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#101 2021-04-11 00:03:04

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,371

Re: Settlement design

louis wrote:

Not sure you read my post correctly.

So you've reference a daily electricity use figure of 5.5KwH average for the USA - one of the most profligate energy usage nations on Earth.  But your  PV array figures for Mars give a usage of 187.5 KwHs per sol per person.

Now that is a huge, huge disparity (183 KwHs per sol/day!) - which you haven't explained. You can explain a lot of it away through extra energy for life support, gas used for heating, and energy used for industry, transport, the private sector and the public sector (ie non residential). But then as explained previously there is no need on Mars to have huge amounts of energy devoted to railways, airports, metalled roads, street lighting , private automobiles, paper production, pollution control or indeed fossil fuel production.

Louis,

I was entertaining your fantasies about power consumption by doing different calculations using different continuous power consumption figures.  It's child's play to run the same calculation different ways, so that's what I did.  I was attempting to show how ridiculous your power consumption figures were, as compared to real life in America, where I don't use any electricity at all to purify the air I breathe.

I did one calculation where I calculated how much energy NASA thought they'd need to both keep everyone alive and make a little bit of propellant for some people to come home, I did another calculation using the much lower Mars One estimates of what they needed to merely keep people alive using a combination of CAMRAS, IWP, and ISRU O2 and H2O reclamation from the Martian atmosphere and surface ice deposits (they simply assumed that they would find them and could melt and desalinate the water).  I think I even did another calculation where I figured out how much power CAMRAS and IWP alone required with no ISRU, which means all the air and water replenishment must come from Earth (which seems a bit impractical to me).  No matter how you slice it, the life support power requirements for 1 million people IS HUGE!

Mars One's calculated bare minimum was 3,708Wh per person per hour to supply air and water ONLY, and nothing else.  One more time, if 1 million people are living on Mars for 1 Earth standard year, this is how that calculation works:

3,700Wh per person per hour * 1,000,000 people * 8,760 hours in one Earth standard year

It doesn't make a scintilla of difference that a Martian year is longer, unless some of those people are coming home after spending some specific number of hours on the surface of Mars.  So long as they're in the colony and still counted amongst the living, the life support systems are consuming power to keep them alive.  That said, colonization generally involves staying in the place you intend to colonize.

3,700 * 1,000,000 = 3,700,000,000 = 3.7GWh <- In any given hour of any given day, this is the amount of power required to keep 1 million people supplied with air and water using CAMRAS and IWP technology, along with ISRU O2 / H2O reclamation from local resources right outside the walls of the pressure vessel you're living in.

3,700,000,000 Watt-hours for 1 million people * 8760 hours per Earth standard year = 32,412,000,000,000 Watt-hours per Earth standard year

32,412,000,000,000 = 32.412TWh

1TWh = 1,000,000,000,000Wh

1 Bhadla Solar Park = 1.3TWh or 1,300,000,000,000Wh per Earth standard year

Mars is a little more than 50% further from the Sun than Earth is, so 1,300,000,000,000Wh becomes 650,000,000,000Wh per year.

32,412,000,000,000Wh / 650,000,000,000Wh = 49.86 Bhadlas

1 Bhadla covers 57km^2

57km^2 land area use per Bhadla * 50 Bhadlas = 2,850km^2

1 City of Houston covers 1,651km^2

1 City of Dallas covers 882km^2

Combined, the City of Houston and City of Dallas cover 2,533km^2.

Even if we can "somehow" cut the energy usage in half, you're still talking about covering a land area the size of the City of Houston to supply those people with air and water.

We need a bare minimum of about 14 NRG Stadiums to provide pressurized living space for a million people, if they all live on top of each other the way they do in New York City.  This buildings will occupy a total land area of 2.52km^2.  In reality, we need at least double that amount of pressurized living space for them to live with any amount of comfort and privacy, and it's still going to be very crowded.

Are we going to Mars to build Solar Panel City or Mars City?

I only ask because the footprint of the arrays is 570 times larger than that of the actual city.

Alternatively, we could build 1 additional NRG Stadium that would generate enough power using nuclear reactors to supply the same amount of power as 50 Bhadlas.  The reactors and their containment vessels will occupy a whopping 1,424.4m^2 of floorspace in that additional stadium.  The 1,424.4m^2 is for a total of 30 small modular reactors (each containment vessel is 7.775m in diameter and the reactor itself is 4.916m in diameter and 5.59m tall) that produce 557MWt / 258MWe each, but only 15 are operational at any point in time.  The remaining 178,575.6m^2 of floorspace in this proposed "Nuclear Stadium" would house everything else required to run the reactors.  In terms of total land area claim for the entire plant, we're looking at 43,320m^2.  I don't know what we'll do with the 136,680m^2 of remaining floorspace, but I'm sure we'll think of something.  Hey, I know.  Maybe we can build enough additional reactors to supply enough power to actually build that city.  Crazy idea, but there it is.

3,700,000,000We for 1 million people / 250,000,000We per reactor = 14.8 reactors

The 50 Bhadla arrays have a physical footprint 65,789 TIMES greater.  Maybe we can use all that extra space to plant those 7.5 million trees that you wanted to have delivered to Mars.

The ThorCon people intended to construct small 500MWe plants (38mW by 38mL by 30mH, that were floated like barges to deep water harbors, using 50,000t of steel per 500MWe power plant.  No concrete at all, but 1m of beach sand shielding between a double wall surrounding the building to deal with Boeing Dreamliner impacts.  There probably won't be any of those on Mars, but there will be Starships.  We're going to substitute concrete for most of that steel on Mars.  I figure 3m of Iron-rich Sulfacrete should be enough to allow someone to walk right up to the reactor since this is vastly more shielding than a reactor on a ship or submarine.  The part that has to be steel, the reactor core / containment can / primary loop pump / heat exchanger, weighs in at 343t, so 10,290t for all 30 of them.  Each reactor needs 43t of fuel salt.  Most of that is just salt, with little actual fuel present at any given time.  We're going to make the balance of plant right about 1 order of magnitude smaller by substituting Supercritical CO2 in the secondary loop for steam.  A 300MW SCO2 gas turbine is smaller than a Big Block V8 engine.  Annual fuel supply for all 15 operating reactors is 29,017.5kg 19.7% enriched U235 and 49,275kg of Th232 to make U233, but since the surface of Mars is apparently covered with Uranium and Thorium, we might want to source that locally.

