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#51 2019-07-08 08:55:15

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

As I've made clear before, really the PV and KP solutions have different strengths and weaknesses.

For PV to work on Mission One, we need a guaranteed energy solution from day one.

My conception for PV would be that during a 2 years mission, you need to plan for maybe a worst case scenario of 9 months' dust storm(s).

The record shows that even during the worst dust storms, substantial insolation at the surface is still available. I've never seen any proof it goes below 20% of the seasonal norm. A figure of 60% of the norm is in reality more typical of dust storms.  Well to be safe, let's say it's only 40% so with a worst case scenario you have a 60% reduction across 9 months.  By my calculation what you need to do is then provide PV "over capacity" of probably  around 30%, so that you can make good the shortfall in the other 15 months.  So do your calculation for what is required in the absence of dust storms and then add on 30%.

I would suggest with a PV solution you arrive with a methalox store of perhaps 50 tons.  That would give you the margin of safety you need. On your calculation that would be over 5 months' of power. But of course with the PV based system. you aren't particularly looking to maintain a completely steady power output. You will do the work when the power is available. So, you could probably get by on a much lower amount. But of course, on the other hand, it's safety first for Mission One, so we might well want to have a large store.

There won't be an "80% fluctuation in power" with a PV based system.  Chemical batteries will ensure we can maintain minimum power levels for drilling and propellant production.  On a worst case scenario - arriving slap-bang in the middle of an historically bad dust storm -  you may have to wait a few months before you can fully power up to begin propellant production.


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

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#52 2019-07-08 19:27:29

kbd512
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Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Louis,

This is just a "thinking out loud" post.

If I understand this scheme correctly, each lander would arrive with an additional 10t of propellants.  Is that correct?  That means we're giving up 10% of our 500t delivered tons, just for the LOX/LCH4, never mind all the hardware required to keep it liquid and use it, if necessary.  We'll also have to redesign the header tanks and the structure of the Starship, but I suppose that's a trivial issue.

How much power do you figure you'll need to keep the propellant cold at night?

Unless you're landing at the poles, the LOX and LNG must remain about 100C colder than night temperatures to remain liquid.  Commercial operations use insulation thick enough to limit the heat transfer rate to ~10Btu/hr/ft^2.  The vacuum of the main tanks and exterior insulation should help with that, but only to a point.

Here's your source for that:

Insulation & Liquefied Natural Gas in Production and Storage - Allen Dickey - Senior Product Manager of Pipe and Equipment Insulation Systems for Pittsburgh Corning

I suggest you consult this document from Northrop-Grumman regarding the performance of their high-efficiency cryocooler, since it comes with a handy-dandy input power requirement chart to achieve a given level of heat removal (TRL9 flight rated hardware):

High Efficiency Cryocooler Performance

The mass of the cryocooler equipment is trivial, but the input power required is not.  The mass of the additional insulation required certainly won't be trivial.

Are the humans and the cargo all landing at the same time, or do these things have to operate unattended for 26 months before the people show up?

I posted a paper not long ago about the energy required to liquefy natural gas.  Actual LNG plants here on Earth consume about ~850kWh/kg to compress CH4 to ~70 bar and then liquefy the natural gas.  That means you either need to burn ~220kg of O2/CH4 for each kg of LOX/LCH4 you put in the propellant tanks, or you'd better have one stupidly powerful solar array.  That number comes from actual LNG plants, rather than fictional designs.  Most of that is compression work, rather than heat removal.  There will be less heat removal required on Mars, but the process will be absurdly inefficient since the only method to dump the heat will be by radiation.

You need 15,556Wh/kg of LOX or 15.556MWh/t.  Starship holds 860t of LOX, so ~13.382GWh over 2 years.  That means you need to supply a bare minimum of ~18.331MWh/day just to make the LOX in 2 years.  That would equate to a farm of 77 10kWe KiloPower reactors running at full power, 24/7.  You need to supply an additional 204GWh, or 279.452MWh/day just to compress and liquefy 240t of LCH4.  You're going to end up building something akin to Topaz on Mars to supply at least ~297.783MWh/day.  That's before considering the power requirements for drilling or the Sabatier reactor or keeping the propellant cold at night or losses or fluids transport.  Honestly, I think that's enough.  At 1kW/kg for absolutely everything, the solar array would weigh 300t to provide 300MWe of peak power output.

Have you figured out why we don't "make" LCH4 on Earth?  The energy requirements to compress and liquefy it are mind blowing.  We use flare off from the wells to supply the power required to liquefy it, and then burn more of the product to keep it cold while we're transporting it.

