NASA's New 'Lesson' from Space

No, they haven't. It's actually less, but they can't reduce it to
zero. The only reason that it seems like more now is because we're
paying a lot more attention to it than we used to.

And the "mileage" of the orbiters is irrelevant. The problem is
caused by the external tanks, which are new every flight, since they
must be expended.

Posted by Michael Bulatovich on August 18, 2007, 5:41 pm

> On Sat, 18 Aug 2007 16:43:33 -0400, in a place far, far away, "Michael

> such a way as to indicate that:

>>> On Sat, 18 Aug 2007 14:06:55 -0400, in a place far, far away, "Michael

>>> such a way as to indicate that:

>>>

>>>>

>>>>> On Sat, 18 Aug 2007 08:37:00 -0400, "Michael Bulatovich"

>>>>>

>>>>>>We've got to be approaching the end of the line for the shuttle...How

>>>>>>many

>>>>>>more missions are planned with it?

>>>>>

>>>>> 14.

>>>>

>>>>Ouch. What are the bookies saying about the chances of another

>>>>catastrophe?

>>>

>>> The "bookies" don't know much about it. If you think that there's a

>>> one in a hundred chance per flight, the probability would be about

>>> 13%. If you think it's two in a hundred, it's about one in four. I

>>> think it's actually less than one in a hundred per flight, so the

>>> chances of losing another one are pretty small in the remaining

>>> fourteen flights.

>>Be that as it may, these guys make odds that generally win for themselves.

>>My (uninformed) sense is that shuttle missions have been meeting with more

>>regular damage requiring repairs or burials than when the vehicles were

>>new.

>>Most of them have around the same mileage, don't they?

> No, they haven't. It's actually less, but they can't reduce it to

> zero. The only reason that it seems like more now is because we're

> paying a lot more attention to it than we used to.

> And the "mileage" of the orbiters is irrelevant. The problem is

> caused by the external tanks, which are new every flight, since they

> must be expended.

What about the tiles?

Posted by Alan Anderson on August 18, 2007, 6:13 pm

> > And the "mileage" of the orbiters is irrelevant. The problem is

> > caused by the external tanks, which are new every flight, since they

> > must be expended.

> What about the tiles?

What about them? They're the *victims* of the damage, not the cause.

Posted by Michael Bulatovich on August 19, 2007, 7:10 am

>> > And the "mileage" of the orbiters is irrelevant. The problem is

>> > caused by the external tanks, which are new every flight, since they

>> > must be expended.

>> What about the tiles?

> What about them? They're the *victims* of the damage, not the cause.

Well..... to use an analogy in this field, consider door casings. Besides
the function of covering joints between materials, it can be argued that one
of their functions is to protect a buildings' more fragile interior finish
at the places where mechanical abrasion is more likely....at door and window
openings.

In doing this, over extended periods, a degradation of the condition of
these elements is normal and expected. You could argue that the "cause" of
the damage is not the casings themselves but the movement of people and
goods through the opening, but the effect is the same. The materials and
their attachment can be weakened without immediate, obvious visual evidence
of that fact. They also get obviously banged up progressively, and
eventually bits start to come off, especially when we start moving
furniture. These casings can be hardwood, softwood, even stone or metal, and
each material will degrade at different rates and in slightly different
ways.

I never said the tiles were the *cause* of any damage, and have heard the
explanations regarding tank insulation, but find it very hard to imagine
that the tiles (which I recall thinking were a dicey idea when I first saw
them) do not suffer any cumulative degradation from repeated exposures to
the kinds of stresses they experience. Ditto for their attachment. I also
know nothing of the inspection regimen, but imagine that it is primarily
visual, which could fail to detect 'invisible' defects or wear.

Posted by Rand Simberg on August 18, 2007, 6:32 pm

On Sat, 18 Aug 2007 17:41:34 -0400, in a place far, far away, "Michael
such a way as to indicate that:

>> And the "mileage" of the orbiters is irrelevant. The problem is

>> caused by the external tanks, which are new every flight, since they

>> must be expended.

>What about the tiles?

They are inspected every flight, and replaced, if necessary. Again,
it has nothing to do with "mileage."

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