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Comment by RandomInteger4 | Hacker News Reader

Moon hotels. Tell Trump he can put his name on it and we'll have them in no time. But seriously, if the safety issues with space travel are reduced to a minimum, and we figure out how to make that whole escape from orbit thing a bit cheaper, I think this is the first interesting activity that people would pay money for.

EDIT: Honestly if someone is downvoting me because I mentioned Trump in a non-partisan fashion, that's rather petty.

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I was close to down voting not for trump but for "more rockets for moon tourism". We are already messing up our planet with air travel. IMHO, make moon tourism a thing, with the associated rise in rockets launched, and rockets go from "amazing tech that sciences" to "yet another thing super rich people use for enjoyment while fucking over literally the entire planet"

From what I understand, the amount of stuff rockets carry into literally every layer of the atmosphere is already concerning. If someone can put my mind at ease with a paper not written by Big Rocket I'd be all the happier. ;)

"From what I understand, the amount of stuff rockets carry into literally every layer of the atmosphere is already concerning. If someone can put my mind at ease with a paper not written by Big Rocket I'd be all the happier. ;) "

Not an expert, but I believe the Saturn moon rockets did run on hydrogen, so there should not have been much pollution. The falcon-9 though runs on RP-1, refined kerosine.

The Saturn V only used hydrogen for its third stage. The first two stages (i.e. the ones that operated while it was still in the atmosphere) ran on RP-1.

Are there fundamental flaws with using hydrogen in the atmosphere?

Too volatile to handle?

The Delta IV Heavy uses hydrogen fuel even for the first stage:

https://en.wikipedia.org/wiki/Delta_IV_Heavy

Hydrogen offers excellent ISP but poor volumetric energy density, and it needs to stay much colder than oxygen to remain liquid. Fuel tanks for containing hydrogen tend to be more complicated and larger than those for other liquid rocket fuels. Upper stages see more relative benefit from the higher performance achievable with hydrogen fuel. The cost:benefit comparison has led to most rockets not using hydrogen for the first stage.

Thanks dor the detailed explaination!

But I assume

"The cost:benefit comparison has led to most rockets not using hydrogen for the first stage."

nobody factored in the long term climate cost with kerosine. But since most hydrogen is generated with fossils, it might not make a big difference right now.

Hydrogen yields higher efficiency (specific impulse) with lower thrust. Larger-molecule fuels, such as kerosene, have higher thrust and lower efficiency. When in the atmosphere, the rocket engines are spending a lot of energy counteracting gravity, so higher thrust is important. Once in orbit, efficiency is far more important (indeed, some deep space engines such as ion engines produce only millinewtons of force, but are very efficient.)

Consider that the moon hotel would enable Moon solar power plant

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