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#126 2021-04-13 07:34:54

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

Re: Settlement design

Environmental Control and Life Support System


Kbd,

I've taken a fairly detailed look at the ECLSS document.

https://www.mars-one.com/images/uploads … ssment.pdf

While it's very thorough, I'm not sure how it relates to a city of one million.

Take for instance the reference to loss of nitrogen and argon (Table 4, page 42). Airlock losses account for over half the loss. And this is on the assumption of four airlock operations every day. So in their calculations they are using one airlock per four persons and four airlock movements per day. That is clearly totally irrelevant to a city of 1 million people.

The One Million City might have, say, 20 airlocks to the outside to allow for buses to run to the Spaceport for instance, and maybe to industrial, science and farm habs or nearby mining locations. 20 per million ie one per 50,000 people not 1 per 4 people. Airlock movement of one per person will also become a tiny fraction of that - maybe 100 airlock movements a day so 1 movement per 100,000 people. In a Mars city most people will not leave the city for weeks or months on end. There will be pressurised access to recreational areas where people can exercise in Earth-like surroundings, go swimming and observation towers so they an see their surroundings. [I would think with 100 airlock movements a day you could allow for the exit and return of 10,000 per day if necessary. People would I think go on short breaks to remote "hotel" locations from which they could go exploring in pressurised rovers or undertake some EVA activity. These would be big airlocks able to accommodate a couple of large buses carrying maybe 50 people each.]

Clearly,on a proportional basis, the energy requirement for replacing lost nitrogen and argon will be a tiny fraction of the per person figure given in the ECLSS document.

There are many examples throughout the document where you can query the scaling up. Would we really need to replace 2.25 million kgs of water per annum, when again a large amount of that is lost to airlock cycling. And if we did, would we need to use such an intensive regolith processing system as set out in the paper? Clearly not. We know there fresh water glaciers on Mars. Once we access those with 95% plus purity, processing will be much less energy-intensive. In fact you could probably have the equivalent of a solar tower to melt the ice, just using mylar reflectors. 

How much could we use oxygen production from trees and plants, including crops, to mitigate the need for oxygen production?


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

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#127 2021-04-13 07:37:38

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,325

Re: Settlement design

I have corrected my previous post.  Getting water out of ice deposits on Mars will have energy cost of around 1000MJ/tonne, not 1MJ/tonne.

I will look in detail at the CO2 tool topic later.  Because CO2 will likely be generated at very high pressure, it will make sense to include inter-stage reheat between high, medium and low pressure turbines.  A supply of tool pressure CO2 could be tapped off of the reheat heat exchanger between the outlet of the medium pressure turbine and LP turbine inlet.  I assume tool pressure to be between 0.5-1Mpa.  There needs to be consideration of pressure drop in lines of course.

As an aside, I presented an idea a while back for using solar thermal energy collected by flat plate panels to boil liquid CO2 to generate power.  My reason for raising this idea was an attempt to get around the high embodied energy requirements of a PV system.  A low temperature thermal system could use ceramic panels carrying plastic brine pipes, which would have much lower energy cost than a PV panel.  Energy can be stored as heat and the same turbine used to generate power whether the sun is shining or not.  My attempt to improve the EROI of solar power on Mars, probably in vain.  Just to demonstrate that I am not averse to solar power in principle.  It's just that the physics is against us.

Last edited by Calliban (2021-04-13 07:44:47)


"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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#128 2021-04-13 09:50:17

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,383
Website

Re: Settlement design

If you want details of "updating Mars Direct", or if you want details of life support equipment, it can be found here: Light weight nuclear reactor, updating Mars Direct

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#129 2021-04-13 10:10:50

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,668

Re: Settlement design

For Calliban re #127

Thank you for noting the opportunity for you to assist with the Pneumatic Tool topic.  No hurry, for sure!  I am hoping your interests will match with some of the concepts under discussion there.

I had to ask Google (as usual) for help with the range of pressure you estimated in MegaPascals, and which I am thinking about in ATM's.

Per Google, 709275 pascals is equivalent to 7 ATM ... one ATM is given as 101325 Pascals

Therefore, your estimate on the high end is close to perfect because (as SpaceNut points out repeatedly) we need more pressure in the boiler than the amount needed by the tool, because of losses in the lines to the tool, and the need to have some resilience to buffer demand with supply.

Because we are in Noah's Settlement topic, the subject of Pneumatic Tools is not out of line, and of course your exploration of nuclear power supply is ** definitely ** pertinent.

The temperature of the effluent from your reactor design may be a problem.  Pneumatic tools need input gas that is low in temperature compared to the working temperature of the tool, to help to cool it while it is in operation.

The Dry Ice supply concept in the Pneumatic Tool topic would (presumably) meet the temperature requirement, because heat would be supplied sufficient to sublime the Dry Ice, and to deliver the needed 90 psi (up to about 120 psi) for the tool.

In the case of the reactor, I'm concerned that the temp ... oh!  I just remembered you'd said the feature of the reactor is ** low ** operating temperature!

Perhaps this is a good fit after all?

On Earth, gas supply for a pneumatic tool starts out at ambient (local temperature) and receives temperature increase due to compression.

After release from the air supply tank, it travels through a regulator and then various lines and fittings to arrive at the tool.

I have not (yet) learned what temperature is "normal" for air supply to a pneumatic tool on Earth, so will attempt to find out.

Edit#1: Here is a resource for temprature:

https://fluidairedynamics.com/how-to-de … equipment/

I cannot see it on the system where I am now, but hope it will answer the question.  It is possible the article is about the external temperature.

I did note citations about trying to operate pneumatic tools in subzero temperatures, which would (of course) be "normal" on Mars.

(th)

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#130 2021-04-13 11:24:10

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

Louis,

This attempt to ignore engineering reality is becoming increasingly bizarre.  I keep responding out of morbid curiosity regarding what a person with either a dogmatic religious belief in solar power or a substantial lack of understanding of some pretty fundamental engineering principles imagines in their mind whenever the engineers start talking about power generation and efficiency.  What I find most depressing is the refusal to accept both engineering reality and straight multiplication, whenever it runs afoul of "green ideology".  I'm not going to argue any more consumption figures with you, but I'll highlight how fantastic what you're asking for actually is.

Energy Generation

I bet those wacky Indians wired up a bunch of resistors into their solar array to ruin your internet argument, didn't they?

I'll bet one of them was like, "You know, Kumar, three years after we've been sweating our rear ends off in the middle of this desert to complete our solar array and make it work, I think kbd512 and Louis are going to have an internet argument about how much power we actually get from our photovoltaic array.  Let's under-report our actual power output by a factor of 3, just to mess with Louis.  We'll say we're making 1.3TWh/yr, just so Louis can ask a question he should've already asked himself.  Yes, Rajah, that's the plan."

So, what the heck happened to that extra 3TWh of power that they should be getting from Bhadla?

