Powering the Lunar Base

NASA’s selection of SpaceX’s Starship within the Human Lander System (HLS) program was both surprising and exciting for space nerds all over.

Previously I have written about how Starship’s ambitious approach could transform the Artemis Program, particularly since Starship’s excessive cargo payload capacity creates a lot of opportunities that were previously curtailed by the harsh reality of razor thin Lunar mass budgets.

As a rough rule of thumb, conventional approaches to Lunar transportation put cargo costs at upwards of $100m/T, while Starship should be able to get as low as $1m/T without any miracles, and perhaps as low as $100k/T long term. 100-1000 times cheaper transport costs is the sort of logistics improvement that creates possibilities, and much of my Twitter feed recently has been full of die hard space nerds coming to terms with this fact.

Of course, if Starship works it won’t be long until other companies and countries replicate its success – there’s nothing magical about it. So when we think of Starship right now we think of SpaceX’s prototypes blazing a trail on a south Texas beach, but long term we should think of it as any launch system that is big, ambitious, fully reusable, readily manufacturable, and above all cheap.

Lunar Starship, c. 2021.

Of course we’ve had these lovely renders from SpaceX over the last few years showing what a Moon base could physically look like but once the sci-fi elements are subtracted we’re left with the basics. A bunch of pressurized spaces covered in dirt.

SpaceX Moon Base Alpha | Space and astronomy, Space travel, Spacex starship
SpaceX plans to build Starships for ‘Moon Base Alpha’

A Starship-enabled Lunar base is not some dismal single room tuna can like Jamestown Base from Season 1 of “For All Mankind”.

Astronaut-led video tour reveals details in 'For All Mankind' moon base |  collectSPACE
Jamestown Base from “For All Mankind”

After all, a single Starship could arrive with more pressurizable volume than the entire ISS and ~215 T of cargo. Instead, a Lunar base could look and feel more like McMurdo “Mactown” Station in Antarctica, the only Antarctic station with a ATM machine.

Overhaul in the works for aging U.S. Antarctic station | Science | AAAS
McMurdo Antarctic Station

Such a base would contain plenty of habitation volume to enable occupation without being cramped, dedicated facilities for sleeping, eating, working, and playing, logistics, transport, etc. Unlike a Mars city, it wouldn’t necessarily be oriented around the audacious goal of locally replicating a complete industrial stack, but it should be capable of comfortably housing more than a thousand astronauts at any one time, from any nation on Earth.

The habitations will necessarily be pressurized, meaning most likely vaults and cylinders with few sharp corners. They will also be covered in a layer of Moon dirt to provide protection from micrometeoroids, temperature swings, and cosmic radiation. Even so, there are ways that natural light could enter the structure, particularly because at the Lunar south pole the sun will never be more than a few degrees above (or below) the horizon.

In Lunar gravity (~0.16 g), roughly 9 meters of Moon dirt would be needed to counter a 0.5 bar working atmosphere, so some kind of tensile pressure-stabilized structure could be employed to enclose large volumes, albeit without the transparent “open sky” permitted by Mars’ thin atmosphere.

But enough of architectural speculation (for now), let’s focus instead on the core of where the battle is won or lost: logistics. And in particular, electricity supply.

A reliable source of electricity is also a challenge for the Antarctic Stations, which generally use diesel generators and occasionally supplement with wind power. Antarctica is a cold, windy, and often very dark place. Indeed, when my wife Christine returned from her winter-over at the Amundsen Scott South Pole Station she did have a slight scent of diesel. Needless to say, getting diesel to the south pole is non-trivial, and in ages past it was flown in by C-130, though three gallons was burned for every gallon delivered. More recently, giant tractors haul it from McMurdo (which is generally supplied by ship) over the ice, taking several weeks to reach the pole. Still better than walking dragging a sledge, as the early explorers did.

Way back in the ancient times, McMurdo even had a nuclear power plant! Though after 8 years of sporadic operation the reactor, by then dubbed “Leaky Poo”, was dismantled and shipped back to the continental US along with 9000 cubic meters (!) of contaminated soil.

This is all a primer for the core problem: powering a station of any size on the Moon is non-trivial.

