Re: How Rockets Differ From Jets


Brad Guth wrote:
> A really good Space plane's aerodynamic body (w/o wings) is going to
> create a fairly uniform pressure wave and subsequent vacuum drag
> coefficient that'll act somewhat like creating an extremely large
> friction buffer zone. Lots of sizable stuff arrives onto the surface of
> Earth without all that much thermal damage, the trick being to keep the
> mass per/m3 down to a dull roar. Besides, the outer-most layer of
> composite basalt would merely fuse back together and intentionally
> sluff off. Your "20,000+ deg. F.!" seems a wee bit on the high side,
> although obviously ceramic tiles and/or spray-on coatings of ceramics
> having a sufficient amount of CNT fibers involved should do quite
> nicely (perhaps a CNT fabric of ceramic beads, as beads having been
> cross threaded onto those spendy CNT fibers could be interesting).
>
> How many minutes each way do you plan upon being the the "hypersonic
> air travel" hot, hot, hot! mode?
>
> You can also use nearly frozen H2O2, which has a great deal more
> volumetric density and thus more thermal transfer capability than LH2.
> You could also sprey out an invisible cloud of Radon(Rn222) as per
> creating an extremely terrific refrigerant, thus creating a sub-frozen
> artificial atmospheric surround (just don't breath the stuff).


A reentry at 17,500 mph results in a maximum of about 7000 deg. F. A
reentry at 100,000+ deg. F. results in about 20,000+ deg. F.

Only ceramic can hold up at these temperatures. Corelle is tough and
can be cast in large thin sheets. Silica tiles are brittle and
delicate but can reflect heat better than anything. They are also very
light weight.

Very recently developed laser spraying of ceramic on to metal surfaces
is a real boost to the space industry. It came from the Department of
Atomic Energy. They are attempting to sell it to the steel industry
for blast furnaces.

The ceramic sprayed on metal is probably not thick enough to protect
the metal underneath against full reentry heat. But it does greatly
increase the metal's ability to withstand heat.

I see this ceramic spray as an added protection and it may help to get
the larger ceramic sheets to adhere. Ceramic on ceramic is probably an
easier cementing process than ceramic on metal. That was the purpose
of the laser spray in the first place. Cementing ceramic on metal
doesn't work too well. Ask NASA. The Shuttle tiles keep falling off
despite their best cements.

The hypersonic temperature problem is the greatest challenge to space
flight. Don't count on 'special' shockwaves or even air spikes to
bring air friction heat significantly down.

There is one trick, though, and that is to use air brakes made of solid
ceramic. Simply stick 3 large ovals into the bottom air flow and they
will take most of the heat sparing the rest of the bottom. Flying
saucers use this. I have seen them in the UFO pictures.

A more powerful air brake would be to stick a ceramic slab up into and
another slab down into the air flow. A lot of pressure on the slabs
but it would protect metal on the other side and slow the ship down
rapidly.

Reverse thrust with subsequent hydrogen cooling of the hull and
interior is great as long as the returning spaceship has a supply of
fuel left. Used with air brakes this should be the best solution of
all. Rapid slowing using a safe reverse thrust/air brake method would
stop the metal melting heat in a minute or so.

You would still need a super thermal capable hull anyway. Even 3 or 4
thousand degrees F. is enough to melt most things.


tomcat

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