Let's bring the moon home

[Finagle]

*Originally posted by Ponder Stibbons *
**
Well, Finagle, since you’re gnawing at this missing tooth anyway, how about considering the Mickey-mouse scenario posted above, where they simply hollow out the moon, leaving the Disney-fied remains of the (vast majority of the mass of) moon in orbit and only bring down a hollowed-out (and, one presumes, structurally reinforced) moon? Again, this would probably require the intervention of some less-than-bright passing super-alien … :dubious: **

Very well, because you asked. More musings with little actual calculation or actual engineering experience to back it up.

So we have a hollowed out shell, 3000 km in diameter, made of soft, frangible material. But let’s pretend that moon rock is strong enough to withstand the stress, or that our alien beings have thoughtfully reinforced it with alien Duct Tape so that we don’t have to worry about falling scree.

What do we structurally reinforce our sphere with? 2x4’s aren’t going to cut it. Neither will steel. Maybe carbon nano-fibers or Ringworld * scrith * would do the job. We’re still talking about a Civil Engineering nightmare. Gravity wants to make it fall down. Tides want to make it disintegrate. And now you have to worry about pressure variations as well.

Do we keep a vacuum in the center of your hollowed out sphere? So much of it is going to be out of the atmosphere as it is. You have to cope with the pressure of the atmosphere on the bottom 100 miles or so, but that’s minor compared to the other forces involved. I’m pretty sure you don’t want to pressurize the interior to help support the structure – for one, we’d run low on atmosphere. For another, you’d probably have to compress it to well beyond the tensile strength of the structure. And finally, you’d hate for it to spring a leak.

The most obvious choice is to put in a few several-kilometer wide vent holes and let the pressure equalize – but there are some problems with this approach.

As the rotation of the sun takes the moon shell into and out of sunlight, it’s going to alternately become very hot or very cold. (It may in time equalize. Dunno.) Add thermal stresses to your list of civil engineering problems. The air contained in the shell is going to undergo pressure changes as the temperature of the shell varies. Depending on the temperature equilibrium achieved, we might see gales of scorching hot or bitterly cold winds emerging from the vent holes. If we vent the ocean waters as well, as suggested in the OP, those winds would be either raging thunderstorms or blizzards.

What else does the shell do to the Earth’s weather? Messes it up good, I will think, even if the moon doesn’t act as a giant heat sink and either freeze or burn us all. Off the top of my head, we’ve got a 3,000 kilometer mountain blocking ocean and wind currents. At the very least, we have severe and unpredictable climactic changes and can stop worrying about piddling changes due to Freon and greenhouse gases. The huge volume of the sphere is going to block sunlight from much of the surrounding ocean. Vast areas will see sunlight only 1/2 the day. Some areas will be pretty much in perpeptual eclipse. Without solar radiation, the equatorial regions will drop in temperature. Another arctic region will form, surrounded by a ring of perpeptual hurricanes. (It’s not going to be easy to get to this tourist mecca.)

But what about the reflected sunlight hitting the moon’s surface? Some of is going to reflect back on Earth. Maybe instead of polar regions we’ll have extreme temperature variations? Or both? Packing for a trip to the Pacific is going to become very challenging.

How about electromagnetic effects? I’m going out a bit on a limb here, but I’m thinking that if you have an enormous structure, one end in space, and one not, surrounded by howling winds, you might see a few billion EV of static build up. The sphere might be surrounded by a ring of constant lightning. Very pretty and it would save on the lighting bill. Just don’t plan on ever using broadcast transmissions in that hemisphere ever again.
I may have missed a few aspects of the impossibly strong superstructure scenario, but the most positive thing you can say about it is that it doesn’t obviously spell the end of all life on earth as we know it. It just makes it far, far more interesting…

[Mangetout]

*Originally posted by Grey *
**No it’s brilliant. Come on guys, the moon is what? the size of a quarter? Check it out, you hold a quarter up and presto! it covers the moon. Sure the moon might be a little bigger but it’d fit like a treat.

