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#51 2017-05-24 14:13:41

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,835

Re: Louis' Solar Power Strategy

While waiting for my car to be serviced, I re-read portions of The Case for Mars. I paid special attention to the food required by the mission, and the reasoning behind taking fresh foods. The water content substitutes for some taken along and also provides some shielding. We can cut lots of things, but substitution of fresh foods with freeze-dried and concentrated caloric sources isn't a good idea. Morale! Having decent food can substitute for a lot of hardships otherwise. Just ask anyone who has served in the Army.

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#52 2017-05-24 14:51:04

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

You haven't explained how you are going to provide 50,000 KweHs per sol (to grow food for a six person mission)  or how a small team with a 101 other things to do are going to construct the growing space for food (or are you importing tonnes and tonnes of structure  in which case how much mass will be involved) and how much nutritional feed and water would be required?

I think a small amount of agricultural production - maybe the equivalent of 10 lettuces a week (a range of salad vegetables such as lettuce tomatoes, and bean sprouts can be produced) - will provide a morale boost.

When choosing the pioneers you need to take into account such things as ability to function well on non-fresh foods. If you have a functional approach to food and a sweet tooth, chocolate and nutrition bars will be very morale boosting. Some people aren't that keen on fresh food. Some foods, like cooked rice, feel fresh even they have been stored for years.


Oldfart1939 wrote:

While waiting for my car to be serviced, I re-read portions of The Case for Mars. I paid special attention to the food required by the mission, and the reasoning behind taking fresh foods. The water content substitutes for some taken along and also provides some shielding. We can cut lots of things, but substitution of fresh foods with freeze-dried and concentrated caloric sources isn't a good idea. Morale! Having decent food can substitute for a lot of hardships otherwise. Just ask anyone who has served in the Army.


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

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#53 2017-05-24 15:25:27

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,835

Re: Louis' Solar Power Strategy

Louis-

I've not been a proponent of using artificial light as the primary source of light for crops. It's simply an inefficient use of the available energy resource. It's the one area where Solar wins! I'm a proponent of initially small agricultural experimental gardening; primary food supply will be brought from Earth. When I say "fresh food," as opposed to everything freeze dried, I'm including frozen foods, canned foods, dried foods, etc.; a somewhat "normal" diet. Lettuce, Swiss Chard, Radishes, Carrots, Beets, Potatoes, Yams, etc., none of which require pollination, should be considered "on the menu."

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#54 2017-05-24 18:08:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,565

Re: Louis' Solar Power Strategy

The question of green food is just how much are we going to try and grow in the first mission as the power for the second would come from the left behind RTG's of the first to create the energy needs for a large green house to feed the crew with a greater quantity of what will be green foods. Where as the first mission will be busy getting dug in and ready so that they can do a bit of science before going into building for a future to come back to.....

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#55 2017-05-25 03:07:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

You have a strange definition of "fresh food".  Sounds like you mean "a variety of foods" with which I agree.  Foods like rice (which can be brought from Earth) are effectively naturally "dried" - they will be a good staple. But if you are serious about having food grown as part of the first human mission to Mars you have to define what percentage of the food the pioneers consume on Mars is going to be produced through farming on Mars.   Once you know that percentage you know what you have to do to produce the food - energy and mass requirement.

The problem with direct light farming is that you might have a dust storm and your crops will not grow in which case if say you were going to use 50% Mars-farmed food to feed your pioneers, then they are going to starve or suffer severe debilitating malnutrition.  You will have made all that effort for no gain and a huge risk. It doesn't make sense.

Oldfart1939 wrote:

Louis-

I've not been a proponent of using artificial light as the primary source of light for crops. It's simply an inefficient use of the available energy resource. It's the one area where Solar wins! I'm a proponent of initially small agricultural experimental gardening; primary food supply will be brought from Earth. When I say "fresh food," as opposed to everything freeze dried, I'm including frozen foods, canned foods, dried foods, etc.; a somewhat "normal" diet. Lettuce, Swiss Chard, Radishes, Carrots, Beets, Potatoes, Yams, etc., none of which require pollination, should be considered "on the menu."


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

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#56 2017-05-25 03:22:01

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

I agree Space Nut...the demands of creating a viable settlement bring about a "natural " rythm to the first few missions.

