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#126 2014-04-08 10:40:51

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,493
Website

Re: Crops

Gas core NTR does not offer Isp as high as explosion propulsion: 200-2500 sec at higher thrust,  6000 sec at low thrust,  vs about 10,000 sec at 10,000 tons with acceleration 2-4 gees for explosion propulsion (and nearer 12K to 20K sec Isp at 20,000 tons and up).  Explosion propulsion offers super-high Isp at super-high thrust,  unique among the ideas I've seen.  It was flight tested successfully as a one-meter long model propelled by pulses of high-explosive (dynamite or something similar) back about 1959,  so we have known for half a century it will work. 

A lot of thinking went into the survivability of the pusher plate.  Some of the structural damage observed in Nagasaki and Hiroshima went into the design,  as did observations from the surface nuclear tests in Nevada,  and in some of the underground tests since.  The verdict was "yes, it'll work,  and for a long time".  All of that was well-defined by the time work ceased in 1965.  In part this is because there is no physical blast wave in the vacuum of space,  there is only the super-bright "light" of the radiation blast.  The blast wave risk is only while in the atmosphere during surface launch.  You only do that once,  she stays in space from then on. 

A piece not well known or remembered from those times is that the charges were actually shaped-charge nuclear fission devices,  with a "working mass" material as part of the package.  You need a spindle-shaped distribution of EM radiation blast,  with the working material in one radiation blast spindle.  The radiation and working material plasma strike the pusher plate.  Key is to intercept all that spike,  so you cannot design small,  or else you cannot get tens of 1000's of sec of Isp.  (Done in really large ships with fusion devices should be almost an order of magnitude more efficient yet.) 

Designing too small and getting too low an Isp to attractive is officially why NASA killed old "Project Orion",  which was originally a USAF program.  NASA really killed it because they viewed it as a competitor to the NERVA solid core NTR they had in development,  instead of the complement that it really was.  All of USAF's space programs were given to NASA in 1965 by presidential order,  save only the orbital spying programs. 

Old "Project Orion" was done at General Atomics in San Diego 1959-1965 with USAF as the sponsoring agency,  based on company R&D done in the prior 5 years.  Their baseline design ship was 10,000 tons,  280 feet long,  185 ft in diameter,  carried a crew of about a hundred,  surface-launched from Earth (at the fallout "cost" equivalent to one 9-MT test),  with a 3-year design mission.  It spun about the long axis like a rifle bullet for artificial gravity.  It was to go to Saturn on its maiden voyage,  stopping off at the moon and Mars on the way.  They were pretty sure it would work just fine and do exactly that.  Remarkable for 1959.

And NASA killed it. 

Sad history,  ain't it?

GW

Last edited by GW Johnson (2014-04-08 10:43:30)


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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#127 2014-04-08 14:57:25

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Crops

SpaceNut wrote:

One of the local movements is for the schools to make use of local grown produce for lunches. Making local food a priority at UNH, one meal at a time

For individuals, it takes a little bit of work to eat locally. For an institution like UNH, which serves an average of 16,000 meals each day during the school year, using locally-grown and produced foods is a serious challenge.
About 23 percent of all the food dining services purchases is considered local—that is, it’s grown or produced within a 250 mile radius of campus. The university is also home to Food Solutions New England, a regional network “dedicated to advancing a sustainable New England food system.” Part of that vision: that the region can build the capacity to produce at least 50 percent of the food New Englanders need, in an environmentally and socially-sustainable way, by 2060. That produce is grown using compost created in part from food waste from the dining halls. As part of the composting system, food waste is washed off plates and trays into a trough. Water pushes the waste down the trough and into a drum, where the waste is ground up and liquid is extracted from it. The waste is then placed in large yellow buckets—each holding 75 pounds of food waste—and sent to Kingman Farm in Durham, where it’s used to make compost. That compost later returns to the university, where it’s used by students in the Food Experience course to help grow salad mix, tomatoes, zucchini and other vegetables that are served at the Dairy Bar and other university locations. Waste cooking oil is processed into biodiesel. Dining services has its own small electric car—like a golf cart, but enclosed—that Hill and Dining Services director John Plodzik use to visit the campus’ dining halls.

Looking at this as a mars building direction a small colony would need to distance the food from earth supply and in order to do that we would need a game plan as well as a timeline for how much resupply would taper off by following each successful mission to mars.