**

I never heard anything so ridiculous; the moon is spherical, so the volume would be at least four or five times that of your quarter. Sheesh, honestly.

[Finagle]

Ah, here’s one aspect of the super-sphere scenario that I missed. The sphere is 3000 km high. Hubble Space Telescope orbits at ~570km. Gone. International Space Station – ~380 km high. Swatted from the sky like a bug hitting a windshield. In fact, any satellite in a near-Earth orbit is going to get swept from the sky. We’ll still have GPS and geo-synchronous satellites won’t be affected (aside from using a bit more of their manuvering fuel to compensate for gravitational fluxes), but all the spy and environmental satellites will be eradicated, with the possible exceptions of those in highly eccentric or polar orbits which might last longer.

The Hubble could be replaced by placing an observatory on the top of the sphere and the lunar shell could be used as a gateway to space, but Earth observation via satellite would become impractical.

[photopat]

Wait a minute. I’ve got it. The moon’s gravity is weaker than the earth’s, right? We’ve seen the footage of the astronauts bouncing around.

Okay, since it’s gravity is weaker, that means acceleration toward the lunar surface is less, so instead of bringing the moon down to the earth let’s just…

don’t get ahead of me now…

bring the earth down to the moon!
Don’t look at me that way.

[Shade]

*Originally posted by Squink *
**You’re right. I’m wrong. Which episode of Baywatch was it ?I shall watch it over and over until I understand the physics ! **

It’s the bit with two great spheres bouncing off each other.

[Shade]

I won’t make any pretense at doing science, just offer a few comparisons to try and imagine the order of magnitude. (The numbers are very rough. ‘Bigger’ means size)

1. The “dinosaur killer” comet was pretty devestating. The moon is 3,000,000 times bigger.

2. Regarding ‘letting it down gently.’ Imagine a space shuttle’s rocket motor. It’s lifting about 1000 tonnes. Imagine a rocket lifting a mountain. It’s lifting about a 100 billion tonnes. Imagine a rocket lifting the moon. That’s about 100 billion times heavier than the mountain. Look a globe. WAG: Imagine a rocket blast covering more area than America, Russia and Australia put together. Imagine you were underneath it.

3. As for ‘splashdown’: Get a football. Wet it. Shake it dry. Throw a tennis ball at it. Did the tennis ball have a splash. It probably would splash magma

In summary, it would (a) be impossible and (b) destroy life apart from a few bacteria and ants.

Of course, I mostly made these numbers up, but it was fun.

[MonkeyMensch]

I gotta talk to my broker about unloading that MoonReallyOverMiami stock I got into at the start of this thread…

[Qwfwq]

I wouldn’t want the moon much closer because the high tides would be horrendous, though surfers might disagree. The Spongmonkey link is great–why can’t they show stuff like that on MTV?

[Billdo]

I think we’re all looking at this the wrong way. The moon currently has a whole mess of rotational kinetic and gravitational potential energy. The question we all seem to be asking is how to overcome that to drop the moon gently into the Pacific.

Instead, we should figure out how to harness it. We have to devise a controlled method through which we can reduce the moon’s kinetic and potential energy and convert it into a usable form on Earth. If we can do that, we can slowly decrease the moon’s orbit and lower it into the ocean and get a bunch of free energy besides.

If we could harness all of the moon’s energy, we could certainly decrease our dependence on fossil fuels for a good long time. The question is if we could perfectly convert the moon’s energy, at current rates of world energy consumption, how long would the energy of the moon last us. And would it give us enough time to figure how to do a similar thing to drop Jupiter into the sun for its energy?

[kniz]

[ul]:mad: [sup]Just leave the damn thing where it is.[/sup][/ul]

[commasense]

You kids just aren’t old enough to remember when the Moon was so close you could climb up on it with a ladder.