The first choice for space power, solar photovoltaic (PV) panels, are challenged by the Moon’s long night. Over most of the Moon, the surface enjoys 14 days of uninterrupted sunlight followed by 14 days of night. During that time, another power source must be available to power station operations that can’t be arbitrarily shut off for 2 weeks. Indeed, environmental control (ECLSS) will have to provide heat during the cold winter night, in addition to atmospheric regulation, lighting, and a million other things. Due to the demands of ECLSS on the Moon, combined with a likely profusion of varying circadian cycles and shift work, I think it’s fair to assume that energy demand on the Moon will be much more regular than on Earth, where demand typically plunges by a factor of 3 or 4 at night.

As a back up system, batteries can work on Earth where nights are short, the air is breathable, and most people are asleep. On the Moon, for any given baseload demand, about 80 times as many batteries would be needed. And while the relative mass of batteries and solar panels doesn’t matter much on Earth where both are typically fixed to structures with copious static capacity, getting a bunch of heavy batteries to the Moon eats into payloads for other things.

One possible way around this problem is to build a base on a mountain at the South (or North) Pole, which due to the Moon’s low axial tilt enjoy much more sun than average, just as the adjacent craters are permanently shadowed regions (PSR) and contain some frozen mud. These “peaks of eternal light” are not quite eternal, however. There are multiple peaks and, particularly during the Lunar winter, they tend to eclipse each other. Even the prime locations on or near the rim of Shackleton Crater endure nights as long as 7 days with shorter periods of darkness during the daily cycle. This is a factor of 2 improvement over the generic case anywhere in the non-polar Lunar regions, but it’s still a huge challenge.

To put this into concrete terms, space-rated solar panels are routinely made incredibly thin and as light as 50 grams per square meter – similar to a sheet of newspaper. If the entire 200 T payload of a Starship was consumed with solar panels, they could produce a peak of 800 MW, assuming 20% efficiency. This is enough power for a small city on Earth.

In contrast, really good lithium-ion batteries can achieve about 100 kWh/T, so a 200 T payload of batteries would store 20 MWh. Attached to the solar panels they could charge completely in about 90 seconds, and after night falls, at the same power draw, would discharge in the same period. 90 seconds is a lot less than 7 days.

Alternatively, if 20 MWh had to last for 7 days, then average power draw would be 120 kW, about the same as the ISS. The panels necessary to provide this would weigh just 60 kg, a rounding error on the total payload.

Arguably overnight power storage could be accomplished by electrolysing Lunar water, then capturing the exhaust from fuel cells. Even using Lunar water, the mass of the cells, condensers, electrolysers, power electronics, storage tanks, and heat exchangers is comparable a Lithium-ion battery, while the round trip efficiency is much lower. And that’s not even including the mass overhead for mining lunar water! For the sake of argument, say a closed cycle Hydrogen energy storage system achieves 1 MWh/T. In this case, the above scenario results in power loss after 900 seconds, or 15 minutes. Still a lot less than 7 days.

One potential approach is to position solar panels in a number of carefully chosen locations around the rim of Shackleton crater and to wire them together, such that at any given time most of them are in sunlight. On the plus side this reduces the odds of a power outage. On the minus side it requires building solar farms many kilometers apart, linking them up with improbably robust, cheap, and light electrical cable that won’t break down due to Paschen’s Law, and doing it all before the winter arrives.

I also looked into mounting solar panels on a very tall tower, similar to a radio mast. These are strong, light, and tall, so perhaps there was some trade between aluminium tower sections and panels that could put the panels high enough that they’d never be shaded, even in the depths of Lunar winter, and thus avoid more batteries than the 2 hours or so necessary to endure a Lunar eclipse.

Indeed, the global trade looks like this.

Diagram showing three way trade between solar power towers, panels, and batteries.

Unfortunately, it turns out that the minimum altitude necessary to avoid any shading is 2750 m, rather taller than any structure ever built on Earth.

Left: Map of the Lunar south pole showing minimum altitude of shade-free space above any given point.
Right: Crop of Shackleton Crater showing regions where shade-free space is less than 3000 m above the surface.