Yes, I like the way you put that.  We should plan to taper off earth supply.  The key really is ensuring we can manufacture enough soil and put in place enough power to create an agricultural surplus. No doubt there will be importation of some "treats" for colonists: beef steak comes to mind.  Let's say a colony of 1000 imported 1 kg of treats per person per month, that would be 12 tonnes a year, a manageable amount I think.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#128 2014-04-08 19:34:55

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,044

Re: Crops

The growth of the enclosure to grow food within must also increment with each launch from Earth. The question is where will the materials come from to make the size growth possible. Referring to the first page list of RobertDyck compared to the footprint from them on page three tells the story when we look at the growing cycle to maturity for the crops that we will grow.

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#129 2014-04-09 15:09:13

Quaoar
Member
Registered: 2013-12-13
Posts: 652

Re: Crops

GW Johnson wrote:

It was flight tested successfully as a one-meter long model propelled by pulses of high-explosive (dynamite or something similar) back about 1959,  so we have known for half a century it will work. 



GW

It was tested in atmosphere, where the plate is cooled convectively. In space the plate will be cooled radiatively so pulse frequency has to be lower and the plate (probably some alloy of tungsten)  has to function as a radiation shield, as a shock adsorber and as a heat radiator. The ship will need also very powerful RCS rockets to mantain attitude douring pulse.
And first of all, the first nuclear pulse has to be fired in high Earth orbit.

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#130 2014-04-09 17:18:13

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Crops

SpaceNut wrote:

The growth of the enclosure to grow food within must also increment with each launch from Earth. The question is where will the materials come from to make the size growth possible. Referring to the first page list of RobertDyck compared to the footprint from them on page three tells the story when we look at the growing cycle to maturity for the crops that we will grow.


1. Use Mars brick Roman arch architecture as recommended by Zubrin (with cut and cover techniques) to create pressurised chambers.

2. Use artificial lighting, and hydroponic agriculture as appropriate. But Mars manufactured soil (based on crushed rock, sand, human excrement and food waste) can be used with some additives brought in from Earth.

3. Within the chambers grow food on several tiers - on the equivalent of garage storage units.  In a 2.5 metre high facility for some foods you might be growing on 5 tiers.

4. Use solar concentrators made from Mars produced polished steel dishes reflecting light on to imported PV Panels to generate power for artificial lighting and heat.

I made the total area required for 12 people to be 1900 square metres (RD's figures).  I think with tiered agriculture that could be reduced to about 400 sq. metres.  That could be provided by 4 x 50 metre chambers of 3.5 metres' width (allows for a 1.5 metres gangway for servicing of the tiers).  I think a group of 12 people using robot diggers and automated brick manufacture could build those chambers within one year.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#131 2014-04-09 17:35:51

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,816
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Re: Crops

I still argue for ambient lighting. Mars will have multiple redundant life support systems, but power is a single point of failure. The only life support system that works without power is a greenhouse.

Materials: glass windows made from Mars sand. One rover did find a tiny deposit of pure silica sand, but it was a cup or two. I presented a paper at the Mars Society convention in Chicago in 2005, about smelting aluminum. Silica gel was a byproduct; add soda and lime to turn that into glass. So glass as a byproduct of aluminum production. Ore is bytownite, a mineral constitutes 21.5% - 27% of Mars surface, according to MGS. We can make steel from hematite concretions: those "blueberries" discovered by Opportunity. We can make fibreglass from glass. All plastics can be made from CO2 and H2O, with enough electricity. Some need a few other things: nylon and melamine need nitrogen, polycarbonate needs salt. All exist on Mars. We can make Portland cement from Mars rocks. I have read that cement requires nitrogen bubbles to cure properly, so not sure how that would work outdoors on Mars. The key to all insitu resource utilization is power. Mars needs lots of power.

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#132 2014-04-09 19:37:40

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Crops

RobertDyck wrote:

I still argue for ambient lighting. Mars will have multiple redundant life support systems, but power is a single point of failure. The only life support system that works without power is a greenhouse.

