Re: How Rockets Differ From Jets

Brad Guth wrote:
> tomcat,
> I have some tile attachment ideas that'll remain reasonably flexible,
> allowing for a great deal of thermal expansion and somewhat self
> aligning as to help spread whatever thermal and physical stress, loaded
> upon the outer composite skin as somewhat Fish-Scale like applications,
> using a mechanical attachment method rather than some fancy bathtub
> cement that's hardly good enough for cooking a roast.


One of the reasons I am reluctant to include metal in the outer hull is
thermal expansion. Metals expand quite a bit, while composite does
not. Composite might expand some, however, and just how much I don't
know.

Your "fish scale" idea is interesting. There might be a problem with
'drag', however. It is also possible that it might help drag too. It
would introduce a turbulance into the airflow.

The fish scales would create, at least some, drag at the end of each
scale. The scales might, however, break loose the mach 1 shock wave as
well. Curved surfaces aid in shedding the 'sound barrier' shock wave.

Thermally speaking, your 'fish scale' idea would be good. It would put
most of the heat on the forward plates, shielding the plates behind
from a good deal of the heat, and air shock. And it would, as you
suggested, allow for thermal expansion.

Best might be a 'feathered scale' that only raises up slightly on the
overlap. Raises up so little that it would be scarcely noticable even
on close inspection. This fish scale concept would 'lock' the plates,
one on top of the other, strengthening the tile surface skin of the
spaceplane.

Fish swim through the water using -- fish scales -- for their outer
layer. It works for them. Water, by the way, is a lot like air under
intense pressure. Shake a scuba tank filled with compressed air and
you will hear it slosh about as if it were water. So, what works for
fish may work for man.


> I totally agree with this composite matrix approach, and don't worry
> about tile breakage if using my fish-scale method of application.


> Isn't there such a thing as being too stiff?
> How much heat can graphite and/or boron epoxy withstand?

Flexibility helps absorb shock. In this sense flexibility adds
strength. Because of an outer skin of brittle and breakable tile,
however, flexibility should be minimized.

Graphite epoxy is very stiff and hard when it hardens. If the material
it laminates is extremely strong and it is backed by stiff ribbing and
spine, then a minimal flexing of the hull should be possible.

> Here's a little more info coming our way, at least I'm hoping others
> will share and share alike without going into their usual need-to-know
> and/or taboo/nondisclosure mode. Just as well if you can provide some
> SME/SRB exhaust velocity and burn-time info would help us village
> idiots to understand a bit more of what's reasonably SME/SRB
> obtainable.

The spaceplane as I have described it shouldn't need a SRB. But every
little bit helps so to make it SRB capable from it's inception would be
a wise move.

The exhaust velocity of a SSME is roughly 450 ISP, which rates well
with most rocket engines of massive thrust. The burn time of a SSME is
almost unlimited except by it's fuel requirement of 1035 pounds per
second at full throttle. The spaceplane has to be a 'flying gas can'.

Burn time for orbital insertion of a spaceplane starting out with
roughly thrust to weight of 1:1 is, roughly, 4 minutes. Add 2 minutes
to that for the Moon and beyond. To add enough speed to get to Venus
or Mars in a couple of weeks, vice forever, add yet another 1 to 2
minutes of burn time.

I am certain that a 6 minute supply of fuel is possible with slush
tanks, though I have yet to work through the complex math of it for a
given spaceplane design. For one thing, I am not sure of just how much
extra the slush tanks hold, or the exact weight of the hydrogen per
gallon. Or, for that matter, the exact number of gallons per cubic
foot, or yard, or meter, or whatever.

So, the upshot is that I am supremely confident of SSTO, and still
groping a little with SSTP. This is why I would need an extra 3 years
to build a SSTP. Fuel requirements as well as radiation protection
would have to be solved.

There is no need, however, as certain 'groups' believe, that astronauts
will have to drink and eat their green and brown stuff. A 'well
designed', and plenty big, cargo hauler spaceplane could bring more
than an adequate supply of water, food, oxygen, and misc. supplies for
both the voyage and have room left over for an emergency supply in case
of maroonment.


tomcat

.