Update:Update: NASA is going to go ahead and their is a good lesson here for the media when comparing my predictions versus what happened. I have been honest about my lack of specific knowledge and access to the details on this issue as it has evolved. That made me more conservative than what happened. It illustrates why the people closes to the situation, those with all the facts, are in the best position and should be given deference. Too bad the media does not have the humility to understand this. God Speed Discovery. Have a safe and successful mission!

Update: Well, the reporting has started to detiorate as the day goes on. Some ‘facts’ for those who are interested. There is no crack in the tank itself. The tank is covered in a layer of foam and there was a section which cracked as a result of the cycling of the fuel over the last few days when the launches were cancelled (and as I predicted in this post earlier this morning). The foam around these feeder lines and the struts connecting the tank to the orbiter have always been problematic for the foam. Foam likes nice sloping surfaces. Joints and corners cause problems.

The problem, as I mentioned before, is that the foam can develop stress fractures as it cools down and then returns to normal temperature as the tanks are loaded and unloaded. It appears the initial crack became a ‘flake’ as a piece around this pipe or joint gave way. I am sure as the sun heated the tank today the foam expanded and pushed off the flake. The problem they have is it will be hard to detect other weaknesses on visual inspection alone. If there are other subsurface cracks, they may only show themselves when the fuel is reloaded and you get a temperature gradient across the crack causing the foam to separate as the colder side shrinks and the warmer side doesn’t. Conversely, when the shuttle launches there will be another thermal cycle on the foam as atmospheric friction (and the use of the fuel itself) heats the foam again, exposing probably more fractures.

To make sure there are no subsurface problems requires a physical inspection. The surface of the foam is ‘crusty’ and tends to be able to retain its cohesion better than the internal structure. Think of a small amount of paint on styrofoam giving the surface a bit more strength than the crumbly inside. My guess (and again, this is not my specialty, I just know a bit more than the average space cadet) is they will end up puting a structure up and inspecting the foam, delaying the launch until next weekend. But if they go then trust these people to know what they are doing. They are the best on the planet in this business and they take it very seriously. – end update

Given the foam problems detected in the Shuttle Discovery, and that this flight is supposed to mark the return of operations since the Columbia’s destruction due to foam hitting the orbiter, and because key safety officials resigned in protest over concerns of flying with risk (unavoidable I am afraid) prudence would dictate a total scrub of this launch. The foam has been a problem since pressure from environmentalists caused the formula to be changed out to eliminate freon (which would have been in such small quantities not to damage the ozone). It has become brittle. Pictures obtained by CBS (h/t Drudge) show what happens when the external tank is loaded and unloaded due to delayed launches. The liquid fuel in the tank is at extremely cold temperatures, and the loading and unloading cause majore temperature gradients to occur repeatedly. While the foam is probably good for one cycle, it clearly has issues with mulitple cycles. Which is probably the true source of the foam issue. If you launch the first time the external tank is loaded, then the foam is fine. As it is cycled thermally, stress fractures occur making it a risk. All speculation on my part (and this is not my area of expertise so take this all with a huge grain of sodium chloride).

Addendum: I should be clear about what I am trying to say here, especially after watching the coverage of the news conference on CNN and Fox. There have been two things driving NASA of late on the Shuttle: Public Impression and Engineering Reality. I know the people at NASA will make the right decision, and if the Shuttle launches it will be as ready as it can be. The foam is not a structural element, it simply poses a debris risk. And as noted, the size of this piece which fell off today is way below the size that would be of concern (ice and foam come off launches all the time). But Public Impressions can outweigh engineering and physics. I am happy to see I was wrong in my previous prediction that NASA would crumple to the impression regardless of the true risks. Clearly they are going on with a countdown until they get to a point where they have to make a call one way or the other (and that may be tomorrow morning in reality). But I am glad to see NASA is going to make an engineering decision and then stand by it and not play it PR safe and waste a lot of money. And I am glad to see top quality coverage from CNN and Fox on this. Maybe there is hope for this country after all?