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Spin-cast a mirror in space?



 
 
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  #1  
Old May 22nd 16, 03:35 PM posted to sci.astro,sci.physics,sci.space.policy
Robert Clark[_5_]
external usenet poster
 
Posts: 245
Default Spin-cast a mirror in space?

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


----------------------------------------------------------------------------------------------------------------------------------
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/
----------------------------------------------------------------------------------------------------------------------------------
"Robert Clark" wrote in message ...

Yes, that is how large mirrors are made on Earth. But the massive size of
the support equipment needed because of the Earth's gravity make them
impractical on Earth beyond a certain size for a single mirror, about 8
meters for a single mirror. Larger telescopes instead are made segmented.

The advantage of doing it in space though is you have zero gravity so you
would not need the massive support structures.

But you are correct about the instabilities. This is illustrated in this
video:

Torque free motion of a prolate axi-symmetric rigid body.
https://www.youtube.com/watch?v=s9wiRjUKctU

What's happening is when you have two rotations around axes both through a
common center, the result is a rotation around an axis at a diagonal line
between the two. It then has the appearance of gyrating wildly, while what
is really happening is it is rotating around an axis that is not on an axis
of symmetry of the body.

BTW, this is not exactly the same effect but it is cool:

Watch: WTF is going on with this object spinning in zero gravity?
Go home, physics. You are drunk.
BEC CREW 21 AUG 2015
http://www.sciencealert.com/watch-wt...n-zero-gravity

For our scenario, it probably could work to apply some restoring force to
maintain both rotations separately. But likely this force would be so large
that you might as well have applied a linear acceleration.

The reason why I was considering the centrifugal force case instead of using
linear acceleration is that this would require a rocket thruster operating
for a long period, perhaps weeks. But if this was by chemical propulsion the
propellant required would be prohibitive. On the other hand, if you used
electric propulsion such as ion thrusters, this would be an extremely small
thrust and acceleration.


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/
----------------------------------------------------------------------------------------------------------------------------------
"dlzc" wrote in message
...

Dear Robert Clark:

On Sunday, May 15, 2016 at 7:54:35 AM UTC-7, Robert Clark wrote:
I wonder what the fluid would look like in a two-axis
rotation system.

That is how very large parabolic mirrors are produced on Earth, using
gravity in place of he second spin axis.
That is, you would have the fluid rotating around a
vertical axis through the center.

The problem is, it is unstable, and unstable in the cooling time of most
liquids. Additionally, with a short "major spin arm", you'd not end up with
a section of a parabola, I wouldn't think.
But also have the entire spacecraft subjected to
a centrifugal rotation via a connection to a
tether with a counterweight at the other end,
as with proposals to simulate gravity with long
space missions.

To simulate this on Earth...

No point in trying, because on Earth, we already make mirrors and mirror
panels this way.

David A. Smith
---


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  #2  
Old May 24th 16, 02:46 AM posted to sci.space.policy
William Mook[_2_]
external usenet poster
 
Posts: 3,840
Default Spin-cast a mirror in space?

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

I have built mirrors like these to test here on Earth as part of an ongoing programme of development.

There are two approaches. One is to vary the thickness of the film and inflate it so that it forms a "Henckey Curve" which approximates a paraboloid. The other is to impress facets into a film so that when the film takes a spherical form, the facets correct the spherical aberration.


A film of aluminum 0.0038" thick (0.09652 mm) and 50 mm wide formed into a ribbon that traces out a spherical helix

http://mathworld.wolfram.com/SphericalHelix.html

forming a highly reflective hemispherical surface that focuses light precisely to a focal point along the axis of rotation of the hemisphere. The polished aluminium roll, is sandwiched between two sheets of PET plastic film only 2 um thick (0.00007874 inches) to maintain brightness, and impart scratch resistance

http://www.dymax.com/index.php/adhes...-hard-coatings

this forms a very stable system. The aluminum is available commercially in great abundance for the manufacture of canned beverages.