Well... Good luck with that.  You'll need it.

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#53 2019-07-08 20:35:53

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Something thats not in the mars numbers is the cold which means 24/7  heating of critical parts of the design to keep them operational.
For the 1 meter of panels on the rover it needed 180wh of what it collected to keep from freezing.

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#54 2019-07-08 22:28:13

kbd512
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Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

SpaceNut,

I sincerely hope people recognize how insane this plan is.  The Topaz Solar Farm in California generates ~3,500MWh per day.  We need to supply at least 350MWh/day for this scheme to have any hope of working.  That's 10% of the scale of Topaz, if insolation levels were the same, which they're not.  That means we require solar panel acreage that would cover roughly 20% of that covered by Topaz- one of the largest solar farms on Earth.  Topaz has little to none of the dust storm and radiation problems of Mars.  That means 3.8 square kilometers / 940 acres of solar panels that cost upwards of $1M/kW just to fabricate.  That's $350B, as in billion, dollars worth of solar panels.  The entire US military's yearly budget is not quite double that figure.  If the cost was reduced by an order of magnitude, it's still more than NASA's yearly budget.  So we just need NASA's $20B budget, for the next 17.5 years, just to purchase the solar panels.  The cheap garbage used at Topaz won't cut the mustard here.  We'll assume shipment is free here, although that's equally silly.

If nobody else can see how nuts that is to achieve, on our first mission to Mars no less, then I guess they can't.  Even if we had the 4MWe reactors that KiloPower was eventually intended to scale to, we'd still need 88 reactors.  That's crazy talk.  The notion that we'd even bother bringing Methane or batteries when we have those kinds of power requirements is the pinnacle of absurdity.

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#55 2019-07-09 10:49:16

tahanson43206
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Registered: 2018-04-27
Posts: 664

Re: NASA and DOE to test kilopower nuclear reactor for space applications

For kbd512 re #38

kbd512 wrote:

Louis,

Joe Blow or Jane Blow down the street won't be getting his or her hands on a nuclear reactor loaded with HEU.  Reality check, please.

I expect anti-nuclear power responses from Louis.  However, in the statement quoted above, you have made an incorrect statement, as you were developing the thought stream which became the full message.

Obviously, I ** had ** just suggested there will be a market on Earth for compact nuclear reactors of this type.

Furthermore, I skimmed through the entire thread and confirmed that this suggestion has come up before.

In the State where I live, we have two large nuclear reactors which are currently unable to compete with natural gas, and the owners are trying to persuade the local legislature to give them a financial lifeline.

The Kilopower technology (and similar small scale fission designs elsewhere) have the potential to power a large number of loads in the United States and around the world.

I tossed in the concern about terrorists because it needs to be taken into account, but just as with large reactors we have in place today, security of reactors ** can ** be taken into account.

Sometime back, I pointed out that your political positions imply (to me at least) that you might have an unusually strong positive influence on the current administration, if you were inclined to exercise it.  I'd like to see (while the Sun is shining, so to speak) reversal of the US position on nuclear fission reactors for space missions.  That was a (to my mind) ridiculous policy decision made decades ago, possibly under the influence of industry lobbyists, but it led to the termination of promising NERVA development.

You may be in a position to reverse that policy decision, and possibly to smooth the way for small-scale fission power designs, such as the one Bill Gates was trying to fund until he ran into regulatory obstacles.  However, the current administration is only guaranteed for a year and some, so if you're going to have any influence, this is a good time to make a few phone calls.

(th)

Last edited by tahanson43206 (2019-07-09 10:50:33)

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#56 2019-07-09 18:19:32

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Hide all of the smoke/ fire and co2 detectors as they could be harvested for like kind acts if you are that afraid of them turning into the wrong hands.

What I find interesting is the fact it was a clean sheet design, build, and test a reactor for less than $20 million...Not bad when you consider that its going to put out power for 20 plus years before starting to need a refill of fuel.

Here is how one might be used on a human rover transport
5ae9f72219ee8645008b4797-960-540.jpg

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#57 2019-07-09 19:08:44

kbd512
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Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

tahanson43206,

They're not handing out anything containing Highly Enriched Uranium or Plutonium to any Tom, Dick, or Harry who thinks it would be great fun to use it- at all or ever, period and end of story.  There has to be a bonafide use case, properly trained personnel to use it, security controls in place to ensure the material doesn't deviate from the specified end use, etc.  That's just the nature of the game with weapons grade materials.