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#102 2021-04-11 01:02:45

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,311

Re: Settlement design

Louis-
From my background in ranching, a figure that is almost universal for all mammals, according to the veterinarians, is 2% of the body weight per day in food consumption. That's a basic maintenance diet and not a weight gain or accounting for heavy work kinda diet.
That calculates to 1 kg of food for that hypothetical average human. I did the math several years ago on this website and calculated what supplies should be prepositioned before sending the Mars Direct style mission. This was before Elon came on the scene with his city of one million people. The number you mentioned earlier of ~2,400 grams sounds about right for a human doing physical labor.

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#103 2021-04-11 02:21:35

Noah
Member
From: Zurich (Switzerland)
Registered: 2020-07-28
Posts: 38

Re: Settlement design

hmwg?

I have seen many calculations for a city with a million inhabitants, this is good and we need to keep them in mind.  For now, a settlement design with about 4 - 20(?) people should be considered. As Oldfart1939 mentioned, we need to discuss "how many will go?" first. Then we can calculate things like energy requirements, etc. I have seen some suggestions for a crew of 6 people and 17 people.
Does anyone have another suggestion or a new argument?

Last edited by Noah (2021-04-11 22:09:24)

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#104 2021-04-11 02:56:27

Noah
Member
From: Zurich (Switzerland)
Registered: 2020-07-28
Posts: 38

Re: Settlement design

RobertDyck wrote:

Ps. When I was part of Mars Homestead Project, I found technical details for life support equipment for ISS. That includes power requirements. I think that's a fair estimate. The manufacturer kept moving their web pages, as if they didn't want me to see. I think that's silly considering I was recommended we plan to buy life support equipment from them. They proved it works on ISS, so just buy more for Mars. Doesn't that mean I'm giving them free marketing? But that means I could give you those power requirements. And we can estimate heat requirements from JPL's work with rovers.

That's great! Could you send me the power requirements or post them?

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#105 2021-04-11 03:11:59

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,389
Website

Re: Settlement design

Mars Direct was designed for 4 crew. For many years, Mars Society members would not consider anything other than Robert Zubrin's plan. In 2002, I presented a modification of Mars Direct. It was not well received at all. Ironically, NASA themselves wanted more crew. Mars Direct was designed for 4 crew because NASA had planned for exactly 4 since 1965. NASA came up with "Design Reference Mission", which Robert Zubrin dubbed "Semi-Direct". That would send 6 crew, including a doctor. Although Semi-Direct would use ISPP for the Mars Ascent Vehicle to carry crew from Mars surface to a craft in Mars orbit, the interplanetary vehicle would carry return propellant from Earth. These changes increased the price. Estimate for Mars Direct was $20 billion in 1989 dollars for research & development, infrastructure, and the first mission to Mars, then $2 billion for each mission thereafter. Or $30 billion if they commit up-front to 7 missions. But Semi-Direct would cost $55 billion. When Congress saw the price climb that much, and still just a paper study, they refused to authorize it.

Mars Homestead was a study for the first permanent human presence on Mars. Bruce Mackenzie was insistent there would be no Earth Return Vehicle; this was a one-way mission. I suggested we use Mars Direct as the spacecraft, since the purpose of the project was to design the first permanent base and how to build it. The guys wanted 12 crew, so they designed for 4 Mars Direct habitats. The first 3 habs would carry 4 crew each. Mars Direct was designed to carry a rover capable of carrying all 4 crew up to 1,000 km one-way, or multiple exploration expeditions. So this would accumulate a total of 3 rovers. The 4th hab would be sent without crew, as a backup. The rover would be a small construction vehicle, capable of moving dirt. This immediately made me think of a Bobcat. There are several models of Bobcat; I suggested a compact track loader considering conditions of our proposed base location. The 4th hab would have life support, inflatable greenhouse, etc, but would be loaded with tools and equipment instead of crew and food.

Mars Direct was designed to use solar panels for the hab. The solar panels would be folded for launch, extend for use in space, then retract and covered for atmospheric entry at Mars. On Mars crew would manually remove the solar panels, erect them on the surface. Cables to connect the solar arrays to the hab would be carried. Mars Direct ERV would include a small nuclear reactor capable of producing 100kW electricity, however as I said this project did not include any ERV.

The permanent base would use larger nuclear reactors. Each reactor so large that a cargo lander would carry nothing but. Yes, the base would have to be supplied by multiple cargo landers. And notice the site plan has 3 reactors.

So again, I'm suggesting a science/exploration mission using Mars Direct. That means just 4 crew for the first missions. Construction of the first permanent base would have 12 crew. Once they finish their own base, they would build a larger facility for 100 crew. That would prepare for the first SpaceX Starship. Those first 100 would then build even larger accommodations for next 1,000 settlers.

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#106 2021-04-11 03:24:28

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,389
Website

Re: Settlement design

Noah wrote:

That's great! Could you send me the power requirements or post them?