Mission One has to be focussed on securing the energy supply, life support systems,  monitoring people's health, water supply, some proof of concept industrial experimentation, some basic construction efforts,  and mapping local resources (with some storing of those resources). Some science will be done but not a huge amount - mostly the geological surveys  with serve the resource mapping (and they find some fossils, well all well and good but we wouldn't focus on that). Some fresh food will be grown, but probably no more than 1% of overall food intake. That will be more for purposes of morale.

As you say a lot of Mission One will be about ensuring Mission 2 is well resourced.  Mission 2 can begin to bring in some serious (small scale) industrial infrastructure and an expanded Farm Hab. Maybe by Mission 2 we will be look to provide something more like 3-4% of the food supply from Mars.


SpaceNut wrote:

The question of green food is just how much are we going to try and grow in the first mission as the power for the second would come from the left behind RTG's of the first to create the energy needs for a large green house to feed the crew with a greater quantity of what will be green foods. Where as the first mission will be busy getting dug in and ready so that they can do a bit of science before going into building for a future to come back to.....

Last edited by louis (2017-05-25 03:54:15)


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#57 2017-05-25 04:04:20

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Louis' Solar Power Strategy

I would agree.  I calculated previously that meeting 1 person’s calorie requirements using plants grown under artificial light would require some 220kWh per day, that’s equivalent to a continuous power output of 9.2kW.  For six people, the energy requirement is about half the mission power supply.  Some plants could be grown this way on the first mission, but unless there is a lot of power to spare, it will not be more than a minor compliment to diet.  Maybe some high vitamin salad plants.

During the northern summer, solar constant is several kWh per day.  A small poly tunnel could be used to compliment crew diet using natural light, provided it was protected by insulation during Martian night.

Fossil methane would be a useful discovery as a reducing agent for metal oxides and a precursor for plastics.  As a bulk fuel, one would need to find an oxidising agent as it will not burn in the Mars' CO2 atmosphere.

Last edited by Antius (2017-05-25 04:18:46)

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#58 2017-05-25 05:17:57

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

On Earth in a temperate zone you might be able to grow enough food for one person over a year on 10,000 square metres (100x100 - though that is probably pushing it).  To replicate the Sun's effect would require through PV about 40,000 square metres of PV (to generate about 16,000 KwHs per day).

Now, I accept that you can make a lot of "savings" by intense crop rotation but even if you saved let's say 75% of that power input that's still 4000 KwHs per day, or 166 Kw continuous power.  Perhaps you can explain how you get to 9.2 Kws which I think is out by a factor of 18!

Of course that's just lighting...haven't mentioned the crop life support which would also require substantial power input in an artificial system.

Also, please note that the more intense the crop rotation, the more intense the nutrition usage, so you would have to have a fully powered up recycling system for human faeces and crop waste or you would have to import additional mass.


Antius wrote:

I would agree.  I calculated previously that meeting 1 person’s calorie requirements using plants grown under artificial light would require some 220kWh per day, that’s equivalent to a continuous power output of 9.2kW.  For six people, the energy requirement is about half the mission power supply.  Some plants could be grown this way on the first mission, but unless there is a lot of power to spare, it will not be more than a minor compliment to diet.  Maybe some high vitamin salad plants.

During the northern summer, solar constant is several kWh per day.  A small poly tunnel could be used to compliment crew diet using natural light, provided it was protected by insulation during Martian night.

Fossil methane would be a useful discovery as a reducing agent for metal oxides and a precursor for plastics.  As a bulk fuel, one would need to find an oxidising agent as it will not burn in the Mars' CO2 atmosphere.


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

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#59 2017-05-25 05:48:00

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,929
Website

Re: Louis' Solar Power Strategy

louis wrote:

To replicate the Sun's effect would require through PV about 40,000 square metres of PV (to generate about 16,000 KwHs per day).

Do I have to say it again? This is a really bad idea. Do not bury your greenhouse, only to illuminate with power generated by PV! That's stupid. The best photovoltaic cell today only produces 30.7% conversion to electricity beginning-of-life, 26.7% end-of-life. And that's using cells just available last August, less than a year ago. And even LED lighting is not 100% efficient. PV and LED are technologies that will not be produced on Mars for a very long time, they have to be imported from Earth at great expense. A much simpler technology is simply ambient light. It's far more efficient to just use available light directly. A science mission will use polymer film, I have recommended PCTFE because it's impermeable, can withstand the cold of Mars, and highly UV resistant. However, a settlement would build a greenhouse with in-situ resources. The most practical is glass; just tempered glass. It's far more efficient; converting light to electricity then back to light is a Rube Goldberg solution, and highly inefficient. And glass can be produced in-situ.

