Scaling Agriculture on Mars

[LMT]

I want you to admit that 40g/cm^2 of CO2 strongly absorbs this vacuum UV. This is well-known and backed by several sources, here's one: https://www.nature.com/articles/s42004-021-00516-z.pdf

But your reference is obviously irrelevant.  The Martian atmosphere isn't warm, supercritical CO2.

To see details of Martian CO2 UV absorption, check a planetary reference; e.g., Venot et al. 2018.  That shows you why only part of the vacuum UV is absorbed, and why most solar UV-C flux punches through.  Fig. 1.

You're getting emotional because it's not true to say, "radiation on Mars is too low for plants to care much."  You've tossed out a google ad misdefinition and a random irrelevant paper, and you're making your own casual interpretations of this-and-that, but you can't actually quote contemporary Mars researchers who are so blase about Mars radiation, because they're not.  The scalable, transparent Mars greenhouse remains a great challenge, due to radiation etc., as above.

Refs.

Venot, O., Bénilan, Y., Fray, N., Gazeau, M.C., Lefèvre, F., Es-sebbar, E., Hébrard, E., Schwell, M., Bahrini, C., Montmessin, F. and Lefèvre, M., 2018. VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres. Astronomy & Astrophysics, 609, p.A34.

[Robotbeat]

...
You're getting emotional because it's not true to say, "radiation on Mars is too low for plants to care much."

A statement that is true. I'm not "emotional." Although I'll admit you're continued gaslighting is frustrating.

You've tossed out a google ad misdefinition...

No, you literally claimed that Vacuum UV includes (all of) UVC and UVB. It doesn't. It's UV below 200nm by your own definition, which under no definition includes UVB and only a portion of UVC. You haven't acknowledged that, yet.

Also, like REGULARLY occurs in your posts, your source and graph doesn't show that 40g/cm^2 CO2 doesn't absorb VUV. In fact, it does, too, absorb virtually all VUV. Source:

https://www.sciencedirect.com/science/article/abs/pii/S0301010403001460
Backup:

pressure on Mars datum is about 6.5millibar. At -5km altitude, like likely landing sites, the pressure increases to 1024 Pascals since the scale height of the martian atmosphere is about 11km. Given the gravity of mars is about 3.7m/s^2 (and goes lower as you go higher, which increases the answer) and the typical slant angle is at LEAST 45degrees, that means you have about 40grams/cm^2 of CO2. Given the atomic mass of CO2 is 44 amu, and the absorption cross section of CO2 at ~200nm is about .003*10^-21 cm^2, we get a transmittance of less than 20%:
T = e^(-40grams/cm^2/(44amu)*.01*10^-21*cm^2)  = ~19%

And at 195nm, that absorption cross section is about .01*10^-21 cm^2, and the transmittance drops to less than 0.5%.

And at 190nm, that absorption cross section is about .03*10^-21 cm^2, and the transmittance drops to less than one in a million.

So yeah, it's safe to say that 200nm is a pretty extreme cutoff for VUV where even Mars' thin atmosphere blocks almost all of it. And I'm ignoring the other aspects of Mars' atmosphere, including O3.

https://www.sciencedirect.com/science/article/abs/pii/S0301010403001460


Of course, no one will operate a greenhouse on the surface without some sort of pressure vessel (until the pressure is increased). Virtually any transparent material will block all VUV, and probably UVC and UVB. The surface radiation on Mars is low enough plants basically wouldn't care much, particularly in a greenhouse or hab. And, in fact, I've long thought that most likely you'll be growing those plants with LEDs as solar panels are cheaper and lighter than pressure-vessel-rated windows that can withstand Martian conditions.

[LMT]

...
You're getting emotional because it's not true to say, "radiation on Mars is too low for plants to care much."

A statement that is true. I'm not "emotional." Although I'll admit you're continued gaslighting is frustrating.

You've tossed out a google ad misdefinition...

No, you literally claimed that Vacuum UV includes (all of) UVC and UVB. It doesn't. It's UV below 200nm by your own definition, which under no definition includes UVB and only a portion of UVC. You haven't acknowledged that, yet.

