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Old 03-19-2019, 12:12 PM
 
Location: Somewhere in northern Alabama
18,547 posts, read 55,485,543 times
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Quote:
Originally Posted by Dane_in_LA View Post
Still not seeing anything worth lowering oneself into that gravity well for, though. Just being there for the sake of being there seems a little futile. Let's get to the asteroids.
Other than what I listed? The moon has much the same mineral resources as the earth, but its gravity well is MUCH more shallow for interplanetary work. Say you wanted to construct a spaceship the size of an aircraft carrier (something that may be needed within a hundred years or less). Smelt and form the parts from moon-sourced material, form the parts there into modules, and then use an solar powered electric railgun to lift them to orbit without the high-G stress of an earth rocket launch. With low gravity, no atmosphere, and lots of land to make what would essentially be a short section of tilted railroad, there is no need for streamlining or structural components with the sole purpose of launch survivability.

The chances of humans building any really large space construction from earth sourced material is zip. The energy costs and environmental costs are just too high. The moon's escape velocity is 2.38 km/s (less than 3 times the speed of a 30 cal bullet) compared to the 11 km/s to escape Earth's gravity.

Asteroid mining has the current public imagination, but it suffers from high energy costs due to distance and relative velocities compared to earth orbit velocity.

Try not to forget that long-term SAFE space habitats need lots of mass to mitigate the effects of various radiations and protect against small particles. Even the ISS doesn't fully meet the requirements; also, with Nautilus-X dead, the moon is about the only gravity source short of Mars that might keep people in space long term.
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Old 03-20-2019, 09:06 PM
 
Location: Earth
4,837 posts, read 3,295,492 times
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Quote:
Originally Posted by davidt1 View Post
I knew it. No one wants to admit it but China's moon landing compels the US to answer the challenge just like with the Soviet Union earlier. We should build a manned base on the moon and claim it for ourselves.

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Old 03-29-2019, 12:06 PM
 
33,821 posts, read 17,312,451 times
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Quote:
Originally Posted by harry chickpea View Post
Say you wanted to construct a spaceship the size of an aircraft carrier (something that may be needed within a hundred years or less). Smelt and form the parts from moon-sourced material, form the parts there into modules, and then use an solar powered electric railgun to lift them to orbit without the high-G stress of an earth rocket launch.
Sorry, but "smelting and forming" implies an entire mining, refining and metalworking industry present on the surface of the Moon. How did that happen? And railguns launch with hundreds of times the G load of a chemical rocket launch.
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Old 03-29-2019, 12:47 PM
 
Location: Somewhere in northern Alabama
18,547 posts, read 55,485,543 times
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Quote:
Originally Posted by Dane_in_LA View Post
Sorry, but "smelting and forming" implies an entire mining, refining and metalworking industry present on the surface of the Moon. How did that happen? And railguns launch with hundreds of times the G load of a chemical rocket launch.
Correct on the need for a metalworking industry of some sort. That will take planning and time, with early attempts being relatively small scale designed to create the materials for larger scale versions. Railguns, as used for weaponry do operate as you say. However, that is not required. Aircraft carrier launchers are perhaps a closer analogy:

https://en.wikipedia.org/wiki/Electr..._Launch_System
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Old 03-29-2019, 01:34 PM
 
33,821 posts, read 17,312,451 times
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Quote:
Originally Posted by harry chickpea View Post
Correct on the need for a metalworking industry of some sort. That will take planning and time, with early attempts being relatively small scale designed to create the materials for larger scale versions. Railguns, as used for weaponry do operate as you say. However, that is not required. Aircraft carrier launchers are perhaps a closer analogy:

https://en.wikipedia.org/wiki/Electr..._Launch_System
Well, yeah, but... There are factors dictating G-forces for a railgun/EM catapult launch - any acceleration at all, actually: Escape velocity needed and the time/distance used for acceleration.

Quick math - feel free to check - based on 5Gs (modest, but not low) and lunar escape velocity:

5 Gs is 49 meters per second squared. Lunar escape velocity is 2300 m/s

Assuming start from rest, time elapsed in acceleration is final v divided by acceleration, so - 46.9 seconds, give or take. Distance elapsed is 0.5 times acceleration times time squared, so - 53980 meters of railgun, or 33.5 miles. That's one heckuva railgun.

Nah, lets launch some hydrogen for fuel instead. We can load it in some suitably magnetic pressure vessel and launch at 100G, hydrogen won't complain. Elapsed time 2.3 seconds, railgun at a mere 2700 meters or 1.7 miles. Now we're cooking. Of course, we'd have to decelerate it where it's going to be used.

TANSTAAFL was conceived in a novel about lunar settlements, very suitably.
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Old 04-01-2019, 10:58 AM
 
Location: Mars City
5,536 posts, read 2,412,499 times
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This is still the same stuff that we've seen in each administration over the past 20 years. All talk, little worth.

Step back from the blinding spotlight, and the "great and powerful Oz" effect, and see reality.
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Old 04-26-2019, 04:12 AM
 
Location: PRC
3,250 posts, read 3,365,783 times
Reputation: 2950
This is going to be unpopular with some of you. However,

"Going to the Moon" does not mean building a base on the Moon. It is politi-speak for building a space station off to one side of the Moon as a way to appease both the folks who want a base and the folks who want a space station. There are no plans to build a space station on the Moon, maybe an outpost, a couple of tents or a Nissen Hut, yes, but nothing anyone thinks of as a proper base. No-one has told us why this is, but anyway...

After all this time, they must have got permission to do 'visits' but not permission to build a base there. :-)
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