From where I'm sitting, it looks as if they're wasting more than twice as much power as their array is producing.

Did they install their panels upside down?  Or maybe they wired them in backwards?

After all this time, am I to learn that Indian engineering schools don't know how to teach math and engineering?

Maybe you should join Rajasthan's internet forum to let them know how "profligate" they're being with their upside down and backwards solar panels, complete with resistors, that they've clearly installed that way to ruin your internet argument.

louis wrote:

Environmental Control and Life Support SystemTake for instance the reference to loss of nitrogen and argon (Table 4, page 42). Airlock losses account for over half the loss. And this is on the assumption of four airlock operations every day. So in their calculations they are using one airlock per four persons and four airlock movements per day. That is clearly totally irrelevant to a city of 1 million people.

The One Million City might have, say, 20 airlocks to the outside to allow for buses to run to the Spaceport for instance, and maybe to industrial, science and farm habs or nearby mining locations. 20 per million ie one per 50,000 people not 1 per 4 people. Airlock movement of one per person will also become a tiny fraction of that - maybe 100 airlock movements a day so 1 movement per 100,000 people. In a Mars city most people will not leave the city for weeks or months on end. There will be pressurised access to recreational areas where people can exercise in Earth-like surroundings, go swimming and observation towers so they an see their surroundings. [I would think with 100 airlock movements a day you could allow for the exit and return of 10,000 per day if necessary. People would I think go on short breaks to remote "hotel" locations from which they could go exploring in pressurised rovers or undertake some EVA activity. These would be big airlocks able to accommodate a couple of large buses carrying maybe 50 people each.]

Clearly,on a proportional basis, the energy requirement for replacing lost nitrogen and argon will be a tiny fraction of the per person figure given in the ECLSS document.

There are many examples throughout the document where you can query the scaling up. Would we really need to replace 2.25 million kgs of water per annum, when again a large amount of that is lost to airlock cycling. And if we did, would we need to use such an intensive regolith processing system as set out in the paper? Clearly not. We know there fresh water glaciers on Mars. Once we access those with 95% plus purity, processing will be much less energy-intensive. In fact you could probably have the equivalent of a solar tower to melt the ice, just using mylar reflectors. 

How much could we use oxygen production from trees and plants, including crops, to mitigate the need for oxygen production?

Environmental Control and Life Support System

If 20 airlocks are large enough to permit 10,000 people to pass through each day, then they're proportionately larger in volume and lose proportionately more air and water when pressure is equalized, because airlocks vent atmospheric pressure into space.

You can cut the air and water losses to nearly zero and you're still talking about 25 Bhadlas to make this fantasy work.

If Mars City only loses 2.25kg of water per person, per year, then you'd best have an awards ceremony where you hang a solid gold medal around the neck of every engineer who made that herculean feat of engineering happen, and present the keys to the city to them while you're at it.  That level of extreme water conservation still boggles my mind.

IWP only returns about 98% of the water filtered through it.  The rest is trapped in the filter with the contaminants.  If you filter enough water to supply a million people, I want you to do some math on what a 2% per day water loss looks like.

To wit, you want an airlock that allows 10,000 people to pass through per day that never looses air or water, you want people huddled together without proper ventilation, rich couch potato midgets who don't do any work so they consume less food, and the list goes on.

What you're really asking for is a science fiction fantasy.

Pretending this place is going to be vastly more efficient than McMurdo Station, especially while it's being built, is pure fantasy.

Nuclear power isn't "black magic", Louis.  It's not stalking you, waiting to pounce on you, when you least suspect it.  It is a form of energy so concentrated that it's a million times more energy dense than Methane.  I know it's hard to imagine how 3,750m^3 of reactor volume can produce the same amount of power as 50 Bhadla arrays, but that's one of many benefits that comes with using concentrated and boringly reliable energy.  You don't need any poor, huddled masses of couch potato midgets, yearning to take their next breath, when you can afford to be "profligate" with your energy use.  I know the media has done their absolute best to terrify you and everyone else with horrific tales of nuclear death, but the last person to die from commercial nuclear power in the US was, as I recall, 1964.  That was more than half a century ago.  It's time to move beyond the media-induced night terrors, which is only their own psychosis on display for all the world to see, and recognize how concentrated and abundant energy helps make this "beautiful dream" of a city of a million people on Mars, an engineering reality.

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#131 2021-04-13 13:17:19

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,668

Re: Settlement design

This is primarily for SpaceNut, but it (hopefully) will be of interest to everyone participating in Noah's topic...

We have discussed before how we (this forum) need a Wiki type fixed environment for accumulation of vetted knowledge

The reason we have these ongoing cycles of repetition is the lack of a fixed location where members can drop off knowledge, and where (as in Wikipedia) that knowledge can be corrected until everyone has arrived at a consensus of it's reasonable approximation to reality.

I know you've approached Mars Society in the past, but I'm hoping you'll keep trying.  Noah's undertaking will suffer from the same fate as all the other topics is we are unable to collect and "lock" the hard earned facts and figures he and his team will need to carry out actual projects.

(th)

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#132 2021-04-13 13:44:36

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

tahanson43206,

We argued about how much power an actual solar array, the world's largest to date, recorded during a year of operations after construction was completed.  Does that seem reasonable to you?  The people in all of the solar power websites were basically bragging about how much power it produced, and they have a right to do so, because it objectively made a LOT of power.

If we move that same array 50% further from the Sun, if all other factors remain equal or roughly equal, then it objectively makes 50% less power.  The only practical way to overcome that energy density problem is to double the cell efficiency of the array.  I don't see what would be the least bit controversial about that fact of life.  From an engineering perspective there's no controversy.  I've been told as much from people who hold electrical engineering degrees who also design home solar arrays for a living.  Why would they lie to anyone about something like that?  It certainly wouldn't help their business if they did.

We could do zero ISRU replenishment of consumables by having a perfectly closed loop, despite the functional impossibility of doing that with current technology, but we're still talking about a solar array 20 (19.93 if we need to get really precise) TIMES larger than anything that exists on Earth, just to keep everyone breathing fresh air (CAMRAS and IWP only, nothing else).  Does anyone here truly believe that that's practical?

Unfortunately, the energy requirements for living on Mars are incredibly extreme, as in McMurdo Station in Antarctica in the winter extreme.  They use 32MWh of power per person in the winter time.  It's unreasonable to think that LESS power would be required in a place that's even more extreme, where you have to make all of the air and water and food you need from raw feedstocks that require massive quantities of energy to transform into anything usable.  The entire premise of that argument is antithetical to basic logic and math.

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#133 2021-04-13 14:26:57

Quaoar
Member
Registered: 2013-12-13
Posts: 644

Re: Settlement design

RobertDyck wrote:

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.


