Stuff about Solar Power for Mars, split from another thread.

[Ultimate Steve]

This may be more relevant to the Mars Colonization thread, but I did some thinking about space based solar today. Space Based Solar has a number of advantages compared to Earth Based Solar, but it suffers from the critical problem that it has to be significantly better in order to offset the cost of launching it into space, even with the potential maturity of fully reusable super heavy launch vehicles.

At Mars, however, in certain respects, the inverse can be true: It can be cheaper to get a ton of payload to Mars orbit than to the surface of Mars (assuming solar panels cannot yet be locally manufactured). If this is true, the case for Space Based Solar for Mars might close.

Normally, if you want to send 100 tons of solar panels to Mars, you would need like 1 normal launch and 2 refueling launches (assuming v3 ship with 200 ton prop capacity). One of those ships has to be a Mars ship. You can either send it to Mars and keep it there, in which case the cost of that ship for that mission is, the monetary cost minus the value of the materials gained on Mars from scrapping. Or you can then send it back to be reused, in which case the cost per mission is the cost of that ship divided by how many flights it makes (which would be somewhere around ten as trips to Mars are very long) plus the cost of having the capacity to refuel it on Mars.

None of those are fairly attractive options unless you truly can crank these ships out for comparative pennies. You've got to make an entire Martian spaceship that either gets discarded after one use, or can only be used once every two years (within a reasonable service life you would be spending 1/10 of a ship per launch and presumably limited Martian refueling resources).

Instead, let's say you make a 100 ton Spaced Base Solar satellite, and say that half of it can be solar panels, so you get 50 tons of solar (I think the ratio would be better than this, but simple numbers for the sake of argument). It will be more effective as it can be placed in Areostationary orbit and can have sunlight for most of the entire day (if not all of it depending on inclinations and such) but it will also be less effective as you will have transmission losses, so let's say it comes out to about the same. You would need ~2 space based solar satellites to replace one load of solar panels to Mars.

The key important thing here is that you would load up a Starship with fuel in LEO, yeet this satellite off to trans Mars injection, and then immediately turn around and return to elliptical orbit, before aerobraking back to Low Earth orbit (or more likely to the surface where it would pick up a new satellite and repeat the process). This would require somewhat more propellant (the exact amount varies on so many factors that I'm not going to bother trying to be more precise). If you didn't aerobrake it would be about twice as much propellant. The satellites would have their own (presumably Argon) ion thrusters (no shortage of solar power) to brake into Mars orbit with.

So in terms of propulsion, you have to do 1 launch for the satellite and let's say 3 refueling launches. Then double this as you need 2 satellites to match one load of Martian panels. So 8 launches for the same effectiveness as 3.

However, you don't have to expend a ship on Mars, and you don't have to have a valuable ship flying a really low flight rate and taking up refueling assets. That ship that you launched the satellite with can instead be used as a normal ship during the majority of the time when there isn't currently a transfer window, and can repeat the above sequence of maneuvers multiple times per transfer window. Instead of (admittedly at worst) building one ship to deliver 100 tons of solar and then be scrapped on Mars, you can pull some existing cargo ships for a few months and have them yeet one satellite off to Mars every few days, and return them to normal service afterwards.

(This would be too long but there's an interesting discussion to be had about whether the ships should be dedicated ships that aerobrake or really light space tug versions that propulsively brake, I'm not sure which one would win out on propellant use especially as putting a reusable heat shield through re entry from a high energy orbit is non trivial)

The counterpoint to that is that you now have to pay for 50 tons of satellite per 50 tons of solar panels you throw towards Mars. And BTW this doesn't have to be one monolithic satellite, I had just assumed that the (presumably microwave) beamed power transmitter would be large, but this could be a lot of smaller sats Starlink style.

SpaceX is the world leader of cheaply mass producing satellites, but even with those advantages it might not come out cheaper but it is interesting to think about.

 

Some additional Mars specific benefits of this method include not having to dust off panels (or build machines to do that), not having to spend the human labor (or robot labor/time/development) to set up those solar panels, not having to build two axis sun trackers for maximum effectiveness into every set of ground based solar panels, not having to deal with putting these far away to avoid FOD from rocket landings/launches, and being able to construct and power new outposts relatively easily (I believe workable microwave power receivers can be created by stringing up a lot of wires on poles, similar to the concepts of those Lunar radio telescopes built by stringing cables over a crater).

