Author Topic: Power options for a Mars settlement  (Read 596871 times)

Offline Robotbeat

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Re: Power options for a Mars settlement
« Reply #240 on: 05/21/2017 07:16 pm »
No, I wasn't referring to ATK's brochure but to actual Mars surface architecture trades which include wind load masses, etc.

Here is a group of slides gathered by fission /advocates/ showing that solar is comparable or better that nuclear (for Equatorial sites), slide 33: http://spirit.as.utexas.edu/%7Efiso/telecon/Rucker_12-7-16/Rucker_12-7-16.pdf

I believe a mix of power makes the most sense, just like on Earth. But I don't see where Mueller is getting this idea that solar is heavier unless you're proposing a much more radical nuclear reactor design as I mentioned up thread (or tap an aquifer and dump heat into the aquifer).

Also, Kilopower units are $70-80 million apiece. SpaceX can't afford that price even for a single ITS worth of power. (This is a good opportunity for collaboration with folks like NASA, by the way... NASA or some international partner contributes some reactors to provide more robustness and diversity to the fledgling settlement's power grid).
« Last Edit: 05/21/2017 07:35 pm by Robotbeat »
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Online meekGee

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Re: Power options for a Mars settlement
« Reply #241 on: 05/21/2017 07:34 pm »
No, I wasn't referring to ATK's brochure but to actual Mars surface architecture trades which include wind load masses, etc.

Here is a group of slides gathered by fission /advocates/ showing that solar is comparable or better that nuclear (for Equatorial sites), slide 33: http://spirit.as.utexas.edu/%7Efiso/telecon/Rucker_12-7-16/Rucker_12-7-16.pdf

I believe a mix of power makes the most sense, just like on Earth. But I don't see where Mueller is getting this idea that solar is heavier unless you're proposing a much more radical nuclear reactor design as I mentioned up thread (or tap an aquifer and dump heat into the aquifer).

Also, Kilopower units are $70-80 million apiece. SpaceX can't afford that price even for a single ITS worth of power.

The question of which power source will be better is complex, and probably not binary.

My objection is that when you bring in specific power numbers for solar that are irrelevant.  The really high numbers used for thin film are disconnected from surface mission design requirements.  I also don't understand why you're stuck on kiloPower.  It's irrelevant.

I brought up the ATK design not because I think that "this is how you'd do solar", but because you brought up UltraFlex.

These "reality factors" is why SpaceX arrived at that conclusion.  They actually have to make it work, and they (as relayed by Mueller) concluded that a solar system that is "long term surface worthy" has a poorer specific power than nuclear does.

They also concluded that initially, since the reactors do not exist, solar will have to do.  For an "initially" concept, you can relax the longevity requirement, and so this probably helped too.
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Offline Robotbeat

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Re: Power options for a Mars settlement
« Reply #242 on: 05/21/2017 07:45 pm »
Kilopower is the only realistic nuclear power source in the near term. As Mueller said, SpaceX is not going to develop nuclear power, they can't afford it. But NASA can (partly because they can partner with DOE who has access to "free" enriched uranium).

Thin film is not irrelevant, as very lightweight structures are possible (yes, compatible with wind loads), and making structure for the thin film arrays is one of the most straightforward structural ISRU things you could do... Compressed soil bricks is one such method (that we know Musk is looking into for other purposes).
« Last Edit: 05/21/2017 07:50 pm by Robotbeat »
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Offline Patchouli

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Re: Power options for a Mars settlement
« Reply #243 on: 05/21/2017 08:26 pm »
No, I wasn't referring to ATK's brochure but to actual Mars surface architecture trades which include wind load masses, etc.

Here is a group of slides gathered by fission /advocates/ showing that solar is comparable or better that nuclear (for Equatorial sites), slide 33: http://spirit.as.utexas.edu/%7Efiso/telecon/Rucker_12-7-16/Rucker_12-7-16.pdf

I believe a mix of power makes the most sense, just like on Earth. But I don't see where Mueller is getting this idea that solar is heavier unless you're proposing a much more radical nuclear reactor design as I mentioned up thread (or tap an aquifer and dump heat into the aquifer).

Also, Kilopower units are $70-80 million apiece. SpaceX can't afford that price even for a single ITS worth of power. (This is a good opportunity for collaboration with folks like NASA, by the way... NASA or some international partner contributes some reactors to provide more robustness and diversity to the fledgling settlement's power grid).