Receiving adequate and reliable power on another planet is a bonafide use case for a highly compact fission reactor containing HEU.  Furthermore, the people operating it there, out of necessity pertaining to the myriad of other potentially life-threatening if seemingly mundane tasks, must be highly trained and competent to run a power generation system, a life support system, a computerized navigation system, etc.

The controls around HEU and Pu239 are exceptionally stringent for very good reasons.  It doesn't mean it's "safe" or "unsafe" to use.  There's no such thing as "safe".  Safety doesn't exist.  Safety never existed.  Safety will never exist.  The only place safety can ever exist is between your ears.  In the objective physical world, your own actions or the actions of others are what are potentially dangerous to you.  Anything and everything can be dangerous in the hands of someone who is ignorant or evil.  Those are the two most fundamental problems that have afflicted humanity since before we could ever talk to each other.  All that considered, loss of life from running out of power is an unacceptably stupid way to die after we spend tens of millions of dollars training and equipping someone to live on another planet.

I would question the hell out of anyone's judgement who thinks they have some silver bullet solution to something as complicated as running an industrial scale drilling and chemical refinery on another planet.  I base that judgement on the numerous problems we have with drilling operations and petroleum refining operations here on Earth.  I don't even believe nuclear reactors of the sort that KiloPower represents are adequate to the task.  In that light, taking a few batteries or tons of liquid hydrocarbon with you is laughably absurd.

Elon Musk hasn't even hinted at how he's providing the equivalent amount of power as that used by a small city, yet that's what this ISRU task represents.  It's a bridge too far with current technology.  It wouldn't matter if we had fusion reactors.  If we did have fusion reactors, we wouldn't even go to the trouble of refining chemical propellants.  Unfortunately, we don't have anything like that.  No matter what, we're still talking about building a generating station with the power output of a half dozen of our nuclear powered super carriers on the surface of another planet.  That kind of power plant gets built on the scale of years here on Earth, with the combined labor of thousands of people, no matter what technology is used.

The thought process behind the belief that some specific power generation technology is a magic totem that will solve all problems is the pinnacle of ignorance or arrogance or both.  I support nuclear for the same reason I support solar, fuel cells, batteries, and combustion engines.  There's a good practical use for all of those technologies, which would be why we created them.  Some just work better than others for specific use cases.

Regarding influencing any decision makers, I assure you that I have no such influence.  Quite frankly, neither the current administration nor any other administration in living memory has seriously pursued nuclear power or space exploration.  To them, it's just another special interest group.  We're still waiting and hoping for something better to come along, despite the total lack of evidence that something better will come along in our lifetimes.  Our grandfathers gave us the power of the atom.  It can be used to do great things or to do terrible things.  What is done with that power all comes down to the desires of the person or people wielding the power.

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#58 2019-07-10 09:18:45

tahanson43206
Member
Registered: 2018-04-27
Posts: 664

Re: NASA and DOE to test kilopower nuclear reactor for space applications

For kbd512 #57 ....

After thinking about your reply for a while, I've decided you're right in your pre-judgement of human nature.

That said, I'm guessing even you will concede that nuclear armed nations have a VERY LARGE NUMBER of citizens certified and trained to build, ship, install, operate and maintain nuclear reactors and nuclear devices of all sizes, from the smallest nuclear powered submarine to the largest on-shore reactor.

While my vision was (and still is) of a nuclear power package that a citizen can purchase or lease (at some point), I concede that for the foreseeable future, nuclear power devices for civilian power supply will be controlled as they are now on naval vessels (of all nuclear nations) and at on-shore power stations.

This concession (on my part) leads to the question ... what is the sweet spot in trades of security expense vs power delivered to customers in competition with natural gas, solar and wind and other energy sources that exist or may come along?  There will be a minimum customer base (such as a large factory) that will match some minimum power supply (with security) capability.

Cities in the high latitudes would be candidates for low power nuclear fission systems before others, because of the costs they incur for non-nuclear supply.

I assume that at minimum, a 24 hour security team would be put in place.  However, the team members might very well be highly qualified technical personnel, but again, the qualifications of team members would arise from cost-benefit analysis.   With the reactors we are discussing here, there would not be a lot of technical work required on a day-to-day basis, but there would be a need for ability to handle emergencies of various kinds that might arise.

Can you imagine yourself hired as manager of one of these facilities?  If so, how would you structure the enterprise to provide security while earning the shareholders a fair return?