 

Of course - Domestic production of Martian solar panels is likely to be a thing eventually - Possibly fairly early on as there is a huge incentive to automate this as power is very heavy to ship from Earth and you need a LOT of it. Now while this is good to just put on the surface, a funny idea has struck me.

Paradoxically, the cost of space launch might actually end up being lower on Mars due to its smaller size and the fact that normally you will have a lot of rockets sitting around doing nothing, so it is really just the (actually quite valuable) power needed to produce propellant that is the main driving cost. And you need significantly lower propellant to get to orbit on Mars. So we could see a future in which domestically built solar panels on Mars are launched to orbit to be used for space based solar power. Though that is unlikely as unless you get creative (more and more solar progressively manually mounted to "core" Earth-built and Earth-launched beamed power satellites with the beam transmitters and attitude control), you would also need Mars to be able to domestically produce everything else needed to build satellites.

More hilariously, there is an (incredibly small) chance that the economics of domestically built and launched space based solar power work out on Mars but not on Earth.

 

TLDR: Space Based Solar Power's biggest disadvantage (the cost to get it to space) may actually be inverted when powering a Mars colony, it may be cheaper, all things considered, to get panels to Mars orbit than to the Martian surface.

[JoeSchmuckatelli]

3 hours ago, Ultimate Steve said:

Space Based Solar Power's

Any idea whether the loss due to distance from the sun is made up for by less atmospheric scattering? 

I. E. Whether it turns out to be efficient? 

I like the idea but I hate it for Earth; you yeet up enough hectares of solar panels to produce a meaningful amount of power to beam down - and you will block the sky and mess up the night. 

(yours is the first SB solar post I haven't had a knee jerk negative reaction to!) 

Edited Tuesday at 12:42 AM by JoeSchmuckatelli

[Ultimate Steve]

4 minutes ago, JoeSchmuckatelli said:

Any idea whether the loss due to distance from the sun is made up for by less atmospheric scattering? 

I. E. Whether it turns out to be efficient? 

I like the idea but I hate it for Earth; you yeet up enough hectares of solar panels to produce a meaningful amount of power to beam down - and you will block the sky and mess up the night. 

(yours is the first SB solar post I haven't had a knee jerk negative reaction to!) 

I'm not 100% sure which two situations you are comparing (Earth ground, Earth space, Mars ground, Mars space). I'm going to assume that's Mars space vs. Earth ground.

 On a clear day with perfect conditions you get about 1000 W/m^2 at noon after what Earth's atmosphere scatters and reflects (compared to 1360ish at the top of Earth's atmosphere). One NASA source said that the average (flat on the surface) square meter of land on Earth experiences roughly 342 W/m^2 averaged over a year but upon closer inspection this is just the amount of light coming towards Earth's disk averaged over the surface area of of Earth - A perfect factor of 4, the NASA figure is just the solar flux divided by 4 and makes no concessions for weather or solar absorption. As I am comparing hypothetical perfect sun tracking that doesn't have cosine losses, this number will not do.

I'm finding it very tricky to figure out what the average production would be for a sun tracking solar panel on Earth. The big factors here would be atmospheric absorption throughout the day, and weather. A hypothetical giant solar farm would likely be built in the desert for the least clouds assuming transmission wasn't a huge problem, so I'll assume 0 clouds. But I'm having trouble (read: googled a few times and gave up) finding data about atmospheric absorption for different times of day.

But at minimum you've got half day and half night (unless you ran your solar plant in the arctic for 6 months and then moved the whole thing to antarctica for the next 6 months for constant daylight and wonderfully low operational temperatures), so 500 W/m2. IDK what the effect of the atmosphere is at times that aren't noon. I could probably do the math if you gave me a few days to figure it out but I don't want to. So let's just call it a (likely higher than reality) 400 W/m2 average. This is going to be lower in raw electricity terms because Solar panels aren't that efficient, but I will ignore that as the choice of panel is arbitrary as long as they are the same one for the sake of comparison (though IRL you might want to optimize the solar panels for the different wavelengths you would encounter at Earth's surface vs. in space).