I directly sent the 4½ page document. Here's the power summary. Power for oxygen generation had to be estimated, I didn't find details of the one for ISS. Sabatier reactor is exothermic, so once it's started it doesn't consume power. I don't have start-up power, so left it out. These numbers are adjusted for 12 person crew:

toilet: 375 watt peak, 0.071875 kWh per day
water processor: 915 watt peak, 1.40 kWh per day
urine processor: 424 watt operating, 108 watt standby, 255.2 watt continuous
oxygen generation: 1.73 kW continuous
CO2 removal: 0.259 kW continuous
dehumidifier: 0.6 kW continuous
circulation fan: 0.312 kW continuous

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#107 2021-04-11 04:33:29

Noah
Member
From: Zurich (Switzerland)
Registered: 2020-07-28
Posts: 38

Re: Settlement design

RobertDyck wrote:

I directly sent the 4½ page document. Here's the power summary. Power for oxygen generation had to be estimated, I didn't find details of the one for ISS. Sabatier reactor is exothermic, so once it's started it doesn't consume power. I don't have start-up power, so left it out. These numbers are adjusted for 12 person crew:
toilet: 375 watt peak, 0.071875 kWh per day
water processor: 915 watt peak, 1.40 kWh per day
urine processor: 424 watt operating, 108 watt standby, 255.2 watt continuous
oxygen generation: 1.73 kW continuous
CO2 removal: 0.259 kW continuous
dehumidifier: 0.6 kW continuous
circulation fan: 0.312 kW continuous

Thanks Robert, for the summary! Where can I find the document? Or rather in my private messages? I am not so familiar with the forum yet, or maybe you can send me the document to my email address nallwicher@yahoo.de?

RobertDyck wrote:

File type is .ppt which is Microsoft PowerPoint. It's not .pptx which is the newer format, for Microsoft Office 2007 and later. Remember, the Mars Homestead Project is from 2005. However, all versions of PowerPoint can open the older format. You can download a PowerPoint Viewer free directly from Microsoft. The free viewer can view only, you would have to buy the full version to create content. US version is here: PPTX Viewer

Ahh okay. Thanks, now it works.

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#108 2021-04-11 04:45:38

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

Re: Settlement design

That's interesting Robert - I never knew the Sabatier process was exothermic. Wikipedia tells me that usually means heat is released. If that is the case with Sabatier then it would be a double win, in terms of providing energy to heat the base! Do you know whether the Sabatier process produces heat?

RobertDyck wrote:
Noah wrote:

That's great! Could you send me the power requirements or post them?

I directly sent the 4½ page document. Here's the power summary. Power for oxygen generation had to be estimated, I didn't find details of the one for ISS. Sabatier reactor is exothermic, so once it's started it doesn't consume power. I don't have start-up power, so left it out. These numbers are adjusted for 12 person crew:

toilet: 375 watt peak, 0.071875 kWh per day
water processor: 915 watt peak, 1.40 kWh per day
urine processor: 424 watt operating, 108 watt standby, 255.2 watt continuous
oxygen generation: 1.73 kW continuous
CO2 removal: 0.259 kW continuous
dehumidifier: 0.6 kW continuous
circulation fan: 0.312 kW continuous


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

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#109 2021-04-11 04:54:02

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

Re: Settlement design

Mars Direct is relevant to energy usage on Mars in that I think when you are beyond the foundation stage of the colony, and into what might be called the migration stage (by which time Mars is largely self-sufficient in energy generation, food supply and everyday goods) , you are not going to waste energy on bringing a huge Starship to the surface of Mars. Much more likely people will be taxied down in much lighter ascent-descent craft. Proportionate to the number of people, the need to refuel Starships will decline I think.


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

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#110 2021-04-11 05:44:03

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,371

Re: Settlement design

Noah,

Here's my source:

Mars One Habitat ECLSS (ECLSS) Conceptual Design Assessment

Barry W Finger, Gary A Lantz, and Tad W Theno all worked for Paragon SDC at the time that document was drafted.  The company they work for is the company that designed the IWP (Ionomer Water Processor) for NASA.

Flip to Page 50 of their report.  In the third column, the one labeled "Avg Power (kw)", locate the row that says "ECLSS Total".  The figure in the column should be "14.8".  Divide that figure by "4".  You should get "3.7".  That is the average power estimate for ECLSS, from a company actively engaged in the design and implementation of ECLSS hardware for NASA.

If the average power being consumed is 3.7kW.  The lowest number I get for only including air and water treatment is 1.48kW.  If we had 100% closed loop life support, basically never lost a liter of air or water, then 1.48GW of continuous power for a million people.  If we gave everyone a 10m^3 box in which to exist for the rest of their natural life, that's 0.01km^2.

For an office building with 3.8m^2 of floorspace per person, the recommended air exchange rate is 0.567m^3 per minute, so how much power do you figure a fan that exchanges 567,000m^3 per minute will require?  I get about 9MW of continuous power, or 216MWh per day just to move air around a structure big enough to house them and exchange it at a rate comparable to that of an office building.

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#111 2021-04-11 06:11:23

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

Re: Settlement design

Mission One Crew Size

I don't think we have anything officially from Space X but they seem to be talking in terms of two Starships. You have to split your pioneers between the two, I would think - unless the idea is that you send two to Mars so you have a back-up.

Assuming the crew is spread across the two Starships, I would say that makes it a 6 minimum. On a worst case scenario, if 3 die, you can probably limp on with 3 people, though it will be highly stressful.

I'd say the key determinants for how many people should go are:

1. The skill pool. What skills are required for Mission One and how many people do you need to supply those skills? Those skills will be medical, electrical engineering, general engineering, computer engineering, rocketry, communications and geological knowledge. For every skill set there needs to be back-up. So two doctors, two people skilled in computer engineering. In some cases there might be two skillsets in one person. I don't think we are necessarily looking for people being top of their profession - we are looking for people who are resourceful and highly skilled but not obsessive specialists. The key tasks the skills are addressing are: keeping everyone alive (e.g. dealing with medical emergencies), finding and mining water ice, making propellant and getting the Starship back to Earth. Everything else - e.g. general exploration, science and growing food - is secondary.

2.  Team Management. The two Starships could theoretically take 200 people to Mars, but that would be an organisational and logistical nightmare. So, yes you definitely wouldn't want to go beyond 20, I think but even that feels too high for me.

3. Resource load. The more people, the more cargo required, especially for Mission One, when you cannot assume ISRU will work as intended.