Another hemisphere formed of aluminum struts fabricated from a similar foil, is sandwiched between two layers, resulting in a largely transparent, but very strong surface. This surface is formed the same way, as a strip of material formed into a spherical helix, and the surface itself is joined to the reflective hemisphere to form a closed system with a flexible join at the equator of the sphere. The sphere is evacuated after test at the factory, and shipped cupped with others to the point of installation. Once inflated a sphere is formed that is quite stable and sits in an altitude azumith drive that tracks the sun.

A radius of 2.6 meters (8ft 6in) has a 21.237 sq m collector area and the resulting 5.2 meter (17 ft) diameter sphere, once inflated. Total material consists of 10.8 kg (24 lbs) of aluminum and plastic. It intercepts and reflects 21,200 Watts of solar energy. This is far heavier than a flightweight system for space use, but very tough and well suited for terrestrial applications. Packed 4 per inch along the length of a 53 foot carrier 2,500 units may be carried totalling 60 tons in a single shipment. Production methods that produce 1200 units per hour have been developed. This is approximately 12 truckloads per day.

Sunlight focused 20,000 to 1 on a 36.77 mm diameter target, efficiently produces hydrogen from rainwater collected from the sphere's exterior and pumped to the solar powered MEMS device.

http://www.microfabrica.com/capabili...-materials.php

A single sphere produces 1.485 kg of hydrogen 11.880 kg of oxygen from 7 litres of rainwater and 7 litres of process water per day. That hydrogen forms 2.970 kg of methane per day whilst absorbing 8.1675 kg of CO2 from the atmosphere per day. The methane is reduced to 2.775 kg of propane per day resulting in 0.2475 kg of process hydrogen.

http://www.cnet.com/news/miracle-tec...ter-into-fuel/

Propane, not counting its value as a carbon neutral fuel, is worth $0.57 per US gallon. ($0.30543/kg) so each sphere produces $0.847578 per day. $309.58 per year. $2,929.72 present value when discounted at 8.5% over 20 years. When used as a clean petrol replacement, and sold for $2.12 per kg (equivalent pricing in NZ for petrol (USD$8/gallon) - this is 7x greater value

The cost of the sphere is $7.70 in raw material, another $2.30 in assembly and transport costs. A total of $10.00!! The wafer type solar device that converts sunlight and water efficiently to hydrogen, costs $24.60 - and another $0.40 to install, creates a device that costs $35.00 complete!

At one bar the sphere holds 6.573kg of hydrogen gas. At sixteen bar it holds 105.17 kg of hydrogen. This is a 36 day (month's) supply of hydrogen.

Supplying a fuel cell system,

http://www.iphe.net/docs/Meetings/Ge...%20-%20PDF.pdf

each sphere supports a 4 kW averaged load. 2500 units 10 MW. At $0.18 per kWh This produces $6,311.52 per year over 20x the value of the propane!

A pipeline that carries a mixture of propane and hydrogen gas from the area of production to home based combined heat and power systems, that also bottle propane as needed when arriving by pipeline, for vehicle use and cooking produces significant returns.

With 100 solar balloons per hectare of land, each hectare produces 297 kg per day of of hydrogen fuel which supports a combined production of easily transmitted sunfuels that are then used in homes, offices, factories and retailers, to produce heat, power and fuels locally, without adverse effect on the environment.







  #3  
Old May 25th 16, 12:54 AM posted to sci.astro,sci.physics,sci.space.policy
Robert Clark[_5_]
external usenet poster
 
Posts: 245
Default Spin-cast a mirror in space?

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

  #4  
Old May 25th 16, 01:11 AM posted to sci.space.policy,sci.astro,sci.physics
Robert Clark[_5_]
external usenet poster
 
Posts: 245
Default Spin-cast a mirror in space?

