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#1 2021-11-24 21:21:59

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 8,110

Mirror for Mars Habitat lighting - Dielectric Mirror

This topic is offered as a follow up to an interesting Question posed by Louis recently.

While it may be generally understood that mirrors that reflect optical wavelengths ** do ** reflect those wavelengths, it is not necessarily obvious that such mirrors do not reflect all wavelengths of electromagnetic radiation.

This topic is available if someone (or perhaps several members) would like to build up a concise collection of knowledge nuggets to help a future Mars resident, or someone planning a habitat for Mars to design the optimum mirror to illuminate a habitat, and to feed Earth plants in greenhouses with just the right photons to insure maximum growth.

I am very much in favor of natural lighting for Mars habitats, and the only practical way to achieve that is by using mirrors to flood living spaces with Solar photons in the optical spectrum.

It appears (from a cursory search of Google's snippets) that mirrors can be designed to reflect only desired wavelengths.

I would be interested in knowing what happens to such mirrors when they are bombarded with energetic protons or alpha particles traveling at near light speeds.

(th)

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#2 2021-11-24 21:59:45

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,913

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

https://en.wikipedia.org/wiki/Dielectric_mirror

Some of the coatings fall into optics as well since they are not reflective but have a thin coating that allows the light to pass until it hits the next layer to be redirected.

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#3 2021-11-25 02:26:11

kbd512
Administrator
Registered: 2015-01-02
Posts: 4,924

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

tahanson43206,

GCR is NOT photons.  GCR is ionized normal matter, atomic nuclei ranging in mass from Hydrogen to Iron.  GCR will sail right through thin mirrors, no matter what the mirror is made from, as if the mirror wasn't even there.  This is a result of the stupendous energy that a particle of matter carries with it when it's traveling at a substantial fraction of the speed of light.  A single Iron nuclei traveling at relativistic speeds has kinetic energy approximately equal to a fastball pitch.  When that much kinetic energy is focused onto a point the size of a single atom, it will penetrate just about anything very deeply.  The forces that will eventually stop it are electrostatic repulsion and elastic collision with another atomic nucleus of similar mass.  Needless to say, there's insufficient volume of matter for that to occur within something as thin as a mirror.

The first thing to understand about light, or electricity for that matter, ultimately "energy" (and photons, aka "light", are quanta of energy), is that it's a combination of perpendicular oscillating electric and magnetic fields, wherein both the electric and magnetic fields are in phase with each other.

Veritasium - The Big Misconception About Electricity

Ever wonder why gamma rays (ultra-short wavelength and ultra-high energy photons, bearing in mind that wavelength and energy are directly correlated with each other) are so hard to stop?

After all, gamma rays are still "just photons", right?

Well, yes, gamma rays are still only photons, but there's a bit more to it than that.  The short answer to why there are no gamma ray mirrors relates to the plasma frequency of a reflective surface, such as a metal.  Sometimes people will refer to materials intended to deflect gamma rays as "mirrors", even though there is no reflectance occurring.

The Dielectric Function of a Metal ("Jellium")

From the lecture paper:

Why are Metals Shiny?

An electric field cannot exist inside a metal, because metal electrons follow the field until they have compensated it. An example is the image charge, which exactly cancels the field of any external charge. This is also true for an electromagnetic wave, where electrons respond to the changing external field. As a result, the electromagnetic wave cannot enter a metal and gets totally reflected in the region with ε > 0.

Above the plasma frequency, however, the external field oscillates too fast for the electrons to follow.  A metal loses its reflectivity. The corresponding photon energy is the plasmon energy Ep= ħωp, typically 10-30 eV (deep into the ultraviolet).

Plasma Frequency and Energy-Saving Window Coatings

The reflectivity cutoff at the plasmon energy can be used for energy-saving window coatings which transmit visible sunlight (photon energy above E p), but reflect thermal IR radiation back into a heated room.

To get a reflectivity cutoff in the infrared one needs a smaller electron density than in a metal. A highly-doped semiconductor fits just right, such as indium-tin-oxide (ITO). This material is also widely used as transparent front electrode for solar cells, LEDs, and liquid crystal displays.