Now, for Mars space, the solar constant averages about 590W/m2, though if you were planning an actual mission, you would note that due to Mars's eccentricity, this varies a lot (anywhere from 493 to 718 ish). In the chosen orbit you'd get daylight essentially all of the time. However now you have to deal with the efficiency losses of beamed power. It is not a mature technology and numbers are hard to come by. In short range (a few meters) laboratory conditions, one paper said they had gotten efficiencies as high as 63 percent. On one hand, you would 100% not get anywhere near the same results from Areostationary orbit. On the other hand, who knows, the technology is new. But even with current lab efficiencies applied to Mars, you get about 372W/m^2 equivalent. It is close enough that the varience introduced by my assessments of beamed power technology and my guess at non-noon atmospheric losses on Earth could easily push the answer to either side.

As for how it compares to Mars ground, this paper gives a good idea of what Mars Ground is like, including factors for non-noon atmospheric absorption and all that: https://ntrs.nasa.gov/citations/19890018252

I haven't read it in detail enough to understand it and I don't think it ever just spits out a number. But it is weird that I was able to more easily find solar power data for Mars than for Earth.

[magnemoe]

4 hours ago, Ultimate Steve said:

This may be more relevant to the Mars Colonization thread, but I did some thinking about space based solar today. Space Based Solar has a number of advantages compared to Earth Based Solar, but it suffers from the critical problem that it has to be significantly better in order to offset the cost of launching it into space, even with the potential maturity of fully reusable super heavy launch vehicles.

At Mars, however, in certain respects, the inverse can be true: It can be cheaper to get a ton of payload to Mars orbit than to the surface of Mars (assuming solar panels cannot yet be locally manufactured). If this is true, the case for Space Based Solar for Mars might close.

Very good point, I say the same is true for the moon. For an sizable base an nuclear reactor is an good option not for landers. It would also boost robotic missions who is even more relevant with an manned base as you don't want the rovers moving some hundred meters a day but some hundred km who is reasonable for an off road in an desert. 

[darthgently]

The case for Mars orbital solar power to ground station configuration is tricky if you are only serving a single or a couple of colonies.  Either most of the sats have nothing to beam to most of the time or you require a lot of ground power transmission lines from dispersed ground stations.

Areostationary orbital altitude is so high (17,000ish km) that distance to ground station makes the beam footprint much larger but lower faster orbits end up with gaps in transmission and more complex aiming issues.  I also wonder if the dust storms would degrade microwave transmission quite a bit.  I suspect so given wifi is in the same band and it doesn’t like bad LOS generally.

Laser relaying of power between satellites is a possible answer to some problems but there would be a lot of conversion losses and heat management issues.

Hard to beat nukes, at least early on, for ground colonies and bases.

Now for a large Mars torus orbital, that could be an entirely different story.  A small constellation of large solar sats lasering constant power could be nice.

 Maybe we should request moving this to the Mars base thread, not sure

Edited Tuesday at 06:50 AM by darthgently

[Nuke]

6 hours ago, JoeSchmuckatelli said:

Any idea whether the loss due to distance from the sun is made up for by less atmospheric scattering? 

I. E. Whether it turns out to be efficient? 

I like the idea but I hate it for Earth; you yeet up enough hectares of solar panels to produce a meaningful amount of power to beam down - and you will block the sky and mess up the night. 

(yours is the first SB solar post I haven't had a knee jerk negative reaction to!) 

you also dont have to send people out in pressure suits to dust the panels all the time.

[Pthigrivi]

On 1/7/2025 at 2:31 AM, Nuke said:

you also dont have to send people out in pressure suits to dust the panels all the time.

I think you could just build in a bar on a track that would sweep the panel with pressurized air periodically. Ideally you’d only send people out when absolutely necessary. 
 

Im not a huge fan of nuclear on earth (its fine, just expensive) but for colonies on the moon and mars it seems ideal, certainly for base loads. Id have to do some math but the energy density of nuclear fuel has to beat solar panels. 

Edited Wednesday at 10:30 AM by Pthigrivi

[Nuke]

1 hour ago, Pthigrivi said:

I think you could just build in bar on a track that would sweep the panel with pressurized air periodically. Ideally you’d only send people out when absolutely necessary. 
 