(th)

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#59 2019-07-11 09:49:45

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

So you're saying it takes the equivalent of two Tesla sports cars running at near full power for a whole hour (ie running at a combined 850 Kws for an hour) to compress one Kg of methane? Nope, I don't believe that. There must be something wrong with that figure - and presumably that puts out all your other calculations...Was it 850 WHs rather than 850KwHs? I could believe that.

kbd512 wrote:

I posted a paper not long ago about the energy required to liquefy natural gas.  Actual LNG plants here on Earth consume about ~850kWh/kg to compress CH4 to ~70 bar and then liquefy the natural gas .  That means you either need to burn ~220kg of O2/CH4 for each kg of LOX/LCH4 you put in the propellant tanks, or you'd better have one stupidly powerful solar array.  You'll need it.


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

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#60 2019-07-11 10:07:12

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Further proof that figure can't be right...

Liquid methane sells for about $1.30 per Kg. But if we assume an energy cost of 4 cents per KwH then, you are claiming just to get it into liquid form would cost over $34!!! So, no, I don't believe that figure.

louis wrote:

So you're saying it takes the equivalent of two Tesla sports cars running at near full power for a whole hour (ie running at a combined 850 Kws for an hour) to compress one Kg of methane? Nope, I don't believe that. There must be something wrong with that figure - and presumably that puts out all your other calculations...Was it 850 WHs rather than 850KwHs? I could believe that.

kbd512 wrote:

I posted a paper not long ago about the energy required to liquefy natural gas.  Actual LNG plants here on Earth consume about ~850kWh/kg to compress CH4 to ~70 bar and then liquefy the natural gas .  That means you either need to burn ~220kg of O2/CH4 for each kg of LOX/LCH4 you put in the propellant tanks, or you'd better have one stupidly powerful solar array.  You'll need it.


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

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#61 2019-07-11 12:12:35

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,502
Website

Re: NASA and DOE to test kilopower nuclear reactor for space applications

I'm with louis on this one. One kWh is 3.6 MJ, meaning you're suggesting it takes 3 GJ/kg to compress and liquefy natural gas.

Compressing gases really is a work-intensive activity, but not *that* work intensive.  Is it possible you've mixed up your units?  850 kJ/kg (0.25 kWh/kg) is a much more believable number for the work required to compress a gas to 70 bar.

A *very* rough ideal-gas approximation at room temperature (methane is not even close to an ideal gas under these conditions): 1 kg of Methane at 70 bar would take up 0.021 cubic meters.  Using W=PV (very rough approximation, *not* a good formula) that corresponds to about 150 kJ/kg of energy.  This should be correct to within +/- one order of magnitude.


-Josh

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#62 2019-07-11 19:17:38

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

off topic
Using the cold of Mars would be the way to get liquid methane but here is another method in liquid nitrogen is used to cool the gaseous methane
https://sciencing.com/compress-methane- … 98367.html

Gas has three quantities:
Volume
Temperature
Pressure

Three major Gas rules govern the behaviour of gases:
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law

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#63 2019-07-11 20:31:12

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Louis,

Argh!  Stupid calculator button presser!  Why yes, that would be me sad

I deserve that for not checking my work.

It's 850Wh/kg (850kWh/t).  That's only 204MWh, not 204GWh, to liquefy 240t of CH4.

204MWh is only ~279kWh/day over 730 days, or about 11.6kW/hr.  That's within the realm of feasibility.

The rosiest projections I've seen for a scaled up version of MOXIE come from here:

Abstract #1666 - The MOXIE Team - Dr. Michael H Hecht

Since these are the people working on the technology, if they don't know how much power they'll need, then I don't know who will.

25.1kW to produce 2kg/hr

Scaling for Starship:

860t / 860,000kg of LOX

860,000 / 17,520 (365 days per year * 24 hours per day * 2 years per launch opportunity) = 49kg / hr

49kg / 2kg = 24.5 times more output per hour to replenish Starship's LOX tank in 730 days, assuming zero boil-off

24.5 * 25.1kWh = 614.95kWh/hr to produce 860t of LOX in 730 days

If MOXIE's power requirement scaled linearly, which it shouldn't with reduced heat losses and improved pump efficiency from using a larger pump, then it would be double that (51kWh/hr for 2kg of LOX per hr).  Even so, that's still 14,758.8kWh / day.  NASA's InSight Lander produced a 4,588Wh in a single day.

614,950Wh * 24hrs per day = 14,758,800Wh/day

14,758,800Wh / 4,588Wh = 3,216.8 times as much solar panel area

InSight has 4.4m^2 of ATK's solar panels / SolAero PV cells, so 14,154m^2, or an area ~119m x 119m.  A NFL regulation football field is 5,351.2m^2, so nearly 3 football fields worth of panels just for making LOX...  Presuming it's a bright sunny day on Mars, every single day.

