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Comment by Zenst | Hacker News Reader

Slight tangent, but I'm wondering and kinda dreading the day that some company pops some large advert upon the Moon so it can be seen on Earth.

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I wouldn't be too worried. Copernicus crater is 93km in diameter... Which is the circle on left hand side of moon.

Anything truly visible from Earth would be absolutely massive and we haven't done anything like that scale on Earth even yet...

Thanks. Picture for anybody else curious:

https://en.m.wikipedia.org/wiki/Copernicus_(lunar_crater)#/m...

Nothing a series of nukes couldnt solve.

It's easier to do that kind of thing on the moon, though, which is the color of asphalt and has almost no atmosphere. If you can manage ISRU, you could sputter a layer of quicklime onto the regolith from a lunar rover; if you fountain the molecules out the top of the rover, you could spread them over an almost arbitrarily large part of the moon. (Maybe a different abundant white mineral with a lower boiling point would be more practical.) If your pixels were 20 km square and 10 microns thick they would only require 13000 tonnes of quicklime each.

Still insane scale of project. Let's say you can spread 10m wide line, you can fit 2000 of these in 20km square each 20km long. At reasonable 40km/h speed it would mean about 1000 hours. ~41,7 days per pixel... Not counting logistics of getting the material ready and so on. And how many pixels you need? Also 10m wide spread might be optimistic, considering moon isn't easiest thing thing to navigate at this scale.

I was suggesting that you spread a line 20km wide by blowing the "paint" molecules out the top of your rover, which makes it 2000 times faster than what you're suggesting. You can't do that on Earth because your vaporized paint immediately crashes into air when it gets out of your smokestack, so it doesn't go high enough to land 10km away, and so smoke just sort of blows around in the wind.

(I think in reality it might be more like only 100 times faster, because I don't think you can maintain 40km/h.)

Hmm, let's say 100 times faster that is 10 hours. Pushing 1300 tons an hour or 0.36 tons per second of any material through sounds somewhat extreme. Hmm, 529 kw for 1 km height. I wonder what height is actually needed for 10km wide spread. That is quite a bit of power specially from rover. Considering it's solar panels would be getting coated at same time... And I suppose dragging kilometers long cable isn't an option.

A kilometers-long cable sounds totally reasonable to me, and you can put an umbrella over the solar panels if the paint is raining at a different angle from the sunlight. There are a lot of existing machines on Earth that handle volumes like that in six times stronger gravity. Big Muskie's shovel held 295 tonnes of rock; over its 20-year lifetime it averaged about 1.5 tonnes per second.

It is much easier to put such advertisement on the LEO.

That sounds like it would be impossibly expensive

i heard at one point Carl Sagan was approached by some element of the US government about possibly calculating what kind of nuke thet'd have to set off to be visible on earth.

oh! seems he was a grad student at IIT Chicago and indeed worked on Project A119! i didnt know it was early in his career, or that he'd accepted. https://en.wikipedia.org/wiki/Project_A119#Research

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