41 ms·

Let's assume 10mm copper wire to the other side of the moon. 3000km long copper wire 10mm in diameter will have 600 ohms resistance. The amount of copper needed

by dvh 4y ago

Let's assume 10mm copper wire to the other side of the moon. 3000km long copper wire 10mm in diameter will have 600 ohms resistance. The amount of copper needed is 235 m³, copper at 9t/m³ weighting 2115 tons in total or 21 starship flights costing $21 milion.

Aspos 4y ago
On poles it would be a few km run to the nearest peak of ethereal sunshine, not 3000km to the other side of the planet. Would heat pumps work on the moon?
- XorNot 4y ago
  Yes, provided they were ground sourced.
orbital-decay 4y ago
>total or 21 starship flights costing $21 milion Where can I book a Starship flight for $1M?
- ben_w 4y ago
  While I think even twice that is more than a bit optimistic, this story was claiming a target price of $2m/launch: https://www.space.com/spacex-starship-flight-passenger-cost-elon-musk.html https://www.space.com/spacex-starship-flight-passenger-cost-... But even at $100m/launch, a big fat copper wire (IIRC aluminium is better per unit mass) would still make more sense than shipping up a nuclear reactor or a huge pile of batteries, and that part of this hypothetical mission would still be about 80% cheaper than the JWST.
  - skykooler 4y ago
    Aluminum is also probably better because it’s easy to source on the moon - many of the surface rocks are made of aluminum oxides. Copper, on the other hand, would need to be entirely transported from Earth.
    - ben_w 4y ago
      Indeed. I wonder, how hard is it to make aluminium from the oxide if you're bootstrapping and in a vacuum? I know the normal process is "melt it with added cryolites and apply current for electrolysis", but if the goal is low mass rather than good energy efficiency, can you do it a different way? Like, what happens if you focus sunlight and just melt it, does the oxygen bubble out in a vacuum, or is this just going to do vapor deposition of sapphire on all nearby surfaces?
      - skykooler 4y ago
        I believe molten alumina does not separate naturally - you’d still need to electrolyze it. This can be done without cryolite although at higher temperature and correspondingly higher energy usage. Otherwise the aluminum and oxygen would remain bound while they evaporate.
  - hericium 4y ago
    There's a price calculator available: https://www.spacex.com/rideshare/ https://www.spacex.com/rideshare/
    - ben_w 4y ago
      Yeah, but (on mobile at least) that's just Falcon 9 ride-shares to [SSO, LEO, polar], not dedicated Starship to the moon. Starship is supposed to be cheaper, the moon is definitely more expensive.
  - dotnet00 4y ago
    The $/launch numbers don't account for the refueling flights, which will be necessary to get to and return from the lunar surface. That would bump that number up to ~$10m/$20m or so. Still ridiculously cheap and not likely to be anywhere close to the price charged as it would absolutely sink the rest of the market, which SpaceX is not interested in doing.
am_lu 4y ago
There wont be much left on the other end because of volt drop in cables. But can be possible to make it into a HVDC transmission line. Will add bit of weight on the starship.
- ben_w 4y ago
  600Ω (WolframAlpha gave me 510, but let's go with the bigger number) isn't that bad, and you don't need anything expect bare metal to run HV on the moon because both the vacuum and the regolith are already insulators.
- Oxidation 4y ago
  You definitely need HV. At 100kV and 10A, the lost power if you send 1MW is around 60kW: a fairly serviceable 6% or 20W/km. However, your losses at a fixed voltage scale quadratically with your power draw: you'd lose 24% of 2MW. If you sent it at 1000V, the I²R losses to send 1000A over that cable outweigh the transmitted power by 600 to 1 and your cable is burning 200kW per kilometre. Which in a vacuum would probably just melt it in fairly short order. Which is why the bigger HVDC links get, the higher the voltage: there's a 1MV+ system in China that sends 12GW over 3000km. Also I'm not sure how lunar regolith will work with regards to the "earth" return path so you might well actually need two wires.
whycome 4y ago
How awesome would it have been if Artemis actually carried a payload to just dump off on the moon? It's just so absurd that this feat of engineering and rocket science just did a fly by/test.
Gravityloss 4y ago
Payload to low earth orbit might be 100+ tons each. But payload to lunar surface is a small fraction of that. We could assume 10 tons. So 210 starship flights. One can see pretty quickly that any larger constructions far from earth would really benefit from maximum use of local materials.
greenbit 4y ago
Local aluminum will be cheaper, and stonkin' high voltage will be needed to combat the ohmic losses. The 'atmosphere' on the moon is rather extremely dry, so corona losses shouldn't be an issue, you could probably run north of a megavolt w/o too much trouble. Now, you could lay both conductors in parallel and only need to build the power line half-way around the moon, probably save some dough on prospecting for and constructing pylon sites that way. Alternatively, you could run a single conductor all the way around. Doing that, you could establish a lunar scale magnetic field, though it'd probably be pretty wimpy unless you ran serious kA (MA?) of current, which would mean much bigger conductors etc, but it's fun to think about. Heck, with a loop that big, you'd probably get significant induction from the solar magnetic field .. which might be something to harness, or might just be a headache for your line operators.
- 6177c40f 4y ago
  This seems like a chicken-and-egg problem. Wouldn't you need power in the first place (and therefore transmission lines) to even extract and refine aluminium locally?
- IIsi50MHz 4y ago
  > Doing that, you could establish a lunar scale magnetic field, though it'd probably be pretty wimpy unless you ran serious kA (MA?) of current, which would mean much bigger conductors etc, but it's fun to think about. Or a stator in orbit? But hrm… for Mars the same idea needs only 1T to 1.5T stator but has to place xt at lagrange between Mars and Sun. So, I naively guess for the stator to be far enough away that the deflected solar wind merges after the moon could /reall/ mean that the stator would be at lagrange between Earth and Sun, which could have perhaps interesting effects on Earth.
burnished 4y ago
Nice. That almost sounds cheap.

by dvh 4y ago

Aspos 4y ago

On poles it would be a few km run to the nearest peak of ethereal sunshine, not 3000km to the other side of the planet. Would heat pumps work on the moon?

