A Question...

louis · 2021-11-24 19:46:41

When you put up a solar reflector on Mars will the reflected light include reflected cosmic and other radiation? Or is there a way of screening out the radiation and keeping the natural light spectrum?

If the latter, then that could be very helpful as you might be able to illuminate living spaces without risk of creating a radiation burden.

tahanson43206 · 2021-11-24 20:01:43

For Louis re new physics topic ...

This is a question worth asking on behalf of the many folks who have not studied physics ...

It appears I am the first NewMars member to show up with a first attempt at an answer, but I hope others will join in to build up a small but sturdy repository of knowledge about reflection of various kinds of radiation.

I asked Google to show: physics of reflection of spectrum of radiation by mirror and it came back with these snippets:

How do mirrors reflect photons? - Scientific American
www.scientificamerican.com › article › how-do-mirrors-reflect-ph
Sep 25, 2006 · A noteworthy feature of dielectric mirrors is that they are highly reflecting only for light in a very limited range of wavelengths. If this ...
Introduction to the Reflection of Light - Olympus Life Science
www.olympus-lifescience.com › ... › The Physics of Light and Color
Reflection of light occurs when waves hit a surface that, instead of absorbing radiation, bounce the waves away from the surface. Learn more with Olympus.

Hard radiation will penetrate the material of which the mirror is made, and I would expect that over time, it would degrade the mirror.

However, there may well have been studies that explore this question, so it is possible a member will post links to them.

(th)

SpaceNut · 2021-11-24 20:08:38

Material type and thickness will come into play as its not really like the one you would have as a vanity. So of its going to bounce while most will simply just go through it to bounce around after words. That striking will also produce a variety of other particles as well.

kbd512 · 2021-11-24 22:18:36

Louis,

GCR is relativistic ions. This is mostly Hydrogen ions, but includes every nuclei in the Periodic Table up to the weight of Iron or so, because it comes from exploded stars. All of it is very high-velocity matter, therefore very high-energy, and is produced by supernovas and black hole ejections that are capable of accelerating matter to a substantial fraction of the speed of light.

There are several ways to mitigate the damage done by GCR radiation. The first is being on the surface of a substantial planetary body, which automatically blocks out 1/2 of all radiation that would otherwise be received. The second is a powerful electromagnetic field, which will deflect the ions around the field lines. The third is electrostatic repulsion.

GCR ions are still ions and subject to all the normal forces that act on matter. What distinguishes GCR radiation from other forms of radiation is the extreme kinetic energy that each ion carries with it. The only Earth-bound analog we have for GCRs are the various particle accelerators, such as the one at CERN. In order to stop one of these relativistic ions cold, like an armor plate stopping a bullet, very dense matter or a lot of matter is required. Deflection around a protected space is much easier to achieve, using electromagnetic fields or electrostatic fields, or some combination thereof, such as a plasma entrained in an electromagnetic bubble surrounding a spacecraft.

GCR ions would simply punch right through something as thin as a solar panel, which would be analogous to expecting a piece of paper to stop a bullet. If you were inside a M1 tank outfitted with depleted Uranium armor, on the surface of the moon, the GCR would both punch through the armor and create secondary particle showers. While the armor is very dense, it's also pretty thin so that the tank remains light enough to be mobile, because it's designed to stop kinetic energy darts and slugs of molten metal. The M1's frontal armor would be sufficient to slow and perhaps stop some of the lighter Hydrogen ions, but all of the heavier ions would sail right through the armor, because there's simply not enough material there. If you wanted to stop most of the incoming ions, which is mostly Hydrogen, then your tank would be "armored" with a Hydrogen-rich material like plastic or simply constructed like a plastic water. It would also have to be very thick, much thicker than the armor on any tank, in order to produce enough elastic collisions to appreciably slow and dissipate the energy of the incoming ions.

Earth's Van Allen belts stop most of the GCR and particles emitted by the Sun by deflecting it off into space. The same applies to the Sun, which is a far more powerful relativistic particle deflector. Earth's upper atmosphere also becomes ionized through particle and photon interactions, stopping even more GCR. The water vapor in the atmosphere stops most of the rest of the Hydrogen GCR. As previously stated, when Hydrogen nuclei encounter other nuclei with the same or very similar atomic mass, they are subject to elastic collisions when they smack into each other. Elastic collisions sap kinetic energy from the relativistic Hydrogen ions. The reason airline pilots are subject to far more radiation is that the altitudes they fly at are above at least 2/3rds of the atmosphere.

Calliban · 2021-11-25 03:25:13

Simple answer: Ion radiation like GCR and solar particles will pass through the mirror without being reflected by it. Likewise, x-rays and gamma rays. Some portion of ultraviolet may be reflected. You can remove this with selective coatings. One complication with GCR radiation is the creation of secondary particles which may produce back scatter. Likewise, low energy neutrons can be tricky to shield because they stream, rather like a fluid flowing through a pipe. But for the most part, mirrors allow the use use of natural light that is screened of GCR and solar particle radiation. But the geometry may be tricky.

Last edited by Calliban (2021-11-25 03:28:11)

louis · 2021-11-25 10:43:27

Thanks for the helpful answers guys - it sounds like those are very positive answers in the sense that as long as you are directing reflected light into your habs you won't be creating a (dangerous) radiation risk.