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

  #5  
Old May 25th 16, 01:25 AM posted to sci.space.policy
William Mook[_2_]
external usenet poster
 
Posts: 3,840
Default Spin-cast a mirror in space?

Microscale devices can easily detect the collision of individual air particles and by measuring the recoil determine their density;

https://www.youtube.com/watch?v=ygiCHALySmM

Soot is 0.1 micron in diameter, whilst nanoscale machinery that self replicates, are on the order of 2 microns in diameter. Molecules include;

CH4 - 16 amu
H2O - 18 amu
N2 - 28 amu
O2 - 32 amu
CO2 - 44 amu

Which cause small cantilevers to recoil when hit, and thus are easily detected in the gas. A surface that is made preferentially reactive based on detection of individual molecules, absorbs the selected species, rotates the cantilever and releases the molecule that is captured into a controlled atmosphere of that molecule.

This is a very low energy way to extract any species from a gas.

At 10,100 Pascals, there are 2.69x10^25 molecules per cubic meter. 8.97x10^16 molecules per square meter 3.41x10^19 molecules striking each square meter per second. With only 0.04% of these CO2 that means 1.364x10^16 CO2 molecules strike each square meter of absorber per second. That's 1 microgram per second of CO2 absorption per square meter. A square kilometer of absorber area absorbs 1 gram per second of CO2. Anyone who understands the structure of clays like montmorillonite which is made up of 2 um diameter particles, understands that a few grams of the material possess a square kilometer of surface area.

A large number of microscopic machine cells 2 um in diameter and 0.1 um thick, have a surface area of 6.912x10^(-12) square meters and occupy a volume of 628.32x10^(-21) cubic meters. Made of silicene (graphenes silicon based cousin) cells that have 0.5x the void volume as cell volume, it masses 776 kg/m3 and contains cells totalling 28,936 square kilometers -thus 28.936 kg/sec can be absorbed by 776 kg/m3 of this smart material. 37.29 grams per second CO2 per kg of the material.

The change in partial pressures of the CO2 in the atmosphere at 0.04% and the CO2 in the bottle, at 100% - is 451,440 joules per kg of CO2. So, to operate the system requires 16.83 kW per kg of active material. 6.78 grams per second of H2 derived from 61.02 cc of water per second requires an additional 961.41 kW per kg of active material to reduce the CO2 to 13.56 grams per second of CH4. 978.24 kW total. 21.7 grams of the nanoscale material is required to operate per 5.2 m diameter collector.


  #6  
Old May 25th 16, 09:19 AM posted to sci.space.policy
William Mook[_2_]
external usenet poster
 
Posts: 3,840
Default Spin-cast a mirror in space?

On Wednesday, May 25, 2016 at 12:11:06 PM UTC+12, Robert Clark wrote:
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


The technology described is not accurate enough for imaging down to the resolution limit at short wavelengths. Newer technology does better.

http://www.sciencedirect.com/science...05109809001721

That is, even though thin film mirrors were not good for astronomical objects better than they can be imaged here on Earth through an atmosphere with smaller optics. Thin films are far better than naked eyesight corrected to 20/20 which goes down to an arcminute without a telescope.

The thin film concentrators are perfectly suited for concentrating sunlight! The image of the sun approximates the size of the moon (hence eclipse) of 32 arc minutes - about half a degree.

So, these films are perfectly suited to concentrate the intensity of sunlight 46,225x - the limit possible with conventional paraboloid concentrators. This reproduces the surface of the Sun on Earth! In my tests I've limited concentrations to 2,600x solar intensity due to limitations in the handling of heat.

(see figure 3 in my patent)

http://www.google.com/patents/US20050051205

Of course as efficiencies improve, intensities can rise to that of the solar surface.

The advantages of concentration is clear. At 1600x solar intensity at Earth, the solar image is 1/40th the diameter of the concentrator. So, a 40 meter diameter concentrator focuses a solar image onto a 1 meter diameter receiver. That receiver can reduce the image further, to about 500 mm by destroying the image, using nonimaging optics. This is 719,079,5 Watts of solar energy focused on to a 500 mm wafer - 1963.4 sq cm in area. 875.52 Watts/cm2.