Im not a huge fan of nuclear on earth (its fine, just expensive) but for colonies on the moon and mars it seems ideal, certainly for base loads. Id have to do some math but the energy density of nuclear fuel has to beat solar panels. 

really depends on the type of colony. if its just an agricultural settlement then yea solar is probibly fine. an industrial base or large scale colony probibly needs the high output and reliable baseload. no matter what you do you are going to need to send a huge payload to mars.

[darthgently]

16 minutes ago, Nuke said:

really depends on the type of colony. if its just an agricultural settlement then yea solar is probibly fine. an industrial base or large scale colony probibly needs the high output and reliable baseload. no matter what you do you are going to need to send a huge payload to mars.

I’m thinking that ag on Mars will be as sophisticated and energy intensive as many industrial processes on earth.  I mean imagine growing 100 acres of food crops in Antarctica but you additionally have to provide very strong  illumination, import/create and maintain your soil, manage microbial life, recycle the water and nutrients. So lots of power involved just in providing the environment, then you have planting, harvesting, and processing.

[SunlitZelkova]

@Ultimate Steve Considering SpaceX is the only organization with an intention to build a colony on Mars that is more substantial than anything before (albeit with few details at the time given focus on Starship itself), you might continue discussion in this thread. There’s also one called A City on Mars, but that was more about habitation and economic factors in a Mars colony.

Also, you might find this article interesting: http://spaceflighthistory.blogspot.com/2016/12/energy-from-space-department-of.html?m=1

Summarized DOE/NASA study of SBSP from the late 70s. They envisioned 60x 10x5 kilometer satellites and 60x receiver antenna spaced approximately 50 kilometers apart stretching across the US at the 35th parallel.

60x such satellite would have been capable of providing 300 gigawatts of power. That’s one quarter of what the entire present day US energy grid can produce, and thus far more than what a Mars colony probably needs, so fewer satellites would be needed at Mars. Dust storms might have deleterious effects on the transmission of the power if microwaves are used though; didn’t Opportunity lose communications because of one? I’m not sure how its communications system’s transmissions would compare with an SBSP satellite’s though.

[Pthigrivi]

2 hours ago, Nuke said:

really depends on the type of colony. if its just an agricultural settlement then yea solar is probibly fine. an industrial base or large scale colony probibly needs the high output and reliable baseload. no matter what you do you are going to need to send a huge payload to mars.

Totally. Im sure it would start with solar and maybe phase in modular nuclear reactors as it grew. I did a little napkin math using US per capita energy consumption and estimate it would take 5x 300mw modular nuclear reactors to serve a million people. It would take 4.5km^2 of solar panels to provide the same amount on earth, but since irradiance is lower on mars you'd need more like 10km^2. Thats about 250 block 3 starship launches. Im not sure how much a modular nuclear reactor weights minus the water but even if you if took 3 launches per reactor thats only 15 for the same output. It very well may be that solar efficiency gets much better by the time we're building a colony on mars but I don't think it will be 16 times better. Maybe if you produce the glass, substrate and frame material in situ and just ship the PV as a film? Also like @darthgently says you might need much more consumption on mars than you do on earth for crops, heating, and air and water filtration, doubling or maybe tripling those numbers. 

[Nuke]

3 hours ago, darthgently said:

I’m thinking that ag on Mars will be as sophisticated and energy intensive as many industrial processes on earth.  I mean imagine growing 100 acres of food crops in Antarctica but you additionally have to provide very strong  illumination, import/create and maintain your soil, manage microbial life, recycle the water and nutrients. So lots of power involved just in providing the environment, then you have planting, harvesting, and processing.

i think were pretty much just talking grow lights. supplemental to natural light unless you need to grow underground. you can hack your grow cycles if you give them an artificially short night cycle and keep the lights on most of the time. running the lights low during day to supplement natural daylight, and also charging batteries so you can run them for at least some portion of the night.  you also have to power water reclamation, but if you use aeroponics or gmo crops, you can reduce water usage greatly. life support is your other power requirement, but plants help with scrubbing co2 and producing oxygen, so you wont be running life support at full capacity. only other thing would be machinery but an ag colony can just to it the old way, and the low gravity should help make the work easier.