The figures regarding how much power was projected to produce 1kg of LOX came from a previous experiment conducted by NASA as part of their ISRU efforts.  It's 3kW higher than the projection for MOXIE, but was made before MOXIE existed.  So, no, you still need to supply roughly the same number of megawatt-hours of power per day just to make 860t of LOX in 730 days, presuming a 6 millibar CO2 atmosphere with no dust (going back to NASA's experiment).

If I recall correctly, Elon Musk's plan is to send 5 cargo flights to Mars.  If he actually intends to get all of his ships back to amortize manufacturing and launch costs, then you can multiply that figure by 5.  So, that'd be 74MWh per day, just to make the LOX.  I don't think he's going to get all of his ships back, though, so let's say he only intends to get 1 of the 5 ships back.  ISS has the largest solar array ever deployed in space and it makes 120kW of power in full sun in LEO.  For his plan to bring 1 ship back, he has to land and then build an array that produces 10 times as much power as ISS, just to make LOX.  This, of course, presumes you care about getting the spaceship back.  Tell me how many megawatt-class solar arrays we have floating around out there, never mind have built on the surface of any other planet.  By my count, which thankfully doesn't require any calculator button pressing, that number is precisely zero.

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#64 2019-07-12 02:50:15

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

We've all done it! - including NASA (who have less of an excuse, there being so many fingers to press the buttons !!).

So, 25 Kws averaged constant is well within the scope of a PV system, and also should not be a problem with a Kilopower reactor system (although in the case of Kilopower there may be issues, no doubt resolvable) over how you integrate that into what might be a mobile mining operation to seek out good local water supplies).

With PV, we should always remember we will have six Starships on the surface (with a Space X mission) which can make a powerful contribution to electricity generation.

The PV solution would require we take some methane/oxygen (I'm thinking maybe something like 50 tons). Again, we should have 5 residual Starships on the surface. Their tanks will have some propellant and fuel left over, and so those could, I presume be tapped. so they may be part of the 50 tons.




kbd512 wrote:

Louis,

Argh!  Stupid calculator button presser!  Why yes, that would be me sad

I deserve that for not checking my work.

It's 850Wh/kg (850kWh/t).  That's only 204MWh, not 204GWh, to liquefy 240t of CH4.

204MWh is only ~279kWh/day over 730 days, or about 11.6kW/hr.  That's within the realm of feasibility.

The rosiest projections I've seen for a scaled up version of MOXIE come from here:

Abstract #1666 - The MOXIE Team - Dr. Michael H Hecht

Since these are the people working on the technology, if they don't know how much power they'll need, then I don't know who will.

25.1kW to produce 2kg/hr

Scaling for Starship:

860t / 860,000kg of LOX

860,000 / 17,520 (365 days per year * 24 hours per day * 2 years per launch opportunity) = 49kg / hr

49kg / 2kg = 24.5 times more output per hour to replenish Starship's LOX tank in 730 days, assuming zero boil-off

24.5 * 25.1kWh = 614.95kWh/hr to produce 860t of LOX in 730 days

If MOXIE's power requirement scaled linearly, which it shouldn't with reduced heat losses and improved pump efficiency from using a larger pump, then it would be double that (51kWh/hr for 2kg of LOX per hr).  Even so, that's still 14,758.8kWh / day.  NASA's InSight Lander produced a 4,588Wh in a single day.

614,950Wh * 24hrs per day = 14,758,800Wh/day

14,758,800Wh / 4,588Wh = 3,216.8 times as much solar panel area

InSight has 4.4m^2 of ATK's solar panels / SolAero PV cells, so 14,154m^2, or an area ~119m x 119m.  A NFL regulation football field is 5,351.2m^2, so nearly 3 football fields worth of panels just for making LOX...  Presuming it's a bright sunny day on Mars, every single day.

The figures regarding how much power was projected to produce 1kg of LOX came from a previous experiment conducted by NASA as part of their ISRU efforts.  It's 3kW higher than the projection for MOXIE, but was made before MOXIE existed.  So, no, you still need to supply roughly the same number of megawatt-hours of power per day just to make 860t of LOX in 730 days, presuming a 6 millibar CO2 atmosphere with no dust (going back to NASA's experiment).