What is a Plasmon?

A plasmon is a density wave in an electron gas. It is analogous to a sound wave, which is a density wave in a gas consisting of molecules.

Plasmons exist mainly in metals, where electrons are weakly bound and free to roam. The free electron gas (jellium) model provides a good approximation.

The electrons in a metal can wobble like a piece of jelly, pulled back by the attraction of the positive metal ions that they leave behind.

In contrast to the single electron wave function that we encountered already, a plasmon is a collective wave. Billions of electrons oscillate in sync.

Bearing in mind that photons / quanta of energy are oscillating electromagnetic waves, what we call "reflection" is actually the result of the electron cloud surrounding the nucleus responding to being struck by said photons, by also oscillating and producing an electromagnetic wave of the same frequency of the incoming quanta of energy.  That process most perfectly / completely results in "reflectance" when the frequency of the incoming photons is at or near the resonant frequency (Eigen frequencies) of the electrons.  As the frequency increases, the electrons are too massive to effectively resonate (reflect the incoming wave of energy), and get knocked out of their orbitals as a result (thus "ionizing" the atoms).  That is also why gamma rays are called "ionizing radiation".  The gammas are not ions themselves, but they cause normal matter to "ionize" when they smacking into the electron cloud or nucleus with such tremendous force that the electrons get completely ejected from the cloud.  After that happens, you're left with ionized matter.

You can shine a very powerful spotlight onto a piece of polished Aluminum, blasting it with photons over a great many low energy ranges (wavelengths of visible and infrared light), but the sheet of metal either stops all of them cold (thermalizes them as energy imparted into the sheet of metal) or reflects them (re-radiates photonic energy in a new direction).  However, further increasing the wavelength and therefore energy of the photons suddenly turns that otherwise seemingly fantastic reflector into a sheet of paper, as the simplified “jellium” model suggests.  The wavelength of high energy gamma rays is so short that it can be smaller than the width of an atomic nucleus.  That brings up an interesting question related to your query about why mirrors work at certain electromagnetic spectrum wavelengths, but not other.

Q: How do you create a resonant / reflective surface (which must be constructed from normal matter- some combination of elements within the Periodic Table), when the wavelength of the photons you're trying to reflect using your "gamma ray mirror", are smaller than the width of the nucleus of any atom?  Basically, how do you prevent gamma wavelength photons from finding their way between both atomic nuclei and their electron clouds that your normal matter mirror is made from, given the fact that atomic nuclei arranged into a macro scale structure like a mirror, are almost entirely empty space (and if these high energy photons do have a chance encounter with the nucleus or electron cloud, it's going to ionize it)?

A: You don't, because you can't.  Even the most tightly packed atomic nuclei, such as those of Uranium or Tungsten, are still almost entirely empty space.  99.9999999999996% of a Hydrogen atom is empty space, for example.  The question is equivalent to asking how a very high energy field can interact with empty space or produce a reflected wave by inducing vibrations in electrons (reflecting the incoming wave of energy) above the frequency at which they resonate.  The ultimate answer to that question is that that can’t and won’t happen.  There are novel telescopes that can focus or concentrate gamma ray energy, but there is no such thing as a gamma ray mirror.

No, Scientists Will Never Be Able To Remove The Empty Space From Atoms - It’s absolutely true that atoms are mostly empty space. But removing even that empty space is impossible, and this is why.

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#4 2021-11-25 06:53:10

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 8,110

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

For SpaceNut and kbd512 ... thanks for helping to give this new topic a running start!

The answer of Calliban to the question of Louis posted in another topic includes mention of particles of sufficient energy passing right through a reflector that is designed to serve only optical wavelengths to a habitat on Mars.

In both the answers of Calliban and kbd512, it seems clear that it is NOT a good idea to stand under a mirror that is busy reflecting sunlight into a habitat, because the cosmic ray particles will pass through the mirror, and the ones that ** don't ** will generate a shower of secondary particles.

