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#51 2016-12-08 22:35:03

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 13,342

Re: Material Choices for Mars

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

The natural gas is then condensed into a liquid at close to atmospheric pressure by cooling it to approximately −162 °C (−260 °F); maximum transport pressure is set at around 25 kPa (4 psi). LNG typically contains more than 90 percent methane. It also contains small amounts of ethane, propane, butane, some heavier alkanes, and nitrogen.

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

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

The density of liquid propane at 25 °C (77 °F) is 0.493 g/cm3, which is equivalent to 4.11 pounds per U.S. liquid gallon or 493 kg/m3. Propane expands at 1.5% per 10 °F. Thus, liquid propane has a density of approximately 4.2 pounds per gallon (504 kg/m3) at 60 °F (15.6 °C).


http://inspectapedia.com/plumbing/Gas_Pressures.php


•LP gas pressure in the LP gas tank: 100-200 psi LP gas pressure
LP gas pressures inside a propane tank (before the LP tank regulator) can be much higher than at the gas appliance, anywhere between 100 and 200 psi, which explains why a pressure regulator is needed at the tank (dropping the supply pressure to the range given just above) and a second regulator is used at the appliance to regulate the pressure to the levels required by the appliance itself.

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#52 2017-09-05 20:22:51

3015
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Registered: 2017-01-08
Posts: 30

Re: Material Choices for Mars

RodbertDyck, I know this is going way back in the history of a very old thread, but a couple years ago you did the math showing that PCTFE thickness would be very high for a 6mx12m greenhouse. This paper mentions a way around that by using pillowing to decrease the radius of curvature and therefore put less force on the bladder. The pressure force would instead be mostly on the restraints between pillows, which could have much greater tensile strength than PCTFE. This would allow the PCTFE film to be quite thin.

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#53 2017-09-05 21:07:44

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 13,342

Re: Material Choices for Mars

The issue for a bladder or pillow approach is that the internal pressure within the structure is going to cause the shape of the outer wall of the pillow to bow outward as the inner wall is compressed since there is no counter pressure pushing on the outer wall.

Either the bladder seams will fail between pillows or it will lose structural shape. The figure 4 in the linked pdf shows the latice net that is used to anchor the inflateable structure to the ground would allow for the bladders or pillows to form in between the cords.

I have been looking at geodesic dome construction techiques using like a slice of pizza tray but shaped out of a thicker form of the material. If you want a double layer use a sandwich of aerogel in between them and make a common inner seam for the joint from one panel to the next. The double seam of the pair of traingular shapes and its adjacent seam wpuld be used to create the framing to make the structure strong.

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#54 2017-09-05 21:30:24

3015
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Registered: 2017-01-08
Posts: 30

Re: Material Choices for Mars

The "pillows" will definitely bow outward, that's why they're used. Force on the wall of a pressure vessel is proportional to the radius of curvature, and the bowed out sections have low radii of curvature and therefore low forces on them. As long as the tethers are close together though I don't think it would change the shape of the vessel much. Or am I misunderstanding your argument?

I'm intrigued by your dome idea. Is aerogel transparent enough for such an idea to be used for a transparent enclosure?

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#55 2017-09-05 22:21:13

SpaceNut
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From: New Hampshire
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Posts: 13,342

Re: Material Choices for Mars

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

800px-Aerogel_hand.jpg

220px-Aerogelflower_filtered.jpg

Make the triangles simular in shape to the flaps of the box but only in halves with the second half stuck inside with the flap still exposed to create the rib to rivet or bolt together.

HTB14oNuHFXXXXcwXpXXq6xXFXXXT.jpg

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#56 2017-09-05 23:16:51

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,519
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Re: Material Choices for Mars

3015 wrote:

RodbertDyck, I know this is going way back in the history of a very old thread, but a couple years ago you did the math showing that PCTFE thickness would be very high for a 6mx12m greenhouse. This paper mentions a way around that by using pillowing to decrease the radius of curvature and therefore put less force on the bladder. The pressure force would instead be mostly on the restraints between pillows, which could have much greater tensile strength than PCTFE. This would allow the PCTFE film to be quite thin.