Also, like REGULARLY occurs in your posts, your source and graph doesn't show that 40g/cm^2 CO2 doesn't absorb VUV. In fact, it does, too, absorb virtually all VUV. Source:

https://www.sciencedirect.com/science/article/abs/pii/S0301010403001460
Backup:

pressure on Mars datum is about 6.5millibar. At -5km altitude, like likely landing sites, the pressure increases to 1024 Pascals since the scale height of the martian atmosphere is about 11km. Given the gravity of mars is about 3.7m/s^2 (and goes lower as you go higher, which increases the answer) and the typical slant angle is at LEAST 45degrees, that means you have about 40grams/cm^2 of CO2. Given the atomic mass of CO2 is 44 amu, and the absorption cross section of CO2 at ~200nm is about .003*10^-21 cm^2, we get a transmittance of less than 20%:
T = e^(-40grams/cm^2/(44amu)*.01*10^-21*cm^2)  = ~19%

And at 195nm, that absorption cross section is about .01*10^-21 cm^2, and the transmittance drops to less than 0.5%.

And at 190nm, that absorption cross section is about .03*10^-21 cm^2, and the transmittance drops to less than one in a million.

So yeah, it's safe to say that 200nm is a pretty extreme cutoff for VUV where even Mars' thin atmosphere blocks almost all of it. And I'm ignoring the other aspects of Mars' atmosphere, including O3.

https://www.sciencedirect.com/science/article/abs/pii/S0301010403001460


Of course, no one will operate a greenhouse on the surface without some sort of pressure vessel (until the pressure is increased). Virtually any transparent material will block all VUV, and probably UVC and UVB. The surface radiation on Mars is low enough plants basically wouldn't care much, particularly in a greenhouse or hab. And, in fact, I've long thought that most likely you'll be growing those plants with LEDs as solar panels are cheaper and lighter than pressure-vessel-rated windows that can withstand Martian conditions.

No, there's no gaslighting; you just don't understand the topic yet.  I gave a wavelength statement -- and corrected yours, too -- but that's trivial, because your "vacuum UV" talk is irrelevant. 

You miscalculated, too.  Absorption starts at ~ 193 nm at Martian temperatures, detailed better in my newer reference above; so your room-temp calc is n/a.  Take 4E-24 cm2 at 193 nm, with a noon slant column of 25 g/cm2.  Calculate that, and realize that the transmitted vacuum UV wavelengths have the highest extraterrestrial flux.  See the log plot.

Image:  Horneck et al. 2010 Fig 1b.  Extraterrestrial UV irradiance spectra.

But again, vacuum UV talk is irrelevant: we see the wide range of UV harm (red) extending up through UV-B.  Blocking some of the shorter vacuum UV wavelengths doesn't protect plants, because harm is much higher at longer UV wavelengths, where flux is much higher:  that's common knowledge.

The surface radiation on Mars is low enough plants basically wouldn't care much, particularly in a greenhouse or hab.

Shielding shields, yes. 

Refs.

Horneck, G., Klaus, D.M. and Mancinelli, R.L., 2010. Space microbiology. Microbiology and Molecular Biology Reviews, 74(1), pp.121-156.

[spacenut]

Growing plants on Mars may not need a "greenhouse" in the same terms of earth "greenhouses", but a closed building or underground facility that used LED grow lights.  This is because it is more efficient on needing heat energy for humans to take care of the plants in a shirt sleeve environment. 

Later greenhouses may have a two layer glass system using clear potable water in between.  This would let light in, but also absorb radiation.  The water may require heating to keep from freezing and that it may also be used to cool batteries in a closed loop system.  But, this is for long term. 

[Barley]

Growing plants on Mars may not need a "greenhouse" in the same terms of earth "greenhouses", but a closed building or underground facility that used LED grow lights.  This is because it is more efficient on needing heat energy for humans to take care of the plants in a shirt sleeve environment. 

The temperature of "greenhouses" will be regulated for the preferences of the plants.  Plants are more productive at certain temperatures (Google Growing Degree Days).  Fortunately humans and plants evolved on the same planet and share biochemistries so their temperature ranges overlap, although personally I find optimum temperature for many plants is higher than I would prefer.

[Paul451]

although personally I find optimum temperature for many plants is higher than I would prefer.

Also the humidity in densely planted growing spaces usually sucks. (And this will be an issue for closed systems. Greenhouses and grow-rooms are notorious for how much they degrade because of humidity and mould.)

Growing plants on Mars may not need a "greenhouse" in the same terms of earth "greenhouses", but a closed building or underground facility that used LED grow lights.