Since I believe powering a Lunar base should be less exciting than exceeding previous antenna height records by a factor of four, there must be a better way.

The lunar surface is subjected to large temperature fluctuations. During the day, it can reach 127 C while at night it can plunge as low as -173 C, a total range of 300 C. In the PSRs it can be even colder, as low as -185 C.

In the lunar south pole region, a heat exchanger system between radiators positioned in shaded regions (even artificially shaded regions, such as in a pit surrounded by MLI) and absorbers placed in sunny regions could produce energy with a Carnot efficiency approaching 75%! Running the working fluid through a (very) large ice bath could ensure energy storage through the dark nights when the absorbers would be shaded.

To maintain a baseline power supply of 1 MW, a large supply of water could be converted to ice, generating 335 kJ/kg from the latent heat of fusion. There is little marginal benefit to preheating the water to near boiling or chilling the ice to lower temperatures. The total volume required is about 100,000 T, or 40 Olympic swimming pools. By comparison, *only* 2000 T of batteries would be required to do the same job, or a mere 10 dedicated Starship flights. So locally procured water would need to be found in vast, easy to access quantities. Still, having 100,000 T of thermal mass floating around is never a bad idea.

The coolant loop, operating between 100 K and 400 K would need something like pressurized supercritical ethane. Unfortunately a gravity fed heat pipe would be upside down in this case. I don’t know much about refrigerants, but using ethane as an example, it has a heat capacity of 2.28 kJ/kg K, or 684 kJ/kg over the 300 K temperature variation. At 75% Carnot efficiency, the coolant loop would need to move 2 kg/s to produce 1 MW of power. With a 16 cm (6.5″) diameter buried pipe and a flow rate of 1 m/s, the fluid would have to move about 5 km to transition between shaded and mostly sunny areas, for a total length of 10 km and a total fluid volume of 200 cubic meters, or roughly 200 T, just for coolant. (Or somewhat less if artificial PSRs can be constructed in a more convenient location).

Poiseuille’s Law enables an estimate of total pumping power at around 25 W for this point design.

Solar heating is fine but what if there was a more reliable way to provide the heat source fed to radiators in the PSRs? Some kind of magical metal that just emits thermal energy? And a stream of neutrons. A scaled up (or multiple) Kilopower reactor could deliver 1 MW of baseline power with less than 150 T of total mass, including 4 T of Uranium. Assembled in any convenient PSR, a nuclear reactor could supply power indefinitely, regardless of lunar phase. Indeed, if used away from polar regions they may be unable to provide much power during the day, due to the difficulty of radiating heat in direct sunlight. It turns out the Sun is also a nuclear reactor and it’s much bigger and hotter. And unlike Lunar water, refining Lunar uranium is probably easier than getting a launch permit for it.

The final crazy idea I’ll consider here is a variation on the space-based solar power trope. I have written more than once about how silly this idea is, but at its core is a concept that may finally have its day: remotely beamed microwave power.

Like peaks of eternal light, there are numerous places on the surface of the Moon, including close to polar regions, that are always in view of Earth. Indeed, anywhere on the Moon’s terminator there are places where the Earth appears to rise and set every few weeks.

Animation of scene depicted in “Red Moon” by Kim Stanley Robinson showing “Earthrise” from Petrov Crater.

Microwave antennas positioned here could receive power beamed up from the surface of the Earth from one of at least three stations such that one is always in view.

A 1 MW baseline could be safely transmitted at a power density of 100 W/m^2, implying a receiving area of about 200 m in width, once beam losses and conversion losses are taken into account. Achieving a beam that narrow (1/2000000 rad) from the Earth would require a phased array spaced out over a much larger area, at least 200 km at 5 Ghz (6cm). Each element of the phased array is a high power gyrotron with a steerable high gain antenna phase locked to a carrier transmitted from the Moon.

The advantages of this approach include the low cost of the surface infrastructure on the Moon and its relatively low complexity scaling. Increasing the power requires adding more gyrotrons to each transmitting site on Earth, which is much simpler than commissioning new nuclear power plants in places so cold that conventional metals used for robots get brittle.