Something to bear in mind when it comes to constructing habs. I am quite taken with the idea of creating large "gallery spaces" with natural lighting at the top. So if one could place over the high arch window (at the top of the gallery) a protective suspended (maybe by steel frame) layer of regolith with reflectors underneath then those underside reflectors could receive light from a system of reflectors beyond the protective/reflective structure. More than that, you can increase the amount of light going into the gallery above and beyond the natural insolation. So, maybe you have 4 x the natural insolation level, meaning inside the gallery it feels like it's a realy bright sunny day outside.

It would help with heating and allow a lot of devices in the gallery interior to be solar powered for convenience e.g. garden lights.

It would be quite a complicated engineering job but on the plus side people could stand in natural light with no fear of developing radiation sickness and the high arch windows could be made of any glass that can deal with the pressure requirements.

Calliban · 2021-11-25 11:14:22

Galactic cosmic rays and coronal mass ejection events do not deliver enough flux to cause radiation sickness on the surface of Mars. It is more a concern about long-term health effects. You could build a house under a dome on Mars and so long as you spent no more than 8 hours a day under the Martian sky, the health risks would be no higher than air pollution does for the average person here on Earth. But it is a health risk none the less. But keep in mind that in mitigating any risk, there are limits to what it is reasonable to pay. The right solutions are about achieving the correct balance between risk and cost.

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

louis · 2021-11-25 16:00:00

Apologies for misnomenclature!

As I understand it, there is a particular concern about effects on the brain in particular.

I have always been confident we can guard against the negative health effects but I am looking for solutions which allow the people of Mars to enjoy natural light and it seems this (using reflectors) does offer that possibility. The idea of a troglodyte existence on Mars holds no appeal for me and won't for potential colonists. We need to connect people to the planet. Ensuring connection with the day-night cycle is one way. Using rovers to get out and about on the surface will be important (I recall the lunar explorers used to have great fun riding about on their moon buggies). Occasional EVAs will help. In summer you might even be able to take off an outer glove and feel the surface with hand covered in a light mesh inner glove. Having observation towers where people can see into the distance will be helpful. We might be able to design swimming/diving facilities where you can scuba or snorkel dive outside the main leisure centre into a glass covered dome which is gives the feel of being part of the landscape.

Calliban wrote:

Galactic cosmic rays and coronal mass ejection events do not deliver enough flux to cause radiation sickness on the surface of Mars. It is more a concern about long-term health effects. You could build a house under a dome on Mars and so long as you spent no more than 8 hours a day under the Martian sky, the health risks would be no higher than air pollution does for the average person here on Earth. But it is a health risk none the less. But keep in mind that in mitigating any risk, there are limits to what it is reasonable to pay. The right solutions are about achieving the correct balance between risk and cost.

SpaceNut · 2021-11-25 16:28:33

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

8 rads/year on Mars is quite a bit

According to Mars one, we’ll need 16-feet of Martian soil to cover us. This should provide us with the same protection we get from Earth’s Atmosphere.
0.62 rads/year

Which is a lot of mars soil to move to cover a habitat.

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

Calliban · 2021-11-26 06:59:33

From SpaceNut's second link, some 2000g/cm2 of shielding is needed to reduce GCR dose rates to Earth standard. That is substantially greater than the column density of Earth's atmosphere and equivalent to about 8m of compacted regolith. But 8m of regolith is sufficient to protect a habitat from diurnal and seasonal temperature fluctuations and its weight is enough to balance internal air pressure. So that regolith layer solves three problems simultaneously.

From SpaceNut first link; tunnelling sounds like a finicky pain in the arse. It is a slow process, that requires a lot of heavy equipment and a lot of power. We are applying it within an alien environment, with a geology we don't understand. It isn't something that sounds at all practical to me within the early colony stage. More likely, habitable space will be created by heaping regolith over frames constructed in depressions.

I have read other plans that suggest a strategy of ignoring radiation protection altogether. Inflatable structures are built on the surface. Radiation dose is just a hit that the colonists have to take. Much depends on how much risk we are prepared to take and what we are prepared to spend reducing that risk. A dose rate of 8 rem per year equates to 100 rem (1Sv) dose every 12 years. That means losing 1 year of life expectancy for every 12 years of exposure. Maybe that is tolerable if living on Mars allows other risks to be avoided. But living on the surface would mean huge heat loads as well. Everything comes down to what balance we want to reach between risk, capital cost and operating cost.

I don't quite understand the aversion to building hab space underground. The above ground isn't exactly green and pleasant. And if people want a view of outside then a short flight of stairs to an observation dome isn't a difficult add on. But all else being equal, an underground hab is a healthier and more comfortable environment. Above ground time should be reserved for tasks that need to be above ground. Work in the agricultural poly tunnels, construction work or surface travel being an example. Martians will be troglodytes.

Last edited by Calliban (2021-11-26 07:16:21)

SpaceNut · 2021-11-26 10:51:06

Traveling to Mars? Top 6 health challenges

louis · 2021-11-26 19:43:08

Mars One were never a very accurate source of information about anything! I think a lot depends on how densely packed material is.

SpaceNut wrote:

Living Underground on Mars – The 9 Drilling Challenges
of the equipment use and duration to actual bore them as well as energy required.
8 rads/year on Mars is quite a bit
According to Mars one, we’ll need 16-feet of Martian soil to cover us. This should provide us with the same protection we get from Earth’s Atmosphere.
0.62 rads/year
Which is a lot of mars soil to move to cover a habitat.
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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