This post is reserved for data on how to design a mirror to serve the residents of Mars by collecting ** just ** the photons from the Sun that are needed and wanted, while the rest of the spectrum is allowed to heat the mirror or just pass through.

This post is also reserved for data on damage to any light mirror that is exposed to galactic and solar radiation for an extended period.

To my knowledge, we have no mirrors on Mars, but there have been (and are) a number of robot devices resident there, so it may be possible to assess damage caused by exposure to radiation at some point.

I would expect the reflective properties of mirrored surfaces to diminish over time, due to the constant bombardment by GCR and Solar particles not attenuated by the thin atmosphere of Mars.

In short, I would imagine the Mars residents will need to plan a maintenance/replacement schedule for light reflecting mirrors exposed to the environment outside of underground habitats.

Thanks again to kbd512 and SpaceNut for giving this new topic a boost.

(th)

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#5 2021-11-25 08:08:14

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 1,338

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

In the design of orbiting habitats, Gérard O'Neil spent a great deal of time designing habitat and mirror geometries that would let sunlight in and keep cosmic rays out.  In his own words, these design requirements are 'severe' and it apparently wasn't easy reaching an appropriate solution.

I suspect that this is not an area where a perfect solution will be found.  But perfect solutions are not needed.  Many buildings on Earth are constructed with light wells that allow natural light to enter the middle parts of buildings.  This reduces requirements for artificial lighting at the expense of greater heat losses.

On Mars, we could use light tubes, passing through soil berms, which are reflective lined tubes with transparent upper and lower seals.  The soil berm provides compressive force that counteracts internal pressure and the tubes pass through it.  Most cosmic rays and secondary particles end up being absorbed in the materials around the walls of tubes, provided they are long enough.  But sunlight is reflected down the tube and enters the habitat.  In this way, gravity stabilised structures covered with regolith can be lit with natural light.  If tubes cover 50% of the surface area of the roof, then the regolith layer is made twice as thick.  The tubes themselves do not require pressurisation, as the lower end caps can transfer pressure load.  So the structure can be constructed entirely from ceramic elements, with glass or plastic lower end caps and glass windows on top of the tubes.  The lower end caps would be sealed around their edges with a sealant like silicone rubber to reduce the rate of air leakage.

It is conceivable that crops could be grown in underground greenhouses using this method.  These units would conserve heat and shield out 99% of cosmic radiation, whilst providing sufficient light for plant growth.  However, it is a relatively expensive way of creating arable space, requiring quite a lot of digging and soil movement for each square metre.  Probably the easiest way of Mars would be polytunnels with steel reinforcing frames and basalt fibre reinforcement.  But subsurface gardens would have value as recreational areas.

Last edited by Calliban (2021-11-25 08:22:35)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#6 2021-11-25 08:18:28

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,913

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

The images RobertDyck does post about hillside habitats all show light coming through or down a light tunnel. These are even here in use on earth as roof lighting domes or sun tunnels. I actually have these on my northern side of my home as its saves on electrical lighting for those rooms during the day.

normal_MHP-4FC-Image014.jpg

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#7 2021-11-25 08:30:44

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 1,338

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

SpaceNut / Robert, that is a good image.  The solution I had in mind would be to remove the concave mirror from the top and just have long reflective tubes.  Sunlight would enter the top and reflect down.  Imagine clustering thousands of these tubes in a hexagonal lattice with regolith in between them.

The tubes themselves could be concrete or Martian soil-crete.  The tops and bottoms would be glass, with the bottom being a glass hemisphere, that transfers atmospheric pressure into its surrounding regolith via compressive force.  The tubes themselves would not be pressurised.  The insides would be vacuum plated with aluminium.  This allows the use of natural light without cosmic rays hazards and reduced thermal losses.  Assuming that tubes take up 50% of the area of the roof, the tubes (and regolith layer thickness) must be 10m instead of 5m.  We would construct the mud brick vault structure in a trench, crater or other depression with the tubes sticking out like porcupine spines.  We would then pump fine regolith on top of the structure, filling the gaps between the tubes.  Glue the upper and lower caps in place and pressurise.