Edited Wednesday at 12:07 AM by Nuke

[darthgently]

3 hours ago, Nuke said:

i think were pretty much just talking grow lights. supplemental to natural light unless you need to grow underground. you can hack your grow cycles if you give them an artificially short night cycle and keep the lights on most of the time. running the lights low during day to supplement natural daylight, and also charging batteries so you can run them for at least some portion of the night.  you also have to power water reclamation, but if you use aeroponics or gmo crops, you can reduce water usage greatly. life support is your other power requirement, but plants help with scrubbing co2 and producing oxygen, so you wont be running life support at full capacity. only other thing would be machinery but an ag colony can just to it the old way, and the low gravity should help make the work easier.

While the symbiosis between animals and plants is easily recognized the other members of this symbiotic structure are often second thoughts.  And this blindspot affects GMO directions and innovation in ag like hydro and aeroponics.  Namely symbiotic microbes and fungi.  These play roles we are only beginning to really understand.

I would not assume that a multigenerational settlement would be viable without the entire shebang.

For a solid foundation for a permanent settlement I’d like actual rich living soil to grow food in even if in a lava tube.  Because the point is life off world.

Edited Wednesday at 03:46 AM by darthgently

[Nuke]

8 hours ago, darthgently said:

While the symbiosis between animals and plants is easily recognized the other members of this symbiotic structure are often second thoughts.  And this blindspot affects GMO directions and innovation in ag like hydro and aeroponics.  Namely symbiotic microbes and fungi.  These play roles we are only beginning to really understand.

I would not assume that a multigenerational settlement would be viable without the entire shebang.

For a solid foundation for a permanent settlement I’d like actual rich living soil to grow food in even if in a lava tube.  Because the point is life off world.

you can farm live soil. it might be more involved than it is on earth since you are washing out perchlorates and introducing compost and bacterial cultures, maybe a few earthworms (insert shai hulud reference here) and imported (or locally "manufactured") fertilizers. doing your aeroponic food crops mostly for food production, and the wastes of that go into soil production. then you can expand to crops that need soil. and you are always making more soil as a byproduct of food production.

you eventually get to the point where you are importing livestock, probibly not for meat initially, less pigs and cows and more goats (eat anything and produce milk and fertilizer) and sheep (human populations require textiles). once the colony is thriving then you can think about pigs and chickens. though in the expanse they seem to be at the point where they have cattle.

[darthgently]

3 hours ago, Nuke said:

you can farm live soil. it might be more involved than it is on earth since you are washing out perchlorates and introducing compost and bacterial cultures, maybe a few earthworms (insert shai hulud reference here) and imported (or locally "manufactured") fertilizers. doing your aeroponic food crops mostly for food production, and the wastes of that go into soil production. then you can expand to crops that need soil. and you are always making more soil as a byproduct of food production.

you eventually get to the point where you are importing livestock, probibly not for meat initially, less pigs and cows and more goats (eat anything and produce milk and fertilizer) and sheep (human populations require textiles). once the colony is thriving then you can think about pigs and chickens. though in the expanse they seem to be at the point where they have cattle.

Agreed overall with the addition of insects and mostly ground birds like chickens, ducks, and quail.  Eggs are an amazing food and these birds can convert bugs to a complete protein like magic by laying an egg.  But they need a rich diet from rich soil to do this well

[Nuke]

1 hour ago, darthgently said:

Agreed overall with the addition of insects and mostly ground birds like chickens, ducks, and quail.  Eggs are an amazing food and these birds can convert bugs to a complete protein like magic by laying an egg.  But they need a rich diet from rich soil to do this well

that should come in handy should someone's science experiment escape.

[darthgently]

 

6 hours ago, Nuke said:

you can farm live soil. it might be more involved than it is on earth since you are washing out perchlorates and introducing compost and bacterial cultures, maybe a few earthworms (insert shai hulud reference here) and imported (or locally "manufactured") fertilizers. doing your aeroponic food crops mostly for food production, and the wastes of that go into soil production. then you can expand to crops that need soil. and you are always making more soil as a byproduct of food production.

you eventually get to the point where you are importing livestock, probibly not for meat initially, less pigs and cows and more goats (eat anything and produce milk and fertilizer) and sheep (human populations require textiles). once the colony is thriving then you can think about pigs and chickens. though in the expanse they seem to be at the point where they have cattle.

So this dropped that references some of the stuff I’ve been reading of elsewhere.  We really don’t know enough to write it off for a serious long term settlement.