Comments and questions

Last night, I guess afternoon your time, I listened to the revealing of the
ongoing foam problem and then went to bed. Waking this morning, a number of
questions and comments were in my mind, so I'll post them here.

Firstly,

The type of foam was changed at some point in the past. is there any
evidence that this foam did a better job of adhering to the tank during the
rigours of launch, or is it, as was mooted in the conference, simply that
the technology to see this was not there at the start.

It is fairly obvious that the ramp area has to be defoamed, as this has got
to be an area whichsuffers more at launch than other places.

Now if we accept that foam has always come off, and again as was said last
night, the tiles are always damaged, and have been designed with a margin
for this, then it seems to me that one mitigation strategy would be to make
sure that fragmentation of the foam occurs in the airstreams, maybe by
changing the formulation of the foam.

Another theory I had was the flexing theory. At launch there is flexing and
stresses on parts which is obviously not fully understood, and with the cold
temperature of some areas, and associated shrinkage and maybe brittlisation
of the foam, then this could account for the sheering off of large pieces.

Is there some form of turbulence between the Orbiter and tank that
effectively sucks at the underside of the Orbiter and tank face facing it?
I'm thinking of how the tile fractured with no impact.

There is certainly some strange airflow around the nozzles of the SRBs as
ahs been noted previously, which has made some feel that there was a seal
burn through, which, having read about how the thing is constructed now,
would seem to be almost impossible.

It the foam that came off was removed just prior to launch, would it affect
performance in any way. I just wondered that if it is indeed airflow
related, aggravated by temperature and stresses, then it might be better to
remove it, assuming Ice build up was not even worse.

Another thought came to mind that suggested vibrations and resonances with
certain tank content amounts could shake foam free.


I note also that the ground the shuttle, dump the station killjoys are out
in force on here again. I do get the feeling that no matter what anyone did,
these people would find a problem with it. As I only know too well, we have
to live in the world as it is. Of course with the benefit of hindsight,
things would be done differently, but that is how you learn. In the
meantime, if you want to keep on doing what you do, you need to just use
what you have.

I'd imagine all the knowledge which is being learned here, particularly on
how to model systems realistically, and test them properly without simply
flying it, will be invaluable in the next generation of vehicles, which your
vehicle will be a long way away with crew on board when a problem occurs.
You need the systems etc, in place to deal with this.

You also of course needed a design philosophy which makes sure that
unexplained things are explained before you fly... Did I mention sensors?
:-)

It is often the case that the most simple of systems, like insulating a
tank, can give the most grief.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
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Brian Gaff wrote:

snip


Another theory I had was the flexing theory. At launch there is flexing and
stresses on parts which is obviously not fully understood, and with the cold
temperature of some areas, and associated shrinkage and maybe brittlisation
of the foam, then this could account for the sheering off of large pieces.

Yep, those are very hard problems to deal with. Possibly unsolvable.


snip


I note also that the ground the shuttle, dump the station killjoys are out
in force on here again.

You could also say that up until now, the Keep Flying the Shuttle No
Matter What faction has held the day against all odds and even though
the premises upon which the shuttle was justified have never been realized.


You also of course needed a design philosophy which makes sure that
unexplained things are explained before you fly... Did I mention sensors?
:-)

Indeed. In the modern world of design, closed loop systems based on
sensors and real-time correction loops along with telemetric datalogging
and analysis are standard ways of designing high end systems. Little
of this was feasible in the days when the shuttle was first designed and
I doubt that it was put fully into place are the decades of retrofitting
and tinker.

It is long, long, long past the time when a clean sheet of paper design
and implementation are needed.


It is often the case that the most simple of systems, like insulating a
tank, can give the most grief.

True enough. Generally this is because of simple-minded, wrong going-in
assumptions that doing these things is simple. Dealing with the
differential expansion and contraction of dissimilar materials under
intense conditions is a fiendishly hard thing to do. Insulating the
tank with spray on foam and expecting that stuff to all stay in place
under the extreme conditions it goes through may simply not be possible.


John

On Thu, 28 Jul 2005 08:20:52 GMT, John Horner
wrote:

Indeed. In the modern world of design, closed loop systems based on
sensors and real-time correction loops along with telemetric datalogging
and analysis are standard ways of designing high end systems. Little
of this was feasible in the days when the shuttle was first designed and
I doubt that it was put fully into place are the decades of retrofitting
and tinker.

You are joking, aren't you? Closed-loop systems were first flown in
the '30s (Lawrence Sperry and his wing leveler), although they'd been
used on steam engines long before that, being as old as the railways.

The '50s X-15 was fly-by-wire and had a finite-state machine for its
FCS. Apollo used a digital FCS, as did the F-8 DFBW airplane. The
DFBW used Apollo computers for the original flight phase and Orbiter
computers for the second flight phase. The LLRV/LLTV FCS was analog,
though.

Mary

--
Mary Shafer Retired aerospace research engineer
We didn't just do weird stuff at Dryden, we wrote reports about it.
or