The wafer costs $29,500 and the film 9 um average thickness, and consisting of a reflective sheet bound to a transparent sheet, masses 45 kg and costs $75. The wafer is 950 um thick and weighs 488 grams. It forms its own nano-satellite with all systems integrated on the wafer, including holographic optics on the 'dark' side that produces a laser beam at very high efficiency. Solar pumped laser energy is beamed with a secondary thin film mirror to any point on the Earth visible to the secondary. The

http://www.microfabrica.com

This is a lenticular device

http://www.lgarde.com/assets/content...af-98-I501.pdf

A 40 meter diameter reflective paraboloid that's 14.14 meters height has a focal point 28.28 meters from the origin of the paraboloid.
40 m diameter
14.14 m height
28.28 m focal point
3515.10 sq meters - film (1757.55 sq m transparent, 1757.55 sq m reflective)
8884.42 cubic meters - gas.

A transparent paraboloid has its origin at that focal point. It has attached to it a 1 meter diameter hyperboloid inflatable secondary made of reflective film that produces collimated beam which illuminates the 0.5 meter diameter wafer attached to the origin of the reflective paraboloid. The light is segmented into colours and processed by bandgap matched solar pumped thin film lasers at an overall efficiency of 80% (see figure 17 in my patent) and pass to an active optical film that operates at the focus of a second lenticular CONVEX reflector 4 meters in diameter with a 167 mm height - 334 mm including the transparent and reflective portion - with a 6 meter standoff distance. This system is deployed at the same time as the larger system, and floats behind it imaging the aperture of the holographic system that directs the laser beams coming out the rear of the larger solar concentrator to any point on the surface of the Earth. The smaller concentrator images the Earth below horizon to horizon projecting that image on to the wafer efficiently.

A terrestrial reflector 1.27 meters in diameter collects laser energy beamed from the 4 meter transmitter. A guide laser is beamed at the satellite as it passes overhead, and a laser connection established.

http://www.telescope.com/Orion-50-Mo...ope/p/9162.uts

http://lasermotive.com

The receiver efficienctly converts laser energy to DC electrical power which drives a Tesla Power wall with 120 kW supercharger technology. So, it can charge a 6.1 kWh Power Wall up in about 3 minutes. It can send six beams simultaneously to Earth, and so, serve 86,400 users anywhere on Earth per satellite. Power is modulated by pulse width modulation of the laser beam.

The system can efficiently link receiver and transmitter over a distance of 7,570 km. A 2 hour sun synchronous orbit above the terminator (sunrise sunset path) of Earth stays in constant sunlight, and covers the entire Earth every 12 hours. The main reflector is perpendicular to the flight path and parallel with the Earth's surface, facing the sun. The secondary reflector is tilted (yaw) at 45 degrees to the center of rotation of the primary, and rotates (pitches) to maintain level flight along the flight path. Any receiver with clear sky above the horizon of the spacecraft can signal and power beamed to the ground station efficiently. The beam itself can be modulated and the satellite operate as a broadband store and forward system for messages between users

719,000 Watts x 8766 hours = 6.3 million kWh per year

x$0.18 per kWh = $1.134 million per year

20 years at 8.5% discount = $10.73 million present value the day it switches on.

A small satellite like this, is a proof of concept version. It masses less than 100 kg - and can be put on orbit as a secondary satellite for $300,000 - and cost less than $300,000 to build.

http://www.spaceflight.com/spaceflig...lite-industry/

The ground station costs another $150,000 - but this could come down as the number of 50" reflectors produced rises. To about $15,000 -

Each power wall produces 500 Watts over 12 hours before being recharged again. With ten power walls at $3,000 each being served by one receiver, costs can be quite low.



 




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