The main disadvantage is that such an array is also a very effective anti-satellite weapon and could cause proliferation concerns.

Starship opens up the possibility of building a large, permanently occupied Lunar base. With this comes the unexpected but ultimate pleasant challenge of ensuring the base is adequately supplied with the electricity it needs to run its systems, no questions asked. How would you approach this problem?

47 thoughts on “Powering the Lunar Base

  1. Or a much much more sensible approach is to ignore the moon – its too big
    And simply go to a smaller source of raw material where your spinning habitat can use the sun 24/7 and you can “mine” your material source and throw the material to your habitat

    Liked by 1 person

  2. The microwave power beaming unfortunately has the diffraction problem, and the receiver would need to be very large at Earth to Moon distances. The Friis equation gives us an approximation of the relative diameters (https://en.wikipedia.org/wiki/Friis_transmission_equation) with the 200m transmitter baseline the receiver would have to be 119,000m diameter to get 84% of that 1MW baseline (Airy disk).

    I suggested highly elliptical lunar polar orbits for a SSP system to NASA as the rectennas on the south pole could always be powered. They declined and are going with Kilopower at first.

    Liked by 1 person

      1. As I said in my other reply (lost? awaiting moderation?) the transmitting antenna has to be filled-aperture, not sparse, for decent efficiency. So you need trillions of transmission elements (probably more practical to have hundreds of millions of steered 10m dishes) at each of three locations on Earth. Even on Earth hat does not seem lower cost than the other choices.

        On the plus side, it would make one hell of a radio telescope during the times when the Moon is not in the sky.


  3. “How would you approach this problem?”

    I’d take the simplest solution as the initial solution and require everything prove it’s merits relative to that.

    Let’s start with solar panels at the top of a ridge in a single location. Your chart shows that as 89% uptime and 19 days of night during the winter. To me that seems perfectly adequate. During the start we only send astronauts during the summer and the base is hibernated during the winter. Minimal power draw during the night.

    As you start talking about keeping astronauts during the winter the question becomes how much of power demand can be shifted to other periods of time. The obvious first step is to schedule all heavy equipment use, construction, excavation, refining, during the times there is power. Life support can be prepared ahead of time. An evac vehicle can be fully fueled. Cryogenics during nighttime will be trivial, just make a reflector to keep away the surface radiation. Power needs for communication can be minimized by having a ring of comm satellites in low polar orbits so the base doesn’t need to transmit very far. The base can be heavily insulated so it doesn’t need any active heating. Hydroponics can be restricted to the germination during that time frame. Power needs per person dont need to be that high.

    There isn’t any reason to keep the base population number constant over the winter any time soon. A year is probably going to be a long time to spend on the moon for almost anyone so people will head home before winter if they dont have work that is exclusively winter work. The big advantage of the night is presumably the unmatched conditions it would offer for telescopes and they dont need much power. I could see a small tower to shrink the night but probably not even one as large as the smallest tower on your chart. And it would be only useful for like 10 days out of the year so you probably dont even put the panels up there, just put some reflectors up there to transmit the light.

    As the population starts to grow you can start wanting more population. At that point it makes sense to have paired bases so one is always in winter while one is always in summer. With larger bases you wouldn’t need unrealistic power transmission masses to transmit between them. Plus you can have paired telescopes so your crew always has that perfect night available. You get to have your cake and eat it too.

    Another intriguing possibility is doing “full spectrum power transmission”. The light from the sun is extremely collimated so in theory a mirror setup could transmit it from the sunny side to the shaded side of a crater without high losses. Transmit it in this fashion and then shine it on the panels or use it for base lighting. I know such mirrors are expensive but hopefully it doesn’t need to be quite the quality as those use in deep space telescopes, we just need a decent percentage of the light to end up somewhere in the solar park.

    Liked by 4 people

  4. I’d go with solar panels (as AiryW described), some batteries (mostly Li-ion, with some electrolysis unit for evaluation) but also with a few Kilopower units ASAP as tech demos and backup to solar+batteries.
    Launching fuel rods and reactor cores is low risk before they’ve been critical, so push for the launch permit.
    Fixed horizontal Kilopower radiators can be edge-on to the sun at the south pole, so should be ok even in sunlight.


