Re: 1teraflops cell processor possible?

Robert Myers  <[EMAIL PROTECTED]> wrote:
>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.

You still don't.  Your arguments against winged reusability are
not well informed.

>[EMAIL PROTECTED] (George William Herbert) wrote:
>>[...]
>
>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. 

Yes, but wings which aren't perfectly even and smooth can fly
safely within certain parameters; wing icing is not immediately
lethal to aircraft, for example, though it is not friendly.
The Shuttle's detailed design and its wing loading / planform
etc are poorly optimized for the results of such a surface
roughening but generalizing to all winged RLV designs is
not reasonable.

If the surface ablation on the leading edge leads to unacceptable
roughness given your ablator and flight profile then an ejectable
ablator covering the leading edge is quite easy to engineer.

>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.

The tiles are both stiff and expand noticably when heated, while
the underlying structure is stiff and does not expand much because
it is not heated; the differential expansion would cause cracks
at peak re-entry heating if the tiles were a single solid sheet.

Surface warping is not critical.  Note that shuttle missions
have suffereed hundreds of tile losses or damaged tiles before
and not had any negative effects of note prior to the thermal
damage done when a whole leading edge RCC panel failed on Columbia
(we think).

>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 constraints are not impossible.

I am not a winged RLV fan, but your claims are not a fair
or accurate insight into the state of the art.
Nobody can do reasonable trade studies without
having an accurate view of the competing concepts
real feasibility, and your vehement rejection of
wings is not accurate or reasonable.

>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.

Yes.  Which is why I like capsules.

> 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
>[...]

The adhesion problems were solved to an acceptable level
years and years and years ago.

Tile adhesion was not adequately analyzed and engineered
during shuttle development, true.  Function of the schedule
and budget constraints and lack of any serious experimental
program to test the technologies.  

>[snipped quote from Apollo hardware reuse for NASA's
> Orbital Space Plane (OSP) program]
>
>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.

And they will continue to be a minor issue if the rates of tile
loss are kept to historical levels.  The design was done with
the assumption that they'd lose tiles; so far, the tile losses
haven't affected anything other than the turnaround time having
to put replacement tiles back on.

>>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.

I'm having to stop banging my head on the wall to finish my
post here.

Robert:

1) I design manned capsules, and not winged RLVs.
2) I had some discussions about participating in OSP.
3) If it were not for a family emergency I would have presented a
   paper on capsule OSPs at the Space Access conference last year.
4) Though I am not participating in OSP, I know people on the
   engineering teams that are.
5) Capsules were under consideration from day one.
6) Capsules are *most* of the designs that have survived the
   initial trade studies, and extremely positive comments about
   them have come out of both NASA and all the vendors.
7) The former head of the astronaut office, now working for one
   of the OSP vendors, is one of the loudest capsule proponents.
8) The odds of the OSP that flies being a capsule are very very high,
   at this point.

9) All of that said, I do not judge that you are fairly or
   reasonably assessing the advantages and disadvantages of
   wings on re-entry vehicles.  You are not showing any awareness
   of the alternative thermal protection systems or the actual
   detailed issues associated with the RCC/Tiles/blankets thermal
   protective system on the Shuttle, and have gotten a bunch of
   the details wrong on the tiles.

I do not like wings because they are expensive and heavy;
your arguments against them are kneejerking.


-george william herbert
[EMAIL PROTECTED]