If I recall correctly, Elon Musk's plan is to send 5 cargo flights to Mars.  If he actually intends to get all of his ships back to amortize manufacturing and launch costs, then you can multiply that figure by 5.  So, that'd be 74MWh per day, just to make the LOX.  I don't think he's going to get all of his ships back, though, so let's say he only intends to get 1 of the 5 ships back.  ISS has the largest solar array ever deployed in space and it makes 120kW of power in full sun in LEO.  For his plan to bring 1 ship back, he has to land and then build an array that produces 10 times as much power as ISS, just to make LOX.  This, of course, presumes you care about getting the spaceship back.  Tell me how many megawatt-class solar arrays we have floating around out there, never mind have built on the surface of any other planet.  By my count, which thankfully doesn't require any calculator button pressing, that number is precisely zero.


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

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#65 2019-07-12 09:21:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Kbd,

My previous response was somewhat rushed.

This is on Wikipedia:

"A preliminary study by SpaceX estimates the propellant plant is required to mine water ice and filter its impurities at a rate of 1 ton per day. The overall unit conversion rate expected, based on a 2011 prototype test operation, is one metric ton of O2/CH4 propellant per 17 megawatt-hours energy input from solar power. The total projected power needed to produce a single full load of propellant for a SpaceX BFR is in the neighborhood of 16 gigawatt-hours of locally Martian-produced power. To produce the power for one load in 26 months would require just under one megawatt of continuous electric power. A ground-based array of thin-film solar panels to produce sufficient power would have an estimated area of just over 56,200 square meters; with related equipment, the required mass is estimated to fall well within a single BFR Mars transport capability of 150 metric tons. Alternatively, extrapolating from recent NASA research into fission reactors for deep space missions, it is estimated that sufficient fission-reactor based electric power infrastructure might mass between 210 and 216 tonnes, requiring at least two BFRs for transport. A Mars power system using solar and vertical axis wind turbine design to produce sufficient power might mass just over 3.15 tonnes."

https://en.wikipedia.org/wiki/SpaceX_Ma … t_and_base

56,200 sq metres of PV sounds a lot but at 237 x 237 metres can easily be laid out. It would have to be carried in two Starships as their load is now at around 100 tons I believe (lower than the BFR spec).

I don't really understand the 3.15 tonnes quote above re a solar/wind system - perhaps that was a typo for 315 tons?

Last edited by louis (2019-07-12 09:22:24)


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

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#66 2019-07-12 17:46:55

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Even as we produce the fuel and cyrogenic Oxygen there is still a boiloff which will occur for each day as we progress to getting a full fuel tank such that the power levels to get there will need to go up to account for the boiloff replacement that we would produce during the total 730 days.

1,000 kg is a 1T metric
so 2kg x 500 to get 1 T
Desire 860T of fuel desire
martian day is just under 25 for the 24.5 hr used
desire product days 730

860t / 730 = 1.18t in day or 1180 kg / 24.5 hrs = 48.16 kg/hr rate of which we are only making 2kg is an issue as you need to multiply the 25kwhr array by call it 50kg/hr/ 2 kg = 25 of them...a 625 kwhr generating array of which we know that power is only developed even in the best places on earth for 4 to 4.5 hrs a day....which means another multiplier of 6 to get all the energy for the rate to run all day....
for a total array of 3.75megwatts....

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#67 2019-07-12 17:55:39

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

I can only presume Space X are aware of boil-off and take that into account when giving their figure for the PV requirement.


SpaceNut wrote:

Even as we produce the fuel and cyrogenic Oxygen there is still a boiloff which will occur for each day as we progress to getting a full fuel tank such that the power levels to get there will need to go up to account for the boiloff replacement that we would produce during the total 730 days.

1,000 kg is a 1T metric
so 2kg x 500 to get 1 T
Desire 860T of fuel desire
martian day is just under 25 for the 24.5 hr used
desire product days 730

860t / 730 = 1.18t in day or 1180 kg / 24.5 hrs = 48.16 kg/hr rate of which we are only making 2kg is an issue as you need to multiply the 25kwhr array by call it 50kg/hr/ 2 kg = 25 of them...a 625 kwhr generating array of which we know that power is only developed even in the best places on earth for 4 to 4.5 hrs a day....which means another multiplier of 6 to get all the energy for the rate to run all day....
for a total array of 3.75megwatts....


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

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#68 2019-07-12 18:13:02

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Space x sized array 56,200 sq metres x 4.0 hr x (460 w insulatory x 30% efficiency) ~138 watts per meter =  31,022,400 whrs for a days production of energy to be stored and used in batteries over what was calculated as the minimum for doing the conversion..
So a factor of not quite 10 greater than is needed for the production of fuel.

