On Wed, 5 May 2004 [EMAIL PROTECTED] wrote:
> > pressure-fed engines, typically makes excellent structure with little or
> > no added stiffening. (Witness the classical Atlas, whose tanks are just
> > sheet-metal balloons, with essentially no strength of their own.)
>
> "Excellent structure"? I doubt it. If nasa did it, it's wrong.
Learn a little history, please. The Atlas tanks were invented by Karel
Bossart at Convair, before NASA even existed. (And the idea goes back
farther, to Oberth if I recall correctly.)
> When you attach a piece of rocket structure to a stressed metal balloon
> fuselage, you create stress failure points.
Not if you do it right... (Mind you, Convair did say that a large part of
their balloon-tank design manual was devoted to the complex details of
attaching external hardware properly.)
> Simply put, a tank needs internal reinforcement to be a strong fuselage.
> You don't want the ship breaking apart when strong aero dynamic turning
> moments are applied.
Again, it is good to learn a little history.
After Atlas had been flying for a while, Convair/GD got permission to
instrument a couple of them thoroughly, as they'd gotten hints that the
bird was stronger than anyone had expected. By sheer luck (bad for the
payload owner, good for GD), one of the instrumented Atlases had a
worst-case failure, an outboard-engine failure around max Q. The stress
instrumentation went off-scale at over 150% of the design ultimate load,
with the tanks and attachments still holding up fine. A second or two
later, the payload fairing came apart, and the RSO lost patience and
pressed his button. The tanks lost pressure only when the destruct
charges tore them open.
No conventional flightweight structure could have equaled that.
Now mind you, I am not convinced that balloon tanks, in the strict sense
of the term, are a good choice for reusable rockets. Not because they
aren't strong, but because they complicate maintenance and handling on the
ground. But relying on pressurization for a majority of the strength
needed in flight is perfectly legitimate -- in fact, most big liquid-fuel
rockets do that.
Henry Spencer
[EMAIL PROTECTED]
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