In space power generation is one of the things NASA should be funding as a nuclear reactor makes a dust storm go from something that would shut down normal operations and possibly force an evacuation to more of a nuisance.

Though large scale chemical fuel storage in the form of methane along with fuel cells or ICE power generators could be another option.
« Last Edit: 05/21/2017 08:35 pm by Patchouli »

Online meekGee

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Re: Power options for a Mars settlement
« Reply #244 on: 05/21/2017 08:28 pm »
Kilopower is the only realistic nuclear power source in the near term. As Mueller said, SpaceX is not going to develop nuclear power, they can't afford it. But NASA can (partly because they can partner with DOE who has access to "free" enriched uranium).

Thin film is not irrelevant, as very lightweight structures are possible (yes, compatible with wind loads), and making structure for the thin film arrays is one of the most straightforward structural ISRU things you could do... Compressed soil bricks is one such method (that we know Musk is looking into for other purposes).

kiloPower only came up in this thread. It's too small for the mission requirements, and I haven't heard SpaceX say they intend to use these micro-reactors on Mars.

I'd expect them to partner with someone like General Dynamics EB, or with one of the newer developers of MWatt-class nuclear power.

As for a surface system - I'll be happy to take a (critical) look...  But irrespective of the structure you come up with (I have to admit I've never heard of a brick-based design before) please use realistic insolation numbers, not peak numbers, and realistic conversion efficiencies at system level, not at single-cell test-stand level..

There's much of that going on.  For example, the panel on Phoenix, which is advertised as 450W, is actually using earth-orbit level insolation for the specification.  That's just playing hide-and-seek.

The figure of merit is kWatt-hr per sol, averaged over the year, with some allowance for doing more ISRU work during the hours-of-plenty, but then bringing into account that the ISRU equipment has to be up-scaled accordingly since it is running at a lower utilization factor, and bringing into account use of excess thermal power.  These are the kind of optimization I expect SpaceX has been fiddling with for several years now.
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Offline Robotbeat

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Re: Power options for a Mars settlement
« Reply #245 on: 05/21/2017 09:28 pm »
what are you talking about as far as insolation values? All I did was link to the study in the FISO presentation.

« Last Edit: 05/21/2017 10:47 pm by Robotbeat »
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Offline john smith 19

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Re: Power options for a Mars settlement
« Reply #246 on: 05/21/2017 10:27 pm »
Quote
Before the storm hit, Phoenix was generating about 2,100 Watt-hours each sol...
  (From news stories at the time).  You can compare that to the insolation graph data I posted upthread.

Also, in practice:

The system was down after a few months.  It was ice, but it would also have gone done due to excessive wind, or wind-induced fatigue over time, etc.  It takes an inordinate amount of effort to make a PV panels that survives the environment for years, and until you do, you don't have an "almost system", you simply don't have a system.
All true, but a settlement has resources that any machine simple does not have.

Humans that can go out and clean PV arrays or pick them up if they fall over or (for extreme simplicity) move them by hand through a certain number of degrees every hour.

I'd also remind people that 75 m/s is a pretty severe storm on Earth, but Mars surface pressure is 1/160.
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Online meekGee

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Re: Power options for a Mars settlement
« Reply #247 on: 05/21/2017 11:25 pm »
what are you talking about as far as insolation values? All I did was link to the study in the FISO presentation.

Here's what seems to be a well researched study:

http://ccar.colorado.edu/asen5050/projects/projects_2001/benoit/solar_irradiance_on_mars.htm

showing values both above the atmosphere and on the surface, as a function of latitude.

(Some interesting insights regarding polar collectors, btw)

The bottom line is that average surface insolation is 60-80 W/m2.  (Averaged over night/day and over the year), or ~100 in the most favorable location/ time-of-year

On top of that you have conversion efficiency (panels are 30-40% efficient, but are probably not tracking, and probably are partially obscured by dirt) and you realize you're scavenging power here.

I quoted above that Phoenix's panels got 87 Watts-avg out of 3.1 m2 of receiver, or 28 W-avg/m2, when relatively clean.

This is in rough agreement with the paper.

Long term solar deployment will do worse.  There will be more dust, more need to clean, more degradation, etc.

If you want a MWatt of power for ISRU, you need 35,000 m2 of installed PV area.  (7 football fields).

Just for 1 MWatt.