Good idea. We have kicked around the idea of reinforcing the film with thermally applied fibreglass gauze. That would form rip-stop as well as reinforcement. The manufacturer of PCTFE film offers that. An old painting by Robert Murray shows straps over the greenhouse. One purpose is to squish the shape: reduce ceiling height while increasing width. That requires hold-down straps. But to reduce tensile force on the film, each cell must be allowed to "pillow" out. If it's pulled taught then the film experiences all the force for the full structure. Hexagonal cells? You can buy Kevlar webbing straps. Curiosity rover parachute cords were Technora; also an aramid fibre. Technora withstands shock loads and fatigue better than Kevlar, and higher tensile strength. So webbing of that material? All aramid fibres are sensitive to UV, so would require UV protection coating.
greenhouse.jpg

Could you post a link to my post, where I did the math?

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#57 2017-09-06 13:16:42

3015
Member
Registered: 2017-01-08
Posts: 30

Re: Material Choices for Mars

I like the fiberglass gauze idea. Some glass fibers have ridiculous tensile strengths, and glass is resistant to radiation and a wide range of temperatures.

I'm somewhat skeptical of the idea of squishing the shape of a greenhouse using tethers though, I worry the force on the tethers would be too much. For a hemispheric dome where all the anchors are pulling straight down, I think that the force trying to lift the dome upward is equal to the area under the dome multiplied by the pressure in it. The dome pictured above looks to be at least 6mx12m, if we assume that and a low pressure of 20 kPa, then the force the anchors would have to counter would be 72 m^2 * 20 kPa = 1.44 MN. If there were 36 tethers spaced around the dome at 1 m intervals, each would have to bear 40 kN, which on Mars is the force exerted by 40/3.7=10.8 tons. Is that a level of force that we could manage by drilling anchors into rock? I don't know but it seems like a huge amount.

You did the math on greenhouse thickness in page 1 of this thread in posts #11 and #18. I haven't checked the math but your results are in the ballpark of math I have done for cylindrical greenhouses.

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#58 2017-09-07 12:41:48

NearryPayob
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From: USA
Registered: 2017-08-31
Posts: 2

Re: Material Choices for Mars

Comparing microstructures in Mars rocks with microstructures in Earth rocks is like comparing clouds with faces? Do you really think so?

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#59 2017-09-07 16:04:10

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 13,342

Re: Material Choices for Mars

only when ignoring that life comes from the same process no mater where we find it and that size is a matter of where it starts as gravity plays a big part in the chemistry of what will happen with that priordial soup.

Not to get the topic to far off topic but Discovery of boron on Mars adds to evidence for habitability and its also another element for making insitu solar cells and other items as well.

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#60 2017-09-07 17:24:37

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,519
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Re: Material Choices for Mars

I thought Opportunity already discovered Borate. That's boron oxide, which can bond to various minerals. Borate acts as a catalyst to form ribose sugar, one of the components of RNA.

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#61 2017-09-07 20:22:55

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 13,342

Re: Material Choices for Mars

Yes made a post a long time ago 2017-01-02

SpaceNut wrote:

Was reminded of last months Boron find...NASA’s Curiosity Discovers Boron On Mars

But found an earlier news story about  Mars Clay Harbored Boron, Key Element For Life, Meteorite Study Suggests

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#62 2018-12-05 21:21:28

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 13,342

Re: Material Choices for Mars

RobertDyck wrote:

Another useful technology for Mars is rock wool. Same insulation as fibreglass but non-flammable, and perhaps more importantly easy to make. It's made by melting rock and extruding. No binder, the hot rock fibres stick together before they cool.
Comfort Batt

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