I don't agree that the "building process" will be a key determinant of numbers. I expect the accommodation to be self-assembly, probably inflatable on the Bigelow model. There may be some experimental work undertaken to produce Mars bricks or Mars cement but I don't think Mission One will be building their own accommodation.

Considering everything, I think a number between 6 and 10 is preferable and I favour the lower end as that improves the survivability factor for the crew. At a minimum we want to ensure the crew can surive an aborted return launch of the Starship and stay alive for another two years until Mission 2 arrives.



Noah wrote:

https://i.imgur.com/1JYL6m9.png

I have seen many calculations for a city with a million inhabitants, this is good and we need to keep them in mind.  For now, a settlement design with about 4 - 20(?) people should be considered. As Oldfart1939 mentioned, we need to discuss "how many will go?" first. Then we can calculate things like energy requirements, etc. I have seen some suggestions for a crew of 6 people and 17 people.
Does anyone have another suggestion or a new argument?


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

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#112 2021-04-11 10:35:40

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,389
Website

Re: Settlement design

louis wrote:

That's interesting Robert - I never knew the Sabatier process was exothermic. Wikipedia tells me that usually means heat is released. If that is the case with Sabatier then it would be a double win, in terms of providing energy to heat the base! Do you know whether the Sabatier process produces heat?

I got that from Robert Zubrin's books. I searched the NASA Technical Reports Server and found 1287 documents with the word "Sabatier". Interesting it includes one published in 1968, and one from 1971, and one from 1974. The abstract for the last says...

A six-man, flight prototype carbon dioxide reduction subsystem for the SSP ETC/LSS (Space Station Prototype Environmental/Thermal Control and Life Support System) was developed and fabricated for the NASA-Johnson Space Center between February 1971 and October 1973. Component design verification testing was conducted on the Sabatier reactor covering design and off-design conditions as part of this development program. The reactor was designed to convert a minimum of 98 per cent hydrogen to water and methane for both six-man and two-man reactant flow conditions. Important design features of the reactor and test conditions are described. Reactor test results are presented that show design goals were achieved and off-design performance was stable.

Interesting! Skylab was in space from May 1973 through July 1979, occupied May 1973 - February 1974. This means NASA looked at Sabatier at the time of Skylab. And Nixon cancelled the Apollo program after Apollo 17, December 1972. After Apollo 11 and before Apollo was cancelled, NASA was serious about a human mission to Mars. After the Soviet Union lost the race to the Moon, they considered skipping the Moon and going straight to Mars. Intelligence told NASA about this, which is why NASA got serious. NASA was interested in Mars since the beginning, but got serious when they heard the Soviet Union was serious. But the Soviets quickly learned how difficult it was so changed focus to space stations. So NASA built Skylab. But my point is NASA has looked at Sabatier for life support on space stations or Mars for a very long time.

Here's one website that describes Sabatier with energy numbers: Open Energy Monitor

The Sabatier Reaction was discovered in 1912 by French chemist Paul Sabatier and involves the reaction of hydrogen with carbon dioxide at elevated temperatures (300-400C) and pressures in the presence of a catalyst (e.g: Nickel, ruthenium or alumina) to produce methane and water.

The reaction is described by the following exothermic reaction:

CO2 + 4H2 → CH4 + 2H2O       ∆H = −165.0 kJ/mol

(some initial energy/heat is required to start the reaction)

The website is for learning, has several example exercises to calculate energy.

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#113 2021-04-11 10:52:38

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,311

Re: Settlement design

As a side note: Paul Sabatier won a Nobel Prize for this discovery. I believe that he shared the award that year with Victor Grignard for discovery of the organometallic Grignard reaction of alkyl halides with metallic Magnesium.

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#114 2021-04-11 10:52:43

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 27,185

Re: Settlement design

The sabetier reactor must stay above an operating temperature as its needed for the reaction within the chamber and if the chamber is cooled the reaction will not produce the methane efficiently....

Noah, have appended first post with the crew size tree and how it effects other things.

We will also need to decide on the size of the rocket as that schedules flight count and payload size to support crew and timelines

Current flying and near future can be part of the tree but untested and  untried refueling on orbit will take time if you are planning on going sooner rather than later.

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#115 2021-04-11 13:14:54

Noah
Member
From: Zurich (Switzerland)
Registered: 2020-07-28
Posts: 38

Re: Settlement design

Mission One Crew Size

For crew size, we have the following suggestions:
Robert 4,
Louis 6 to 10 (but on the lower end),
Oldfart1939 17.

(If I missed a comment, I am sorry)

Louis,

Point 1 -
I will add the skill pool point to the diagram.

Point 3 -
regarding the "building process": I think I misstated the point. I agree that the accommodations will be self-assembly or 3D printed. By the "building process" point, I meant that if we go with many people, we will need a larger accommodation and therefore more materials, energy.... thus also a more complex / larger construction process. 

SpaceNut,

The energy and payload points have been combined in the diagram, but I will create a separate point for clarification.

Last edited by Noah (2021-04-11 13:32:10)

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#116 2021-04-11 13:17:41

Noah
Member
From: Zurich (Switzerland)
Registered: 2020-07-28
Posts: 38

Re: Settlement design

kbd512 wrote:

Flip to Page 50 of their report.  In the third column, the one labeled "Avg Power (kw)", locate the row that says "ECLSS Total".  The figure in the column should be "14.8".  Divide that figure by "4".  You should get "3.7".  That is the average power estimate for ECLSS, from a company actively engaged in the design and implementation of ECLSS hardware for NASA.

Sound interesting and I appreciate that you added a source. Thanks!

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#117 2021-04-11 14:05:51

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,371

Re: Settlement design

Noah,

Here's an energy estimate for indoor grow operations:

Greenhouse Energy Profile Study - Reporting Findings

Flip to Page 59 of that report to locate the annual energy consumption figures.  Multiplying those figures by 10.7639 provides kWh/m^2.

