The Water Tent - radiation protection

louis · 2008-04-02 02:15:40

I have been thinking about the problem of radiation protection for working on the surface of Mars over extended periods.

I would like to suggest a solution I call The Water Tent.

Think of a large plastic water containing object - think water bed, super large duvet, tent cover. There would be internal cells to provide some rigidity. It would be maybe between 5 and 10 cms thick.

The tent cover would be filled with water and suspended over a metal cage to provide cover for human activity. I think we would need it to cover an area of about 5X5 sq. metres to be useful and to be a height of about 4 metres, to allow for mini digger work. It could be lifted into position by the mini digger.

The cage would have to support somewhere between 500 kgs and 1000kgs weight.

However, as most of the weight would be water it would not add significant mass to the payload. The thing itself with cage might have a mass of about 50-100 kgs.

SpaceNut · 2008-04-02 06:30:34

One other problem is the water will freeze within the layers making it hard to take down once deployed.

Also I think there suits should have taken care of the issue and if not what is the monitoring methods to be used.

louis · 2008-04-02 11:40:05

Whoops - I do have a tendency to forget that. But energy will be abundant, so feel free to incorporate heating elements.

On the other hand, could you just get it to stand of itself as an "ice sculpture"?

You think Space Suits woudl suffice? Well, I'm not one to overdesign. I'm glad to forget the whole thing. But I was getting the impression for other sources that the cosmic rays are going to go through suits and helmets.

Rxke · 2008-04-02 12:14:19

energy will be abundant.

Initially it won't be, far from it.

JoshNH4H · 2008-04-02 13:32:06

cosmic rays are basically unstoppable with human-manufactured shielding, no matter what you do. I believe the thin atmosphere on mars stops everything but X-rays and UV. In other words, just bring some sunscreen, with some iron or iron oxide dust mixed in to add x-rax shielding.

zhar2 · 2008-04-02 14:10:10

The water could be doped with antifreeze to preent it frezzing.

louis · 2008-04-02 20:55:40

Doesn't even anti-freeze freeze at the lower temperature rang on Mars.

zhar2 · 2008-04-03 01:02:18

There are mny types with different freezing points.

RobertDyck · 2008-04-03 07:34:02

Way too much worry about radiation. Do you realize the radiation intensity on the surface of Mars is half that of ISS? In the case of a solar flare or coronal mass ejection, astronauts on ISS would get in their spacecraft and escape to Earth. On Mars they can't do that, so you need radiation shielding. That's why you put sand bags on a Mars Direct hab, or burry a base under Mars dirt.

Nuclear reactor workers have a certain radiation exposure limit per year. Astronauts are exposed to a little more when they're on ISS. Keeping astronaut exposure down to equal nuclear reactor workers means you again need to pile dirt on the hab roof, and limit time in a spacesuit on the surface of Mars to 40 hours per week. Hmm, that's the same as a work week on Earth. I don't think any astronaut would object to that.

Going tenting on Mars means keeping things simple. Engineers follow the KISS rule: Keep It Simple Stupid. This is due to Murphy's law: anything that can go wrong will. If you keep it simple, there are fewer things to go wrong. A water tent is likely to freeze solid, then not be able to melt. Freezing can cause a tear, releasing pressure.

Let's keep it simple. I came up with a simple tent design as well. Use PCTFE film because that is the most impermeable polymer to water, and also very impermeable to oxygen and CO2. The only polymers more impermeable to oxygen will not survive the cold of Mars, they become brittle at temperatures of -60°C or warmer. Mars at night gets below -75°C. Mars Pathfinder measured temperatures over 3 days, the high during the day was -8°C, the low at night was -78°C. Viking 2 measured temperatures for more than a Martian year, the low it recorded was -111°C. Mars Global Surveyor recorded a planet-wide low at the south pole during southern winter of -140°C. PCTFE doesn't become brittle until -240°C, so cold on Mars will never be a problem for this stuff. Furthermore, aluminizing the polymer plugs the pores making it even less permeable. Aluminum reflects radiant heat, staying warm on Mars at night is an issue. So design the tent to be aluminized PCTFE with a small transparent window, and a flap that can cover the inside of the window. Open the flap to look out, close the flap at night to keep heat in. The floor would be an air mattress. The tent and air mattress floor would be all one integrated piece, designed to keep air in. The air mattress would have more pressure, well pressurized like an air mattress. Inside the air mattress there would be multiple layers of very thing aluminized plastic, suspended by threads. A single layer is sufficient where it contacts Mars atmosphere since it's so thin, but contact with the ground will be cold. Heat may be an issue, so a small muffin fan like the case fan of a personal computer can circulate air within the air mattress. Cold air from the bottom of the air mattress can be circulated to the top. A thermostat can regulate temperature, turning off the fan when the tent gets cold. So the tent won't need a liquid cooling system or sublimator or anything fancy, just an air mattress with a fan inside.