4 crew for an almost two year stay on Mars means a lot of cross training capabilities: you need 2 pilot engineers for flying the MAV/ERV and two doctors able to perform basic surgery, orthopedic, because you cannot risk to lose an astronaut for a stupid appendicitis or a broken leg, and possibly even dentistry. So the doctors must be cross-trained in basic research in biology to study possible martian microbial biota and engineers must be cross trained in geology and geochemistry.  You can do it but a six crew has far better chance to survive.

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#134 2021-04-13 15:21:47

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

Re: Settlement design

Kbd,

I've never queried the figures for the Indian array output, just the way you've read across to Mars in terms of power output, material usage and so on.

Many of these large arrays on Earth are relatively low power - the big one at Aqua Caliente in Arizona seems to be at 17% or lower efficiency. I think the Mars arrays will be more efficient (probably around 25%) because that is a money problem and money will not be a problem on Mars!

Maybe the array will cost $100 billion. That's $3.3 billion per annum over 30 years. Space X and Tesla will be earning many multiples of that and companies or individuals would be contributing to covering the costs as well. If, for instance, a university wants to set up a campus on Mars, they will no doubt be required to pay the full amount to cover the cost of PV installation.

I have queried your application of the Mars One ECLSS report to a one million person community. There is simply no way you can read across from an analysis looking at 4 pioneers living in tin cans (I never liked the model in any case) to a million strong city. There are many points of departure - air lock losses, water loss, no oxygen production from plants or other organisms.

The comparison with Antarctica is also unhelpful. Having seen video of the station I don't think minimising energy usage is top of their priority list. I was surprised to see people going in and out of isolated huts, cold air coming in each time. More importantly everything I have read suggests heat loss on Mars is a much slower process than in Antarctica.



kbd512 wrote:

tahanson43206,

We argued about how much power an actual solar array, the world's largest to date, recorded during a year of operations after construction was completed.  Does that seem reasonable to you?  The people in all of the solar power websites were basically bragging about how much power it produced, and they have a right to do so, because it objectively made a LOT of power.

If we move that same array 50% further from the Sun, if all other factors remain equal or roughly equal, then it objectively makes 50% less power.  The only practical way to overcome that energy density problem is to double the cell efficiency of the array.  I don't see what would be the least bit controversial about that fact of life.  From an engineering perspective there's no controversy.  I've been told as much from people who hold electrical engineering degrees who also design home solar arrays for a living.  Why would they lie to anyone about something like that?  It certainly wouldn't help their business if they did.

We could do zero ISRU replenishment of consumables by having a perfectly closed loop, despite the functional impossibility of doing that with current technology, but we're still talking about a solar array 20 (19.93 if we need to get really precise) TIMES larger than anything that exists on Earth, just to keep everyone breathing fresh air (CAMRAS and IWP only, nothing else).  Does anyone here truly believe that that's practical?

Unfortunately, the energy requirements for living on Mars are incredibly extreme, as in McMurdo Station in Antarctica in the winter extreme.  They use 32MWh of power per person in the winter time.  It's unreasonable to think that LESS power would be required in a place that's even more extreme, where you have to make all of the air and water and food you need from raw feedstocks that require massive quantities of energy to transform into anything usable.  The entire premise of that argument is antithetical to basic logic and math.


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

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#135 2021-04-13 15:44:07

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,383
Website

Re: Settlement design

Quaoar wrote:

4 crew for an almost two year stay on Mars means a lot of cross training capabilities: you need 2 pilot engineers for flying the MAV/ERV and two doctors able to perform basic surgery, orthopedic, because you cannot risk to lose an astronaut for a stupid appendicitis or a broken leg, and possibly even dentistry. So the doctors must be cross-trained in basic research in biology to study possible martian microbial biota and engineers must be cross trained in geology and geochemistry.  You can do it but a six crew has far better chance to survive.

Yup. Expect a lot from the first astronauts to Mars. But Mars Direct was designed as 6 months from Earth to Mars, then 500 days on the surface (16 months & 2 weeks), then 6 month back to Earth. I would shorten that a little. Still 6 months to Mars, because that's the free return trajectory. If something goes wrong, the gravity of Mars will turn the craft back to Earth. Not were Earth was when they departed, but where Earth will be when the craft gets there. But launch a little late, which will require a little more propellant. Still a free return trajectory. Then leave Mars at little early; still 6 month return. This would reduce the surface stay to about 14 months. The reason is to reduce round trip to 26 months. That means the first mission will return to Earth surface before the second mission departs. Mission control would only have to track one spacecraft at a time. And crew from the first mission could meet the second before they depart; pass on lessons learned. And the second crew gets reassurance that the first crew returned safely, so a very good chance they will too.

Astronauts to ISS are already cross trained for basic paramedic and dental work. In Robert Zubrin's book, he recommended 2 scientists and 2 engineers. The engineers could fix a Mars rover so they could get back to the hab. Every scientist would have an engineer with him for any significant distance from the hab. Yes, the engineers would have to be cross trained to pilot, and paramedic and dental work. You would need at least one geologist, and one astrobiologist.

I'm concerned about cost. Past missions were cancelled because cost increased too much. NASA intended to go to Mars after Apollo 11, made a news announcement to the public that the first mission would be 1981. Then it slipped to 1983. Then indefinitely postponed. Budget cuts. President George H. W. Bush announced his Strategic Exploration Initiative on July 20, 1989. NASA came back 90 days later with the "90 Day Report on Human Exploration of the Moon and Mars", commonly called the 90-Day Report. Price tag was $450 billion in 1989 dollars. That would have been spread over many years, but still Congress balked. Cancelled. Martin-Marietta asked their engineers to come up with a mission plan that was sane; Robert Zubrin and David Baker came up with Mars Direct. Price estimate was $20 billion for research&development, infrastructure, and first mission to Mars, then $2 billion per mission thereafter. Some in NASA loved it, but Congress was wary, afraid NASA would balloon the price back to the 90-Day Report. Then others in NASA didn't like the fact it was "Not Invented Here", so came up with the Design Reference Mission aka Semi-Direct. Price estimate was $55 billion. When Congress saw the price inflate that much, and it was still a paper study, they got seriously afraid NASA would try to bring back the 90-Day Report. So not approved.

Notice what's happened since: ISS, and SLS and Orion. And plans to build a base on the Moon. And a second space station. All part of the 90-Day Report. The Report called for a shipyard in LEO to build the Mars ship, but past attempts to get a second station in Earth orbit were rejected by Congress. So the second station is in Lunar orbit. But contractors do get money for a second station. This is the 90-Day Report in pieces.

VentureStar was started to replace Shuttle, then cancelled. SEI was proposed but cancelled. Constellation was started, then cancelled. Lunar Gateway should be cancelled. If we don't keep the Mars mission under control, it'll get cancelled too.

