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Comment by iamthemonster | Hacker News Reader

If you were on the moon you would only need to match spinlaunch's launch velocity of 8000 km/h and you wouldn't even need rocket fuel. You would only need a $200 battery and a $200 solar panel to fling 1 kg into space every hour of the day, assuming 100% efficiency.

I was quite surprised to discover how cheap it is to fling chunks of the moon into space. I mean... I'm not sure why you'd bother, but still, it interested me.

(My working: 2380 m/s escape velocity, 0.5 * 2380^2 energy in Joules required, convert to kWh, googled battery and solar panel costs, totally didn't consider efficiency anywhere)

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> fling chunks of the moon into space. I mean... I'm not sure why you'd bother

Hmm. The Moon Is a Harsh Mistress builds a compelling case to do so.

All that sweet, sweet lunar wheat.

Or space rocks ... Lots of big space rocks ;-)

>I was quite surprised to discover how cheap it is to fling chunks of the moon into space.

It is easier to send something to low Earth orbit from the Moon than from Earth.

> I was quite surprised to discover how cheap it is to fling chunks of the moon into space. I mean... I'm not sure why you'd bother, but still, it interested me

Mass drivers are powerful weapons. Haven't you read the classic "The Moon is a Harsh Mistress"?

If your goal is a weapon system, there are far, far better options. Like rods from god and orbital nuke launchers, it just has too many limitations to be practical.

now you have me imagining some strange field of lunar rock flingers, ejecting mass into space ceaselessly until the sun stops, all for a very motivated PhD student's thesis

How about liquid oxygen and aluminum tanks made from high-temperature electrolysis of regolith? Now you have rocket propellant and parts. 90% of the propellant mass that Starship uses is oxygen. If you could refuel Starship in space this way, it would reduce the number of launches needed from 10 to 1 (well, maybe 2 if the lower-density liquid methane is too bulky for one launch).

> I'm not sure why you'd bother

Raw material for space station construction.

Could we throw enough moon rocks into an orbit which would block some % of sunlight hitting the earth (to cool it)?

Among other drawbacks, that would interfere with satelites

I think I'd prefer no satellites to global warming

Why? You like being cold?

I would be very carefull with any climate intervention where there is no easy way to adjust the effect. Preferably whatever we do should be part of a designed-in feedback loop to stabilize the climate.

You wouldn’t bash in a window at work if the office is too hot. It is super easy to see that that is a hard to undo intervention you might regret later. The climate of a whole planet is much more complex than that, much less well understood and we only have one. Be suspicious of any plan which doesn’t have “knobs” we can adjust as we learn more.

Also we now maybe have the tech to make moon trebuches to fling dirt to shade our planet. Do we have the tech to clean it up too if it blows back in our face? Will we always have the tech? Civilization is not a straight linear progression. Even if we could do the adjustment now who knows maybe thousands of years from now humanity won’t be able to do the same. So it is better if we design our interventions such that they are making the climate stable even without continous tweeking by a technologically advanced civilization. I don’t know how this would be possible without properly designed feedback loops. And I don’t know what feedback system a dust cloud could have.

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