    1. At the south pole you could probably put the generators in perpetual shadow so they dont need to worry about orientation to the sun.

      I’d be more worried about the problems that lead to the retirement of the reactor in the linked article. If you need a crew on hand to make sure the reactor is operating at night that’s adding crew at exactly the most difficult time to have them around.


      1. Shorter power cables if Kilopower was up on crater rims near the habs.

        Kilopower is much simpler than the PMA-2A in Antarctica. Designed to operate unattended for decades. Little if any fluid to leak (Stirling generators, probably using helium ), and there’s decades more experience in operating PWRs too.


  5. An amusing point of comparison might be to a diesel generator.

    Assuming oxygen can be stored during the day when power is abundant and liquid oxygen storage at night takes negligible energy, diesel could actually work as last resort emergency backup at night. We hardly need to worry about releasing greenhouse gasses, it’s trivially easy to store and extremely reliable. Small generators could get you 4 kWh of power per kilogram of fuel and the mass of the generator itself would be negligible compared to the fuel. That’s giving you 4 times the energy density of the hydrogen. It’s single use of course but it shows how you’d need to use the hydrogen for 4 years to break even compared to just using diesel. Decent benchmark for how much utility you get from adding that complexity to the system.

    For kilopower if we assume 10 kWe for 1.5 tons, you’d need to run it for 600 hours in order to break even with diesel. With floor level solar panels you’d have 965 hours of darkness so it could do that in a year if using it for all those dark periods without batteries eating into the night. With the 360 meter tower, you’d need 3 years to beat diesel assuming batteries dont eat into the night.

    Liked by 1 person

  6. 1) If a majority of your energy use for ECLSS is to generate heat, why not store it as heat? Cover a large chunk of rock in insulating cladding and run a bunch of pipes attached to heat pumps through it. Speaking of, is there an opportunity for reducing heating costs through geothermal heat pumps and/or much better insulation for a larger scale colony?

    2) Since you bring up microwaves, if you really want to use them they’re a great way to replace those long cables. Especially if your solar panels are on hills already.


  7. Nuclear power generation would solve many problems. Next gen LFTR reactors perhaps? Distributed power generation means a large area of infrastructure to construct and service. Single point (relatively) generation keeps the infrastructure in a much smaller and easier to maintain configuration.

    Liked by 2 people

    1. I think you would probably go with a reactor design that’s simpler than LFTR, at least for the first set of reactors. Long term, though, Thorium could be attractive because it’s available on the lunar surface, and we’d only need to “prime” it with some spare uranium or plutonium to get U-233.

      Liked by 1 person

  8. It would seem we need to be more power rich on the Moon than on Earth.

    “Excess” power at our Amundsen South Pole station seems geared to the idea of margin, having more than enough diesel should the supply line get interrupted, and similarly toward the unforeseen failure, so having redundancies. For a lunar South Pole station “excess” power is all this and so much more. Excess becomes creating more than enough power any day to store for not just a long night, or a bad day, but possibly for making oxidizer and fuel for transportation (or back to power) – both not on the Earth side of the power budgeting notions.

    A power rich lunar station would seem inevitable, from having to be much more independent of long supply lines than the antarctic case.

    Liked by 1 person

  9. I think you just have to bite the political bullet and go for nuclear power on the Moon. It’s just so much more of a good fit for a lunar base with extended dark periods than any other source of power. Heat rejection is a challenge, but you can re-arrange local terrain so that the thing is never sitting in sunlight.


    1. I don’t think you would even need to rearrange the terrain. Just put up a sun-shade: a frame holding a few layers of aluminum-coated mylar, and leaving a view of a decent-sized patch of always-dark sky.

      Liked by 2 people

  10. Storing heat is relatively easy, if you have a large amount of rock sitting around. So the heat-engine option seems reasonable. My other favorite is aluminum-oxygen batteries, because of how the moon is made of rock, and rock is full of both aluminum and oxygen. As for beamed microwave power, perhaps it would be less of an anti-satellite proliferation issue if the solar panels were in cis-lunar space.