XorNot 4y ago
Yes, provided they were ground sourced.

orbital-decay 4y ago

>total or 21 starship flights costing $21 milion Where can I book a Starship flight for $1M?

ben_w 4y ago
While I think even twice that is more than a bit optimistic, this story was claiming a target price of $2m/launch: https://www.space.com/spacex-starship-flight-passenger-cost-elon-musk.html https://www.space.com/spacex-starship-flight-passenger-cost-... But even at $100m/launch, a big fat copper wire (IIRC aluminium is better per unit mass) would still make more sense than shipping up a nuclear reactor or a huge pile of batteries, and that part of this hypothetical mission would still be about 80% cheaper than the JWST.
- skykooler 4y ago
  Aluminum is also probably better because it’s easy to source on the moon - many of the surface rocks are made of aluminum oxides. Copper, on the other hand, would need to be entirely transported from Earth.
  - ben_w 4y ago
    Indeed. I wonder, how hard is it to make aluminium from the oxide if you're bootstrapping and in a vacuum? I know the normal process is "melt it with added cryolites and apply current for electrolysis", but if the goal is low mass rather than good energy efficiency, can you do it a different way? Like, what happens if you focus sunlight and just melt it, does the oxygen bubble out in a vacuum, or is this just going to do vapor deposition of sapphire on all nearby surfaces?
    - skykooler 4y ago
      I believe molten alumina does not separate naturally - you’d still need to electrolyze it. This can be done without cryolite although at higher temperature and correspondingly higher energy usage. Otherwise the aluminum and oxygen would remain bound while they evaporate.
- hericium 4y ago
  There's a price calculator available: https://www.spacex.com/rideshare/ https://www.spacex.com/rideshare/
  - ben_w 4y ago
    Yeah, but (on mobile at least) that's just Falcon 9 ride-shares to [SSO, LEO, polar], not dedicated Starship to the moon. Starship is supposed to be cheaper, the moon is definitely more expensive.
- dotnet00 4y ago
  The $/launch numbers don't account for the refueling flights, which will be necessary to get to and return from the lunar surface. That would bump that number up to ~$10m/$20m or so. Still ridiculously cheap and not likely to be anywhere close to the price charged as it would absolutely sink the rest of the market, which SpaceX is not interested in doing.

am_lu 4y ago

There wont be much left on the other end because of volt drop in cables. But can be possible to make it into a HVDC transmission line. Will add bit of weight on the starship.

ben_w 4y ago
600Ω (WolframAlpha gave me 510, but let's go with the bigger number) isn't that bad, and you don't need anything expect bare metal to run HV on the moon because both the vacuum and the regolith are already insulators.
Oxidation 4y ago
You definitely need HV. At 100kV and 10A, the lost power if you send 1MW is around 60kW: a fairly serviceable 6% or 20W/km. However, your losses at a fixed voltage scale quadratically with your power draw: you'd lose 24% of 2MW. If you sent it at 1000V, the I²R losses to send 1000A over that cable outweigh the transmitted power by 600 to 1 and your cable is burning 200kW per kilometre. Which in a vacuum would probably just melt it in fairly short order. Which is why the bigger HVDC links get, the higher the voltage: there's a 1MV+ system in China that sends 12GW over 3000km. Also I'm not sure how lunar regolith will work with regards to the "earth" return path so you might well actually need two wires.

whycome 4y ago

How awesome would it have been if Artemis actually carried a payload to just dump off on the moon? It's just so absurd that this feat of engineering and rocket science just did a fly by/test.

Gravityloss 4y ago

Payload to low earth orbit might be 100+ tons each. But payload to lunar surface is a small fraction of that. We could assume 10 tons. So 210 starship flights. One can see pretty quickly that any larger constructions far from earth would really benefit from maximum use of local materials.

greenbit 4y ago

Local aluminum will be cheaper, and stonkin' high voltage will be needed to combat the ohmic losses. The 'atmosphere' on the moon is rather extremely dry, so corona losses shouldn't be an issue, you could probably run north of a megavolt w/o too much trouble. Now, you could lay both conductors in parallel and only need to build the power line half-way around the moon, probably save some dough on prospecting for and constructing pylon sites that way. Alternatively, you could run a single conductor all the way around. Doing that, you could establish a lunar scale magnetic field, though it'd probably be pretty wimpy unless you ran serious kA (MA?) of current, which would mean much bigger conductors etc, but it's fun to think about. Heck, with a loop that big, you'd probably get significant induction from the solar magnetic field .. which might be something to harness, or might just be a headache for your line operators.

6177c40f 4y ago
This seems like a chicken-and-egg problem. Wouldn't you need power in the first place (and therefore transmission lines) to even extract and refine aluminium locally?
IIsi50MHz 4y ago
> Doing that, you could establish a lunar scale magnetic field, though it'd probably be pretty wimpy unless you ran serious kA (MA?) of current, which would mean much bigger conductors etc, but it's fun to think about. Or a stator in orbit? But hrm… for Mars the same idea needs only 1T to 1.5T stator but has to place xt at lagrange between Mars and Sun. So, I naively guess for the stator to be far enough away that the deflected solar wind merges after the moon could /reall/ mean that the stator would be at lagrange between Earth and Sun, which could have perhaps interesting effects on Earth.

burnished 4y ago

Nice. That almost sounds cheap.