At one time, according to Sir George H. Darwin, the Moon was very close to the Earth. Then the tides gradually pushed her far away: the tides that the Moon herself causes in the Earth’s waters, where the Earth slowly loses energy.

So begins “The Distance of the Moon,” the first of a series of quirky and amusing short stories by Italo Calvino in Cosmicomics. In it, the narrator, old Qfwfq, tells about how he and his friends would climb up on the moon and collect the cheese that formed there “through the fermentation of various bodies and substances of terrestrial origin which had flown up from the prairies and forests and lakes, as the Moon sailed over them.”

From the top of the ladder, standing erect on the last rung, you could just touch the moon if you held your arms up. We had taken measurements carefully (we didn’t yet suspect that she was moving away from us); the only thing you had to be very careful about was where you put your hands. I always chose a scale that seemed fast (we climbed up in groups of five or six at a time), then I would cling first with one hand, then with both, and immediately I would feel ladder and boat drifting away from me, and the motion of the Moon would tear me from the Earth’s attraction. Yes, the Moon was so strong that she pulled you up; you realized this the moment you passed from one to the other: you had to swing up abruptly, with a kind of somersault, grabbing the scales, throwing your legs over your head, until your feet were on the Moon’s surface. Seen from the Earth, you looked as if you were hanging there with your head down, but for you, it was the normal position, and the only odd thing was that when you raised your eyes you saw the sea above you, glistening, with the boat and the others upside down, hanging like a bunch of grapes from the vine.

All the stories in this thin volume start with a basic scientific fact (or at least ideas that were considered facts in 1965), from which Calvino spins off tales about what it was like for Qfwfq and the other people who were around at the time–at the Big Bang, when everything in the Universe was condensed into a single point, or when the Sun and the solar system began to condense out of interstellar dust, for instance. They are all delightful, and I highly recommend them.

[Shade]

*Originally posted by Billdo *
Instead, we should figure out how to harness it. We have to devise a controlled method through which we can reduce the moon’s kinetic and potential energy and convert it into a usable form on Earth.

Tidal turbines?

[Somnambulist]

How about, instead of bringing down the whole moon we just take a slice of the far side (no one will notice) and create a giant millennium-dome-style beach in the middle of the pacific? It would still look pretty impressive if it was a big enough ‘slice’, and you could throw the biggest beach parties ever.

[Bosda_Di_Chi_of_Tricor]

We need to address the concerns of the Werewolf-American community in our plans.

[tarfu]

Just in case this does work out, I think I’ll invest in some moon pies stock…

[Gyrate]

*Originally posted by Qwfwq *

Any relation to old Qfwfq? I love that book.

I wouldn’t want the moon much closer because the high tides would be horrendous, though surfers might disagree.

Surf Des Moines!**

The Spongmonkey link is great–why can’t they show stuff like that on MTV? **

Apparently Joel Veitch, the creator of the aforementioned linked song, currently has a VH1 ad in circulation on US TV (and a Crusha ad in the UK).

[Q.E.D]

Ok, I’ve done the calculations I suggested earlier, since no one else did. Surprisingly, although the total mass increases, the surface gravity would decrease slightly if the material of the moon were spread evenly over the survace of the earth. Now, the surface gravity has an acceleration of 9.801 m/s[sup]2[/sup], but after calculating the new radius of the earth and the total mass of the Earth-Moon material, I find that the surface gravity becomes 9.79. m/s[sup]2[/sup] after we cover the Earth evenly with ground-up Moon.

[Grey]

Damn, it does. Very neat, the lower density of the moon mucks about with surface gravity.

[Q.E.D]

Another interesting bit of information that I learned in doing the calculations is that if we did grind op the Moon and distribute its material evenly over the Earth’s surface it would only cover it to a depth of 42.5 kilometers.

[Gyrate]

Only 42.5 km? So that’s, what, through the troposphere and well into the stratosphere?