If you want more crew on the first mission, then please tell us how to do so while keeping cost down. Reminder: Dragon is designed for 4 crew to the Moon or Mars and back. Dragon has a PICA-X heat shield, already able to return from Mars. It could accommodate up to 7 crew, but that's cramming them in, not even enough room for rock/soil samples. Boeing Starliner can accommodate 4 crew. Again, it could accommodate up to 7 for a trip to ISS, but that doesn't leave room for rock/soil samples. Orion? Ptttt! Orion can accommodate 4 crew, but it's heavy and expensive. Orion can accommodate up to 6 for a trip to ISS, but same problems as the other two capsules. But the mass of Orion will drastically increase any propulsion stage, increasing cost, and Orion itself is unreasonably expensive. Anything with Orion is guaranteed to get cancelled.

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#136 2021-04-13 16:14:16

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

Louis,

I'm not even talking about cost.  For what moving 1,000,000t of PV array and equipment would cost, we could afford to hire an army of workers to fab the arrays to exact specs.  Also, who cares about slightly more expensive silicon with the transport costs we're looking at?  It's worth it.

You haven't said what ECLSS your power requirement is based upon.  CAMRAS and IWP were developed for long duration life support with high efficiency and low power consumption.  Either name off the flight-ready ECLSS hardware you think will consume less power, or admit that there isn't any and you're just throwing out numbers that don't tie back to any actual life support hardware.

You can't read across from 1 person requires 3 liters of water per day to survive to 2 people require 6 liters of water per day to survive?

Get real.

The comparison to living in Antarctica was unhelpful because it flies in the face of your assertions about how much power will be required, despite the fact that Dr. Zubrin himself said it would require MORE POWER THAN LIVING IN ANTARCTICA.

You're being deliberately obtuse about this because you don't like what the implications are.

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#137 2021-04-13 16:19:29

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,992
Website

Re: Settlement design

Robert (post 135,  last paragraph):

I beg to differ:  Dragon is OK for the moon.  It has 2 weeks' life support capability for a crew of 4-ish.  Less at max crew = 7. That is the round trip time for an Apollo-type lunar mission.  The one way travel time to Mars is months long.  Far beyond what Dragon is capable of.  Far beyond what NASA's Orion is capable of,  too.  You don't spend months cooped up in a cramped capsule,  we already found that answer on Gemini 7 in the mid 60's,  and verified it in the lunar missions,  and on every space station mission since.

I do agree that the heat shield of Dragon is designed for above-escape returns to Earth.  From the moon,  that is just below 11.19 km/s to just above 11.19 km/s,  depending upon the exact trajectory.  I dunno if if it is good for returns from Mars:  those are in the vicinity of 12.5 km/s from a Hohmann min-energy return,  to around 13-14 km/s for high-speed transfer ellipses,  to a worst case of around 17 km/s for a really fast return with most-adverse planetary orbital conditions,  which was NASA's design criterion for its planned 1980's Mars mission,  back during the moon landings in the late 60's and early 70's.

GW

Last edited by GW Johnson (2021-04-13 16:24:21)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#138 2021-04-13 16:32:29

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,383
Website

Re: Settlement design

GW Johnson:

Thank you for joining. Yes, I did describe how to use Dragon for an updated Mars Direct. However, I also gave my preferred mission architecture. I've been talking about that since 2002. My architecture includes a separate habitat that provides roughly as much room as the upper floor of Mars Direct. Some of that room will be occupied by recycling life support equipment. And I want to use artificial gravity with the TEI stage used as a counterweight. I got the idea from Mars Direct; just applying Mars Direct technology for the return trip. The Dragon capsule is in case aerocapture into Earth orbit fails. Once in Earth orbit, you can either leave the Dragon capsule attached for the next mission and send something to fetch astronauts, or just use the Dragon for crew return.

Ps. Elon Musk said the PICA-X heat shield is enough for 4 missions to ISS, or one return from Mars.

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#139 2021-04-13 16:41:57

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

Noah,

General Mission Architecture

This thread is Exhibit A as to why we've never left Earth to explore and colonize the moon or Mars.  Instead of admitting to technological reality and selecting existing or technologically feasible equipment that's flight-qualified and thoroughly tested, every attempt to do a worthwhile mission devolves into a pointless ideology battle with various dogmatic, ideologically-motivated special interest groups who do everything in their power to derail productive strategies and technologies selected to achieve the stated program objectives for minimum cost, weight, and power consumption, in favor of some undefined or impractical futuristic technology that doesn't physically exist.  They'd much rather prevent a mission from happening in the first place than they would see anything other than their pet project or technology used in another meaningless crusade to prop up their ideology.  Now you know why we still haven't been to Mars decades after we had the basic requisite technology to go there and come back, with a reasonably good chance of returning a crew alive and in good physical condition.  It was never a matter of technological readiness, but a matter of development priorities and ideology over engineering.  Unfortunately, ideology can't make a round peg fit in a square hole, not that that will ever stop the ideologues from trying.

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#140 2021-04-13 17:23:31

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,383
Website

Re: Settlement design

kbd512, you talking to me?

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#141 2021-04-13 17:51:54

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

Robert,

No, of course not.

I'm talking about this belief that things can only be done one way, and that all other consideration are moot.  I can't do anything about the fact that the power requirements are bonkers for a city of a million people on Mars.  A lot of engineers from around the world have poured their souls into inventing the technology to simply survive.  I do not understand the necessity to ignore basic engineering reality.  I'm not saying we shouldn't develop better solar panels or batteries or that at some future point in time, solar and battery power won't be practical for everything.  However, at this juncture in our technological development, we're asking more of said technologies than they can realistically deliver, and we're ignoring other possibilities and considerations for dogmatic reasons.

We either develop much more efficient solar panels and energy dense batteries, or we admit to ourselves that, given present technological limitations, nuclear power is the only marginally feasible answer we have for providing enough power for a million people on another planet.  I do not see why progress should be held up to appease beliefs that run directly counter to good basic engineering practices.  I simply fail to understand it, but I've never really held any dogmatic beliefs, except about basic math, and maybe that's what I fail to see.

Put another way, if solar was as energy dense as nuclear and nuclear was as intermittent and unreliable as solar, then if someone came here telling me that nuclear power was the only way, I'd be making the exact same arguments about why we need to use solar so the mission can proceed, and for the exact same reasons.  Sometimes I wonder if designers or visionaries, like Louis, are more enamored with the idea than the mechanics of seeing their ideas made into reality.  I thought the dream was to build a city of a million people on Mars.  If we have to power Mars City with squirrel turds, who cares as long as we get our city built?

You know what my greatest fear is.  We spend all this effort and money to build this dream, but because we were dogmatic about how to go about doing it, everyone there dies, and all the funding and pioneering spirit to go forth from the cradle of life vanishes, and then my children are stuck in the dark ages for who knows how long.  We need this to work reliably and to inspire confidence in the general public.