Materials: glass windows made from Mars sand. One rover did find a tiny deposit of pure silica sand, but it was a cup or two. I presented a paper at the Mars Society convention in Chicago in 2005, about smelting aluminum. Silica gel was a byproduct; add soda and lime to turn that into glass. So glass as a byproduct of aluminum production. Ore is bytownite, a mineral constitutes 21.5% - 27% of Mars surface, according to MGS. We can make steel from hematite concretions: those "blueberries" discovered by Opportunity. We can make fibreglass from glass. All plastics can be made from CO2 and H2O, with enough electricity. Some need a few other things: nylon and melamine need nitrogen, polycarbonate needs salt. All exist on Mars. We can make Portland cement from Mars rocks. I have read that cement requires nitrogen bubbles to cure properly, so not sure how that would work outdoors on Mars. The key to all insitu resource utilization is power. Mars needs lots of power.

I've nothing against greenhouses and we should indeed start experimenting with them as soon as we are established on the planet. But we cannot rely on greenhouse technology. For one thing, an early Mars colony could be wiped out by a single meteorite shower if we relied on greenhouses exclusively. 

Power is much more reliable, from that point of view.

Whilst it is true we need a lot of power, that is only per capita.  In the early stages, let's say up until Mars's population exceeds 1000 even very high power requirements e.g. 100KWs per capita amount in total to a max of only 100 MWs, or 20 large wind turbines on earth. 

A population of 1000 might involved something like 200 missions to Mars, during which you can transfer a huge amount of energy producing equipement.  With solar concentrators, we can produce 90% of the power equipment on Mars once we have small scale smelting and metal processing in place.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#133 2014-04-09 20:01:37

RobertDyck
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From: Winnipeg, Canada
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Posts: 7,816
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Re: Crops

Well, yea. And a global dust storm will block all sunlight. Ambient light will drop to a fraction, and those storms can last months. So we need artificial lights in the greenhouse as a backup. But I still argue, not for normal operations. Reserve power for industrial and other operations.

We will also need chemical/mechanical oxygen and water recycling. Use the exact same system as ISS: regenerable sorbent, water filtration, water electrolysis, sabatier reactor. But we need multiple backups: direct CO2 electrolysis (from both recycled CO2 and Mars CO2), collect CO2 from Mars atmosphere, melt and filter Mars ice, stored O2, stored whole air, spacesuits, and even oxygen candles. And the ability to mix and match life support components.

But an ambient light greenhouse has to be part of that mix. Plants recycle CO2 into O2. And they transpire water from their leaves; you can process sewage from the toilet to form grey water for plants. Then plants convert that into humidity. Condense that humidity on cold walls/windows of the greenhouse, with a water collection trough along the bottom. That water tastes better than the best filtered water that NASA can produce. And energy is entirely sunlight. So if the power plant dies, you can still breathe and drink while working to fix it.

And another backup: seed bank in a buried chamber. Plants can endure a lot more radiation than humans can. But a coronal mass ejection directly at Mars, hitting during daylight? That could kill all the plants. That's about the only thing that can. Guelph University did an experiment with spinach: they tested how low they can push pressure and plants still grow. They found plants will transpire more water through their leaves as pressure drops, but as long as that humidity is condensed and run back into the soil, it's no net loss. The minimum is 10kPa, below that plants wilt. Humans require at least 17kPa, and can only endure that after months of high altitude training, and only if they're young  and strong, and only if it's pure oxygen, and high humidity. But any human can handle 20kPa. Normal Earth pressure is about 100kPa, depending where you live. But Guelph tried one additional experiment: they decompressed their spinach to Mars ambient, and left it there for 1 hour before re-pressurizing. The spinach wilted, but as soon as pressure came back it perked up and continued to grow. So plants can handle complete decompression for brief periods. So I repeat: the only thing that will kill your plants is a coronal mass ejection.

Last edited by RobertDyck (2014-04-09 22:38:20)

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#135 2014-04-10 02:02:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Crops

RobertDyck wrote:

Well, yea. And a global dust storm will block all sunlight. Ambient light will drop to a fraction, and those storms can last months. So we need artificial lights in the greenhouse as a backup. But I still argue, not for normal operations. Reserve power for industrial and other operations.

We will also need chemical/mechanical oxygen and water recycling. Use the exact same system as ISS: regenerable sorbent, water filtration, water electrolysis, sabatier reactor. But we need multiple backups: direct CO2 electrolysis (from both recycled CO2 and Mars CO2), collect CO2 from Mars atmosphere, melt and filter Mars ice, stored O2, stored whole air, spacesuits, and even oxygen candles. And the ability to mix and match life support components.

