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Old 10-14-2022, 12:43 PM   #13 (permalink)
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While brushing up on the tyranny of the rocket equitation, I was wandered into mass drivers, which led me down the Youtube rabbit hole, and this video is where I landed last night.

Rockets are 90% fuel, 8% rocket, and 2% payload.
Boeing 737 is 25% fuel, 50% plane, 25% payload
Toyota Camry is 3% fuel, 66% car, 30% payload

Obviously building any sort of colony anywhere else, or mining other objects in our solar system is going to require getting materials into space more efficiently than a rocket can deliver.

While watching the video I was assuming the entire structure would have to be built in space, which would totally defeat the purpose of building such a structure. It would actually levitate from the ground as the internal mass was accelerated beyond orbital velocity.

Originally Posted by Piotrsko View Post
Take a CO2 cartridge and poke a hole in it, let the gas out really fast and they frost up. My theory is rusty but I think some dude named Pascal had things to say about pressure vessels. Now it might be that the CO2 stream isn't colder, but something is radiant to get the frost.

Otoh, perhaps you mean to say that compression could occur without a major heat rise. No practical expertise there, I have no reason to compress CO2
Temperature is a measure of the concentration of heat energy, not the total quantity of energy. Sparklers emit sparks up to 3,000 F, but it's such a small amount of energy that you hand can hardly feel it.

Compressing a volume of gas concentrates the heat energy into a smaller space, raising the temperature. Once a temperature differential exists between the compressed gas and the surrounding environment, entropy tries to equalize equalize the temperature differential, and energy from the hot gas is lost to the environment until they reach equilibrium.

A compressed gas that is allowed to expand distributes the heat energy over a larger volume, absorbing heat around it and causing the vessel to become cold and frosty.

Losses can be minimized with insulation. I expect losses are minimized if the compressed gas is immediately released too, but then that defeats the point of compressing it in the first place.

The thing that fascinates me is endothermic chemical reactions. Usually chemical reactions produce heat (it's impossible to produce cold, because it isn't a thing), but endothermic reactions absorb heat to facilitate the reaction, and that's why cold packs work.
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Last edited by redpoint5; 10-14-2022 at 01:17 PM..
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