If you're worried about radiation, ISS has twice the radiation of Mars surface, and they have an experiment growing food crops right now.

Robert Zubrin pointed out medieval maps had dire messages written on unexplored areas: "there be monsters here" or "there be dragons here". Dr. Zubrin called the radiation argument a dragon that had to be slain. I thought we had slain that dragon long ago.
images?q=tbn:ANd9GcQgTQQ6_3dwX4MeSCVWfkw3Qe1TnTKYieeiA_KWQhZFDcfHqp-k

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#60 2017-05-25 07:08:28

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

This part of the debate is focussed on Mission One...whether to attempt to grow all or a substantial part of the pioneers' food supply on Mars. I think it's a bad idea however you attempt it. If you attemp it with direct sunlight, then if there is a dust storm your pioneers will starve. But even if they don't the demands in terms of mass, power, labour time and expertise will be substantial - too much for Mission One in my judgement which should have other priorities.


RobertDyck wrote:
louis wrote:

To replicate the Sun's effect would require through PV about 40,000 square metres of PV (to generate about 16,000 KwHs per day).

Do I have to say it again? This is a really bad idea. Do not bury your greenhouse, only to illuminate with power generated by PV! That's stupid. The best photovoltaic cell today only produces 30.7% conversion to electricity beginning-of-life, 26.7% end-of-life. And that's using cells just available last August, less than a year ago. And even LED lighting is not 100% efficient. PV and LED are technologies that will not be produced on Mars for a very long time, they have to be imported from Earth at great expense. A much simpler technology is simply ambient light. It's far more efficient to just use available light directly. A science mission will use polymer film, I have recommended PCTFE because it's impermeable, can withstand the cold of Mars, and highly UV resistant. However, a settlement would build a greenhouse with in-situ resources. The most practical is glass; just tempered glass. It's far more efficient; converting light to electricity then back to light is a Rube Goldberg solution, and highly inefficient. And glass can be produced in-situ.

If you're worried about radiation, ISS has twice the radiation of Mars surface, and they have an experiment growing food crops right now.

Robert Zubrin pointed out medieval maps had dire messages written on unexplored areas: "there be monsters here" or "there be dragons here". Dr. Zubrin called the radiation argument a dragon that had to be slain. I thought we had slain that dragon long ago.
https://encrypted-tbn0.gstatic.com/imag … ZFDcfHqp-k


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#61 2017-05-25 07:39:41

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

http://www.abc.net.au/news/2017-05-15/p … st/8526868

Looks like we are no longer in the realm of the possible and plausible, but the actual and doable.

"1000m2 of this material would weigh about 100 kilograms."

So 10,000 sq. metres would weigh in at only a tonne.

If efficiency was 3% that might give you about 400 KwHs per sol from 10,000 sq. metres. 

If efficiency could be raised to 12% then that would be 1600 KwHs - we'd need less than a couple of tonnes for mission one.


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#62 2017-05-25 08:00:52

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,835

Re: Louis' Solar Power Strategy

Louis-

If you go back and read many of my posts on other threads in addition to this one, I have proposed sending a massive food reserve to Mars ahead of the first manned landings. I'm not counting on growing ANY food other than experimental gardening the first missions. When I state fresh foods, I'm referring to non-dehydrated or freeze dried food. Yes. we'll also be taking stuff like rice and dried beans as additional, reserve foods. Having food when needed is NOT an option, but I'm a believer in Murphy's Laws, and also devoutly believe Murphy was an optimist.
I'm also in 100% agreement with RobertDyck about the overblown concerns about GCR. The way to moderate GCR exposure is by sleeping in habitats with some overburden of Mars regolith. The Sol is slightly longer than an Earth day, and we shouldn't be out working in darkness. Even a couple feet of regolith over the habitat structure (whatever it may be) will attenuate the radiation. Even if we reduce GCR exposure by 50%, that's significant. I'm a believer in below-ground shelters for the crew. By attenuation of the prevailing GCR we can safely extend mission times, should a problem occur with an ERV or fuel production. This is also why I'm suggesting a larger crew for the exploration phase of the mission. My food estimates may seem outrageous to others, but the standard normal food consumption of whole foods is rated at 2% of body weight per day. The FAA considers an average airline passenger to weigh 170 pounds, but I'm erring at 10% heavier ( so I could go!). So--(187)x(6)x(0.02) = 22.44 pounds, or rounding off to 10 kg per day. The stay time on Mars is desired to be 550 days, so that comes to 5500 kg of food. I'm also calculating a slightly slower Hohmann ballistic path to Mars of 200 days based on the current available EDS boosters in order to bring more food and supplies. Then 200 days Earth return. That's a total of 950 days of food required should all crew members return to Earth. This is where my 9.5 metric tonnes of food come from--which I'd rather have along than a bunch of batteries and PV panels. I would like to see a huge food cache on Mars for emergencies and future missions. Certainly enough to feed everyone well. "The condemned man ate a hearty meal." I'd consider having a reserve of 10 metric tonnes none too much. The point frequently overlooked is increased caloric consumption while doing heavy exercise or work. Wearing EVA gear will define "heavy exercise." The field geologists will be tasked with climbing steep hills for sample collection--not your standard "walk on the strand."