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#142 2021-04-13 21:10:51

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,383
Website

Re: Settlement design

I checked the Starship users guide, directly from the SpaceX website. Cargo Starship has a payload fairing with 9 meter outside diameter, can accommodate payload of 8 meter diameter in the cylindrical portion of the fairing. That cylinder is 8 metres long. Cone tapers to 1.80 meter radius (3.60 meter diameter) at 17.24 meters above payload floor. "An extended payload volume is also available for payloads requiring up to 22 m of height." Sounds like we could launch a Mars Direct habitat with Starship. Hab would be a little smaller: 8.0 metre outside diameter instead of 8.4 metre, but that's Ok. Right now Starship is expected to be able to lift 100 metric tonnes to LEO. SLS block 2 can lift 130t to LEO. So not quite enough for direct launch, but a Starship fuel tanker could do an on-orbit refuelling. Considering Starship is reusable, and how much less expensive it is, this may be a better idea. One cargo Starship for vehicle with both habitats (surface and interplanetary) and empty TMI stage. One fuel tanker Starship. And one Crew Dragon launched on Falcon 9. Before that, one cargo Starship for MAV, one fuel tanker Starship for propellant. Total 4 Starships and 1 Falcon 9, and you get a modified Mars Direct with a return habitat. smile
screen-shot-2020-04-06-at-2-18-22-pm-1586197293.png?resize=480:*

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#143 2021-04-14 05:49:18

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,668

Re: Settlement design

For kbd512 Re #132

Your post started out indicating it was about #131, but it seemed (to my eye anyway) to veer off in some other direction.

What is your post about?  What does it have to do with creating a repository for knowledge for Noah's topic?

(th)

tahanson43206 wrote:

This is primarily for SpaceNut, but it (hopefully) will be of interest to everyone participating in Noah's topic...

We have discussed before how we (this forum) need a Wiki type fixed environment for accumulation of vetted knowledge

The reason we have these ongoing cycles of repetition is the lack of a fixed location where members can drop off knowledge, and where (as in Wikipedia) that knowledge can be corrected until everyone has arrived at a consensus of it's reasonable approximation to reality.

I know you've approached Mars Society in the past, but I'm hoping you'll keep trying.  Noah's undertaking will suffer from the same fate as all the other topics is we are unable to collect and "lock" the hard earned facts and figures he and his team will need to carry out actual projects.

(th)

If there's something in my post that doesn't look like worthwhile improvement in the forum structure, please point it out.

(th)

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#144 2021-04-14 06:46:49

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,325

Re: Settlement design

Kilopower units are able to produce 1-10KWe and would presumably be available to SpaceX. The base power supply is likely to consist of a mixture of solar power and small baseboard nuclear units. I am researching an alternative if Kilopower is for some reason unavailable to SpaceX or if base power requirements outgrow what Kilopower is able to provide.

The technically easiest nuclear reactor to develop would be an aqueous homogenous reactor. This is a reactor in which uranium sulphate or nitrate salts are dissolved in water or heavy water. These were the first reactors considered for bulk power generation, with the first experimental units operating in the 1940s. Benefits include excellent neutron economy, self-controlling reactivity characteristics, design simplicity and high power rating - I.e. power produced per kg of uranium. This reactor type has the lowest critical mass of all reactors, allowing for the production of extremely compact nuclear cores with high thermal power density. The principle disadvantage is low operating temperature due to the need to reduce corrosion rates in an acidic environment. This places limits on efficiency of conversion of thermal energy into mechanical and electric power. Below is a link to an early text on the topic, dating 1958.
https://fluidfueledreactors.com/

I am investigating the possibility of building an aqueous homogenous reactor plant on Mars that can be assembled from native resources. The specifics of the design depend on the answer to a number of questions: (1) Can we access enriched uranium (a) from Earth or (b) make it on Mars? (2) Can we access pure heavy water (a) From Earth; or (b) Make it on Mars? If enriched uranium can be sourced from Earth, then building a nuclear power plant on Mars, becomes far simpler. If it isn't, but we can source deuterium from Earth, then a heavy water based AHR can use Martian natural uranium as fuel.

If neither enriched uranium nor heavy water can be sourced, the only option is to build graphite moderated reactors using Mars sourced natural uranium. A graphite moderated AHR would probably be a pebble bed, with pebbles consisting of graphite produced through methane pyrolysis. The space between pebbles would be filled with a natural uranium sulphate water solution. The majority of moderation would be provided by the graphite, so it may be possible to produce a critical assembly even if the solute is ordinary light water. I need to run the four factor formula to check this. Voiding in the core would not result in power surges. Whilst the water is a better neutron absorber than graphite, it also carries the dissolved fuel. So voiding would remove fuel from high flux regions of the core in addition to water. Radiolysis in the core would generate free oxygen radicals that would corrode the hell out of the graphite. A pebble bed design allows graphite moderator balls to be removed before corrosion becomes too extensive. I would anticipate that the reactor would run at about 100°C in order to keep corrosion at tolerable levels. The reactor vessel would be a cylindrical tank made from, or clad with, stainless steel or nickel alloy.

Operating the reactor at 100°C and rejecting heat at 0°C, implies a Carnot efficiency of 26.8%. Steam cycle efficiency is usually about 2/3 carnot efficiency, so generation efficiency can be expected to be in the region of 18%. A combined heat and power mode is possible. Direct nuclear heat could be used to heat habitats using water as the heat transfer fluid. Or the cycle could dump waste heat at a temperature of 20°C for greenhouse heating.

Early designs of AHRs envisaged using a natural uranium sulphate heavy water solution in the core. This has the best neutron economy of any known reactor. One plan was to surround the core with thorium oxide conversion blankets, which would absorb leakage neutrons and transmute into fissile 233U. A second generation AHR would use 233U sulphate salts as fuel and could function as a net breeder. Alternatively, plutonium produced in the natural uranium fuel salts could be used to fuel sodium cooled fast breeder reactors. Using tube-in-duct fuel, these reactors have a breeding ratio of up to 1.8. Hence, nuclear capacity can be increased very rapidly even if uranium is relatively rare on Mars.


"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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#145 2021-04-14 08:09:19

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

Re: Settlement design

The nuclear option is problematic

Remember Kbd claims the Million Person City on Mars will need continuous power of something like 3.7 million Kws (constant).

So, for the 10 Kw Kiopower Units weighing in at 1.5 tons IIRC,  that would mean you need 370,000 Kilopower Units at 555,000 tons or 5,550 Starship cargo loads. That's without cabling and other equipment.

Only one problem with using Kilopower units - none has yet been tested and approved in space conditions. It's not even designed for the Mars surface, being designed for use with deep space missions.

As for building a nuclear power station - I am sure it can be done but it will be a big project involving a lot of labour time and then contiued monitoring and maintenance involving substantial human resources. The alternative of manufacturing PV panels on Mars using largely automative processes and ISRU (including robot mining of silica and other materials), coupled with battery production, continued manufacture of methane and oxygen (needed for Starship refuelling in any cases) and manufacture of methane electricity generators, is much more straightforward in my view and will be far less labour-intensive.



