Re: Shuttle fleet grounded again?


"Martin Brown" <|||newspam|||@nezumi.demon.co.uk> wrote in message
news:dcacps$95q$1@xxxxxxxxxxxxxxxxxxxxxxx
> Roger Hamlett wrote:
>
>> "Martin" <nospam@xxxxxxxxxx> wrote in message
>> news:42e898e3_1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>>>"has.mac" <has.mac@xxxxxxxxxxxxxxx> wrote in message
>>>news:PA%Fe.4587$_k2.77165@xxxxxxxxxxxxxxxxxx
>>>
>>>>"Martin" <nospam@xxxxxxxxxx> wrote in message
>>>>news:42e81735_4@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>>
>>>>>Sky News are reporting that NASA have decided to ground the Shuttle
>>>>>fleet
>>>>>again once the current mission is complete. Looks like they are worried
>>>>over
>>>>>the external tank foam yet again.
>
> And with good reason. Big chunks of something were spotted on the initial
> launch video - the live feed I was watching replaed it within about 10
> minute of the launch. Nature seemed not to have noticed.
>>>>>
>>>>>Does make you wonder why the insulation wasn't put on the inside of the
>>>>>structure in the first place.
>
> Too difficult to install it internally in a pressure vessel.
>
>>>>Didn't they used to paint the external tank. Would this help keep the
>>>>foam
>>>>in place, at the cost of weight?
>
> The external foam system is a lot more complicated than you imagine. The
> leading edges of the tank (and the bits near the engines) are subject to
> serious aerodynamic and thermal stresses. Several foams are used.
>>>
>>>All I know is that an aeroplane has its cabin insulation on the inside of
>>>the skin and my loft insulation is inside not stuck on the roof.
>>
>> However if you think on, your hot water tank (which like the external
>> tank, has to hold materials inside), is insulated on the outside, as is
>> the cold water supply cystern. In fact your 'loft insulation', is 'on'
>> the ceilings, and has the complete extra layer of the 'roof' outside it.
>
> It has to cope with thermal expansion/contraction over a huge range of
> temperatures and in an environment often at 100% humidity and weaknesses
> in the closed cell foam structure allow ice patches to form.
>>
>>>Its a design flaw and I'm betting that without a fundemental re-design
>>>they may have to live with it. I don't think paint would help as its
>>>breaking away from the outer surface of the tank. Could they perhaps fit
>>>something (like a giant condom) over the top end of the tank (where bits
>>>coming off are more likely to hit the Orbiter) to help hold the foam in
>>>place?
>>
>> The problem is the huge range of temperatures and pressures the 'condom'
>> would have to survive. The odds are that unless it is made of something
>> like aluminium, you would end up with bits of this falling off as well...
>
> The best solution for reentry is the old traditional ablative heat shield.
> Very robust, low tech and entirely protected from damage during launch.
>
>>>I think we may well have seen the last shuttle flight.
>
> Me too. And that is a pity since there is nothing even on the drawing
> board to replace it. The ISS I would happily dump into the ocean tomorrow
> so that space *science* and astronomy got more funding.
>
>> What puzzles me, is that they didn't expect this (maybe they did...). If
>> you watch the old Apollo launches, you have so much ice falling, ignoring
>> any 'insulation' materials, that damage has to be expected. Every shuttle
>> launch has had tile damage during take-off, what was exceptional in the
>> Columbia launch, was not that it occurred, but the size of the piece
>> involved, and that it managed to damage the leading edge structure (which
>> is much tougher than the 'tiles'). Something like an alloy 'net condom',
>> should have been possible, if necessary at the cost of one crew place, to
>> keep the maximum size of pieces involved down to reasonable limits...
>
> They did. There is some circumstantial evidence that the change to non-CFC
> blown foams for the bulk tank insulation may have made it slightly more
> brittle. OTOH some of the bits known to have fallen off in the past were
> manually applied still using CFC-11 blowing agent.
>
> NASA short report online at:
> http://spaceflight.nasa.gov/shuttle/rtf/otte/et_thermal_protection_fact_sheet.doc
>
> Intrinsically there is a very nasty problem that huge changes in
> temperature typically from 300K down to 20K for the LH2 tank has bad
> effects on plastic to metal bonding. If foam cell integrity gets
> compromised then cool spots develop and water ice ingress becomes an
> issue.
>
> Regards,
> Martin Brown

Hi Martin


I think you will find they did expect bits to hit the Shuttle, they even
developed simulation software to predict it. The problem was they didn't
think that it could do the sort of damage to the structure that it did. If
you saw any of the testing of the leading edge panels, they were rather
shocked by the damage created.

The real problem is the whole shuttle was built as cheaply as possible and
at a time when the technology was primative and the shuttle has chugged on
and on for years with these faults. NASA has had a lot of luck over that
time, but a 40% loss rate on the fleet would not be something an airline
would be proud of!!

Best to close it down and put the three remaining orbiters in museums before
they kill anyone else. The ISS is a white elephant anyway. Nice idea but
that money could be better spent on more interesting projects. Who wouldn't
like to see a rover sent to Europa for example?

Just out of interest anyone know if the Russians had the same problem with
their copy of the shuttle? I think it flew once?

Martin




.

Relevant Pages

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