Are you accounting for the weight of the wire? A mere 12AWG aluminum wire the circumference of the moon (10900km) would be 10 metric tonne, but I’d expect you’d need vastly thicker cable than that. 00 would run you upwards of 200 tonne, and that’s probably nowhere near sufficient either. Honestly not sure how to do the math to figure out how heavy a cable you’d need at those kinds of lengths.
No, a fairly thin wire is sufficient. Something like a 1 mm aluminum wire with some surface protection would weigh a few tons for a 628 km route (100 km from a pole). Note that I’m assuming the first version won’t go around the full equator; it just needs to be far enough from a pole that the sun is a few degrees over the horizon, which means you should be able to find many spots along the way with good visibility.
The wire only needs to carry an amp or so. Each solar station along the way boosts the voltage. A 1 mm diam Al wire would be around 20 kOhm, which is a lot–the voltage drop would be 20 kV all the way around! But that’s ok, we can have a dozen stations, each of which boosts the voltage by 10 kV, so the 6 that are online at any time will give 60 kV, leaving a constant 40 kV @ 1 A of good power (equivalent to the reactor above). That’s not bad for a starting version.
There are a number of other details that I could go into, and quite a few more that I haven’t thought of yet, but that’s the basic gist.
Leaving aside the debate about which is the best solution to the problem, I have serious doubts about how much the prior research from Phase 1 will hold up under the current situation, to wit (quoting from the first article):
NASA has discussed building a reactor on the lunar surface, but this would set a more definitive timeline — according to documents obtained by POLITICO — and come just as the agency faces a massive budget cut.
And
The reactor directive orders the agency to solicit industry proposals for a 100 kilowatt nuclear reactor to launch by 2030, a key consideration for astronauts’ return to the lunar surface. NASA previously funded research into a 40 kilowatt reactor for use on the moon, with plans to have a reactor ready for launch by the early 2030s.
So as I read it, they want to keep nearly the same timeline, but a reactor with 2.5 times the power generation, and AFTER major budget cuts. This sounds like it would be quite hard to do with MORE money than the prior efforts, much less with far less money to apply. Though I grant that the current budget plans seem to offer more money for manned flight and crippling all other purposes.
Leaving out the other cynical political considerations that may apply, I wonder if this is designed to “encourage” various members of the earlier teams or new partners to deflate costs (whether less profit based, or to below their own cost) to curry favor with the administration, or even a cynical ploy to punish Elon for his prior “disloyalty” by demanding he provide the means by 2030 or have his company nationalized because this is “key to winning the second space race”.
Though again, I fully grant that if Trump or a (successful) heir (be it his kids, or some other sycophant) is still in a position to do so by 2030 we have a LOT of other more serious problems to worry about.
Yes, nuclear energy is the most ‘independent’ power source - in the sense of needing no refueling, no sunlight, etc. It has dangers of course, but there are 100 other things that could kill the astronauts, and a reactor is the most reliable power source they could have.
I find this extremely surprising, but I can’t see why you’d be wrong. Huh. Intuition completely off base.
It’s definitely counterintuitive, but only because we rarely think of high voltage, medium current applications. If it were 240 volts, you’d need a huge wire for any significant power. But at 40 kV, even 1 A gives a very decent amount of power.
There are high losses, but they’re distributed around the entire loop. 20 kW loss seems like a lot, but not so much when dissipated equally along >600 km of wire.
Another nice feature is that you can tap into the power at any point along the route, and you don’t even need sophisticated power systems if the needs are modest. Need 100 W for a radio relay or something? Easy–you just need a design that assume a constant current, varying voltage source and gives you a constant voltage output. Just cut the loop at the desired point and hook the wires up. You do want to make sure that every device along the route is extremely reliable with multiple backups, though, since any one failure brings down the whole system (like old-school Christmas lights).
At 100 km from a pole, there’s about 2.9 km of “drop” relative to the pole, which I think gives a fair margin for finding good spots. You’d probably still want to put the solar stations on a modest hill or something, but the requirements aren’t nearly as stringent as the “peaks of eternal light” mentioned above. In fact I suspect you could get quite a bit closer to the pole, but I picked 100 km as a nice round number.
I haven’t worked out yet whether the cable should be suspended, buried, or laying on the surface. Some up/downsides to each. The low gravity and lack of weather on the Moon means a suspended cable isn’t too bad, but it’s still mass that you’d rather not have.
The issue here is that a nuclear reactor can be built and tested on Earth, while your idea can only be built and tested on the moon. So let’s call it “Phase II”.