Last edited by Calliban (2021-11-25 08:37:16)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#8 2021-11-25 08:34:59

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 8,110

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

For SpaceNut re image ...

The graphic design is by Georgi Petrov ... I asked Google about him and got a lot list of references back:

36 Georgi Petrov ideas | painting, art, abstract - Pinterest
www.pinterest.com › Busteliya › georgi-petrov
Apr 7, 2019 - Explore Irina Golik's board "Georgi Petrov" on Pinterest. See more ideas about painting, art, abstract.
Georgi Petrov - Artist - LinkedIn
bg.linkedin.com › georgi-petrov-24279a22
View Georgi Petrov's profile on LinkedIn, the world's largest professional community. Georgi has 1 job ... Academy of Music, Dance and Fine Arts Graphic ...
Georgi Petrov - Freelance designer - GPdesign | LinkedIn
bg.linkedin.com › georgi-petrov-0799115a
View Georgi Petrov's profile on LinkedIn, the world's largest professional community. ... Graphic Designer - web designer and digital publishing specialist.
Georgi Petrov - Design Freelancer - PeoplePerHour
www.peopleperhour.com › freelancer › design › georgi-petrov-graphic-de...
Meet Georgi Petrov, Graphic Design • Stationery • Branding • WordPress • Product Photography. Find experienced freelancers at PeoplePerHour!
Georgi Petrov : contemporary Bulgarian Painter - SINGULART
www.singulart.com › Buy art › Artists › Painter
Rating 4.9  (2,498)
Discover artworks by Georgi Petrov : Painter on SINGULART ! ... Georgi Petrov is a Bulgarian artist whose paintings have been widely exhibited nationally, ...
Missing: graphic | Must include:graphic
Georgi Petrov - Simpliv
www.simplivlearning.com › author
Graphic Design My name is Georgi Petrov, the founder of DESIGNROOM1229 a design studio helping businesses to stand out with their branding and web presence.
Georgi Petrov on Behance
www.behance.net › georgippetrov
My name is Georgi Petrov, the founder of DESIGNROOM1229 a design studio helping businesses to stand ... initially selling flyer templates on the Graphic River.
About Georgi Petrov | Flickr
www.flickr.com › people › designroom1229
Creative Graphic Designer, Founder & CEO of designroom1229.com and flyerroom.com stepping into photography with so much to learn.
Georgi Petrov Speaks at 2019 ETEM Facade Conference in Sofia
www.som.com › news › georgi-petrov-speaks-at-2019-etem-facade-confer...
Nov 11, 2019 · On Saturday, November 16th, Associate Director of Structural Engineering Georgi Pertov will give a keynote presentation at the 2019 ETEM ...

I'm pretty sure that somewhere in the many posts of RobertDyck there is a passage about his participation in (or familiarity with) the study that produced that graphic.

(th)

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#9 2021-11-25 08:38:24

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,913

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

pages in the my hacienda show lots more for RobertDyck these are from the marshome.org homestead

Roberts post in Chinese greenhouses

solar_radiation_spectrum.jpg

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#10 2021-11-25 08:51:33

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 8,110

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

A web site about growing plants from seeds contained a response to a question about growing tomatoes on Mars.

The solar flux estimated in the reply was 590 vs 1000 on Earth.

Elsewhere in the forum (and quite recently) it was suggested that solar flux on Mars is about half that on Earth.

Mirrors are going to be needed on Mars, if residents want to enjoy "normal" lighting conditions.

I am hoping that this topic will eventually include information a Mars resident would need to order a mirror from Earth, or to make one on Mars.

Recently kbd512 mentioned aluminum as a reflective material that might serve as a mirror.

This web site includes an article on the history and present state of mirrors...

http://www.madehow.com/Volume-1/Mirror.html

In some cases, a plastic substrate will do as well as a glass one. In particular, mirrors on children's toys are often made this way, so they don't break as easily. Plastic polymers are manufactured from petroleum and other organic chemicals. They can be injection molded into any desired shape, including flat sheets and circles, and can be opaque or transparent as the design requires.