But an ambient light greenhouse has to be part of that mix. Plants recycle CO2 into O2. And they transpire water from their leaves; you can process sewage from the toilet to form grey water for plants. Then plants convert that into humidity. Condense that humidity on cold walls/windows of the greenhouse, with a water collection trough along the bottom. That water tastes better than the best filtered water that NASA can produce. And energy is entirely sunlight. So if the power plant dies, you can still breathe and drink while working to fix it.

And another backup: seed bank in a buried chamber. Plants can endure a lot more radiation than humans can. But a coronal mass ejection directly at Mars, hitting during daylight? That could kill all the plants. That's about the only thing that can. Guelph University did an experiment with spinach: they tested how low they can push pressure and plants still grow. They found plants will transpire more water through their leaves as pressure drops, but as long as that humidity is condensed and run back into the soil, it's no net loss. The minimum is 10kPa, below that plants wilt. Humans require at least 17kPa, and can only endure that after months of high altitude training, and only if they're young  and strong, and only if it's pure oxygen, and high humidity. But any human can handle 20kPa. Normal Earth pressure is about 100kPa, depending where you live. But Guelph tried one additional experiment: they decompressed their spinach to Mars ambient, and left it there for 1 hour before re-pressurizing. The spinach wilted, but as soon as pressure came back it perked up and continued to grow. So plants can handle complete decompression for brief periods. So I repeat: the only thing that will kill your plants is a coronal mass ejection.

The evidence from the Rovers on Mars is quite the opposite. Even in dust storms, substantial amounts of radiation get through (I don't think they have ever dipped below 20% of expected insolation). But of course, with any solar energy system, you will be storing energy, most likely as methane, which can then be deployed to power generators.

I agree power demands will probably be a lot higher on Mars. But while we do need all that life support and so on, we won't be for instance cooking in ovens for hours or watching TV on huge screens or using our washing machines to wash a couple of socks etc etc. In other words we won't see the sort of profligate personal energy use that is common in rich countries on Earth.


As I say, I have nothing against ambient light greenhouses - but they will be far more vulnerable to global dust storms. The fact that plants can operate at low pressure, is certainly in their favour, I would agree.

As you indicate, chambers also protect against radiation events.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#136 2014-04-10 08:24:46

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,816
Website

Re: Crops

louis wrote:

The evidence from the Rovers on Mars is quite the opposite. Even in dust storms, substantial amounts of radiation get through (I don't think they have ever dipped below 20% of expected insolation). But of course, with any solar energy system, you will be storing energy, most likely as methane, which can then be deployed to power generators.

I agree power demands will probably be a lot higher on Mars. But while we do need all that life support and so on, we won't be for instance cooking in ovens for hours or watching TV on huge screens or using our washing machines to wash a couple of socks etc etc. In other words we won't see the sort of profligate personal energy use that is common in rich countries on Earth.


As I say, I have nothing against ambient light greenhouses - but they will be far more vulnerable to global dust storms. The fact that plants can operate at low pressure, is certainly in their favour, I would agree.

As you indicate, chambers also protect against radiation events.

Huh? What? Do you understand what I said? I said plants endure a lot more radiation than humans. They continue to grow and just ignore radiation. The MARIE instrument on Mars Odyssey measured radiation in Mars orbit, and were able to estimate how much would get through to the surface based on a formula devised by NASA and the US military nuclear bomb guys. It's a very accurate estimate. That was verified by an instrument on Curiosity rover. The result is about twice was much radiation gets to Mars orbit as ISS, but only a quarter of that gets to the surface. So radiation on Mars surface is about half of ISS. Roughly, it depends on altitude of your landing location. They also found radiation in space measured by Curiosity was about 50% more than measured by Odyssey. That was because Curiosity launched during solar maximum, Odyssey didn't. Furthermore, the atmosphere of Mars blocks about 90% of heavy ion radiation at high altitude locations like Meridiani Planum where Opportunity landed, and 98% at a low altitude like Gale Crater where Curiosity is. So Mars atmosphere shields against the worst, nastiest type of radiation. The plastic film of an inflatable greenhouse will block all alpha and beta radiation. The same metal coating used by NASA to block UV on spacecraft windows and spacesuit visors would be applied to the greenhouse, that would block UV. Since it's metal, it also blocks a little X-rays, but X-rays in space are so slight that the metal coating is enough to block it all. The aluminized Mylar used for thermal protection in the white fabric of a spacesuit will protect that. On Mars we want something else for thermal protection, such as Thinsulate, but a single layer of aluminized Mylar would act as X-ray protection. So all you have left is proton, light ion, and medium ion radiation. Plants can endure that. Plants can endure more radiation than exists on Mars. Global dust storm or not, plants can ignore far more radiation than is there.