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Offline Robotbeat

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Re: Power options for a Mars settlement
« Reply #248 on: 05/22/2017 12:04 am »
The previous study I pointed to assumed tracking for solar because it both increased output nominally and helped solve the dust and wind problem (by tilting to aid dust removal and by feathering in order to minimize wind loading). It's really a no-brainer (and even if it gets stuck, it still produces power, unlike if the moving parts of a reactor gets stuck).
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Re: Power options for a Mars settlement
« Reply #249 on: 05/22/2017 12:43 am »
The previous study I pointed to assumed tracking for solar because it both increased output nominally and helped solve the dust and wind problem (by tilting to aid dust removal and by feathering in order to minimize wind loading). It's really a no-brainer (and even if it gets stuck, it still produces power, unlike if the moving parts of a reactor gets stuck).

That's fine.  Then the design should include the benefits of tracking in terms of power output (~30% more), but also the mass penalty since the panels need to be supported on a central torque tube with the ability to pivot.  (Or on a gimbal if you're doing 2 axis tracking).

As for cleanliness, there are 100 designs for cleaning systems.  It's just a function of weight.  You can have robots run along the panels, for example, using the edges as rails.  It's just that your panels now have to be sturdy enough for that. 

With solar, everything is possible. It's just the resultant kg/kWatt that ends up being high.

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Offline Robotbeat

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Re: Power options for a Mars settlement
« Reply #250 on: 05/22/2017 01:43 am »
The previous study I pointed to assumed tracking for solar because it both increased output nominally and helped solve the dust and wind problem (by tilting to aid dust removal and by feathering in order to minimize wind loading). It's really a no-brainer (and even if it gets stuck, it still produces power, unlike if the moving parts of a reactor gets stuck).

That's fine.  Then the design should include the benefits of tracking in terms of power output (~30% more), but also the mass penalty since the panels need to be supported on a central torque tube with the ability to pivot.  (Or on a gimbal if you're doing 2 axis tracking).
That is included all that in the study I pointed to.
Quote

As for cleanliness, there are 100 designs for cleaning systems.  It's just a function of weight.  You can have robots run along the panels, for example, using the edges as rails.  It's just that your panels now have to be sturdy enough for that.
Um, it's included in the design. Tilting arrays mounted high will keep the dust off. (We know this based on operational experience from Spirit and Opportunity, this isn't just hand-waving... We can keep dust off the arrays by parking at an angle on top of a hill, simulating mounting higher and having tilting capacity.)

Quote
With solar, everything is possible. It's just the resultant kg/kWatt that ends up being high.
No, it's still better than fission (or essentially equivalent) in the study I showed. And the design they picked wasn't particularly novel and innovative, either.
« Last Edit: 05/22/2017 01:48 am by Robotbeat »
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Online meekGee

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Re: Power options for a Mars settlement
« Reply #251 on: 05/22/2017 04:18 am »
Well, we've circled back, so I'm not going to reply directly.

All I can say is that when you wonder why Mueller stated what he did - the explanations are in the posts upthread.
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Offline john smith 19

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Re: Power options for a Mars settlement
« Reply #252 on: 05/22/2017 06:52 am »
The bottom line is that average surface insolation is 60-80 W/m2.  (Averaged over night/day and over the year), or ~100 in the most favorable location/ time-of-year

On top of that you have conversion efficiency (panels are 30-40% efficient, but are probably not tracking, and probably are partially obscured by dirt) and you realize you're scavenging power here.

I quoted above that Phoenix's panels got 87 Watts-avg out of 3.1 m2 of receiver, or 28 W-avg/m2, when relatively clean.

This is in rough agreement with the paper.

Long term solar deployment will do worse.  There will be more dust, more need to clean, more degradation, etc.

If you want a MWatt of power for ISRU, you need 35,000 m2 of installed PV area.  (7 football fields).

Just for 1 MWatt.
IIRC 40% needs rigid triple junction solar cells and AFAIK they are normally installed in a concentrator configuration. People have pointed out that's not a good system on Mars due to diffuse lighting caused by regular atmospheric dust storms.

AFAIK 20%+ is at or close to cutting edge on thin film PV so 50-100% bigger. OTOH you should get a much lighter structure, and a much lighter support structure to mount it.