Last edited by Oldfart1939 (2017-05-25 08:14:09)

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#63 2017-05-25 10:21:58

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Louis' Solar Power Strategy

louis wrote:

http://www.abc.net.au/news/2017-05-15/p … st/8526868

Looks like we are no longer in the realm of the possible and plausible, but the actual and doable.

"1000m2 of this material would weigh about 100 kilograms."

So 10,000 sq. metres would weigh in at only a tonne.

If efficiency was 3% that might give you about 400 KwHs per sol from 10,000 sq. metres. 

If efficiency could be raised to 12% then that would be 1600 KwHs - we'd need less than a couple of tonnes for mission one.


Impressive.  Organic solar cells.  These ones have been encapsulated in PET to reduce photo-degradation, which would otherwise destroy them after a few hundred hours of irradiation.

I think the problem with printed organics is the relatively short lifetime (a few thousand hours at best) due to photo-degradation.  These are Earth surface values, where the ozone layer effectively filters out most UV and all UVC.  I am not sure what the effective lifetime would be on Mars.  I guess you are talking a few months rather than years.  If the cells really are that light, maybe that is enough time to produce the propellant needed for the trip home and to power surface operations.  A system generating a time-average power of 400kW running a propellant plant with 50% efficiency, would generate nearly 160 tonnes of methane oxygen bipropellant over 90 days.  That is enough to power the surface expedition for 2.5 years and provide propellant for the trip home.  The propellant plant and storage tanks would need to be big, much bigger than under the nuclear scenario, because the tanks need to contain twice as much propellant and the propellant plant has to work at a much greater rate, as it only operates during the day and all propellant must be produced before the cells degrade after just a few months.

The solar panels themselves would cover a huge area, but maybe it could be made to work.  A 400kWe average power output system, would cover an area of about 30,000m2 at 10% efficiency.  If some allowance is made for cell degradation, maybe 40,000m2 (10 acres).  Total cell mass would be ~4 tonnes.  Power cables and transmission would increase this substantially, as the voltage output of the cells is necessarily low to prevent breakdown of the cells.  The mass of the propellant plant would be several times greater, as it must produce twice as much fuel in less than one third as much time.  Due to the large area of the panels, it would take a lot of man-hours to deploy the system.  So there is a lot of inherent risk here, since you cannot deploy before crew arrival.

Last edited by Antius (2017-05-25 10:46:35)

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#64 2017-05-25 10:57:05

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Louis' Solar Power Strategy

louis wrote:

On Earth in a temperate zone you might be able to grow enough food for one person over a year on 10,000 square metres (100x100 - though that is probably pushing it).  To replicate the Sun's effect would require through PV about 40,000 square metres of PV (to generate about 16,000 KwHs per day).

Now, I accept that you can make a lot of "savings" by intense crop rotation but even if you saved let's say 75% of that power input that's still 4000 KwHs per day, or 166 Kw continuous power.  Perhaps you can explain how you get to 9.2 Kws which I think is out by a factor of 18!

Of course that's just lighting...haven't mentioned the crop life support which would also require substantial power input in an artificial system.

Also, please note that the more intense the crop rotation, the more intense the nutrition usage, so you would have to have a fully powered up recycling system for human faeces and crop waste or you would have to import additional mass.

Going off subject a bit, but here is a crude approximation.