  11. This posting seems to have been lost, so repeating…

    At the pole, vertical surfaces facing the Sun will be hot (in the daytime) and horizontal surfaces will be cold day and night (you add shadowing structures so that the surface never sees the Sun).

    With 9 m of Moon dirt for insulation, heating will not a be a problem for any base consuming a megawatt of power. Cooling can be handled by a few square meters of (horizontal, shadowed) radiator per kilowatt.

    For power transmission on the Moon, the Paschen’s law curves in Wiki go vertical at about half a Torr. On Mars, there’s a problem. On the Moon, just run a few kilometers of vacuum insulated transmission line and carefully mark it so no one runs into it. There’s no safety difference between dying from your spacesuit touching a kilovolt line vs a megavolt line, so crank up the voltage and keep the amps low. Pick a surface treatment that radiates to the night and reflects the sun to keep the temperature down and you will get colder and so better conduction than on Earth.

    If there is always some point on Shackleton’s rim(or nearby) that gets sunlight, then this seems like the way to go with photovoltaics. A few kilometers of 4-gauge wire is easier than a few hundred meters of tower.

    For heat engines, coolant loops don’t have to stretch 10 km to go from sunny to shady. You can make your own shade anywhere you want.

    You probably don’t want to go between 100 K and 400 K, small (few meter) sun-tracking focusers will give you much higher temperatures, allowing the cold side (probably still above 400 K) to radiate to space much more effectively. On the Moon, with no wind load, you don’t have to build the reflector to the robust standards required of, e.g., a patio umbrella.

    How many tonnes of molten salt will give you a MWmonth of power?

    Liked by 2 people

    1. There has been some work in storing heat (an hence power) in hot lunar soil, heating it during the day and running a heat engine at night. I’d be interested in your opinion on this. The search term is “lunar regolith energy storage”.


  12. Some other notes:

    * Shading on the moon can get areas very cold – cold enough to allow some superconducting tapes/wires to remain superconducting without active cooling. (E.g. the VIPER cables designed by MIT’s Plasma Science and Fusion Center, or maybe magnesium diboride wires, etc.)

    * Superconducting cables have a big up-front cost, but would eliminate transmission losses over their lifetime – which may be worth it if they can be made durable and reliable (and shading/radiators can be kept simple).

    * Superconducting coils are also great for energy storage. According to Wikipedia, “the round-trip efficiency is greater than 95%”. If you don’t need to pay for cooling, it becomes an interesting alternative to batteries.

    * It would be interesting to see if an energy storage magnetic field could provide limited protection against solar flares, etc.; or maybe funnel the solar wind for scientific studies. (It’s always good to get multiple uses out of everything you pay for.)

    With Starship coming on line, new, big dreams seem worth exploring.

    Liked by 2 people

    1. I decided to dig a little deeper, and found that NASA has explored these ideas. A web search for “Lunar Superconducting Magnetic Energy Storage” turns up some good stuff, including a 1988 “Lunar Base Applications of Superconductivity” which describes energy storage, railguns, and magnetic shielding; and a 2018 “Survive and Operate Through the Lunar Night Workshop” – which has lots of ideas related to this post and others’ comments, including using regolith for nighttime heating, and a few about nuclear power on the moon.

      For earth-based applications, a 1987 conference paper describes construction of systems for anywhere from 100 to 10,000 MWh. So it can scale to systems that large. (“Superconducting Magnetic Energy Storage for Electric Utility Load Leveling: A Study of Cost vs. Stored Energy”) Systems for the moon would obviously need their own design considerations.

      And a magnesium diboride-based MRI magnet was tested using solid nitrogen (at 28K) – above the 26K of some natural locations on the moon. Magnesium and boron are cheap and plentiful, so raw materials cost doesn’t have to be significant. But higher-temperature superconductors would likely win out in the end.

      Liked by 1 person

  13. Some version of a Molten Salt Reactor makes the most sense as the primary baseboard power source, for the lunar colony, the Martian colony, everywhere on Earth, and as the heat source for rocket engines to make interplanetary travel much quicker and practical.