From Page 59:

Heating: 42.01kWh/ft^2; 452.19kWh/m^2
Lighting: 27.86kWh/ft^2; 299.88kWh/m^2
Pumping: 1.82kWh/ft^2; 19.59kWh/m^2
Other: 1.26kWh/ft^2; 13.56kWh/m^2

SkyFarm intends to use a 59-story building to produce enough food to feed 35,000 to 50,000 people per year using 743,224m^2 of floorspace.  This is also where that 20 greenhouses figure comes from.

SkyFarm Vertical Farm by Gordon Graff

The article notes that the structure will use 82 million kWh per year to grow that food.  That's 82,000,000,000.  82GWh per 50,000 people, but they don't have to pressure or filter the air or do any ice mining for the water source.  We're going to use genetic engineering of the crops and every other trick in the book to ensure that we always produce enough food for 50,000 people.  Even so, we're going to completely ignore engineering reality, for sake of entertaining our science fiction fantasies, and go with 1,640,000,000,000Wh or 1.64TWh per year.  That's another 2.5 Bhadlas.  Alternatively, we use another 2 of those 250MWe Thorium-fueled molten salt reactors which provide 4.38TWh per year (which also helps to contend with engineering reality, where we'll need even more power than that to pressurize the building, supply enough water from ice deposits, etc).

It also occurs to me that we haven't even touched on the power requirements for construction.

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#118 2021-04-11 15:02:25

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,757

Re: Settlement design

For kbd512 re #117

SearchTerm:Greenhouse power for SkyFarm Vertical Farm with Mars estimates
SearchTerm:Farm SkyFarm Notes by kbd512 in #117

(th)

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#119 2021-04-11 15:50:43

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

Re: Settlement design

Food mass requirements

The idea there's no difference between carnivore and a herbivore mammals is bizarre. Of course there's a difference. A gorilla eats an incredible mass each day. A polar bear doesn't.

The Mars pioneers will be in zero G and then low G. I doubt they'll be doing much physical work but if they do, it will be a lot less demanding than on Earth.

This link indicates research suggests we eat between 3 and 5 pounds of food each day - that's between 1360 grams and 2260 grams.

https://www.stack.com/a/forget-calories … ly-matters

As with fighter pilots, I think the pioneers are going to be of smaller stature than average. Given the lower G demands and that smaller stature, I think the figure of 1.5 Kgs of food per day is a more reasonable one, especially as we will tend to select energy dense foods (e.g. olive oil) so that we can lower the mass of cargo.

Oldfart1939 wrote:

Louis-
From my background in ranching, a figure that is almost universal for all mammals, according to the veterinarians, is 2% of the body weight per day in food consumption. That's a basic maintenance diet and not a weight gain or accounting for heavy work kinda diet.
That calculates to 1 kg of food for that hypothetical average human. I did the math several years ago on this website and calculated what supplies should be prepositioned before sending the Mars Direct style mission. This was before Elon came on the scene with his city of one million people. The number you mentioned earlier of ~2,400 grams sounds about right for a human doing physical labor.


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

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#120 2021-04-11 16:07:34

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 27,185

Re: Settlement design

If a Dragon capsule or any of the Nasa units are used they have limited internal volume and depending on how these are joined in orbit to make the travel to mars possible that crew would be as indicated under the dozen mark.
Sizing for limited time use is typically 4 to 7 for how seating internally might be applied to the current capsule use.
Connecting habitat and modules such as the ISS makes it possible for what we have to make a journey once linked in orbit for the journey to Mars.
The only issue is we have no landers for Mars for a crewmen to make use of. GW did run numbers for the dragon and it was possible to land with some crew and payload but it could not return back to orbit.

This is the one stumbling area for man to over come for any crew size....


edit
Robertdyck's follow up can also be seen as the business proposal to get humans to mars

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#121 2021-04-11 18:40:49

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

Re: Settlement design

Kbd,

I still haven't seen an explanation of how you end up with such a large PV panel allowance per person. From a previous post of mine commenting on your overall figure of 500 sq km (assuming 25% panel efficiency) for a million person community:

So taking the smaller 500 sq km figure, that's 22360 x 22360 metres, which gives a per person figure of near enough 500 sq. metres per person which would produce 250 KwHes per sol (assuming you can get 0.5 KwH per sol per sq. metre of PV panel).

Lop off 25% for energy storage, and I make that 187.5 KwHes per sol, or a constant of 7.6 KwHes.

7.6 KwHes is more than double the figure of 3.7 KwHs you started with. For a 2.5 person average household it produces a huge figure of 486 KwH  - nearly half a MwH.

There's no way that figure makes sense in relation to on Earth energy usage where a household might use maybe 30 KwHs with heating (usually gas rather than electricity) or air-con thrown in.

The likelihood is that people on Mars will be living together in a much more huddled situation with heat being retained within the residential complexes, as people live in the equivalent of small apartments.

Yes, they need to operate life support and pump air around to some extent (probably less than you are assuming from office data where you can have maybe a hundred people working in the safe office space). We may well find that natural convection currents do a lot of the "pumping" in terms of moving air around, so it doesn't deoxygenate.

Of course per capita energy will be used in farming (though less as the colony matures and develops natural light farming), retail, offices, public spaces, industry, transport, mining and so on but if we assumed a generous 50KwHes "private" household usage, that leaves a whopping surplus of 436 KwHs per household for those purposes.  For one million people this would produce constant average power of 17 Gws. On the basis of total energy usage (ie all forms of power) in the UK, one million people in the UK would be using a constant average of nearly 4 Gws of power (2014 figures). So again that's a huge difference - of 13 Gws of power. Why so much when the people of Mars concentrated in a million person city will have little need of private automobiles, metalled roads, railways, shipping, seaports, huge airports etc. Where will all that additional power be used? This is additional power on top of accounting for life support and air flow, remember.

I would accept that construction at the equivalent of something like 13,200 residential household units per annum for 33000 people would be a significant demand but that sort of construction effort is already absorbed in the much lower UK comparison figure.  Construction on Mars might or might not require some more energy, but even if it was double the energy it wouldn't explain the huge difference. 