The average human being consumes about 10MJ of food energy per day.  Plant crops are about 1% efficient at converting photons into glucose and starch in Earth sunlight, but only about 40% of that light is photosynthetically available.  If you could tailor the input light to the frequencies best suited to photosynthesis (which you can with LEDs), you would need to provide 400MJ of light per day to meet the food needs for one person.  The best LEDs are about 50% efficient in the red spectrum.  So to produce 400MJ of light, you need 800MJ of electricity, or 222kWh.

Again, an estimation only.  Some plants are more efficient, others less so.  And I am probably on the optimistic side with LED efficiency.  Other energy inputs would likely be dwarfed by the lighting requirement, which is undeniably large.  Growing food in this way depends upon cheap and abundant power.  It would only make sense if the capital and operating costs of greenhouses on Mars, exceed the cost of power needed to grow crops in higher density spaces.

In theory, a well maintained garden here on Earth can be very efficient.  If we apply the same assumptions on plant efficiency as above, and assume an annual insolation of 1000kWh/m2/annum (South East England insolation) it would take 101m2 of land to sustain one person.  In reality, that would be extremely difficult as it would require all other conditions to be perfect (i.e. eating all the plant, no weed plants, no unexpected temperature extremes, use of winter insolation, etc).  But it does illustrate that a lot of food can be grown in small spaces if necessary.  Using artificial light, these sorts of limits can be approached, as we are growing plants in perfectly tailored conditions.

Last edited by Antius (2017-05-25 11:13:59)

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#65 2017-05-25 12:24:40

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,452

Re: Louis' Solar Power Strategy

Antius,

Here's a potential solution from 2012 that requires more basic R & D (click on the download link):

Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency

30 picowatts of input electrical power, 69 picowatts of emitted light radiation from a LED, or about 230% efficiency.  Over-unity is not only possible, but a predictable aspect of physics.

LED Lighting Efficiency Jumps Roughly 50% Since 2012

LED efficiency keeps going up, year over year.

MIT very recently created a Tungsten filament incandescent bulb with 275lm/We, which handily beats the best LED's available.  They used a special IR reflective crystal to reflect emitted IR from the filament back onto the filament, so far less power was required to produce a given level of output.

There was a CREE white light LED's that can achieve 303lm/We in 2014, but there were issues with implementing that technology as a commercial product.  Current CREE SC5 LED's achieve 134lm/We with an incandescent-type output spectrum.

There are apparently LED's that use AC current, too:

Lynk Labs AC LED Technology

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#66 2017-05-25 13:08:21

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,929
Website

Re: Louis' Solar Power Strategy

louis wrote:

This part of the debate is focussed on Mission One...whether to attempt to grow all or a substantial part of the pioneers' food supply on Mars. I think it's a bad idea however you attempt it. If you attemp it with direct sunlight, then if there is a dust storm your pioneers will starve. But even if they don't the demands in terms of mass, power, labour time and expertise will be substantial - too much for Mission One in my judgement which should have other priorities.

Well, that depends what you mean by "Mission One". The first human mission to Mars will be a science mission. I have argued construction of the base should start with the first human mission. If we wanted to scout Mars as Robert Zubrin described, it should have started in the 1990s. We've had literally two decades of robotic exploration instead of human exploration. Starting over would treat those years as waste. If Mars Direct was started in 1990, we could have had an unmanned test of equipment in 1997, and the first human mission in 1999. Trump has said he wants a human mission to Mars in 2024, so it would be within his second term. NASA just said "No". Are we now talking about a mission to Mars delayed 3 decades? Four?

But I have argued the first mission will be a science mission. The science mission will bring an inflatable greenhouse as an experiment, but will not rely on it. Every science mission will bring enough stored food for the entire mission. They will use a greenhouse, as experiment to prove a greenhouse works. And to produce some fresh vegetables, a treat for the astronauts so many miles from home. But science missions certainly will not depend on a greenhouse for all food.

Science missions will go and come home. Are you talking about the first permanent settlers? That will not be the first human mission. The first permanent settlers will have to build greenhouses capable of growing all their food. But it will take time to build them. They will initially live off stored food and vegetables grown in the experimental greenhouse(s) left by science missions. Yes, greenhouses will require artificial lights during a dust storm, but only during a dust storm. That means power reserved for mining/refining/manufacturing will have to be directed to the greenhouse(s) during dust storms. But the rest of the time the fact greenhouses do not means they will draw minimal power. That will leave power for construction and science.