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#69 2019-07-12 21:14:10

kbd512
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Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Louis,

Going off those estimates, that's 10.5 football fields worth of solar panels.  For whatever reason, that seems a tad bit larger than anything we've ever laid out on another planet.  However, that's not something you're going to unfurl and lay on the ground.  It's just not.

Here's the application for Ascent Solar's space-rated 1kW/kg thin film solar array technology that I mentioned some time ago:

Direct Exploration of Jupiter Trojan Asteroid using Solar Power Sail

Ascent Solar Custom Solutions

However, the modules that actually protect the cells are 200W/kg and I presume that any environment with airborne abrasive dust would require minimal protection.  So, a 3.75MW thin film array would weigh at least 18.75t, not 3.15t.  That's just for the modules, exclusive of any wiring or packaging canisters.  I've no idea how long those would last on Mars, but I seriously doubt it'd be more than 10 years.  The power conversion equipment for that kind of juice would weigh at least several tons, the wiring several more tons, presuming we're using lightweight CNT wiring.

Apart from vehicles and equipment, I would leave the giant batteries at home.  Storing 3.75MWh in batteries like the ISS ORU's would require 59.7t worth of batteries, so those packaging materials must become drastically lighter for battery backup to be practical.  A 75% efficient CH4 fuel cell would require ~324kg of CH4 and 648kg of O2 to produce 3.75MWh.  Waste heat from a fuel cell could potentially keep SOXE fuel cells warm at night to avoid hundreds of drastic thermal cycles that might crack the ceramic plates.  We'll see how well MOXIE survives the thermal cycles when the 2020 rover lands on Mars.  If backup power in the 10's of kW range is required for life support and keeping the propellant cold at night, then it'll be more mass-efficient to just burn some propellant in a fuel cell to reduce boil off than it will be to do that with batteries.

In the end, it's going to be a lot more power-efficient and mass-efficient to keep a series of small nuclear reactors running 24/7/365 to keep the lights on at night and the propellant frosty.  The 5 KiloPower reactors that NASA wanted to bring to Mars could produce 3.75MWh in just under 4 and a half days if they were kept running at 70% of rated output.  That's plenty of juice to keep the fuel cells hot, the solar panels warm, the propellant cold, and the humans warm and happy at night.

If I was going to take 50t of any propellant with me to Mars, it'd be 50t of LH2, just like Dr. Zubrin suggested.  To make 240t of CH4, you only need 60t of H2.  You still need to obtain an additional 100t / 100 cubic meters of H2O.  Alternatively, just take 60t of LH2.  If you don't get as much H2O as you need, then you can still make nearly all of the fuel required to get home from LH2 brought from home and the fission reactors can be built into that particular Starship with adequate shielding to keep the LH2 cold.  That would also drastically lower the power requirements.

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#70 2019-07-13 05:13:16

louis
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From: UK
Registered: 2008-03-24
Posts: 4,589

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Regarding layout of the PV, I don't see any reason why assembly shouldn't be a simple matter. For one thing everything weighs less on Mars and for another you don't have to worry about strong winds, rain or other inclement weather conditions.  PV film might be laid attached to a wire strung between brackets, angled for maximum insolation. You might do it in 10 metre sections. Obviously it would need to be tested but I think this could become a simple procedure and that a robot rover could achieve the assembly in a matter of days.


kbd512 wrote:

Louis,

Going off those estimates, that's 10.5 football fields worth of solar panels.  For whatever reason, that seems a tad bit larger than anything we've ever laid out on another planet.  However, that's not something you're going to unfurl and lay on the ground.  It's just not.

Here's the application for Ascent Solar's space-rated 1kW/kg thin film solar array technology that I mentioned some time ago:

Direct Exploration of Jupiter Trojan Asteroid using Solar Power Sail

Ascent Solar Custom Solutions

However, the modules that actually protect the cells are 200W/kg and I presume that any environment with airborne abrasive dust would require minimal protection.  So, a 3.75MW thin film array would weigh at least 18.75t, not 3.15t.  That's just for the modules, exclusive of any wiring or packaging canisters.  I've no idea how long those would last on Mars, but I seriously doubt it'd be more than 10 years.  The power conversion equipment for that kind of juice would weigh at least several tons, the wiring several more tons, presuming we're using lightweight CNT wiring.