Radiation is not a dragon. As Robert Zubrin said, Medieval maps often had "dragons be here" for areas not explored. This scared sailors away. We need to slay the "dragons". Radiation is not an issue. For long term settlement, a human habitats would have a minimum of 2 metres of regolith on the roof. For exploration, a single layer of sand bags filled with Mars regolith. However, greenhouses would not. This is supposed to be the Mars Society. The people here are supposed to be the ones knowledgeable about Mars. *DO NOT* fall into the trap of treating radiation as a hazard that prevents humans from Mars. Every time you talk about burying a greenhouse underground, what the public hears is it's not safe for humans to leave Earth.

Yes, a greenhouse on the Moon would have to be buried. The Moon does not have an atmosphere, Mars gets 47% as much sunlight as Earth but the Moon gets full sunlight, and the Moon gets 2 weeks of sun followed by 2 weeks of night. So any greenhouse on the Moon must be buried. But not Mars. On Mars you can build a greenhouse on the surface. This is one of the many reasons for going to Mars instead of the Moon.

And I already addressed dust storms. Yes, you need artificial light during dust storms. That takes power. Expect no industry during the dust storm, so power for the greenhouse would take away all power for mining and refining. Just make sure you don't have a power failure during a dust storm; that would mean death. And this is one of the many reasons why I keep saying solar power on Mars is not good enough.

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#137 2014-04-10 08:40:20

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,493
Website

Re: Crops

So,  get out your backhoe,  and build a roof up on supports,  covered in regolith,  with transparent walls.  Put reflective stuff around the building to bounce light into the building through the transparent walls.  You can even concentrate it to Earth-standard light intensity,  especially if you build it in a small depression or crater. 

That's a greenhouse that is completely radiation-protected.  It would work on Mars or even airless places like the moon,  if you stack up your sandbags deep enough.  I had one design concept for such a thing posted over at "exrocketman".  It was titled "Aboveground Mars Houses",  dated 1-26-13.  Some sort of concrete substitute would be nice,  but you could build the thing entirely with imported steel and glass,  and the local regolith.  The foundation,  since it is buried,  could be "icecrete". 

GW
http://exrocketman.blogspot.com


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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#138 2014-04-10 09:05:56

RobertDyck
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From: Winnipeg, Canada
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Re: Crops

Do you need to protect fish from drowning? Protecting plants from Mars level radiation is like protecting fish from water.

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#139 2014-04-10 15:25:51

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,493
Website

Re: Crops

It's not so much the garden you need to protect.  It's the gardeners.

GW


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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#140 2014-04-10 15:54:37

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,546
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Re: Crops

I would think that working in the greenhouse would be a mandatory communal activity for its psychological and physiological benefits, so radiation exposure to any one person would be less of a concern.


-Josh

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#141 2014-04-10 16:46:13

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,816
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Re: Crops

An ambient light greenhouse would provide the same protection to workers as a spacesuit.

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#142 2014-04-10 18:29:52

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Crops

RobertDyck wrote:
louis wrote:

The evidence from the Rovers on Mars is quite the opposite. Even in dust storms, substantial amounts of radiation get through (I don't think they have ever dipped below 20% of expected insolation). But of course, with any solar energy system, you will be storing energy, most likely as methane, which can then be deployed to power generators.

I agree power demands will probably be a lot higher on Mars. But while we do need all that life support and so on, we won't be for instance cooking in ovens for hours or watching TV on huge screens or using our washing machines to wash a couple of socks etc etc. In other words we won't see the sort of profligate personal energy use that is common in rich countries on Earth.


As I say, I have nothing against ambient light greenhouses - but they will be far more vulnerable to global dust storms. The fact that plants can operate at low pressure, is certainly in their favour, I would agree.

As you indicate, chambers also protect against radiation events.

