# [ExI] question re "honkin' big cannon" space launch

Jeff Davis jrd1415 at gmail.com
Sat Mar 7 02:48:33 UTC 2009

```On Thu, Mar 5, 2009 at 2:53 PM, spike <spike66 at att.net> wrote:

> Your post brings back fond memories from the 1980s when I was doing a bunch
> of these calculations.

>>  I figured if the nose cone was pointy enough, then the
>> acceleration of the surrounding air molecules could be kept
>> low enough to get around those difficulties

> At the time I mighta mentioned something about hitting max Q (maximum
> dynamic pressure) at the exit from the barrel.

>I found that the projectile hits max Q before it reaches the end of the tube,...
>  But I had an idea...put a cap on the end of
> the tube, then evacuate the tube to about .01 atm, then open the cap just
> before the projectile gets there.

To the extent that I dealt with this issue, I applied a similar
solution.  A concave
foil seal over the tube end, as thin as possible, to be pierced by the
"pointy" end
as the vehicle exits the tube.

However, to avoid talking at cross purposes, let me specify more of
the details of
my proposed launch system.

First, I dispensed with the gun notion almost immediately, retaining
only the tube,
and my tube was derived from a 1965 Scientific American article
(August, I think)
about an "advanced" (back then) transport system employing trains in evacuated
tubes.  Loved that article.  Have spent many, many hours in a blissful
reverie musing thereon.

Anyway, the tube, connects Asia to  N &  S  America, runs along north of the
equator and is dual use (if possible) as terrestrial transport and
space launch.
Starting as far west as necessary to allow both human-tolerable levels
of acceleration
and reduced power requirements, the space vehicle would accelerate
eastward, and at
some point be shunted from the terrestrial transport tube into the
leave-the-planet tube,
the end of which would be elevated to the appropriate altitude.
Appropriate here means
as low as possible in order to minimize the size of the elevating
structure, which of course
is mega big, but high enough to reduce the maximum dynamic pressure to
a managable level.

> Jeff, I don't know if the previous was helpful...

It was fun, but now it's time to move on.

The mountain method and the space pier are both compression
structures.  I'd like you all to
consider an inflated, ie  tension, structure, like a giant flexible
plastic dome.  One can easily
see how such a dome, air tight and its edge anchored to the ground
will have its apex way up
high.  Make the dome big enough, and the apex starts to get waaaay up
there.  You see where
this is going. The exact configuration is yours to ponder.  I use a
dome in this example to make
the principle as clear and simple as possible.  My first notion was a
bit more complex: an
axially-bisected half-cone, lying in a west to east orientation, flat
on the plane of axial bisect,
with the bottom end of the cone capped by half a dome.  The dorsal
spine of the cone provides
the ramp for the launch tube.

There are questions in regard to this design which I cannot answer,
and many that I cannot see.
You know, "The unknown unknowns."  Perhaps you all would enjoy
fiddling with this.

Some of my thoughts:

I believe that the tensile strength required for the cone material is
easily within reach of conventional
materials.

Trade winds can inflate the structure.

What will it take for the structure to withstand the weather?  And how
will so large a structure in the
eastern Pacific effect the weather?

In light of decrease in gas pressure with altitude can the stucture
as envisioned be inflated to launch altitude?  If not, can the problem
be solved
by a revised design with multiple separate compartments piggy-backed
on one another?

I think that's enough for y'all to chew on for a while(or dismiss as silly).

As for me, I'm retired and have plenty of time to devote to such musings.

Hope you're all doing well.

Best, Jeff Davis

"When I am working on a problem I never think about beauty.
I only think about how to solve the
problem. But when
I have finished, if the solution is
not beautiful, I know it is wrong."
- Buckminster Fuller

```

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