The Mars Homestead Project - phase 1, Hillside Settlement included light pipes. The large atrium was designed with parabolic reflectors on the top of the hill that would direct light through light pipes to the ceiling of the atrium (apex of groin arches) where a diffuser would distribute the light through the space. Trees and other plants would make the space feel more comfortable, as well as help recycle oxygen and provide some food. But realize a parabolic mirror does not work with diffuse light. That means the light pipes won't provide any light during a dust storm. An ambient light greenhouse that just uses windows, whether polymer film or glass, will be able to use light that gets through the dust storm. How much light will get through? One member on this forum was able to give an estimate once, but I don't remember. However, the parabolic reflector that feeds the light pipes will not get any light. The atrium or any underground greenhouse would be entirely dependent on artificial light during a dust storm.

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#67 2017-05-25 13:51:50

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

Personally I think propellant manufacture for Mision One is unnecessary and a diversion. Of course, I believe in a minimalist Apollo style
lander/ascender, so we won't need to land too much fuel/propellant for the ascent. Last time I looked, I think maybe 5 tonnes of fuel/propellant should do it.  NASA seems to overdesign for this sort of thing.


Antius wrote:
louis wrote:

http://www.abc.net.au/news/2017-05-15/p … st/8526868

Looks like we are no longer in the realm of the possible and plausible, but the actual and doable.

"1000m2 of this material would weigh about 100 kilograms."

So 10,000 sq. metres would weigh in at only a tonne.

If efficiency was 3% that might give you about 400 KwHs per sol from 10,000 sq. metres. 

If efficiency could be raised to 12% then that would be 1600 KwHs - we'd need less than a couple of tonnes for mission one.


Impressive.  Organic solar cells.  These ones have been encapsulated in PET to reduce photo-degradation, which would otherwise destroy them after a few hundred hours of irradiation.

I think the problem with printed organics is the relatively short lifetime (a few thousand hours at best) due to photo-degradation.  These are Earth surface values, where the ozone layer effectively filters out most UV and all UVC.  I am not sure what the effective lifetime would be on Mars.  I guess you are talking a few months rather than years.  If the cells really are that light, maybe that is enough time to produce the propellant needed for the trip home and to power surface operations.  A system generating a time-average power of 400kW running a propellant plant with 50% efficiency, would generate nearly 160 tonnes of methane oxygen bipropellant over 90 days.  That is enough to power the surface expedition for 2.5 years and provide propellant for the trip home.  The propellant plant and storage tanks would need to be big, much bigger than under the nuclear scenario, because the tanks need to contain twice as much propellant and the propellant plant has to work at a much greater rate, as it only operates during the day and all propellant must be produced before the cells degrade after just a few months.

The solar panels themselves would cover a huge area, but maybe it could be made to work.  A 400kWe average power output system, would cover an area of about 30,000m2 at 10% efficiency.  If some allowance is made for cell degradation, maybe 40,000m2 (10 acres).  Total cell mass would be ~4 tonnes.  Power cables and transmission would increase this substantially, as the voltage output of the cells is necessarily low to prevent breakdown of the cells.  The mass of the propellant plant would be several times greater, as it must produce twice as much fuel in less than one third as much time.  Due to the large area of the panels, it would take a lot of man-hours to deploy the system.  So there is a lot of inherent risk here, since you cannot deploy before crew arrival.


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#68 2017-05-25 13:54:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

These are all interesting technologies. One thing that we do know, is that for the Mars Mission cost will not be a major consideration. Even if an energy or lighting system costs ten times the equivalent on Earth, if it is low mass and high efficiency, that will be good enough for us.


kbd512 wrote:

Antius,

Here's a potential solution from 2012 that requires more basic R & D (click on the download link):

Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency

30 picowatts of input electrical power, 69 picowatts of emitted light radiation from a LED, or about 230% efficiency.  Over-unity is not only possible, but a predictable aspect of physics.

LED Lighting Efficiency Jumps Roughly 50% Since 2012

LED efficiency keeps going up, year over year.

MIT very recently created a Tungsten filament incandescent bulb with 275lm/We, which handily beats the best LED's available.  They used a special IR reflective crystal to reflect emitted IR from the filament back onto the filament, so far less power was required to produce a given level of output.

There was a CREE white light LED's that can achieve 303lm/We in 2014, but there were issues with implementing that technology as a commercial product.  Current CREE SC5 LED's achieve 134lm/We with an incandescent-type output spectrum.

