No antennae radiate all the power fed to them!
 

On 11/2/2014 3:58 PM, wrote:
Lostgallifreyan wrote:
wrote in :

Apples and oranges; we already know what will happen if one were to
build an antenna from a superconductor.

Fire up EZNEC and set material loss to zero; done.


Yeah, anyone with a map could say a great deal about the shape of West Africa
based on ocean travel.

Again, apples and oranges as we know EXACTLY and in DETAIL what would happen.

My point isn't so much about antennas, as about
exploring the easy availability of cold environments for superconductors in
space.

Easy availability measured in thousands of dollars an ounce to get
stuff there.

Not having to lug heavy coolers up there might be an offer someone
cannot refuse, and that someone might come back with all kinds of
discoveries, things no models or predictions are going out there to find.

The only thing that makes a superconductor different is the lack of
resistance.

We already know exactly what that means and what we would do with them
if room temperature superconcductors were available.

Here are a couple of things: electric motors and generators that would
be very close to 100% efficient, small, light, and lossless power
transmission lines, lossless transformers, big honking magnets.


It's a little more than just no resistance. For instance,
superconductors will "reflect" (for lack of a better word) a magnetic
field. That's now a superconducting disk will levitate over a magnetic
field. So just setting the resistance to zero doesn't necessarily cut
it. There are other things to consider which EZNIC may not handle properly.

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No antennae radiate all the power fed to them!
 

On 11/2/2014 6:06 AM, Lostgallifreyan wrote:
Jeff wrote in :

...or looking at it another way the dissipation in the radiation
resistance is not in the form of heat it is the power radiated into space.


Well, I did say I didn't know the terminology. On the other hand, I'm not
talking about antenna's radiation resistance. The only thing I'm sure of here
is that some body, at some temperature, can not emit heat faster than some
rate, and that superconductors in space will warm up too fast to stay
superconducting without support to cool them.

What is going to warm them up? The point of using them for the antenna
is because they have no resistance which means the signal is not turned
into heat.

This discussion looked like it had strayed some way from the earlier talk of
antennas and radiation resistance.

No, the topic was antenna radiating all the power fed to them. The
other two things that happen to the power is to be reflected back to the
source or dissipated as heat. Superconductors eliminate the heat
dissipation.

--

Rick

No antennae radiate all the power fed to them!
 

rickman wrote in :

You are aware that a standing wave still moves up and down, no?

Sorry about this.. even after my last post, I have a thought I can't drop
easily. A few years ago someone showed me a speaker cone in a video, driven
by AC current, and it had ferrofluid on it, but I think there was soem
comment that any thixotropic fluid will do. It had peaks and troughs, in a
sort of semi-random 2D form across the cone that held it. These peaks and
troughs did not oscillate up and down on the spot, they stood rigid as
merings peaks after drying in an oven. (Actually they did shift a little, but
not a lot, and that was mainly due to erratic vibrations in the whole
doings.) Anyway, would that effect not also be called a standing wave?

No antennae radiate all the power fed to them!
 

Jerry Stuckle wrote in news:m36bbu$pou$1@dont-
email.me:

I also don't know how steerable the solar panels are - but I would
expect them to be somewhat steerable.

That;s something I did see once, I think on a BBC article. They are a bit
like louvre windows, fairly limited movement of each panel on its own axis,
but enoughm given the gaps between their edges. And I think an entire branch
array can be rotated on its own axis too, but I'm less sure about that bit.

No antennae radiate all the power fed to them!
 

On 11/2/2014 4:55 PM, wrote:
Lostgallifreyan wrote:
wrote in :

There is no undiscovered magic in superconductors.

There was no magic in any of the materials used for Gemini and Apollo either,
but countelss things were learned just by using them out there.

Care to name a few specifically from Genini and Apollo?

And BTW, 99.9% of the materials used is aluminum.



Much of the medical monitoring technology came out of the early space
program, for one thing. So did advances in propulsion systems and
remote controls (more than just model planes and cars) for another.

--
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Remove the "x" from my email address
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No antennae radiate all the power fed to them!
 

rickman wrote in :

No, the topic was antenna radiating all the power fed to them.

Specifically, doing it efficiently. :) Just being hard to match.

Never mind the other bits, beginning to look like old ground already today.
What I might be missing about my comment on some body at some temperature
being limited in its rate of dissipation might be flawed anyway. Never mind
the risk of confusion between an antenna's radiation resistance and what I'm
trying to get at, there's another angle to this...