I agree. For an entirely artificial, closed environment, grow-chambers/grow-rooms make vastly more sense than trying to build "greenhouses" on Mars.

Even when the settlement has the resources to build/maintain that kind of structure in excess of simple need, I don't think such greenhouses will make up the primary agricultural volume. They might serve as a mixed-use area for slower growing trees and other perennials that don't tolerate as much light as faster growing crops like grasses, giving colonists access to wide, green spaces with human-friendly spectrum lighting which are none-the-less more productive than purely aesthetic "parks". High production areas will still be highly optimised grow-chambers/grow-rooms.

However,

This is because it is more efficient on needing heat energy for humans to take care of the plants in a shirt sleeve environment.

In general, useful crop plants are less tolerant of climate variation than humans. Even CO2 levels: many plants have a smaller tolerance for high-CO2 levels than humans (it causes acidification (and damage) in the leaves.) Similarly, variations in temperature/humidity/etc. Even if the plant can "tolerate" it, they often do so by shutting down growth until conditions improve, reducing crop yields.

Besides a bit too much humidity, the only thing where humans will struggle to work in an environment optimised for plants is lighting. Especially during the high-growth phase when you can focus on red/blue lighting. I don't think it's damaging to people's eyes, but it's weird and uncomfortable. That said, during that part of the growth cycle, the amount of time you need to actually spend time in the plant area (as opposed to the equipment area(**)) is pretty low, so you can flip on human-friendly lighting during periods where you are working in there.

**(The "plant room" is not the room with the plants. That's the "green room", which is usually white.)

[Robotbeat]

Growing plants on Mars may not need a "greenhouse" in the same terms of earth "greenhouses", but a closed building or underground facility that used LED grow lights.  This is because it is more efficient on needing heat energy for humans to take care of the plants in a shirt sleeve environment. 

Later greenhouses may have a two layer glass system using clear potable water in between.  This would let light in, but also absorb radiation.  The water may require heating to keep from freezing and that it may also be used to cool batteries in a closed loop system.  But, this is for long term.

The absorb radiation part simply isn't needed. Regular glass or plastic already filters out UV just fine to Earth-like levels, further UV absorption is a pretty simple matter, and the other radiation is too low to matter for food production.

Agree you wouldn't even want transparent greenhouses anyway, though.

[Robotbeat]

...
No, there's no gaslighting; you just don't understand the topic yet.  I gave a wavelength statement -- and corrected yours, too -- but that's trivial, because your "vacuum UV" talk is irrelevant. 
...

Here you are claiming that Vacuum UV means UVC and UVB:

I mean, unless you use window material intentionally transparent to UVC, etc, like fused silica, most likely the windows letting in light will filter out the deeper UV.

But you claimed, "Mars doesn’t have vacuum UV", or rather, damaging UVB and UVC. 

It's irrelevant, yes, because there's almost no way to get even UVC (which includes longer wavelengths than VUV) inside a greenhouse unless you're using windows specifically engineered to allow passage of UVC. And why would you do that? And, in fact, since windows in a pressure vessel are so heavy, it wouldn't even make sense to use natural light vs just LEDs and solar panels.


EDIT: And the reason why data ends at 193nm isn't because absorption stops there. That's just the limit of their experiment. Average temperature on Mars is about 210K, too, BTW. But fine, if you want to quibble and say the cutoff is more like 198nm than 200nm, then sure. Basic point is totally correct. To first order, Mars doesn't get vacuum UV.

[LMT]

Podlaha 2017 gives hab specs with potential application to a transparent surface greenhouse.  A relatively mass-efficient architecture is conceivable.

Mods:

- Podlaha's ETFE / Dyneema membrane can be treated as a greenhouse inner tensile membrane.  Meters of ISRU MgCl2 salt water could be added outside this membrane as radiation shield, to match hab radiation environment.  A second tensioned membrane completes the saltwater annulus.  Extra non-tensioned membranes can give IR reflection and surface protection.  A highly transparent ETFE such as F-Clean Clear can maximize transmission PPF.

- Angled reflector membranes could parallel greenhouses, to boost PPF and extend the natural-light growing season.

- Integrated sub-floor ISRU battery farm compartments and radiant flooring could give efficient heating, plus lighting for year-round harvest. 

Notes:

1.  Such a scheme could lower greenhouse areal mass toward that of habs, while targeting year-round harvest.  A self-sufficiency greenhouse would still have total volume and mass greater than settlement habs, but plausibly < 10x.