Huh? What? Do you understand what I said? I said plants endure a lot more radiation than humans. They continue to grow and just ignore radiation. The MARIE instrument on Mars Odyssey measured radiation in Mars orbit, and were able to estimate how much would get through to the surface based on a formula devised by NASA and the US military nuclear bomb guys. It's a very accurate estimate. That was verified by an instrument on Curiosity rover. The result is about twice was much radiation gets to Mars orbit as ISS, but only a quarter of that gets to the surface. So radiation on Mars surface is about half of ISS. Roughly, it depends on altitude of your landing location. They also found radiation in space measured by Curiosity was about 50% more than measured by Odyssey. That was because Curiosity launched during solar maximum, Odyssey didn't. Furthermore, the atmosphere of Mars blocks about 90% of heavy ion radiation at high altitude locations like Meridiani Planum where Opportunity landed, and 98% at a low altitude like Gale Crater where Curiosity is. So Mars atmosphere shields against the worst, nastiest type of radiation. The plastic film of an inflatable greenhouse will block all alpha and beta radiation. The same metal coating used by NASA to block UV on spacecraft windows and spacesuit visors would be applied to the greenhouse, that would block UV. Since it's metal, it also blocks a little X-rays, but X-rays in space are so slight that the metal coating is enough to block it all. The aluminized Mylar used for thermal protection in the white fabric of a spacesuit will protect that. On Mars we want something else for thermal protection, such as Thinsulate, but a single layer of aluminized Mylar would act as X-ray protection. So all you have left is proton, light ion, and medium ion radiation. Plants can endure that. Plants can endure more radiation than exists on Mars. Global dust storm or not, plants can ignore far more radiation than is there.

Radiation is not a dragon. As Robert Zubrin said, Medieval maps often had "dragons be here" for areas not explored. This scared sailors away. We need to slay the "dragons". Radiation is not an issue. For long term settlement, a human habitats would have a minimum of 2 metres of regolith on the roof. For exploration, a single layer of sand bags filled with Mars regolith. However, greenhouses would not. This is supposed to be the Mars Society. The people here are supposed to be the ones knowledgeable about Mars. *DO NOT* fall into the trap of treating radiation as a hazard that prevents humans from Mars. Every time you talk about burying a greenhouse underground, what the public hears is it's not safe for humans to leave Earth.

Yes, a greenhouse on the Moon would have to be buried. The Moon does not have an atmosphere, Mars gets 47% as much sunlight as Earth but the Moon gets full sunlight, and the Moon gets 2 weeks of sun followed by 2 weeks of night. So any greenhouse on the Moon must be buried. But not Mars. On Mars you can build a greenhouse on the surface. This is one of the many reasons for going to Mars instead of the Moon.

And I already addressed dust storms. Yes, you need artificial light during dust storms. That takes power. Expect no industry during the dust storm, so power for the greenhouse would take away all power for mining and refining. Just make sure you don't have a power failure during a dust storm; that would mean death. And this is one of the many reasons why I keep saying solar power on Mars is not good enough.

Think you misunderstood my response. My reference to radiation was to solar radiation in the context of your claim that dust storms put a stop to PV power generation on Mars. I was making the point that this has not been the experience with the Rovers.  I don't think of other radiation as dragon that cannot be defeated, though it must be respected.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#143 2014-04-10 19:08:22

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,546
Website

Re: Crops

RobertDyck wrote:

An ambient light greenhouse would provide the same protection to workers as a spacesuit.

I agree with this in an order-of-magnitude sense (depending on the particular design of the spacesuit and greenhouse, though speaking again in general terms I would expect that the greenhouse would probably provide somewhat more protection), but I don't know what you're suggesting with this post.  That total time in spacesuits should be limited?  Agreed.  That there are more important safety issues besides radiation and that, fairly often, the importance and necessity of the work being done trumps the importance of various dangers?  Also agree.