Once again I can only conclude you've totally inflated the energy demand for no good reason.


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

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#122 2021-04-11 18:52:25

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,389
Website

Re: Settlement design

I did post a couple threads with alternate mission designs. One was "updating Mars Direct". Premise was use modern equipment (before Starship), but sticking with Mars Direct basic architecture. ERV would be a Dragon capsule with Cygnus pressurized cargo module docked to the nose. Recycling life support equipment based on ISS installed in the Cygnus. Barely enough room for one man to float up into the Cygnus, with equipment packed all around. One row of 4 seats in Dragon. Lower row of seats removed, one exercycle, small toilet, and storage for Mars samples. Dehydrated food would have to be stored in every nook and cranny. Would require a two stage LOX/LCH4 rocket to launch the ERV into TEI. Original Mars Direct included a rover that could drop an SP100 nuclear reactor in a crater, then the rover would back a way. The robotic rover could be used by crew when they arrive. My alternate was a SAFE-400 nuclear reactor, which is a newer design by the exact same team, produces exactly the same electrical power but is lighter. Instead of a rover with arms, the wheels and NAVcam from Curiosity rover would be bolted directly to the reactor. So the reactor drives itself into a crater, and parks. This is lighter, but no robot rover for crew.

Alternate architecture: Mars Orbit Rendezvous. With this, a Mars Ascent Vehicle is sent ahead, with ISPP. Crew rides in habitat, but with 2 habitats. One is the surface habitat, the other optimized for space. You could make the surface habitat smaller, and send a laboratory ahead on a cargo lander. MAV would just barely have enough room for crew and samples. MAV would dock to interplanetary habitat parked in Mars orbit. MAV would carry additional propellant so it would be the TEI stage. That means all ISPP for return. A Dragon capsule would be docked with the interplanetary vehicle. It would aerocapture into Earth orbit, but if anything went wrong with aerocapture, astronauts would be in Dragon capsule so would survive. Interplanetary vehicle would be reused for multiple missions. Since it would be in Earth orbit between missions, it could be cleaned and restocked. TMI stage would act as counterweight for artificial gravity, as Mars Direct. MAV which acts as TEI stage would also act as counterweight, so artificial gravity on return to Earth as well. If something goes wrong and free return is require, crew are with both surface habitat and return habitat, so have access to both supplies of food. That means plenty of food for free return.

Criticism of Mars Orbit Rendezvous: requires both surface rendezvous and orbit rendezvous. Surface hab must land within walking distance of MAV, and MAV must rendezvous with interplanetary hab. But after all the automated cargo ships have docked with ISS, I don't see orbit rendezvous is a risk. And after all of SpaceX precision landings on drone ships, I don't see surface rendezvous as a risk either. This is just current technology.

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#123 2021-04-13 04:35:21

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,371

Re: Settlement design

Louis,

louis wrote:

Kbd,

I still haven't seen an explanation of how you end up with such a large PV panel allowance per person. From a previous post of mine commenting on your overall figure of 500 sq km (assuming 25% panel efficiency) for a million person community:

Simple math doesn't work for computing array performance.  You can't use array area multiplied by panel efficiency to compute photovoltaic array performance, even if you know exactly how many Watt-hours per day that the Sun provides.  I decided to educate myself on this since the numbers weren't adding up.  You could just as easily do the same if you decide it's worth your time.  I'm not sure how to make that point any more clear.  I'll illustrate the discrepancy created by attempting to use simple math later in this post.  That's why I used empirically-derived array output from the largest commercial solar array on Earth.

I already explained the ECLSS power requirement, but you're still arguing over this point.  You're not arguing with me, though, you're arguing with aerospace engineers who know more about ECLSS power requirements than either of us ever will, from testing and operating ECLSS on actual space flights where actual lives were and are at stake.  I computed how much power that represents over time for your convenience.

3,700Wh per person per hour * 8,760 hours per year = 32,412,000Wh (32.412MWh) per person per year

Energy efficiency and renewable energy under extreme conditions: Case studies from Antarctica

From the case study:

Most stations have been designed to accommodate up to approximately 50 people, while the larger stations can accommodate 100–200 people, the largest permanent station in Antarctica, US’s McMurdo station, has power requirements of 16,000 MWh/yr to provide for a peak population of 1000 people in the summer and a winter population of 250 (See Fig. 3). McMurdo also serves as the primary logistics hub of the US Antarctic Program, where multiple small research camps are originated and supplied by air or over- land. At McMurdo nearly 5 million liters of fuel are used annually for electricity production and additional fuel is needed for heating.

McMurdo Station in Antarctica uses 16,000MWh per year for a population of 250 to 1,000 people.  Simply divide 16,000MWh by 1,000 and you arrive at 16MWh per person, except that only a quarter of those people are living in the station during the winter.  If half the power is used during the summer and the other half is used during the winter when there's only 250 people at the base, then you arrive at 32MWh per person.  McMurdo's per person winter power consumption is nearly exactly like living on Mars.  If you consider everything they're not doing at McMurdo, NASA's ECLSS technology is at least twice as efficient.  When put into the context of an extreme environment found right here on Earth, the notion that they'd use the exact same amount, per person, as McMurdo uses during the winter, isn't all that outlandish.

You know what they're not doing at McMurdo?

They're not melting ice because there's a giant pool of liquid water under the station.  They're not scrubbing CO2 from the air that they breathe, nor producing "fresh air" from a 6 millibar pressure atmosphere that they have to liquefy first, so can then use SOXE to produce O2 from CO2.  They're not filtering their urine and feces to extract the water.  They do treat the grey water before they discharge it, but that's about it.  Mars summer night time temperatures also happen to be colder at night than Antarctica in the winter.  You don't have to deal with so much convection, but a thermal soak is a thermal soak.  All of those activities that they're not doing at McMurdo drastically increase power consumption.