It’s exactly the opposite. Solar panels work exactly the same on the Moon as on Earth (or in orbit), as do power converters and the like (some things need to work in a vacuum, and in the presence of lunar dust, etc., but those can be simulated).
But every nuclear reactor depends in some way on gravity. Anything with fluid works differently in different gravity. And we can’t test 1/6 g on Earth. Does your reactor design depend on convection for passive safety if the pumps fail? Whoops–that only works 1/6 as well on the Moon.
Obviously, I’m not against nuclear power! And the designers know all these things. But a reactor like this is an extreme challenge. Solar power on the other hand is highly understood.
No but the consequences of a meltdown are a lot more serious on Earth than they would be on the moon. The worst case scenario of a nuclear reactor melting down on the moon would be irradiating a small uninhabited area with no danger of the radiation being spread by the climate.
Interesting. I suppose then that one more piece of technology we need to develop is a nuclear reactor that is not dependent on gravity. Something like that would definitely be necessary for space travel in the future.
The Soviet Union developed some reactors:
So, it’s not that it can’t be done. Just that it takes a different approach. The TOPAZ reactors were only 5 kW and I’m not sure what kind of safety systems they had (my guess is that since they were intended for use on unmanned systems and, well, it was the Soviet Union, the answer is “not much”).
The TOPAZ reactors also used thermionic conversion–basically a solid state heat->electricity generator. These are reliable and simple but not very efficient. So they avoided a fair bit of the complexity by not needing a turbine, Stirling engine, etc.
Sounds like an interesting direction for research.
It’s for use to power moon-based stuff, not sent to Earth.
Not the kind of closed cycle one they’re proposing.
Pretty sure it will.
Thanks. As I said, I’m not a physicist.
This is just not true. Boiling and pressurized waters reactors built for use on Earth are designed to account for gravity and utilize the gravitational field of the planet for natural convection or to aid with safety mechanisms because they operate on Earth. This would almost certainly not be a reactor using water as a coolant. The Kilopower Project that immediately proceeded this designed and built the Kilopower Reactor Using Stirling TechnologY reactor with a solid state core using liquid sodium heat pipes to convey thermal energy to a Sterling cycle generator. Other systems using such as high temperature noble gas (typically helium) or other salts could also be used. We use water as a coolant on Earth because it is readily available, virtually free, and has some nice phase change properties but it is also problematic in many ways as anyone familiar with pressurized steam systems can readily attest.
Stranger
Dumb question of mine, but wouldn’t liquid sodium function similarly to water as a reactor coolant since it’s also just a liquid (in terms of being gravity-effected?) Although yes, you pointed out that helium gas or other things could be used instead, and I’m assuming liquid sodium doesn’t turn into “sodium steam”.
Everything old is new again.
Isn’t this putting the cart before the horse, so to speak? Is it assumed that the US will have a permanent manned base on the moon and that a nuclear reactor will be needed to provide power to it?
Although the density of liquid sodium is in a comparable range to liquid water, the viscosity is about three orders of magnitude greater than water @ STP, and it won’t boil off and go through a phase change at 100 ºC like water; the vapor temperature of pure sodium is ~600 ºC and even higher for many sodium salts like NaK and NaF. It also isn’t a moderator so it isn’t used as a fail-safe the way water is in many PWR and BWR systems. Despite the claim that it would be impossible to design or test a reactor on Earth intended for use on the moon because of the affect on natural convection, this just isn’t true. A system in which convection is heavily dependent upon the weight of fluid and pressure due to depth would be affected (albeit in ways that could be simulated) but many systems using natural convection are not strongly coupled to gravity. The KRUSTY experimental reactor linked above uses sodium-filled heat pipes to convey thermal energy in which natural convection (from the hot end to the cold end) is used to pump the fluid through vapor flow down the center from the evaporation region to the condensation region. Such a device on the scale being considered for this size of reactor will have negligible difference whether it is operating in a 1 g field or a 1/6 g field.
The objective is a permanently (or at least, indefinitely) crewed base, and as discussed above nuclear fission power is really the only way to assure sufficient power for all of the needs (filtering air and water, environmental control, computing, et cetera). Unless, of course, you’re going to send a team of linemen up to string hundreds of kilometers of power line encircling the body and build multiple solar arrays, all of which would be vulnerable to both natural hazards (degradation from unfiltered UV exposure, dust, micrometeorites) and intentional sabotage by an opposing power. Whether this is something that is actually needed for any useful purpose is another question.
Stranger
My understanding is that the ISS has cost billions but hasn’t really justified itself. So why would a permanent manned lunar base be needed?