      1. Why not land a Starship with a lot of methane and oxygen on board, and use it with methane fuel cells? Minimize the number of different fuel sources required.


  14. “If the entire 200 T payload of a Starship was consumed with solar panels, they could produce a peak of 800 MW, assuming 20% efficiency.

    In contrast, really good lithium-ion batteries can achieve about 100 kWh/T, so a 200 T payload of batteries would store 20 MWh. Attached to the solar panels they could charge completely in about 90 seconds, and after night falls, at the same power draw, would discharge in the same period. 90 seconds is a lot less than 7 days.”

    I am a massive fan of your work but I do have one quibble with this.
    You are assuming a 800 MW draw to power the lunar base. 800 MW is the power draw of a decent sized city – say a Charlotte NC for example – on a hot summer afternoon. It will be a very, very long time before a lunar base scales to that kind of power demand even if you 5x the power usage per occupant compared to the average American. If the initial lunar base can accomodate 100 people at 10kw nightime demand per person, that is 1MW of demand. Let’s double that to accomodate battery round-trip efficiency, battery temperature management and give an adequate margin of safety. That is still just 672MWh to get through a 14 earth-day lunar night. With high energy density chemistries, that is about 135T. One starship worth of batteries. It sounds eminently doable.

    Liked by 2 people

    1. That’s a good point. The underlying fact is that, on a mass basis, nearly all the power infrastructure on the Moon will be batteries or some other kind of storage.


    2. I had more than a quibble with the math in that paragraph.

      First, that assumes that all the power to the city is completely diverted to charging the batteries. Could they handle that kind of current?

      Second, that’s bad news for the city during that 90 seconds when everything goes black. I think the 90 seconds was there just for dramatic purposes.

      Most importantly, where did 800 MW come from? Drawing a comparison to the ISS, the hypothetical thousand-person lunar base described above would actually pull about 20 MW. It seems the 800 MW number comes solely from how many solar panels could be sent in one starship payload, and is not actually based on the energy draw needed for the facility.


  15. Here’s an idea: Use mass drivers to launch 100 Kg moon bricks every few minutes into a two week orbit. Harness energy by catching the returning bricks, converting kinetic energy to electricity.

    lunar escape velocity: 2300 m/s
    100 MW base requirement
    50 Kg brick guidance system (ion thruster, solar panels)
    100% conversion efficiency

    200 MW installed solar (100 MW local + 100 MW launch)
    2 week orbit would require initial velocity ~2000 m/s
    100kg@2000 m/s = .05 MWh
    Launch frequency: 20 / hour
    Two weeks of power would require ~7000 vehicles
    Total guidance system mass: 350T

    Open questions:
    Mass of track?
    Conversion efficiency?


    1. Why beam power from earth – could you not build the hypothetical microwave tower from simcity 2000 but receiving solar power from panels in a lunar orbit? Then instead of beaming power 250,000km you might be doing just a thousandth of that?


  16. Two additional thoughts:
    Building a tower 4x the height of anything on Earth is not that big of a deal because you have 1/6 the gravity and no wind. It would look quite flimsy to our eyes, but would be perfectly fine.
    What about beaming microwave energy from satellites in lunar orbit, instead of all the way from Earth? There’s talk about beaming microwave energy from Earth orbit down to Earth, despite the risks to birds and airplanes that might get in the beam’s path, so doing the same on the moon should be much safer.


  17. For energy storage, an above-ground flywheel a hundred meters across could store quite a lot of energy. I would build a 50m vertical tower, with weights hanging vertically on cables–initially, just two. As it spins up, they spread out. To add capacity, just bolt on bigger weights. Later, add more cables and more weights, up to dozens or even hundreds.

    You can stop it to work on whenever the sun is shining, immediately after sunrise when it is at its slowest.

    To get a bigger radius, you could use a series of scissoring beams with springs instead of cables, so that as it slows they get shorter. You might get to a km radius that way. A km radius flywheel would be pretty unusual in other places.

    Or, the weights could interlock into a ring as it slows, so that the cables never need to hang vertically.

    Precession as the moon rotates would require some cleverness to counter, but the moon rotates pretty slowly.

