Spin-cast a mirror in space?

hmm... meniscus. will if you have air pressure - which you could do, you could put it in a pressurized container - i thing for sufficiently narrow tubes, it's a sphere. not sure what happens in large tubes, though. i feel it would be flatter in the middle.

another way you could create a sphere - two other ways - is using either the electric or magnetic force.

somehow charge the liquid and have a charged ball at the desired focal point

or likewise for magnetic. though the ball at the focal point - you're not going to have a spherical field.

but back to the meniscus thing - i'm reminded of a bubble. it forms spherical between two gases because that minimizes gibbs free energy.

maybe instead of even spinning, you could just essentially blow a bubble, then let it solidify.


On Sunday, May 22, 2016 at 9:35:03 AM UTC-5, Robert Clark wrote:
Found an interesting article after a Google search:

The shape of a liquid surface in a uniformly rotating cylinder in the
presence of surface tension.
http://maeresearch.ucsd.edu/~vlubard...s/Acta2013.pdf

This calculates the shape of the meniscus under both gravity and zero
gravity.

A topic I'm interested in is whether the method of making large parabolic
mirrors on Earth by rotating the glass in molten form to form a parabolic
meniscus then allowing it to solidify can also work in space.

This will have an advantage over transporting the already formed mirrors
into space because for large mirrors you have to concerned about the size of
the rocket fairing. But in fact in zero g you would have an advantage in
that you wouldn't have to worry about the mass and cost of the support
structures and of the mirror deforming under it's own weight.

You could emulate the Earth's gravity during the formation stage in space
by using either centrifugal force due to rotation around a second axis or by
using linear acceleration. Rotation around a second axis though could create
instabilities. On the other hand doing a linear acceleration for the weeks
of cooling time would require a prohibitive amount of propellant.

That is why I wondered if it is possible to do in zero gravity just using a
rotation around a single axis as on Earth. In the article ther were able to
only solve numerically the equations for the zero gravity case. So my
questions is, is it possible to set the starting parameters such that the
meniscus shape is a good approximation to parabolic? Note it would also be
sufficient to get a good approximation to a spherical surface since then you
can use a combination of spherical mirrors to cancel out the distortions due
to a non-parabolic surface:

Spherical Aberration.
https://starizona.com/acb/basics/equ...spherical.aspx

It may be possible to get it to work no matter the shape of the curved
meniscus by using a mirror of similar shape to cancel out the aberrations
due to the non-parabolic shape. For instance, the Hubble uses a combination
of hyperbolic mirrors to cancel out aberrations.



Bob Clark

Dear happy:

On Tuesday, May 24, 2016 at 11:54:09 AM UTC-7, wrote:
hmm... meniscus. will if you have air pressure -
which you could do, you could put it in a pressurized
container - i thing for sufficiently narrow tubes,
it's a sphere. not sure what happens in large tubes,
though. i feel it would be flatter in the middle.

Meniscus will be a serious problem in vacuum, since any liquid should act more like a superfluid.

....
but back to the meniscus thing - i'm reminded
of a bubble. it forms spherical between two gases
because that minimizes gibbs free energy.

But bubbles in microgravity do not center, do not necessarily leave, and a sphere is formed (given enough time for oscillations to dampen.

maybe instead of even spinning, you could just
essentially blow a bubble, then let it solidify.

.... having removed all the gases...

David A. Smith

On Tuesday, May 24, 2016 at 2:54:58 PM UTC-5, dlzc wrote:

But bubbles in microgravity do not center, do not necessarily leave, and a sphere is formed (given enough time for oscillations to dampen.

they wouldn't be free-floating, they'd be on a lip, like when you blow bubbles.

| |
|= ---- =|
| |



... having removed all the gases...

why would a tiny amount of gas be a problem?

do they make mirrors in an absolute vacuum on earth?

I like these ideas. About the magnetic field idea perhaps we could have a
flat plate magnet at the bottom. Instead of the entire fluid being charged
or magnetized, perhaps we could have a flexible metallic cover above the
fluid that would then apply a downward force.

Bob Clark

----------------------------------------------------------------------------------------------------------------------------------
Finally, nanotechnology can now fulfill its potential to revolutionize
21st-century technology, from the space elevator, to private, orbital
launchers, to 'flying cars'.
This crowdfunding campaign is to prove it:

Nanotech: from air to space.
https://www.indiegogo.com/projects/n...ce/x/13319568/
----------------------------------------------------------------------------------------------------------------------------------
wrote in message
...

hmm... meniscus. will if you have air pressure - which you could do, you
could put it in a pressurized container - i thing for sufficiently narrow
tubes, it's a sphere. not sure what happens in large tubes, though. i feel
it would be flatter in the middle.
another way you could create a sphere - two other ways - is using either the
electric or magnetic force.
somehow charge the liquid and have a charged ball at the desired focal point
or likewise for magnetic. though the ball at the focal point - you're not
going to have a spherical field.
but back to the meniscus thing - i'm reminded of a bubble. it forms
spherical between two gases because that minimizes gibbs free energy.
maybe instead of even spinning, you could just essentially blow a bubble,
then let it solidify.