For air, use the life support backpack from your spacesuit. Run the air mattress fan from batteries in that backpack. The technical name for the backpack is Portable Life Support System (PLSS).

So we're talking about a 7-foot dome tent with built-in air mattress floor. That's enough room to set your spacesuit and PLSS beside your sleeping bag. Bring an extra oxygen bottle to inflate the tent. Maybe some extra CO2 sorbent cartridges and extra PLSS batteries.

louis · 2008-04-03 16:25:36

Robert -

Sorry - meant to go on and comment on the other points you make.

That's really interesting about the PCTFE film. That's very encouraging.

Can I ask a question about that - does it let through the solar radiation necessary for solar power facilities? I was just wondering whether we might be able to encase ultrathin PV film in this plastic film as protection.

Regarding the tent - I'm all for the simplest solution. If you are right that radiation is less of problem than some imagine then maybe your approach is the right one - in fact I'm almost certain it is - just one problem. I was thinking in particular about protecting the worker in a digger, digging a trench. So it's got to be something like an arch. Presumably your approach could be adapted to provide an arch.

idiom · 2008-04-03 22:47:47

Radiation is most serious only during the day.

A sturdy SunShade with Sandbags piled on should work just as well without pumping water all over the place.

RobertDyck · 2008-04-04 00:32:14

I'm thinking of a dome tent without any ribs. Just use pressure to hold the tent up. Higher pressure in the air mattress will keep its shape, so a dome tent on a relatively flat disk air mattress.

PCTFE is highly transparent. It's the second most transparent polymer, only Teflon AF is more transparent; "AF" stands for amorphous fluoropolymer. Amorphous is the same molecular structure as glass, which is rigid. You don't want to use a thin film of that for your tent. Furthermore, Teflon AF is highly permeable; you want something that will keep air in. But PCTFE will transmit 97% of all light, including UV and IR. That transmission spectrum even extends well into UV-C, it tapers off at the boundary between UV-C and X-rays.

PCTFE is also the second most resistant to UV degradation. Teflon FEP is more UV durable, but it is also more permeable and less transparent. Actually it's a lot more permeable, which is why I don't want to use it for anything that contains gas, at least not something that retains air and pressure for astronauts. The main reason PCTFE is so UV durable is that UV just goes right through, very little interaction.

To protect a rigid PV cell, you could use Teflon AF. A true amorphous is also harder, so more scratch resistant. But it would be prone to crack when flexed. A flexible PV array could use PCTFE. Both will transmit more light than a glass cover slide.

As for a worker in a digger, I would be worried about anyone attempting to tent at the bottom of a freshly dug trench. I wouldn't do that on Earth much less Mars. Erect your tent on the surface where it's flat, level, and the ground is secure. If you want to burry a permanent habitat module, make it out of fibreglass or aluminum. Something rigid that can hold up the weight of dirt when depressurized, and also hold pressure.

SpaceNut · 2008-04-04 20:03:55

Well if you have the time to read it online then go to Managing Space Radiation Risk in the New Era of Space Exploration

Authors:
Committee on the Evaluation of Radiation Shielding for Space Exploration, National Research Council
Aeronautics and Space Engineering Board (ASEB)
Engineering and Physical Sciences (DEPS)

RobertDyck · 2008-04-04 23:03:09

I'm unemployed right now so there is no way I'm going to pay for it. Either provide a direct link to the document or don't waste my time.

Besides, I'm rather sceptical. I've read several papers about radiation, some repeat the same information over and over again, others talk about radiation with fear rather than any quantitative analysis. When you look at the numbers the issue isn't as great as the media would have you believe, and an unfortunately large number of so called "science" papers are formatted in a very professional way, but don't actually say anything. So I am very hesitant to pay any money for a paper when I don't know if this one actually says anything.

I'll give you an example of an actual useful paper. Four papers were published by the science team for the Marie instrument on Mars Odyssey. They were published on the JSC website, although that website has disappeared. I kept a copy of all 4 papers, PDF files. Here is one chart that appeared in two of the papers:

This one is actually useful. It shows radiation in cell hits for an astronaut on the surface of Mars, broken down by type of radiation: proton, alpha, light ion, medium ion, and heavy ion. That is shown for altitude above the datum: 0km, 2km, 4km, 6km, and 8km. Notice the "h" column, heavy ions. At 0km the bar is so small it's practically a circle. Next notice the scale, it's logarithmic. There are two copies of this chart, one for solar maximum, the other for solar minimum. Actually during solar maximum there is more solar wind, but that wind blows cosmic radiation away from the inner solar system so there is less cosmic. What I take from this is effect of Mars atmosphere on heavy ions. Deep atmosphere dramatically reduces heavy ions, there are practically no cell hits from heavy ions at 0km altitude. That's why I keep saying we need to pick a landing location at or below the datum.