    You could launch a vehicle from the end (and a sacrificial counterweight from the other, for balance) when it has spun up enough.


    1. Further notes…

      Increased radius in a flywheel provides lower acceleration experienced by a mass at the rim for a given amount of stored kinetic energy, resulting in less stress on the structural parts of the system, whether radial (via cables connecting across a hub) or circumferential (forming a ring at the edge).

      To minimize stress on the hub tower, mechanisms on the kinetic masses or radial cables would provide dynamic balance, automatically moving a small mass radially along the connecting cable.

      An advantage to relying mainly on circumferential tension structure is that all of its mass contributes to energy storage capacity, as compared with radial cables most of whose mass is moving much more slowly. Thus, a solid ring supported by just enough cabling to support its dead weight when stopped would provide maximally efficient use of material. That represents the end state of construction as mass is incrementally added to the system: a system with just two masses and radial cables is immediately useful, and gets increasingly useful as more mass is added. Once the masses can connect circumferentially, most of the radial cabling can be removed.

      Kinetic mass would be mainly materials extracted locally, starting with lunar regolith loose in bags, later melted into blocks, and finally refined to metal and formed. Over the lifetime of the structure the nature of the mass used would naturally evolve along with the sophistication of the facilities the flywheel provides power storage for.

      Gyroscopic precession forces would be minimized if it were constructed at the lunar pole. A Ferris-wheel-like configuration, vertical at the equator and angled at other latitudes, would also work; it would need a full rigid wheel structure from the outset, although kinetic mass could still be added incrementally. A ride on one of these might be uncomfortable.

      If it turns out that long periods exposed to only lunar gravitation is harmful to human health, habitation (or, anyway, gym) modules could be used as flywheel mass. In that case, one would enter and exit via the hub and lifts running along the radial cabling. Alternatively, smaller wheels at the rim, spinning at the same radial speed but in the opposite direction, could snatch up parcels held up to them on their way past. The terror could be expected to fade with experience.

      In later generations, once there is more experience, there could be reasons to want to add to the system without stopping it. Additional masses would be attached at the hub and “descend” to the rim. On the way out, they would hang lower from the hub until they reach the rim.


  18. I think you dismissed fuel cells too quickly. In particular, they may have similar power density to batteries when considering the whole system, but power really isn’t the limiting factor, as you point out very clearly. In terms of *energy* density, fuel cells should be a huge win, particularly if you are at a large enough scale that you can afford to liquefy the hydrogen and oxygen and have a large insulated tank. Storage efficiency is lower than batteries, but probably comparable to thermal storage, and as you astutely pointed out, solar panels are cheap and light so it’s not a big deal anyway.


    1. Also, if the main power requirement during the winter is for heat, you can use hydrogen combustion, reducing the bed for fuel cells


  19. Quickest short-term solution since payload is now cheap is to do quick modular builds in say 3 locations allowing for constant power from PV in at least 1 site. First settlers (lunatics!?) will be nomads, hopping from base to base with the Sun & power until we get long term battery or thermo power or nuke power sorted. Also allows redundancy & modularity in builds & settlements.
    Next step is then transport between bases. Probably sub-orbital rockets (don’t need starship for 1/6g!). Allows for rapid build of the colony though & spread of tourism/mining, plus good practice for Mars.


  20. Rather than building a 3km tall tower, dump aluminium foil in lunar orbit to reflect light onto your south pole based solar panels during winter.


  21. Quasi closed loop system with aluminum as fuel:
    1. Elysis (Canadian company) has a process to extract Al from alumina (17-18% of lunar regolith), producing pure Al and oxygen as a byproduct (using solar power during lunar day).
    2. During lunar night: aluminum reacts with steam (exothermic reaction), produces heat which is used to run a turbine with e.g., superheated steam; hydrogen & alumina (recycled to Step 1) are byproducts
    4. Oxygen from Step 1 and hydrogen from Step 2 combined in a fuel cell to make water (recycled to Step 2), producing power
    The Elysis process is proprietary and so I’m not sure of the proportions but apart from the seed substances, this process is closed loop and can be scaled.


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