Calliban wrote:

Kilopower units are able to produce 1-10KWe and would presumably be available to SpaceX. The base power supply is likely to consist of a mixture of solar power and small baseboard nuclear units. I am researching an alternative if Kilopower is for some reason unavailable to SpaceX or if base power requirements outgrow what Kilopower is able to provide.

The technically easiest nuclear reactor to develop would be an aqueous homogenous reactor. This is a reactor in which uranium sulphate or nitrate salts are dissolved in water or heavy water. These were the first reactors considered for bulk power generation, with the first experimental units operating in the 1940s. Benefits include excellent neutron economy, self-controlling reactivity characteristics, design simplicity and high power rating - I.e. power produced per kg of uranium. This reactor type has the lowest critical mass of all reactors, allowing for the production of extremely compact nuclear cores with high thermal power density. The principle disadvantage is low operating temperature due to the need to reduce corrosion rates in an acidic environment. This places limits on efficiency of conversion of thermal energy into mechanical and electric power. Below is a link to an early text on the topic, dating 1958.
https://fluidfueledreactors.com/

I am investigating the possibility of building an aqueous homogenous reactor plant on Mars that can be assembled from native resources. The specifics of the design depend on the answer to a number of questions: (1) Can we access enriched uranium (a) from Earth or (b) make it on Mars? (2) Can we access pure heavy water (a) From Earth; or (b) Make it on Mars? If enriched uranium can be sourced from Earth, then building a nuclear power plant on Mars, becomes far simpler. If it isn't, but we can source deuterium from Earth, then a heavy water based AHR can use Martian natural uranium as fuel.

If neither enriched uranium nor heavy water can be sourced, the only option is to build graphite moderated reactors using Mars sourced natural uranium. A graphite moderated AHR would probably be a pebble bed, with pebbles consisting of graphite produced through methane pyrolysis. The space between pebbles would be filled with a natural uranium sulphate water solution. The majority of moderation would be provided by the graphite, so it may be possible to produce a critical assembly even if the solute is ordinary light water. I need to run the four factor formula to check this. Voiding in the core would not result in power surges. Whilst the water is a better neutron absorber than graphite, it also carries the dissolved fuel. So voiding would remove fuel from high flux regions of the core in addition to water. Radiolysis in the core would generate free oxygen radicals that would corrode the hell out of the graphite. A pebble bed design allows graphite moderator balls to be removed before corrosion becomes too extensive. I would anticipate that the reactor would run at about 100°C in order to keep corrosion at tolerable levels. The reactor vessel would be a cylindrical tank made from, or clad with, stainless steel or nickel alloy.

Operating the reactor at 100°C and rejecting heat at 0°C, implies a Carnot efficiency of 26.8%. Steam cycle efficiency is usually about 2/3 carnot efficiency, so generation efficiency can be expected to be in the region of 18%. A combined heat and power mode is possible. Direct nuclear heat could be used to heat habitats using water as the heat transfer fluid. Or the cycle could dump waste heat at a temperature of 20°C for greenhouse heating.

Early designs of AHRs envisaged using a natural uranium sulphate heavy water solution in the core. This has the best neutron economy of any known reactor. One plan was to surround the core with thorium oxide conversion blankets, which would absorb leakage neutrons and transmute into fissile 233U. A second generation AHR would use 233U sulphate salts as fuel and could function as a net breeder. Alternatively, plutonium produced in the natural uranium fuel salts could be used to fuel sodium cooled fast breeder reactors. Using tube-in-duct fuel, these reactors have a breeding ratio of up to 1.8. Hence, nuclear capacity can be increased very rapidly even if uranium is relatively rare on Mars.

Last edited by louis (2021-04-14 08:10:04)


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

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#146 2021-04-14 09:19:30

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

tahanson43206 wrote:

For kbd512 Re #132

Your post started out indicating it was about #131, but it seemed (to my eye anyway) to veer off in some other direction.

What is your post about?  What does it have to do with creating a repository for knowledge for Noah's topic?

(th)

tahanson43206,

No, it's about Noah's topic.  I have no objections to creating a repository of knowledge.

What I responded to related to why these threads so frequently veer off topics.  Colonizing another planet always comes back to energy production or storage and consumption rates, because we're talking about building a city on another planet, from scratch.  As simple as it is to say, all of that requires enormous quantities of energy.  If we were talking about colonizing a planet like Mercury and someone stated that we needed nuclear power to do that, I would be asking them why they thought 9,116W/m^2 of input solar power wasn't sufficient for that purpose.  However, we're frequently talking about colonizing Mars, where we have 591W/m^2 to work with.  Absent highly efficient solar panels to work with, that's always going to be a very challenging energy source to use to sustain human life, never mind building a city of a million people, if that's all that we're given to work with.

My point was this:

All actual space flight missions have defined timelines, because they're tangible activities requiring capital / resources / labor, undertaken by groups of people using tangible equipment with known performance from actual testing conducted under expected realistic operating conditions.  It would be grossly unrealistic to think that the same technology that worked so well on Earth's surface at 70F would work equally well at Pluto where the temperature can be -400F.  In general, every one of these space flights represents the sum total of human knowledge and use the most performant equipment available (that has been thoroughly tested) at the time that the mission occurs.  All new and experimental or untested technology is first demonstrated on a robotic science mission that either proves or disproves the basic feasibility of the technology for a space flight mission.  There's no issue at all with having fantastic visions of the future, but then those visions require tangible engineering activities and technological progress to accomplish.  That said, if you want this mission to occur within our lifetimes, then it needs to be based upon technology that could realistically develop to deliver the power / propulsion / life support / scientific measurement, with the required output and level of efficiency.  History should be used as a measuring stick, as it relates to technological development.  If it took 10 years to improve battery efficiency by 5%, then it's not realistic to think that it will improve by 50% over the next 10 years, unless you can point to a specific "game changing" development that occurred.

Example:

When the Apollo missions went to explore the moon, they used chemical rocket engines burning hypergolic propellants to orbit the moon / descend to the surface of the moon / ascend off the surface of the moon to return to the command module / return to Earth, Alkaline fuel cells provided power to the command module and batteries provided power to the lunar module, with a combination of photovoltaic panels and radioisotope thermoelectric generators for providing power to science experiments.  When Skylab was launched, it used a Saturn V third stage propellant tank as the pressure hull for the station, with a combination of photovoltaic panels and batteries for supplying power, and Apollo command modules to deliver the crew, because that was the thoroughly tested and proven technology for long duration missions in LEO at that point in time.

If someone had come along and demanded the use of solar electric propulsion or nuclear thermal propulsion to send astronauts to the moon, the net result would've been that the mission wouldn't have happened in 1969, or likely would've failed if it was foolishly attempted without proper development and testing, as was the case for the Soviet lunar missions, because neither of those propulsion systems were capable of reliably powering a crewed spacecraft at that point in time.  Simply placing a demand on a technology doesn't automatically equate to technological development meeting the demand.

