Re: 1teraflops cell processor possible?

On 26 Nov 2003 22:31:19 -0800, [EMAIL PROTECTED] (George William
Herbert) wrote:

>Robert Myers  <[EMAIL PROTECTED]> wrote:
>>>> Sorry, Del, but Blue Gene makes about as much sense as the Space
>>>> Shuttle did.
>>>
>>>Actually the space shuttle made sense.  It just didn't work out like
>>>they envisioned.  It was to be a prototype for a next generation of
>>>reusable orbital vehicles, as I recall.  Instead folks lost interest and
>>>the prototype became the final.  How like computer architecture is that?
>>
>>Well, no it didn't, and it still doesn't.  Trying to fly something
>>with wings to the ground from orbit and to get it to land like an
>>airplane is a dumb, and, as we have learned, a very dangerous idea.  
>>
<snip>
>
>Uhhhh.... ok.  You aren't an aerospace engineer or historian.
>And it shows.
>
<snip>
>
>I am an aerospace engineer and have designed re-entry
>vehicles (not that have flown, but done concept design
>work) and I have *no* idea what you are talking about
>regarding the lifting body shape not being 'safe'.

I am an aerospace engineer.  I am not a historian.  I have a pretty
good idea of the state of re-entry vehicle engineering was when the
shuttle first flew because I was involved in it at the time.

>There are tradeoffs from ablative thermal protection
>systems (heavier than tiles and metallic shingles and
>the like, but can withstand higher peak loads) that
>make them work better with capsules.  But there is no
>law of nature that reusable thermal protection is unsafe
>or that lifting re-entry / lifting bodies are somehow
>inherently unsafe.  I say this as a capsule bigot and
>someone who pushed very hard for OSP to consider capsules.
>Capsules are cheaper.  Safety can be done right or wrong
>with either capsules or lifting bodies.
>

There may be no law of nature, but the engineering constraints are
pretty obvious.

One of the proposals for providing a lifeboat for present-day
astronauts is to pull one of the Apollo vehicles out of a museum,
modernize the electronics, put a new ablative heat shield on it, and
fly it again.

You can't put a new ablative heat shield on the shuttle because there
isn't one.  If you allow a surface that you later intend to use like a
wing to cool iself by ablation, you are left with the aerodynamics of
whatever shape the erosion that occurred during reentry produced.  You
can't even allow the surface to warp and ripple unpredictably, which
is why we have gaps in these foam tiles that are glued onto felt.
When the man on the street hears about the design details of shuttle
tiles, his common sense reaction is, "You've got to be kidding me."
It all comes from the impossible constraints produced by trying to put
an airplane wing through re-entry.

The aerodynamics of a capsule are pretty simple, and you can allow the
surface that takes the heat to ablate.  It works, it is very
forgiving, and the aerodynamic surface you are counting on to get you
back to sea level at a reasonable speed is a parachute that was safely
stowed during reentry.  By comparison, those damn foam tiles were
falling off faster than they could glue them back on at one point. 

http://www.house.gov/science/hearings/space03/may08/myers.htm

Testimony to the House Subcommittee on Space and Aeronautics

On the Assessment of Apollo Hardware for CRV and CTV
by Dale Myers (no relation)
May 8, 2003

Although the team was not asked to compare the capsules to winged
vehicles, and we did not, I have some comments relative to wings vs.
capsules. 

The Apollo Program never had a parachute failure in operation,
although we had failures during the test program.  We had one
parachute fail due to N2O4 leaking onto the shrouds, but the vehicle
landed safely on two parachutes.

The Shuttle has had a wing failure, but the failure was apparently
caused by the foam insulation from the tank.  Shuttle runway landings
have been 100% successful.

It appears to me that the robust launch escape system of Apollo, which
worked over a wide range from the launch pad to high altitude, will be
hard to beat in a winged vehicle.

This Apollo based system, without aerodynamic controls, wings, and
landing gear is clearly simpler.

The ablative replaceable heatshield is simpler to build and install
than the corresponding winged vehicle thermal protection system. We
already know the thermal distribution on the vehicle.  With a land
landing, a reusable heatshield might apply to the Apollo system.

<snip>

If all things were equal, I’d choose winged vehicles.  Unfortunately,
they are not known to be equal, and that’s why the team recommended a
thorough study of the Apollo CM/SM as a CRV/CTV.

<end quotation>

CRV/CTV=Crew rescue vehicle, crew transfer vehicle for the orbiting
space station.

As it is, Mr. Myers (again, no relation) is being very kind about
those fragile wings.  You can put more engineering effort into the
foam insulation on the external fuel tank, but shuttle tiles have
fallen off in previous flights, and they will continue to fall off if
the current shuttle thermal management system continues to be used.

>
>The comments regarding pilots and flying things are off
>base as well.  To reuse a large vehicle it has to be
>flown to a relatively low velocity pinpoint landing.

There is no reason that I know of that an Apollo-type system cannot be
used to meet all future needs of the US space program.  Vehicles like
the shuttle never have and, in my opinion, never will get us beyond
LEO.  The real reason capsules won't be given serious consideration is
the one I mentioned.  The blue suits want an airplane.  Have an
apoplectic fit if you like, but that's how it works.

<snip>
>
>If you would like to continue this thread,
>the sci.space.policy and sci.space.shuttle newsgroups
>might be more appropriate.  
>
I have very little interest in pursuing this discussion.  I answered
at length here because you, in effect, said that I did not know what I
was talking about here.

RM