2.  Further scale reduction could be obtained with excellent volume utilization.  A vertical gardening system would be useful, but you'd want low cargo mass.  Might CO2-derived plastics play a leading role in such mechanisms?  Maximum use of high-intensity wheat lighting would also be beneficial, because this method gives unmatched caloric yield.  What might be a reasonable max wheat dietary calorie %?

3.  Some popular foodstuffs are not suited to greenhouse production, and greenhouse scale shrinks with foodstuff import.  What popular and useful supplemental foodstuffs might maximize cargo calorie density?

4.  A scaled greenhouse invites innovation.  One innovation of note:  GM-yeast Perfect Day milk.  Many true dairy products could be obtained from such a system.  What are some other innovations with special greenhouse potential?

Refs.

Podlaha M. 2017.  NEW HOME - A First Martian Habitat.  M.Sc. Thesis.

[Coastal Ron]

Podlaha 2017 gives hab specs with potential application to a transparent surface greenhouse.  A relatively mass-efficient architecture is conceivable.

I'm not sold on large inflated structures housing critical infrastructure yet, not when we don't know how to find leaks, and quickly repair major leaks/tears. We have to remember that failure IS an option, so until we understand how to recover from failure, we shouldn't rely on "hope" for survival.

Which is why I'm hoping that tunneling will become an option, since tunnels are far more stable and far less likely to develop catastrophic leaks.

The challenge with tunneling is that the area available can't be increased as quickly as surface inflated structures can be, so I'm sure we will see some inflatables to start, and maybe they will be limited to crops that are not critical to the survival of the colony?

[LMT]

Podlaha 2017 gives hab specs with potential application to a transparent surface greenhouse.  A relatively mass-efficient architecture is conceivable.

I'm not sold on large inflated structures...

The inflatable BEAM has served the ISS crew since 2016.  It's slated for use through 2028, maybe longer.  That exercise has proved much.

You might examine Podlaha's thesis to see how he met his particular architectural challenges. 

For comparison:  how would you shore up hundreds of meters of fragile regolith or sediment, to get your tunnel started?

Image:  BEAM inflated on ISS, 2016.  NASA.

[Barley]

I'm not sold on large inflated structures housing critical infrastructure yet, not when we don't know how to find leaks, and quickly repair major leaks/tears. We have to remember that failure IS an option, so until we understand how to recover from failure, we shouldn't rely on "hope" for survival.

Which is why I'm hoping that tunneling will become an option, since tunnels are far more stable and far less likely to develop catastrophic leaks.

The challenge with tunneling is that the area available can't be increased as quickly as surface inflated structures can be, so I'm sure we will see some inflatables to start, and maybe they will be limited to crops that are not critical to the survival of the colony?

You can prevent anything from being critical to survival by redundancy.  You need to look at the numbers to see if a larger number of somewhat frail structures is better than a minimal number of more robust ones.

Also: a failure in a surface structure can usually be repaired with no more effort than was required to build in the first place.  OTOH a cave in may be, in practice, irreparable.  Even with redundant access loss of an important node could substantially degrade operational efficiency.

[Coastal Ron]

Podlaha 2017 gives hab specs with potential application to a transparent surface greenhouse.  A relatively mass-efficient architecture is conceivable.

I'm not sold on large inflated structures...

The inflatable BEAM has served the ISS crew since 2016.

Which means nothing, since the BEAM is not a large structure.

[Coastal Ron]

I'm not sold on large inflated structures housing critical infrastructure yet, not when we don't know how to find leaks, and quickly repair major leaks/tears. We have to remember that failure IS an option, so until we understand how to recover from failure, we shouldn't rely on "hope" for survival.

Which is why I'm hoping that tunneling will become an option, since tunnels are far more stable and far less likely to develop catastrophic leaks.

The challenge with tunneling is that the area available can't be increased as quickly as surface inflated structures can be, so I'm sure we will see some inflatables to start, and maybe they will be limited to crops that are not critical to the survival of the colony?

You can prevent anything from being critical to survival by redundancy.  You need to look at the numbers to see if a larger number of somewhat frail structures is better than a minimal number of more robust ones.

Redundancy is good, and it may be the answer, but we really have no idea what the failure rate would be, nor the failure mode, of large inflated structures.

Also: a failure in a surface structure can usually be repaired with no more effort than was required to build in the first place.

