Fuel Tank foam queation

[juliemac]

I undertand that the contraction and expansion during fill cycles is a primary cause of the foam failure in the form of cracks.<br />When I am using fiber glass epoxy or plaster, I can add fibers to add/strengthen the mix. Why can't they add a small weight addition of the fibers into the blown foam mix?<br />I'm no dummy, but neither are the engineers working on the problem. Is it really that heavy to add the fibers? <br /><br />Or a thin (fishing line) net that is sprayed in in selected damage areas?

 

[henryhallam]

Lots of extra weight (a tonne or more at a WAG. The tank is BIG and the foam is mostly air/gas at the moment), but more importantly lots of extra time to redesign, requalify, test etc. The STS programme only has 4 years left before retirement.<br /><br />The foam is a flawed design but at this point it is too late to make drastic changes. So the risk is managed, the probability and consequences of failure are minimised as much as possible and there is the "escape route" of the rescue mission.

 

[vogon13]

Fibres might make bigger pieces come off.<br /><br />Big engineering project to decide if that is a good idea.<br /><br />Only 15 flights left, how big a change do you want to put in the system at this point?<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[propforce]

Back in STS 1 and 2, the ET foam was painted white. The paint has helped to keep the foams from falling off, but it adds 700~800 lbm of weight so they decided to take it off. <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

Did the paint really help keep the foam together? I had heard it didn't have any favourable effect at all other than for pretty pictures. It would be interesting to know if it was actually useful and how.

 

[tomnackid]

The white paint in no way helped to keep the foam on. In fact, aside from adding a lot of weight and prep time it actually added to the debris problem. The white paint on the first few launches was a hold over from the von Braun/Saturn years. Apparently von Brauan insisted that his rockets be painted white. There was technical reason for this. Early test rockets like the V2s confiscated after the war were painted white with bold black patterns so that researches looking through spotting scopes could tell if the rocket was rolling in flight. Electronic telemetry made visual inspection less necessary, but the tradition persisted up to the Saturn V.

 

[CalliArcale]

White also has significant thermal advantages -- it doesn't absorb heat from the Sun as quickly as other colors. But I doubt it makes much of a difference for something like the ET. It's incredibly huge, and its filled with stuff that's incredibly cold. It wouldn't really help the ice problem. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[vulture2]

Getting back to the foam, the real problem is that the foam problem wasn't recognized. The foam is now much smoother than before, and only very small bits come off. The last couple flights the tile damage has been greatly reduced. Given all the flights before 117 without major damage, I doubt this particular problem will occur again.

 

[klreed]

The real problem was that NASA decided to change to an inferior foam because the new brand-x would conform to EPA emissions regulations. NASA had been previously using foaming agents that were bad for ozone. X-aerogel insulation has been suggested to replace the foam and this would seem to be a much better choice. With not many missions left I do not foresee anything changing now.

 

[vulture2]

>>>The real problem was that NASA decided to change to an inferior foam because the new brand-x would conform to EPA emissions regulations.<br />-----------------------------------------------<br />Not so. Columbia was lost because of a glue-on block at the base of the bipod strut that came loose because the two-art adhesive used to glue it in place had set and lost its tackiness by the time the block was put in place. It had nothing to do with the sprayon foam, and neither did the piece that came loose during the 114 launch.