-Josh

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#144 2014-04-10 19:34:02

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,816
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Re: Crops

Oh, past discussion, and I think I did give a presentation about radiation at a past Mars Society convention. It started when one woman made the observation that neutron spectrometers on Mars Odyssey measured neutrons coming up from Mars. That means neutron radiation. Interaction of radiation from solar wind with Mars regolith generates neutron radiation. Ok. So through contacts I got a student at MIT to estimate dose. The result was 0.5 REM per year (just neutrons). We then estimated what it would take to keep radiation exposure for a permanent settler on Mars down to limits for a US nuclear reactor worker. The result was 40 hours per week outside in a spacesuit, assuming radiation in the habitat was negligible. The minimum to achieve that was 2 metres of regolith on the roof of the habitat. So my argument was time in an ambient light greenhouse counts toward time in a spacesuit. By the way, time in an airlock does not count since that's in the habitat so also protected by thick regolith. But restricting time outdoors to 40 hours per week? That's a work week; I don't think any astronaut would object to that.

Last edited by RobertDyck (2014-04-10 19:35:34)

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#145 2014-04-10 19:51:23

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,546
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Re: Crops

I'd caution that the precise amounts of radiation on Mars are still unknown, and that hab material is likely to have some amount of residual radiation, no matter what you make it out of, from the neutron flux on the surface.  I don't know how much that will be, though, and if you use material from farther under the ground this will be less of an issue than aboveground.

I agree with the thrust of your analysis, though the amount of allowable surface time might be off.

2+ meters of shielding works nicely with the necessity of 4-5 m of regolith to contain 500 mb of pressure.


-Josh

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#146 2014-04-10 20:21:02

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
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Re: Crops

Second time trying to post thoughts on the technique, the equipment and technology to construct any building is going to be limited at first unless we pick the lowest of techology to make it happen as we will not have a mission plan that ships heavy equipment for processing or moving mars surface soils or crushing to grinding it to make glass. To do these things requires seperate site preloading of such items for the base camp to make use of prior to sending man.

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#147 2014-04-10 21:32:03

RobertDyck
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Re: Crops

I was part of the Mars Homestead Project Phase 1: Hillside Settlement. The premise was to cut a notch into the side of a hill, build the base, then push regolith from the hill down onto the roof. That assumed equivalent to a Bobcat skid-steer loader.

The initial mission, the first humans to Mars, will be a science mission. That will be a Mars Direct habitat or equivalent. The surface of Mars has half the radiation of ISS, which is more than a US nuclear reactor worker, but still something that NASA can live with. Assume sandbags filled with Mars regolith on the roof.

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#148 2014-04-10 22:22:25

JoshNH4H
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From: Pullman, WA
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Re: Crops

Other than radiation shielding, I never quite understood why the Mars Homestead project chose the side of a hill to site the colony.  It seems to me that that would be limiting insofar as a more hilly area is likely to be less congenial to transportation and additional construction.

I did read an Isaac Asimov story once about how it's relatively easy to dig into horizontal walls than vertical floors; Was this perhaps the reasoning, and if so is this true?


-Josh

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#149 2014-04-11 02:39:48

louis
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From: UK
Registered: 2008-03-24
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Re: Crops

JoshNH4H wrote:

Other than radiation shielding, I never quite understood why the Mars Homestead project chose the side of a hill to site the colony.  It seems to me that that would be limiting insofar as a more hilly area is likely to be less congenial to transportation and additional construction.

I did read an Isaac Asimov story once about how it's relatively easy to dig into horizontal walls than vertical floors; Was this perhaps the reasoning, and if so is this true?

Also tunnelling is a lot more difficult and dangerous than cut and cover.  You'll still need some sort of structure to go in the tunnel unless you want to take a gamble on there being no roof collapse.


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#150 2014-04-11 05:51:33

RobertDyck
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From: Winnipeg, Canada
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Re: Crops

JoshNH4H wrote:

I never quite understood why the Mars Homestead project chose the side of a hill to site the colony.

No need to dig at all. No nead to lift dirt onto the roof. We started with Bruce MacKenzie's masonary arches. By the way, Robert Zubrin got the idea from Bruce. Providing enough regolith for counterpressure for masonary arches would require a lot of dirt. Digging into the side of a hill meant we didn't need to lift any up, just push down. Besides, any location that is close to the equator yet has water ice tends to be a river valley. That means we're going to be at the bottom of a valley anyway. That was before the pack ice at Elysium Planetia was found. So yea, cut and cover.

If you don't like it, then Phase 2 was a Plains Settlement. It had a big platform to hold the soil, basically a giant tray with support pillars. Beneath was cylindrical pressure modules. I never liked it, too much structure. I wasn't involved with that one.
thumb_plains-cover-2007-06.jpg

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