That assumes you still have the manpower and equipment used to build the original large inflated structure. You may not, since that manpower and equipment may have moved on to some other distant location. It also assumes you are stockpiling spare parts, which isn't bad, just that we initially won't know how many spare parts will be needed.

OTOH a cave in may be, in practice, irreparable.  Even with redundant access loss of an important node could substantially degrade operational efficiency.

If that cave was on Earth you might have a point, but Mars has 1/3 the gravity of Earth, and from what we can tell no large Marsquakes. So inflatable structures inside of tunnels and caves may be enough to keep cave-ins from happening.

As to the actual topic of the thread, the real challenge will be power for lights and operation of agriculture that is contained with a controlled environment. Because I'm thinking the initial agriculture will actually be vertical farms and aquaculture, which can be a small percentage of the overall space needed for each group of humans added to the colony.

[LMT]

OTOH a cave in may be, in practice, irreparable.

...inflatable structures inside of tunnels and caves may be enough to keep cave-ins from happening.

Loads are MPa.  Air pressure, kPa.

Air pressure (inflatables) couldn't compensate.  No one seems to have a practical method for tunneling through Martian regolith or sediment.

And weren't you worried about inflatable leaks, tears, and repairs?  Under such pressure...  "...we shouldn't rely on 'hope' for survival", etc.

[lamontagne]

For once it's not strawberries and tomatoes.

Paper on intensive grow room wheat production.  Refers back to Bugbee NASA papers but adds some nice building and power information.

Not cost competitive on Earth, but seems really interesting for Mars.
Interesting number of about 70 days per production cycle.
700 proven and 2000 tonnes per heactare production, so hundreds of times higher than in fields.
In 10x 1m high hydroponic shelves.

Seems infinitely simpler than surface greenhouses.

[LMT]

For once it's not strawberries and tomatoes.

Paper on intensive grow room wheat production.  Refers back to Bugbee NASA papers but adds some nice building and power information.

Not cost competitive on Earth, but seems really interesting for Mars.
Interesting number of about 70 days per production cycle.
700 proven and 2000 tonnes per heactare production, so hundreds of times higher than in fields.
In 10x 1m high hydroponic shelves.

Seems infinitely simpler than surface greenhouses.

Yes, you'd expect hydroponics and vertical gardening there, with truly intense LED lighting.  We were just talking about it in the Mars power thread.  Doesn't Fig. 2 really stand out?

[lamontagne]

For once it's not strawberries and tomatoes.

Paper on intensive grow room wheat production.  Refers back to Bugbee NASA papers but adds some nice building and power information.

Not cost competitive on Earth, but seems really interesting for Mars.
Interesting number of about 70 days per production cycle.
700 proven and 2000 tonnes per heactare production, so hundreds of times higher than in fields.
In 10x 1m high hydroponic shelves.

Seems infinitely simpler than surface greenhouses.

Yes, you'd expect hydroponics and vertical gardening there, with truly intense LED lighting.  We were just talking about it in the Mars power thread.  Doesn't Fig. 2 really stand out?

Yes, impressive.  The power requirements are about the same as for more spread out farming, but the surface area is much smaller and construction costs much reduced.   Fig.2 from the paper.
So we seem to be on about a one year cycle or going over the same ground in this thread, more or less   

[Coastal Ron]

OTOH a cave in may be, in practice, irreparable.

...inflatable structures inside of tunnels and caves may be enough to keep cave-ins from happening.

Loads are MPa.  Air pressure, kPa.

Air pressure (inflatables) couldn't compensate.

An inflatable doesn't have to completely compensate for wall pressure, and there couldn't be other methods for shoring up the carved out space.

No one seems to have a practical method for tunneling through Martian regolith or sediment.

Not true. What we have done here on Earth with tunneling would be applicable to Mars, since the elements are the same, and the only difference is the atmosphere and gravity - neither of which are a big factor in tunneling.

And weren't you worried about inflatable leaks, tears, and repairs?

Above ground inflatables are exposed to far more potential puncture events than underground inflatables, and the likelihood of a blowout in a tunnel is far less than on the surface.

Tunnels don't solve everything, but they do have a number of advantages regarding holding in an atmosphere.

[LMT]

Above ground inflatables are exposed to far more potential puncture events than underground inflatables, and the likelihood of a blowout in a tunnel is far less than on the surface.

For comparison:  Technical considerations for TBM tunneling for mining projects