The Average Annual Daily Potential Solar Energy map shows that the best opportunities for commercial solar power generation are located in the southwestern U.S. Large commercial solar developments are most profitable in areas with average annual daily potential greater than 6 kWh/m2/day.

The word "potential" is the operative word in that last sentence.  Much like the Southwest US, Bhadla also has plenty of "potential".  The mere fact that the integrated TSI is impressively large doesn't mean the panel can actually convert all of it into electricity.  The specific solar array performance example that I used is based upon the empirical performance of the Bhadla array in India.  Bhadla is located in a desert where it virtually never rains (a few mm of rainfall per year) and maximum wind speeds are below 15mph.  The panels do get quite dusty from the fine powdery sand, kinda like Mars, so they're routinely cleaned off by both robots and humans.  Most of the panels in the array are fixed in place and they're very low to the ground, so it's a pretty good approximation for what you routinely talk about doing.  With that said, let's demonstrate why simple math doesn't work for calculating photovoltaic array output.

Mars surface receives a yearly (Mars year) average of 3kWh/m^2 per day where Viking landed.  Earth surface where Bhadla is located receives an average of 6kWh/m^2/day.  GHI alone at Bhadla is 2,010kWh/yr, or 5,506.85Wh/day.  That is the amount of direct beam solar power the array could potentially use, but NOT indicative of what it actually collects.  Anyway, this is what grossly over-simplified math (regarding solar array performance) would (falsely) seem to indicate about the Bhadla array (and the exact reason I used that array's published empirical power output):

6000Wh/day (with DHI added to BHI, it's even more than this) * 0.25 = 1,500Wh/m^2

Actual array area is 10,000,000m^2 (10km^2).  I computed effective array area to be 85% of that (solar panel fill factor; aka, the part that's filled with beautiful shiny silicon, like the PV panels mounted on my roof), so 8,500,000m^2 (I posted the photo of the Bhadla array taken from space, so you can use your imagination by looking at all the blue areas on that photo to visualize the 10km^2 of "actual panel area", out of the 57km^2, by visually "assembling all the pieces" into a perfect square).

8,500,000m^2 * 1,500Wh/m^2 = 12,750,000,000Wh/day = 12.75GWh/day (if only)

12,750,000,000Wh/day * 365 days per year = 4,653,750,000,000Wh/year = 4.65TWh/yr (or 4.27TWh/yr from BHI alone)

Even if the panels were only 10% efficient, they're still producing 1.86TWh/year!  So, what happened to our missing 3TWh?  How is this thing not producing 3 times as much power as its published output?  You can monkey with the panel efficiency to your heart's content, but unless the panels are less than 10% efficient, simple math is clearly "off" by a considerable amount.  There's a good explanation, though.  Panel efficiency is NOT a constant.  Once you understand that, then it's pretty simple to figure out where our missing power went.

Solar Panel Behaviour as Light Decreases

From the article:

Generally speaking, current from a solar panel decreases linearly with decreasing irradiance, while the voltage drops logarithmically. However, there is significant variation among various types of solar panel with respect to these declines.

The low-light functionality of a solar cell is primarily reliant on the shunt resistance and series resistance of the cells, which are the resistance related to contacts at the top and the bottom of the cell and the resistance related to the current that circulated the emitter.

At low light levels, the impact of shunt resistance becomes increasingly relevant. As intensity decreases, the bias point and current also decrease, with the equivalent resistance of the solar cell starting to approach the shunt resistance. When these two resistances are nearly equal, the fraction of the overall current flowing through the shunt resistance rises, in so doing, it increases the fractional power loss as a result of shunt resistance. Therefore, under cloudy conditions, a solar cell with a high shunt resistance keeps a greater portion of its original power compared to solar cell with a low shunt resistance.

louis wrote:

So taking the smaller 500 sq km figure, that's 22360 x 22360 metres, which gives a per person figure of near enough 500 sq. metres per person which would produce 250 KwHes per sol (assuming you can get 0.5 KwH per sol per sq. metre of PV panel).

Lop off 25% for energy storage, and I make that 187.5 KwHes per sol, or a constant of 7.6 KwHes.

7.6 KwHes is more than double the figure of 3.7 KwHs you started with. For a 2.5 person average household it produces a huge figure of 486 KwH  - nearly half a MwH.

If this is how solar array output actually works, then we should be getting a LOT more output from the Bhadla array, shouldn't we?

There's no way that figure makes sense in relation to on Earth energy usage where a household might use maybe 30 KwHs with heating (usually gas rather than electricity) or air-con thrown in.

Unless, of course, you live at McMurdo in the winter, and then your energy usage is exactly the same as it would be on Mars.

The likelihood is that people on Mars will be living together in a much more huddled situation with heat being retained within the residential complexes, as people live in the equivalent of small apartments.

The bulk of the power requirement is for supplying fresh air and water, unlike McMurdo Station, where loss of heat through convection is the biggest energy sink.

Yes, they need to operate life support and pump air around to some extent (probably less than you are assuming from office data where you can have maybe a hundred people working in the safe office space). We may well find that natural convection currents do a lot of the "pumping" in terms of moving air around, so it doesn't deoxygenate.

The office air circulation requirement assumes a rather generous amount of floor space per person, but you just said you're going to cram everyone together.

Everyone's going to be huddled together, but we don't need a bunch of fans going to keep the atmosphere fresh, because we're going to use convection to eliminate pumping losses?  Umm...  What?...  Can you understand how contorted your logic is becoming?

Of course per capita energy will be used in farming (though less as the colony matures and develops natural light farming), retail, offices, public spaces, industry, transport, mining and so on but if we assumed a generous 50KwHes "private" household usage, that leaves a whopping surplus of 436 KwHs per household for those purposes.  For one million people this would produce constant average power of 17 Gws. On the basis of total energy usage (ie all forms of power) in the UK, one million people in the UK would be using a constant average of nearly 4 Gws of power (2014 figures). So again that's a huge difference - of 13 Gws of power. Why so much when the people of Mars concentrated in a million person city will have little need of private automobiles, metalled roads, railways, shipping, seaports, huge airports etc. Where will all that additional power be used? This is additional power on top of accounting for life support and air flow, remember.