Apart from vehicles and equipment, I would leave the giant batteries at home.  Storing 3.75MWh in batteries like the ISS ORU's would require 59.7t worth of batteries, so those packaging materials must become drastically lighter for battery backup to be practical.  A 75% efficient CH4 fuel cell would require ~324kg of CH4 and 648kg of O2 to produce 3.75MWh.  Waste heat from a fuel cell could potentially keep SOXE fuel cells warm at night to avoid hundreds of drastic thermal cycles that might crack the ceramic plates.  We'll see how well MOXIE survives the thermal cycles when the 2020 rover lands on Mars.  If backup power in the 10's of kW range is required for life support and keeping the propellant cold at night, then it'll be more mass-efficient to just burn some propellant in a fuel cell to reduce boil off than it will be to do that with batteries.

In the end, it's going to be a lot more power-efficient and mass-efficient to keep a series of small nuclear reactors running 24/7/365 to keep the lights on at night and the propellant frosty.  The 5 KiloPower reactors that NASA wanted to bring to Mars could produce 3.75MWh in just under 4 and a half days if they were kept running at 70% of rated output.  That's plenty of juice to keep the fuel cells hot, the solar panels warm, the propellant cold, and the humans warm and happy at night.

If I was going to take 50t of any propellant with me to Mars, it'd be 50t of LH2, just like Dr. Zubrin suggested.  To make 240t of CH4, you only need 60t of H2.  You still need to obtain an additional 100t / 100 cubic meters of H2O.  Alternatively, just take 60t of LH2.  If you don't get as much H2O as you need, then you can still make nearly all of the fuel required to get home from LH2 brought from home and the fission reactors can be built into that particular Starship with adequate shielding to keep the LH2 cold.  That would also drastically lower the power requirements.


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

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#71 2019-07-13 09:16:13

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

The panels which we talk about is not a plastic flexible solar array which is down in the 15% at best efficiency levels. The ridgid panels of 30% need poles for the vertical and one for the horizontal by which the framing for the solar panel to form a traingle shape between the pieces. The verticle pole is the anchor to the arrays layout such that when it is windy they do not move and get damaged.

If you can go see a large farm of arrays come to a site in trucks and see just what that volume they will need. This of course will be less the batteries which on mars will be required along with the protection shelter for them. Of course the powerwall for the AC votage excess storage comes to mind but that also means converting the output to AC rather than leaving it as DC for battery charging.

Even the kilopower units will have some batteries to take away any voltage fluctuations from current draw surges but its small in comparison.

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#72 2019-07-13 11:19:33

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

Louis,

Nobody has ever demonstrated 100% robotic assembly of a generating station here on Earth, no matter what kind of generating station we're talking about.  The reduced weight only helps with energy requirements supplied to the assembly robots.  The real issue is that nobody has ever done what you're talking about doing.  This has to at least be demonstrated once to prove that it can work.

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#73 2019-07-13 12:23:38

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

I went and searched for a video of a solar farm being built

https://www.youtube.com/watch?v=1iCV_WS-mMQ

Edit company link removed

Oskomera completing work on one of the fastest solar parks ever to be built in the UK. The ground based solar system in Marston, Lincolnshire took just six weeks to build from start to finish.

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#74 2019-07-13 13:15:50

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,769

Re: NASA and DOE to test kilopower nuclear reactor for space applications

SpaceNut,

Since I watched the video, I couldn't help but notice all the people, shipping containers, and diesel powered equipment at the construction site.

How much of that are you going to have on Mars?

Regarding Oskomera Solar Power Solutions, the second link you provided doesn't work.  Their website link from their Facebook page goes to some asian pornographic website.

Could we deduce from this that they didn't do a very good job of building that solar power station in 6 weeks?

Edit:

Nevermind, Oskomera Solar Power Solutions has already been declared bankrupt.

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#75 2019-07-13 14:43:31

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 15,321

Re: NASA and DOE to test kilopower nuclear reactor for space applications

They happened to be the first with a mars scape for setup but it was intended to also show the shear volume of all of the wooden crates and how one is assembled for Louis...Would need to take more time with the video to get answers to the number of crates for the volume that we would take up inside a BFR...15 acres per MW on earth for a foot print

US superfund site where another was constructed in 6 months. There is an embedded video onthe page.
https://www.app.com/story/news/military … /95622600/

The 16.5-megawatt solar energy project is in a remote section of Joint Base McGuire-Dix-Lakehurst. More than 51,000 solar panels are to be installed there and eventually produce more than 21,000 megawatt-hours of renewable energy each year, enough to power more than 2,500 homes across Jersey Central Power & Light's electric grid, according to the Joint Base Public Affairs Office.


https://www.epa.gov/sites/production/fi … _solar.pdf

This is week 5 of a coop installed did not search for the other weeks...
https://www.youtube.com/watch?v=eysZvubPIoU

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