There are apparently LED's that use AC current, too:

Lynk Labs AC LED Technology


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

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#69 2017-05-25 17:51:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

Well apologies if I misunderstood your comments...sounds like we agree on the extent of food farming for the first mission.

I agree as well we need to over-provide food for Mission One. Maybe we have the gourmet menu (a nice mix of food types for two years) and then some absolutely basic dried food mix (for up to two years, in the event of some malfunction re the ascent vehicle). It's important to take along a load of multi-vits and minerals (MVM) as well because they can fend off hunger as long as the body is getting nutrients. I am also wondering whether we could manufacture some basic sugar like glucose on Mission One using PV power, hydrogen, oxygen  and carbon (derived from water and the Mars atmosphere).  If we could then glucose plus the MVM pills might be enough to keep the pioneers alive in an emergency situation.

Oldfart1939 wrote:

Louis-

If you go back and read many of my posts on other threads in addition to this one, I have proposed sending a massive food reserve to Mars ahead of the first manned landings. I'm not counting on growing ANY food other than experimental gardening the first missions. When I state fresh foods, I'm referring to non-dehydrated or freeze dried food. Yes. we'll also be taking stuff like rice and dried beans as additional, reserve foods. Having food when needed is NOT an option, but I'm a believer in Murphy's Laws, and also devoutly believe Murphy was an optimist.
I'm also in 100% agreement with RobertDyck about the overblown concerns about GCR. The way to moderate GCR exposure is by sleeping in habitats with some overburden of Mars regolith. The Sol is slightly longer than an Earth day, and we shouldn't be out working in darkness. Even a couple feet of regolith over the habitat structure (whatever it may be) will attenuate the radiation. Even if we reduce GCR exposure by 50%, that's significant. I'm a believer in below-ground shelters for the crew. By attenuation of the prevailing GCR we can safely extend mission times, should a problem occur with an ERV or fuel production. This is also why I'm suggesting a larger crew for the exploration phase of the mission. My food estimates may seem outrageous to others, but the standard normal food consumption of whole foods is rated at 2% of body weight per day. The FAA considers an average airline passenger to weigh 170 pounds, but I'm erring at 10% heavier ( so I could go!). So--(187)x(6)x(0.02) = 22.44 pounds, or rounding off to 10 kg per day. The stay time on Mars is desired to be 550 days, so that comes to 5500 kg of food. I'm also calculating a slightly slower Hohmann ballistic path to Mars of 200 days based on the current available EDS boosters in order to bring more food and supplies. Then 200 days Earth return. That's a total of 950 days of food required should all crew members return to Earth. This is where my 9.5 metric tonnes of food come from--which I'd rather have along than a bunch of batteries and PV panels. I would like to see a huge food cache on Mars for emergencies and future missions. Certainly enough to feed everyone well. "The condemned man ate a hearty meal." I'd consider having a reserve of 10 metric tonnes none too much. The point frequently overlooked is increased caloric consumption while doing heavy exercise or work. Wearing EVA gear will define "heavy exercise." The field geologists will be tasked with climbing steep hills for sample collection--not your standard "walk on the strand."


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

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#70 2017-05-25 17:55:03

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

For me Mission One shouldn't be a "science" mission (though science will be done) it should be a "Mission Two" Mission - preparing the ground for what follows. So for me that is ensuring life support is in surplus (lots of water and breathable gas mixes) , ensuring the settlement has a huge energy surplus, carrying out practical ISRU experiments and beginning (mostly) ISRU hab construction.

RobertDyck wrote:
louis wrote:

This part of the debate is focussed on Mission One...whether to attempt to grow all or a substantial part of the pioneers' food supply on Mars. I think it's a bad idea however you attempt it. If you attemp it with direct sunlight, then if there is a dust storm your pioneers will starve. But even if they don't the demands in terms of mass, power, labour time and expertise will be substantial - too much for Mission One in my judgement which should have other priorities.

Well, that depends what you mean by "Mission One". The first human mission to Mars will be a science mission. I have argued construction of the base should start with the first human mission. If we wanted to scout Mars as Robert Zubrin described, it should have started in the 1990s. We've had literally two decades of robotic exploration instead of human exploration. Starting over would treat those years as waste. If Mars Direct was started in 1990, we could have had an unmanned test of equipment in 1997, and the first human mission in 1999. Trump has said he wants a human mission to Mars in 2024, so it would be within his second term. NASA just said "No". Are we now talking about a mission to Mars delayed 3 decades? Four?