On Sunday, May 22, 2016 at 9:35:03 AM UTC-5, Robert Clark wrote:
Found an interesting article after a Google search:

The shape of a liquid surface in a uniformly rotating cylinder in the
presence of surface tension.
http://maeresearch.ucsd.edu/~vlubard...s/Acta2013.pdf

This calculates the shape of the meniscus under both gravity and zero
gravity.

A topic I'm interested in is whether the method of making large parabolic
mirrors on Earth by rotating the glass in molten form to form a parabolic
meniscus then allowing it to solidify can also work in space.

This will have an advantage over transporting the already formed mirrors
into space because for large mirrors you have to concerned about the size
of
the rocket fairing. But in fact in zero g you would have an advantage in
that you wouldn't have to worry about the mass and cost of the support
structures and of the mirror deforming under it's own weight.

You could emulate the Earth's gravity during the formation stage in
space
by using either centrifugal force due to rotation around a second axis or
by
using linear acceleration. Rotation around a second axis though could
create
instabilities. On the other hand doing a linear acceleration for the weeks
of cooling time would require a prohibitive amount of propellant.

That is why I wondered if it is possible to do in zero gravity just using
a
rotation around a single axis as on Earth. In the article ther were able
to
only solve numerically the equations for the zero gravity case. So my
questions is, is it possible to set the starting parameters such that the
meniscus shape is a good approximation to parabolic? Note it would also be
sufficient to get a good approximation to a spherical surface since then
you
can use a combination of spherical mirrors to cancel out the distortions
due
to a non-parabolic surface:

Spherical Aberration.
https://starizona.com/acb/basics/equ...spherical.aspx

It may be possible to get it to work no matter the shape of the curved
meniscus by using a mirror of similar shape to cancel out the aberrations
due to the non-parabolic shape. For instance, the Hubble uses a
combination
of hyperbolic mirrors to cancel out aberrations.



Bob Clark



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

Dear happy:

On Tuesday, May 24, 2016 at 3:05:12 PM UTC-7, wrote:
On Tuesday, May 24, 2016 at 2:54:58 PM UTC-5, dlzc wrote:

But bubbles in microgravity do not center, do not
necessarily leave, and a sphere is formed (given
enough time for oscillations to dampen.

they wouldn't be free-floating, they'd be on a lip,
like when you blow bubbles.

No. There are videos of microgravity taken on the ISS, and bubbles formed in balls of liquid do not always "gravitate upwards or outwards" and leave.

... having removed all the gases...

why would a tiny amount of gas be a problem?

Void spaces. Defects in the optics, if you used them as lenses. As mirror frames, no problem.

do they make mirrors in an absolute vacuum on earth?

They have gravity to allow bubbles to rise, and leave.

David A. Smith

Dear Robert Clark:

On Tuesday, May 24, 2016 at 4:54:49 PM UTC-7, Robert Clark wrote:
I like these ideas. About the magnetic field idea
perhaps we could have a flat plate magnet at the
bottom. Instead of the entire fluid being charged
or magnetized, perhaps we could have a flexible
metallic cover above the fluid that would then
apply a downward force.

Or use magnetic induction, to induce eddy currents, depending on the fluid.

David A. Smith

Thanks for that. They discuss inflatable mirrors. According to the refs,
they should work for infrared wavelengths but couldn't maintain sufficient
accuracy for optical wavelengths. They be tested though if they can form
large infrared mirrors. Is there a limit to their size? Could they be made
large enough to image extrasolar planets in the infrared?

Bob Clark

----------------------------------------------------------------------------------------------------------------------------------
Finally, nanotechnology can now fulfill its potential to revolutionize
21st-century technology, from the space elevator, to private, orbital
launchers, to 'flying cars'.
This crowdfunding campaign is to prove it:

Nanotech: from air to space.
https://www.indiegogo.com/projects/n...ce/x/13319568/
----------------------------------------------------------------------------------------------------------------------------------
"William Mook" wrote in message
...

http://www.techbriefs.com/component/...machinery/7062

http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf

https://www.google.com/url?sa=t&rct=...73rrKo2WfKxvxg

On Tuesday, May 24, 2016 at 7:07:55 PM UTC-5, dlzc wrote:
Dear happy:

On Tuesday, May 24, 2016 at 3:05:12 PM UTC-7, wrote:
On Tuesday, May 24, 2016 at 2:54:58 PM UTC-5, dlzc wrote:

But bubbles in microgravity do not center, do not
necessarily leave, and a sphere is formed (given
enough time for oscillations to dampen.

they wouldn't be free-floating, they'd be on a lip,
like when you blow bubbles.

No. There are videos of microgravity taken on the ISS, and bubbles formed in balls of liquid do not always "gravitate upwards or outwards" and leave.

makes sense, if you do the process very slowly and carefully (such as injecting liquid slowly in a ring, letting adhesion guide it, and keeping pressure variations minimal, you can minimize this.

otherwise not sure how one'd pull the bubbles out without a mass-dependant force


... having removed all the gases...

why would a tiny amount of gas be a problem?

Void spaces. Defects in the optics, if you used them as lenses. As mirror frames, no problem.

it would be a mirror. so i guess no problem them. no surface defects, 'cause a buble on the surface is not a bubble.


do they make mirrors in an absolute vacuum on earth?

They have gravity to allow bubbles to rise, and leave.

touche.


David A. Smith