Now does the paper you are trying to sell even address the unique radiation environment of Mars? Or does it go on and on about radiation in deep space? Most "space" papers assume interplanetary space, no atmosphere at all. Those may be useful for the transit to Mars, but are not useful at all for anything on Mars itself.

I posted a copy of all 4 papers on the local chapter website:
http://chapters.marssociety.org/winnipeg/radiation

louis · 2008-04-05 05:16:51

Robert -

Thanks for that very informative post.

I am not the world's most diligent researcher but your post has definitely gone in my Mars information file for future reference.

V. interesting that there is LESS cosmic radiation at the solar maximum - makes sense once you realise why.

So it seems from what you are saying that it is the travelling through non-atmospheric space that will be the problem - one I feel could be addressed by making a virtue of the water tanks and shaping them into a surrounding wall/floor/ceiling to act as a radiation barrier around the crew.
This would mean that there would be only a minimal increase in mass perhaps (not that I've done any detailed calculations). Having said that, I have no idea whether cosmically irradiated water presents any dangers to human health.

I agree by the way that there is in any case probably scope to choose a location for habitat and the industrial above-surface working zone which is shielded to a certain extent by crater walls or in a canyon. This would probably greatly reduce the hits as well - were it necessary to do so. But from what you write it would appear that a space suit, which they will be wearing outdoors in any case will suffice as protection.

Terraformer · 2008-04-05 05:51:22

Igloos with an airtight interior?

louis · 2008-04-05 06:05:34

I was thinking about igloos yesterday. Certainly something to consider. Suitable material could be transported from the poles perhaps.

Going back to my original point though, when I thought there might be a serious radiation issue (not convinced since reading Robert's post) - I was thinking of a cover for outside working. You can't have an all around igloo or all around tent when you are digging a trench - you need an arched cover.

HOwever, as indicated, I feel the health threat may have been exaggerated and that space suits will provide adequate protection.

idiom · 2008-04-05 06:50:08

You only need an overhead Sun Shade at Noon.

You need a Sunshade on a large manipulator, on a large trailer that you can hitch up to your rover.

It could have a Solar panel on it

louis · 2008-04-05 12:50:50

I see you've got one on!

And yes you could easily apply PV film to a sun shade for a power boost.

idiom · 2008-04-05 16:18:43

Here you actually want a nice thick high efficieny Solar Panel, to absorb as much enrgy as possible and pass as little as possible through.

Secondly, it could power itself and remote drilling equipment etc, and be used as auxillary power back the Hab.

If you put flood lights on the back of it then you have an itelligent mobile flexible lighting rig for those times when someone has to go fix a pump at 3am.

SpaceNut · 2008-04-05 18:06:29

I'm unemployed right now so there is no way I'm going to pay for it. Either provide a direct link to the document or don't waste my time.

I am sorry to hear that as I am in the same boat with no end in sight for gainful emplyment.

Further down on the page you can read each chapter of the book for free.

Table of Contents
Select a link below to start reading online free!
Front Matter i-xiv
Summary 1-6
1 Introduction 7-23
2 Current Knowledge of the Radiation Environment 24-64
3 Radiation Effects 65-81
4 Shielding Approaches and Capabilities 82-102
5 Strategy for Radiation Risk Mitigation 103-120
6 Findings and Recommendations 121-125
A Statement of Task 126-126
B Committee Biographies 127-130
C List of Meetings and Speakers 131-131
D Glossary and Acronyms 132-138

Mars_B4_Moon · 2024-05-15 12:20:38

Some have fears of a Betelgeuse supernova which considering time scales seems kind of reaching or far fetched

maybe a good thing Boeing Star-liner did not launch, the Solar Flare and Aurora event would have perhaps made things more complicated

There are bigger events, the historical recording of the Carrington Event was the most intense geomagnetic storm in recorded history in September 1859

This was one of the largest solar flare in years from spot that triggered auroras, the event some of the more intense ever recorded.

' The Earth could easily fit under this long-extended prominence. '

https://apod.nasa.gov/apod/ap240515.html

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Re: The Water Tent - radiation protection

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