But I have argued the first mission will be a science mission. The science mission will bring an inflatable greenhouse as an experiment, but will not rely on it. Every science mission will bring enough stored food for the entire mission. They will use a greenhouse, as experiment to prove a greenhouse works. And to produce some fresh vegetables, a treat for the astronauts so many miles from home. But science missions certainly will not depend on a greenhouse for all food.

Science missions will go and come home. Are you talking about the first permanent settlers? That will not be the first human mission. The first permanent settlers will have to build greenhouses capable of growing all their food. But it will take time to build them. They will initially live off stored food and vegetables grown in the experimental greenhouse(s) left by science missions. Yes, greenhouses will require artificial lights during a dust storm, but only during a dust storm. That means power reserved for mining/refining/manufacturing will have to be directed to the greenhouse(s) during dust storms. But the rest of the time the fact greenhouses do not means they will draw minimal power. That will leave power for construction and science.

The Mars Homestead Project - phase 1, Hillside Settlement included light pipes. The large atrium was designed with parabolic reflectors on the top of the hill that would direct light through light pipes to the ceiling of the atrium (apex of groin arches) where a diffuser would distribute the light through the space. Trees and other plants would make the space feel more comfortable, as well as help recycle oxygen and provide some food. But realize a parabolic mirror does not work with diffuse light. That means the light pipes won't provide any light during a dust storm. An ambient light greenhouse that just uses windows, whether polymer film or glass, will be able to use light that gets through the dust storm. How much light will get through? One member on this forum was able to give an estimate once, but I don't remember. However, the parabolic reflector that feeds the light pipes will not get any light. The atrium or any underground greenhouse would be entirely dependent on artificial light during a dust storm.


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

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#71 2017-05-25 18:02:01

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,835

Re: Louis' Solar Power Strategy

As science is being used by administrators and politicians for justification of the enormous sums of money required, SCIENCE WILL NOT BE AN OPTION! If we take a realistic view of things, we just don't know how many missions bodies such as NASA can get funded, so the return on the investment must be huge.

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#72 2017-05-25 18:35:27

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,565

Re: Louis' Solar Power Strategy

What is this science for Mars first mission?

Can we create a list? Making topic for this....

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#73 2017-05-25 18:41:11

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,792

Re: Louis' Solar Power Strategy

I am guessing:

1. Geology/minerals

2. Mapping/topography

3. Evidence of Mars life.

4. Seeking out meteorites.

5. Atmospheric measurement.

6. Methane sourcing.

7. Seismology.

8. Magnetic science. 


SpaceNut wrote:

What is this science for Mars first mission?

Can we create a list? Making topic for this....


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

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#74 2017-05-25 18:42:03

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,835

Re: Louis' Solar Power Strategy

louis wrote:

Personally I think propellant manufacture for Mision One is unnecessary and a diversion. Of course, I believe in a minimalist Apollo style
lander/ascender, so we won't need to land too much fuel/propellant for the ascent. Last time I looked, I think maybe 5 tonnes of fuel/propellant should do it.  NASA seems to overdesign for this sort of thing.

I disagree respectfully, but the entire Mars Direct concept was built around ISPP. I offered a "compromise" architecture in another post, wherein only LOX ins manufactured by ISRU. That's 75% of the mass, anyway. That way we don't need to bring along the initial H2 for the Sabatier reaction chemistry. The most long-term stable fuel is Aerozine 50, the 50% Hydrazine. 50% UDMH mixture which is not cryogenic and is also compatible with regeneratively cooled rocket motors. It has the highest Isp of available/storable fuels when burnt with LOX.

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#75 2017-05-25 18:43:48

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,565

Re: Louis' Solar Power Strategy

No need to carry inflateable green house on first mission as any empty cargo lander can serve as the space to grow food in.

In fact the second mission we can make use of all of the empty units if we are really going to grow food all that is needed then is supplemental power, lighting via colored LED, additional water, soil and other forms of trays to grow the plants with in and more seeds....

So where are we will daily intake of water for consumption and washing for the crew of 6? Keeping in mind that we know that we can always do with less water in the end. So we can add in the recycling masses later and efficiency rates to consider lowering the base level amount especially on the second mission onward.

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