It still remains a very big structure to erect and to keep clean.   
In space power generation is one of the things NASA should be funding as a nuclear reactor makes a dust storm go from something that would shut down normal operations and possibly force an evacuation to more of a nuisance.
To be clear NASA is funding Kilopower and has in fact moved to it for planning future DRMs. A live Kilopower ground test is scheduled for Dec this year (2017) excluding the radiator design but including a full reactor and Stirling generators up to 1Kw(e). The design is expected to stretch to 10Kw(e) and possibly up to 100Kw(e). This will be the closest that NASA has gone toward actually building a full space nuclear (where it's used has a big impact on the detailed radiator design, hence that's the part they are not testing) power reactor since 1965. Incidentally it'x actually 2x bigger in terms of electrical power generation but about 50x more efficient (Stirling Vs 1st gen thermoelectric modules).
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Online meekGee

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Re: Power options for a Mars settlement
« Reply #253 on: 05/22/2017 11:05 am »
Multi junction cells are indeed rigid, but can be thinned, and are used in concentration on earth for economic reasons that do not apply on Mars.

The diffuse light thing is caused by concentration, not by the mere use of MJ cells.

You can assume 35% conversion at the system level before dust, alignment, etc.

The weight comes from the substrate.
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Offline IRobot

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Re: Power options for a Mars settlement
« Reply #254 on: 05/22/2017 01:28 pm »
It still remains a very big structure to erect and to keep clean.   
I've already proposed a possible solution before: slighly tilted panels with an electroacoustic transducer attached to the surface (or support beams), to make it vibrate. Should be enough to kick out the dust on the low g of Mars.
« Last Edit: 05/22/2017 01:29 pm by IRobot »

Online meekGee

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Re: Power options for a Mars settlement
« Reply #255 on: 05/22/2017 01:43 pm »
It still remains a very big structure to erect and to keep clean.   
I've already proposed a possible solution before: slighly tilted panels with an electroacoustic transducer attached to the surface (or support beams), to make it vibrate. Should be enough to kick out the dust on the low g of Mars.
So for that to even have a chance to work, the panels have to be rigid.

2 mm thick glass?

So 5 kg/m2, before the railing and acoustic generators...  Now add the support structure, and you're at 7-8 kg/m2.

So with 28 W/m2, you get 4 W/kg, and a MWatt weighs 250 tons.

Now add cabling to cover the several football fields, batteries for winter night time, and you see the problem.
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Offline IRobot

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Re: Power options for a Mars settlement
« Reply #256 on: 05/22/2017 01:48 pm »
It still remains a very big structure to erect and to keep clean.   
I've already proposed a possible solution before: slighly tilted panels with an electroacoustic transducer attached to the surface (or support beams), to make it vibrate. Should be enough to kick out the dust on the low g of Mars.
So for that to even have a chance to work, the panels have to be rigid.
No, no reason to be rigid. You just have to adjust the oscillation frequency to avoid damping from the film.


So 5 kg/m2, before the railing and acoustic generators...  Now add the support structure, and you're at 7-8 kg/m2.

Now add cabling to cover the several football fields, batteries for winter night time, and you see the problem.
You can power it directly from the solar panel and commands are sent wireless. There is no cabling or batteries required.
« Last Edit: 05/22/2017 01:51 pm by IRobot »

Offline guckyfan

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Re: Power options for a Mars settlement
« Reply #257 on: 05/22/2017 01:54 pm »
Now add cabling to cover the several football fields, batteries for winter night time, and you see the problem.

No need to do it at night. The devices can be fed from the panel. They can do regular shakes or be activated by wireless control. No need for a lot of cabling.

Online meekGee

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Re: Power options for a Mars settlement
« Reply #258 on: 05/22/2017 01:55 pm »
Now add cabling to cover the several football fields, batteries for winter night time, and you see the problem.

No need to do it at night. The devices can be fed from the panel. They can do regular shakes or be activated by wireless control. No need for a lot of cabling.
Power cabling, for the field...  And general usage batteries, sized to work even in winter when days are short - just adding to the mass of the system.

So for a MWatt system, it's about 1-2 kg/sec, so another 50-100 tons.

---

The point of all this is that in-space PV advertises kWatt/kg power levels, and that's actually within the realm of possibility for very specific systems in 1 AU orbit...  But by the time you deploy a true Mars surface system, you're 3 (!) orders of magnitude lower, at single digit W/kg...
« Last Edit: 05/22/2017 02:32 pm by meekGee »
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Offline IRobot

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Re: Power options for a Mars settlement
« Reply #259 on: 05/22/2017 02:46 pm »
Power cabling, for the field...  And general usage batteries, sized to work even in winter when days are short - just adding to the mass of the system.
We are talking about something not much more complex than a buzzer with a wireless uController, with a small cable (a few cm), weighting a few grams per panel, that would vibrate once in a while, perhaps once a day for 10 minutes. You could even ditch the remote control and just use a timer.

Easy, simple, self contained.

 

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