A really good example of that is battery technology.  If you follow this closely, you will see at least one promise made per week of a revolutionary new battery technology that's at least 10 times better than whatever came before it, and only 2 years or 5 years away from mass manufacturing.  However, if you need a commercial product based upon that revolutionary new battery technology, there aren't any available for purchase.  I can't know what the reason is in every single case, but my hunch is that the technology dead-ended because it wasn't ready or caused some other unforeseen (at the time) problem.  At the end of the day, it doesn't matter what the reason was, because if you were relying upon that new battery technology being made available for a particular application, the only batteries to be had are what come from the major manufacturers.  NASA does lots of battery development work, but these days, for every single one of their actual missions, they purchase an off-the-shelf product that's being mass-manufactured.  And why wouldn't they?  After something's been mass manufactured for a few years, you have really good understanding of how well it works in operational uses.  They're betting lives on it being utterly reliable, so that makes perfect sense.

If Mars City absolutely must be solar powered for everyone to be onboard with it, then start specifying the energy efficiency and mass targets for the solar panels, energy storage system, life support systems, food growing operations, and manufacturing required to make it completely solar powered.  After that, pay close attention to the technological readiness over time, to see if actual development progress matches expectations.  If not, then maybe the city needs to be scaled back, or maybe further development is required, or maybe you accept alternative energy solutions so that you can get the city built, then look at phasing in solar power afterwards.  Since we have so many alternatives to solar panels on Earth, backup power generating systems or schemes can be devised to deal with production shortfalls.  However, those systems don't have extreme mass, volume, or performance constraints.  Almost nobody was thinking about the feasibility of transporting the equipment in a major power station off-world when they designed it.  Related to that, the mass and volume of the system needs to be taken into account when we consider how it impacts other missions areas, such as mass / volume allocation for colonists / food / construction equipment.

Anyway, that's what I was thinking about.

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#147 2021-04-14 09:31:42

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 12,668

Re: Settlement design

For kbd512 re #146

Thanks for addressing my concern!  That's a relief!

Your points about this environment include elements that are inspiring my effort to try to persuade Mars Society to sponsor/support this forum with permanent storage, and the most flexible system with the best information finding capability seems (to me at least) to be the Wiki style.

In my vision of how this would work, Noah (for just one example) would be able to set up a repository of information he has gleaned from discussions in the forum, and from other resources as they become available.

The point is, at some point, Noah (or other future Mars settler/supporters) would need to decide on a specific course of action.

The forum will constantly be churning out better ways of doing things, and pointing out errors with the ways that existing activity is proceeding, but the fact remains that in order for ** anything ** to get done someone, somewhere !!! has to decide on a course of action and then pursue it.

The beneficiaries of this repository need not be limited to Noah.  Every member who would like to pursue a specialization would be free to do so without interference from others.  Every member is (of course) free to criticize, but each member with a repository is (or would be) free to follow a specific path even if is is less than ideal.

As with so many of your posts, there is valuable content that will flow under the bridge, never to be seen again (except by SpaceNut restoring old topics).

SearchTerm:energy options for  Mars Settlement kbd512 Post 146

Edit#1: If we can put this concept into motion, even someone like Louis would be free to develop his concepts in a place where he is responsible for content, and if he wishes to pursue an all-solar concept as far as it can go, more (solar) power to him.

Others, with perhaps a more practical frame of mind, might chose another path altogether.

(th)

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#148 2021-04-14 10:10:57

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,325

Re: Settlement design

Importing power supply equipment for a 1 million person city is a tall order, whatever system we use. Kilopower units are optimised for small power requirements. They would definitely be useful for early missions, but aren't something that anyone would even consider attempting to power a city with. Which is why I am looking at Aqueous Homogenous Reactors for meeting those GWatt scale power requirements for a city on Mars. Electric power consumption per capita in the US is 13,000KWh per year. That is equivalent to a constant power of 1.5KWe each. That is electricity- it doesn't cover heating, which is mainly natural gas, or transportation, which is petroleum products. So a 3.7KWe power requirement per capita on Mars may actually be optimistic, especially when you consider the amount of manufacturing that will be going on. I think a fair chunk of the power consumption in Kbd512's estimate is heat, which would be needed to makeup thermal losses in the Arctic temperatures prevalent on Mars. Guess what nuclear reactors produce in great abundance? Heat. Low grade heat at temperatures <100°C is a waste product of nuclear power generation and requires some sort of heat sink. Apparently, it will be useful on Mars.

You keep suggesting that building a power supply using PV panels on Mars is going to be a less labour intensive and easier process than building a nuclear reactor. That doesn't ring true to me. A PV array capable of generating average power of 3.7GW would cover an area of about 100 square kilometres on Mars (assuming no gaps between panels) and would weigh about 1million tonnes for the panels alone. Much of that mass is going to be high grade semiconductor material. Also, you are going to need silver for the panel conductors, large amounts of copper, inverters and transformers for each cluster of PV panels. You are going to need a large mass of batteries for night time energy storage. Storing 16 hours worth of power in lithium-ion batteries would require 250,000 tonnes of Li-ion batteries. Are we going to be making those on Mars as well? These are all materials that must be mined as ores and reduced using energy into metals.

I don't have a precise weight breakdown for what a nuclear reactor based solution would look like. For one thing, it will depend on system design. I could probably work it out if given enough time. But a pressurised water reactor has power density of 80MWth per cubic meter of core volume. That is extremely compact. This link gives an idea of the size of a reactor system needed to generate 1GWe power.
https://www.nuclear-power.net/nuclear-p … nt-system/

Total primary circuit volume is 285m3. That is for the reactor vessel, pressuriser, pipework and steam generators. If we were to squeeze it into a compact cubic geometry, with the equipment occupying 50% of the volume say, it would fit onto a square 8.3m aside, 69m2. We need 4 of those units to generate 3.7GW. So that is 1140m3 of plant, occupying an area of 276m2.  Let's assume that the primary circuit is made from solid steel.  It obviously isn't, but it makes the sums a lot easier.  The mass of 1140m3 of primary circuit would be 8,600 tonnes. I have not included here the mass of the secondary steam plant, which includes the steam turbine and condenser, which are both quite massive items. But even if we triple the total mass to account for that, we get 25,800 tonnes.

So that's 25,800 tonnes of mostly steel vs 1.25million tonnes of semiconductor grade silicon, copper, silver, steel, glass and Li-ion batteries. The difference in mass for both systems is a factor of 50. In terms of embodied energy, the difference will be even greater, because most of the mass of the nuclear plant is steel. These are crude calculations admittedly, but they don't lend much support to the idea that it will be easier and less labour intensive to build solar power plants on Mars instead of nuclear power plants. Just mining the required materials will be a severe challenge.


"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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#149 2021-04-14 10:18:00

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,342

Re: Settlement design

louis wrote:

The nuclear option is problematic

Remember Kbd claims the Million Person City on Mars will need continuous power of something like 3.7 million Kws (constant).