Am I wrong? Could it be that just as an antenna is efficient regardless of
size, IF you can feed it all the energy you're trying to transmit, is it also
true that regardless of size, that hot body will also equally transmit all
its heat? In other words, is the 'limit' analogous to matching, as in getting
the heat from the bulk volume out to its surface?

I'm hoping that answer(s) to this one might help solve a heap of confusion
for me..

No antennae radiate all the power fed to them!
 

On 11/2/2014 3:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m36209$kk3$1@dont-
email.me:

No, I don't think any part of the ISS is in "constant shadow". I
believe it rotates as it orbits the earth, and different parts of it are
in the shade at different times. I could be wrong, though - I've never
been there :)


Fair enough. I know that Apollo used to do the 'barbeque roll', but as far as
I know there's less need of it on the ISS for whatever reason. Maybe they use
the solar panels for shade part of the time, there's a lot of those... Or
maybe it's in Earth's shadow often enough to get by... Or maybe it rolls
constantly and I just had no idea.

I think the barbeque effect is because the capsule does not spread the
heat very evenly. The temperature of space (including the sun's
radiation) at earth's orbit is about the temperature of the surface of
the earth. Here is the page where I found this.

http://www.wwheaton.com/waw/mad/mad5.html
*****
For the special case of a perfectly black, highly conductive sphere in
the Solar System a distance R from the Sun, absorbing solar radiation
from one side, but radiating in all directions equally, it turns out
that the temperature drops with distance from the Sun as the square root
of 1/R:

T = 277 K (1 AU/R)½
*****

Assuming this equation is correct, the temperature of the object
described is just 4 °C at Earth's orbit. Of course the earth is warmer
because it is warmed from the inside as well as from the sun.

Somewhere around 13 AUs the temperature reaches 77 °K, the boiling point
of N2, which is much cooler than the critical temperature of a number of
superconductors.

--

Rick

No antennae radiate all the power fed to them!
 

rickman wrote in :

I think the barbeque effect is because the capsule does not spread the
heat very evenly. The temperature of space (including the sun's
radiation) at earth's orbit is about the temperature of the surface of
the earth.

That fits. I think they were just averaging it on that basic principle. (And
specifically, protecting the oxygen tanks above pretty much all else, if I
remember the books right, I read a few at one point, over ten years ago).

No antennae radiate all the power fed to them!
 

rickman wrote in :

Somewhere around 13 AUs the temperature reaches 77 °K, the boiling point
of N2, which is much cooler than the critical temperature of a number of
superconductors.


Ok, but that goes with what I was saying about variable margins. Until there
is much going on out that far, there will likely be a development more
locally, of higher temperature materials that are useful enough somehow to
justify putting them there. I don't doubt that shading them will help but
that is more weight to haul out there too, so experiment will likely be
needed to find compromises. The modelling might be harder than just doing
it, starting small.

No antennae radiate all the power fed to them!
 

On 11/2/2014 5:49 PM, rickman wrote:
On 11/2/2014 3:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m36209$kk3$1@dont-
email.me:

No, I don't think any part of the ISS is in "constant shadow". I
believe it rotates as it orbits the earth, and different parts of it are
in the shade at different times. I could be wrong, though - I've never
been there :)


Fair enough. I know that Apollo used to do the 'barbeque roll', but as
far as
I know there's less need of it on the ISS for whatever reason. Maybe
they use
the solar panels for shade part of the time, there's a lot of those... Or
maybe it's in Earth's shadow often enough to get by... Or maybe it rolls
constantly and I just had no idea.

I think the barbeque effect is because the capsule does not spread the
heat very evenly. The temperature of space (including the sun's
radiation) at earth's orbit is about the temperature of the surface of
the earth. Here is the page where I found this.

http://www.wwheaton.com/waw/mad/mad5.html
*****
For the special case of a perfectly black, highly conductive sphere in
the Solar System a distance R from the Sun, absorbing solar radiation
from one side, but radiating in all directions equally, it turns out
that the temperature drops with distance from the Sun as the square root
of 1/R:

T = 277 K (1 AU/R)½
*****

Assuming this equation is correct, the temperature of the object
described is just 4 °C at Earth's orbit. Of course the earth is warmer
because it is warmed from the inside as well as from the sun.


That's part of it. But it's also because the Earth doesn't radiate all
that well, either. It holds a fair amount of the heat that strikes it.
Air is a great insulator :)

Somewhere around 13 AUs the temperature reaches 77 °K, the boiling point
of N2, which is much cooler than the critical temperature of a number of
superconductors.


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