I'm guessing you won't accept the energy usage stats associated with McMurdo Station, either.  Somehow, we're going to use less energy than we do in a place where the air and water are free and all the food is delivered via C-130.  Got it (throws hands up in the air).

I would accept that construction at the equivalent of something like 13,200 residential household units per annum for 33000 people would be a significant demand but that sort of construction effort is already absorbed in the much lower UK comparison figure.  Construction on Mars might or might not require some more energy, but even if it was double the energy it wouldn't explain the huge difference.

I'm thinking about the problem in terms of space-efficient structures and power supplies, specifically because the energy consumption is so gosh darned high that I question our ability to meet it with nuclear power, never mind solar power.

Once again I can only conclude you've totally inflated the energy demand for no good reason.

You're arguing over the empirical output of the world's largest solar array, which also happens to be located in a place that receives more than twice as much solar irradiance as Mars does, by virtue of being located in a desert on Earth.  Look at the power output of Bhadla and explain to me why it's not three times higher than it is.  Power companies don't lie about how much electricity they produce to support or refute internet arguments over solar array output.  Aerospace engineers working for NASA don't lie about the power requirements of their ECLSS to support or refute internet arguments over power consumption.  Your beliefs about solar power and energy consumption rates don't seem to coincide with objective reality.  The array output is what it is.  The ECLSS has a voracious appetite for electrical power.  I wish it was lower than it is, but apparently that's as good as it gets for $240M.  If you have $240M of your own money, then maybe you can do better than NASA's contractors.

Argue the power output figures with the government of Rajasthan, India.

Argue with Paragon SDC over the power consumption of IWP.

Argue with NASA over the power consumption of CAMRAS.

I've reached my limit.

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#124 2021-04-13 06:05:39

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,336

Re: Settlement design

The energy requirements per capita for a growing colony on Mars will be huge.  There is no way of avoiding that.  Every space with breathable air (including agricultural space) must be a pressure vessel.  That is a level of engineering far beyond anything we need to consider on Earth.  Once you have agriculture up and running, photosynthesis will regenerate O2 from CO2.  But you need to manufacture the air in the first place and make up for losses.  The amount of energy we need to grow food is an open question at present.  If we do it using natural light, then we need pressurised greenhouses covering a very large area, which probably need heating.  If it is done using artificial light, then the arrangement is more compact, purpose built heating isn't needed, but electrical power requirements will be high.

Water costs 1000MJ/m3 on Mars.  That's what it will take to mine it, heat it up, melt it and pump it.  Human beings need a lot of water.  Even basic drinking needs amount to about 1m3/person/year.  Including washing, cooking, agriculture and heat transfer fluids, the average person needs tonnes per capita.

The biggest energy expenditure is going to be manufacturing.  To build a city of 1 million during our lifetimes, implies a very rapid buildup of infrastructure on Mars.  We are going to have to make this stuff by reducing metals from ores and making plastics from CO2 and water.  These are very energy intensive processes, implying energy investments in the region of tens - hundreds of MJ per tonne of materials.  And we are talking millions of tonnes of materials for a city of 1 million people.  And the power supply itself needs to expand to accommodate the rapid growth of the settlement.  Energy needs to be cheap because we are going to need so much of it.  Cheap energy means keeping capital costs low.  That means high power density.  That means nuclear power or some thermonuclear energy source if it is available by this point.  No way around it.  Solar power isn't going to cut it on a planet with 43% of Earth solar constant, where a lot more energy is needed just to survive.  You may not like it.  But there is no cheating the laws of thermodynamics.  They apply whether you like it or not.

Colonising Mars will require the use of nuclear power on a scale that far exceeds anything yet considered on Earth.  We need far more energy per capita to survive and there are no fossil fuels that we know of.  I think our philosophy towards nuclear energy needs to change.  We need to get comfortable with idea of having a nuclear reactor down the road, providing not just the electricity needed in our home, but our transporting, our heating, the goods we consume, our food.

It was the obvious need to build up reactor capacity quickly and cheaply using native resources, that prompted me to suggest building aqueous homogenous reactors on Mars.  These are extremely simple and inherently safe reactors that could be built rapidly using low grade materials.  The problem is that they are limited to relatively low operating temperature.  If liquid CO2 or dry ice is available on Mars in large quantities, then liquid CO2 can be injected into boilers at temperatures beneath the normal boiling point of water and the supercritical gas passed through turbines directly into the Martian atmosphere.  This is a simple system that can be built very rapidly.  There may be other systems that work better.

Last edited by Calliban (2021-04-13 07:32:32)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#125 2021-04-13 06:20:37

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,757

Re: Settlement design

For Calliban

A member of the forum (most likely) doesn't have time to follow every topic, even if they wanted to.

For that reason, is is likely you have not followed the discussion of pneumatic tools in another topic.

But I am struck by the similarity between the output of the proposed reactor design and the needs of the pneumatic tool ...

In that topic, extension of a student experiment (done with a retired NASA mentor) to practical application is under consideration.

The venting of the output of the reactor to the atmosphere seems (to me at least) incredibly wasteful.

I've been hoping to enlist your review of a design for a pressure vessel for generating CO2 from dry ice, using ordinary heat such as CO/O2.

The Parr Instruments company makes pressure vessels for laboratories and for specialized industries such as pharmaceutical.

In the Pneumatic Tools topic I have pasted email from an employee of Parr Instruments. He provided a link to YouTube type videos showing the pressure vessels, and he directed our attention to one that tilts over to allow contents to be dumped into a  retort.

That particular design is (probably) overbuilt for Mars pneumatic tools, but in any case, I'm hoping you will have time to review the video to see if the design might be adapted for the Mars concept.

(th)

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