contrary to what some naysayers believe, this failure is not a reason to worry. The way SpaceX does operations allowed them to safely detect this problem. Now they can easily fix the problem (just swap the valve) and try again. In addition they can use the time until the next launch (the one after COTS2+) to figure out WHY the valve has failed and how to prevent this from happening again.

Exactly. And I read somewhere that their simulations indicated that the thing would have launched successfully even with the broken valve. That makes sense, since they do have an engine-out capability. But since they also have a hold-down, they didn't need to use it this time. It really does feel as if SpaceX are cheating somehow. Fast, cheap and good. That's not supposed to be possible in engineering .

Thanks Marcus and Laurens, that was illuminating for me.

I don't think this abort should be a source of embarassment for SpaceX, but what about that early tweet by Elon Musk that they would simply increase the pressure limit and try again on Tuesday. Gwynne Shotwell dismissed it as being based on "early data", but it seems to me that he was suffering from what airline pilots call "get-there-itis". Has his personal credibility taken a dent, or am I being unfair?

I think it's not the case here. SpaceX has previously had to abort launch due to very tight safety envelopes. If the pressure spike they observed was outside their limits, but well within construction limits of the engine, one of viable solutions would be expand safety limits. As more data came in, it became obivious that the spike was due to mechanical failure instead, and can not be resolved by software trocks.

All looks good thus far!

This was sooo exciting! I can't feel my thumbs any more :p
(hint: in German speaking countries we hold/press our thumbs to wish for luck instead of crossing fingers )

Haha, do you push your thumb into your first finger? Or wrap your knuckles around them?

we wrap the other four fingers around the thumb, so basically you make a fist with your thumb inside. Something you never, ever want to do in a fist fight, lol!

here is a really good (technical) article on the pad abort on Saturday:
http://www.wired.com/autopia/2012/05/sp ... lve-abort/

I wonder if we will be able to see it approach the station as the ISS crosses the night sky?

Just so everyone knows, Dragon made it successfully to orbit. More at the press conference, goto spacex.com