So, for the 10 Kw Kiopower Units weighing in at 1.5 tons IIRC,  that would mean you need 370,000 Kilopower Units at 555,000 tons or 5,550 Starship cargo loads. That's without cabling and other equipment.

Only one problem with using Kilopower units - none has yet been tested and approved in space conditions. It's not even designed for the Mars surface, being designed for use with deep space missions.

As for building a nuclear power station - I am sure it can be done but it will be a big project involving a lot of labour time and then contiued monitoring and maintenance involving substantial human resources. The alternative of manufacturing PV panels on Mars using largely automative processes and ISRU (including robot mining of silica and other materials), coupled with battery production, continued manufacture of methane and oxygen (needed for Starship refuelling in any cases) and manufacture of methane electricity generators, is much more straightforward in my view and will be far less labour-intensive.

The nuclear option is less problematic than solar, if weight is a consideration

1 Bhadla array of 10km^2 in total panel surface area (not total active area) could realistically produce 650GWh on Mars per year, under ideal conditions.

On a per square meter basis, let's consider exactly what that means:

650,000,000,000Wh per year / 365 days per year = 1,780,821,917.8Wh per day

1,780,821,917.8Wh / 10,000,000 = 178.08Wh/m^2/day (we're presuming 20% efficiency commercial grade panels, so add 10% to that for space-rated triple-junction silicon like the silicon I suggested using from FullSuns)

A single 10kWe KiloPower reactor weighs 1,500kg and can produce 240kWh/day.

10,000W/hr * 24 hours/day (24.65/24 is the actual multiplier for 1 Martian day) = 240,000Wh/day or 246,500Wh/Martian day

A lightweight solar panel with a CFRP back weighs 2.128kg per square meter.

282 cells at 4g per 4cm x 8cm piece of Silicon with 1kg CFRP backer board (4 plies of Toray T1000G with a Nomex honeycomb core, each high-modulus CF cloth ply weighs 200g for a 1m^2 sheet- ATK's MegaFlex and UltraFlex deployable arrays use a very similar setup with Aluminum honeycomb which is heavier than Nomex, with the weight of the resin and honeycomb excluded; no mounting frame at all, just a rigid panel so it can be "pointed" at the Sun by using a mound of dirt piled up underneath it)

240,000 / 178 = 1348m^2

2.128kg * 1,348 = 2,868.5kg for a photovoltaic array that can produce as much power as a 10kWe KiloPower reactor under ideal conditions

Even if we consider the use of LEU (per President Trump's order that no HEU be used for space nuclear power), then the KiloPower reactor still weighs less than a competing solar power solution.  If KiloPower is using LEU fuel, then mass ranges between 2,016kg and 2,187kg dependent upon the exact Uranium fuel alloy used (Figure 4 from the White Paper linked below) vs 1,519kg for the HEU reactor.  LEU is civilian legal for purchase and NASA has stated that they will make LEU variants of KiloPower available to anyone planning a Mars mission.  Since all commercial nuclear reactors and nuclear fuels are in the hands of qualified civilians in the US, this is not seen as a major problem.

White Paper – Use of LEU for a Space Reactor

My weight estimate for the solar array doesn't include a single strand of wiring to connect the cells within the panels, nor to wire up the arrays together in strings to deliver the power to an inverter or transformer.  If we included required wiring and power inverters in the solution, then the mass increases.  It's pretty hard to argue that you don't have to connect all the cells on a panel.  For the on-panel wiring, it's about a quarter of a kilo for ETP Copper or Silver.  For a thin iPad-style Gorilla glass cover panel, about half a kilo.  For a truly durable piece of ALON cover glass that you can physically brush the abrasive regolith off of without worrying about scratching it, half a kilo to a kilo, dependent upon thickness.

If we consider the mass of the complete KiloPower reactor and the mass of the unusable solar arrays (no electrical connections between cells or other panels in the array), we're 681.5kg ahead.  If we consider that the 282 individual cells in the array at least require on-panel connections with the other cells in the array, then KiloPower is 1,018.5kg lighter.  If we consider the wiring to connect all 1,348 panels in the array, then we're lighter still.  All said and done, KiloPower winds up weighing less than 2/3rds of what the competing solar solution weighs.

Edit:

If we consider the fact that the solar array has to store 160,000Wh or 160kWh of energy to make it through each night, the nuclear solution is lighter still.

The best commercial batteries available achieve about 160Wh/kg at the pack level.  This uses Rolls Royce's actual electric aircraft battery pack-level energy density (a stripped down battery pack that uses Tesla's battery technology), which would be unsuitable for Mars as it would be unable to dissipate any heat generated (and we're also presuming it generates it's own heat from discharge at night), but it adequately illustrates the point.

160,000Wh for nightly power / 160Wh/kg of Lithium-ion battery pack = 1,000kg

At this point, our solar array solution actually weighs 4,023.5kg (which is still completely unusable because no mass allocation has been included for the wiring between the 1,348 panels in the array)

At this point, we have the mass allocation to include a pair of 10kWe KiloPower reactors, so now we are achieving double the power-to-weight ratio of the competing solar panel solution, using the most rinky-dink excuse for a nuclear reactor that anyone has ever created.

The real question is whether or not you want any mass allocation for food / clothing / fuel / etc.

If we wanted to "play dumb" and act like KiloPower or photovoltaic panels were the only available options for powering a city, then the mass allocation for nuclear power is still half of that for the competing solar and Lithium-ion battery solution, using one of the most mass-inefficient nuclear reactor designs currently available.

We haven't even arrived at the best part.

KiloPower has a ground footprint of approximately 1m^2.

If I was going to create a "power field" of nuclear reactors or solar panels, and intended to put a power device of either kind in 1m^2 of ground, then a "reactor farm" vs a "solar farm", would produce 323,520,000Wh of power each day from the same physical surface area used by photovoltaics to produce 240,000Wh.  In short, my per-square-meter power density is 1,348 times that of the solar and battery solution, except that I didn't include the physical space occupied by the batteries, so it's even better than that.

Last edited by kbd512 (2021-04-14 10:35:27)

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#150 2021-04-14 10:22:42

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

Re: Settlement design

It appears that we go through this same cycle with Louis about every 6 months, and then we get a respite until the "next time."

As a "user and contributor" to the forum, it seems we to beat his particular topic to death. The outcome is always the same: use of Solar Power alone isn't gonna cut it.

When Robert Zubrin and his colleague James Baker formulated the original Mars Direct plan, they relied exclusively on a small nuclear reactor for power production. Where we went with this topic really mystifies me, looking back.

I also have some serious reservations about Elon's scheme for a city of one million people within 50 years. All based on the energy requirements to simply maintain such a system, not to mention the construction of the infrastructure.

Last edited by Oldfart1939 (2021-04-14 14:53:01)

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