[ExI] structural scale dependence, was: RE: IQ and beauty

spike spike66 at att.net
Wed Oct 21 15:59:55 UTC 2015



From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Dave Sill

>>Indeed sir?


>…Sorry, don't know what I was thinking. :-) Um...cat walked across my keyboard?




My cat did stuff like that too.  Third time it happened, she was banished from using the computer and sent to live the outdoors.


The whole notion lets me jump off to another unrelated topic not having to do with antlers (although that has been a cool discussion from which I learned much.)  


It appears our future in space is dependent upon getting launch costs down because the old LOX/kerosene and LOX/H2 stages will not advance much.  They were fairly mature fifty years ago.  To move ahead we need an air-breathing first stage.  You can do the calcs a hundred different ways and get the same solution: to go hypersonic while still in the atmosphere, you need to cool the air downstream of the bow shock, and to do that requires an extraordinary heat exchanger, and every way I have seen or imagined to do that requires scaling an ordinary heat exchanger way down, waaaaaay down, to increase the surface area to volume ratio, which makes it very delicate, nowhere near robust enough to carry the load.


OK so the Brits are claiming they did it or can do it.  I was skeptical of the claim, but I have seen something that gives me hope, an experiment you can reproduce at home.  Find some out-of-the-way thing in the yard which has spider webs on it, then get your garden hose and spray the webs.  Notice even a high velocity spray doesn’t tear down the web.  It is hard to remove spider webs with a garden hose, even one with a good nozzle on it.  Do try it, see for yourself.


Spider web has a much higher specific strength than metals and are more flexible of course.  But if you do the scaling calcs, you see that something is going non-linear somewhere once you get down far enough.  The observation gives me hope that the Brits are right: perhaps a heat exchanger with tiny enough tubing really can survive and operate (somehow) in the violent chaos downstream of a shock wave, like a spider web in a blast from the garden hose.


If it is true, we can do all those holy grail visions: create a single stage to orbit, or a good two-stage-everything-recoverable lifter, send the cost of launch to LEO way down, realize Keith’s dream of space based solar power (which eventually results in world peace and prosperity) all of that cool dreamy stuff, we can do it all.  


We know how to guide and control big structures in orbit, we know how to transmit  it from there and recover the energy on the ground, we can set it up high enough that space junk won’t spoil our day.  All we still can’t do is put it up there cheaply enough.  The Brits are claiming they can.  Those guys are known for doing their calcs right and telling the truth.  Let’s hope they are doing so in this case.


Is this a fun time to be alive, or what?




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