These base materials must be coated to make a mirror. Metallic coatings are the most common. A variety of metals, such as silver, gold, and chrome, are appropriate for this application. Silver was the most popular mirror backing one hundred years ago, leading to the coinage of the term "silvering." Old silver-backed mirrors often have dark lines behind the glass, however, because the material was coated very thinly and unevenly, causing it to flake off, scratch or tarnish. More recently, before 1940, mirror manufacturers used mercury because it spread evenly over the surface of the glass and did not tarnish. This practice was also eventually abandoned, for it posed the problem of sealing in the toxic liquid. Today, aluminum is the most commonly used metallic coating for mirrors.

Scientific grade mirrors are sometimes coated with other materials, like silicon oxides and silicon nitrides, in up to hundreds of layers of, each a 10,000th of an inch thick. These types of coatings, referred to as dielectric coatings, are used both by themselves as reflectors, and as protective finishes on metallic coatings. They are more scratch resistant than metal. Scientific mirrors also use silver coatings, and sometimes gold coatings as well, to reflect light of a particular color of light more or less well.
Read more: http://www.madehow.com/Volume-1/Mirror. … z7DF0ZSFQo

Silicon is reported to be abundant on Mars, so it would seem (to me at least) reasonable to propose manufacture of mirrors on Mars using glass as the substrate and aluminum for the reflective surface.

However, initial supplies of mirrors for habitat illumination are likely to be shipped from Earth.

I would expect such mirrors to be ordered in flat configuration,  They could be mounted on Sun tracking frames, to deliver light into habitat windows throughout the Sol.

For SpaceNut ... mirrors would seem likely to be worth including in the My Hacienda topic, if they are not there already.

(th)

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#11 2021-11-25 09:26:31

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,701
Website

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

You will get quite a bit of light in through a window by simply placing flat salvaged panels of polished aluminum sheet propped up on rocks outside.  Put multiple such mirrors in a curved ring,  and you won't have to aim them to track the sun.  You'll have to take a broom and sweep off the dust every day or three.  Real low-tech,  but it works.  Well-suited for the mushroom buildings with the window ring-wall.  Not so much for a light pipe rig. 

GW

Last edited by GW Johnson (2021-11-25 09:27:44)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#12 2021-11-25 09:32:34

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,913

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

Any unused cargo starships the stainless steel shell will be a good mirror once polished and shaped for solar concentrating.

The processes for vapor depositing of mirror reflective material can also be used on plastics or mylars.


RobertDyck's post51AzHGLBW8L.jpg for Greenhouses


Living Underground on Mars – The 9 Drilling Challenges
of the equipment use and duration to actual bore them as well as energy required.

https://arxiv.org/pdf/2012.09604.pdf
Health threat from cosmic radiation during manned missions to Mars

https://agupubs.onlinelibrary.wiley.com … 19JE006246
Subsurface Radiation Environment of Mars and Its Implication for Shielding Protection of Future Habitats

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#13 2021-11-25 15:03:02

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,913

Re: Mirror for Mars Habitat lighting - Dielectric Mirror

Scientists create 'ultrahard' GLASS that's even harder than a diamond

They synthesised it by placing 'buckyballs' — a soccer-ball like form of carbon — in an anvil press and subjecting them to extreme temperatures and pressures.

The sample pictured below, for example, formed at 30 GPa and 1,598°F, although production was possible at lower pressures and higher temperatures and vice versa.

The hardness achieved — around 102 GPa — makes it one of the hardest glasses presently known, second only to the recently-synthesised AM-III carbon (113 GPa).

The discovery of buckyballs was honoured with the Nobel Prize in Chemistry back in 1996.
buckminsterfullerene, a form of carbon composed of 60 atoms arranged in a hollow, cage-like structure that resembles a soccer ball, a fact that has given it the popular name of 'buckyball'.

'The trick is to find the right starting material to transform with the application of pressure.'

Because of its extremely high melting point at a whopping 7,280°F (4,027°C), it is impossible to use diamond as a starting point to make diamond-like glass.

Wow that is hot to melt a diamond...

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