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Space Elevator

neal.fun

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Re: Space Elevator

#291

Post by mrguyorama »

senkora wrote: post #229
georgeecollins wrote: post #213

Earlier quoted context omitted.

I'm fine with series not following the books. But the show bugs me because it has great production values -- particularly the third season -- and great actors. But the writing and plotting is all over the place ranging to very bad. It is a bit dumb and always pretentious. It's the 70's version of Battlestar Galactica of our age.

This is the issue that I have with many Apple TV+ shows. The production value is always very high, but it has no correlation with whether the writing is actually good.

This is just the state of American video media production right now.

Projects are massively expensive, including a lot spent on "looking expensive", but the writing cannot be as expertly crafted because the high expense means upper management craves purpose and control and meddles with things, and the giant "target" audience means you can't do anything interesting.

Re: Space Elevator

#292

Post by hermitcrab »

bombcar wrote: post #245
hermitcrab wrote: post #210

Earlier quoted context omitted.

To get to the Kármán line (100k) a mountain with a 60 degree slope would require a base of 115km. A cone with 115km diameter base has a volume of 3.5×10^5 km^3. Which is 3.5x10^14 m^3, which is about 10^15 kg of rock. So it is going to take you a while!

3.5x10⁵ km³ you say? 1.08321×10¹² km³ is the volume of Earth, feasibility study done! Implement!

The molten core probably isn't going to be much use.

Surface area is 5x10^8 km^2. So it it 'only' the first ~2m of the crust (~6m if you don't count ocean).

Re: Space Elevator

#293

Post by mk_stjames »

amflare wrote: post #248
jvanderbot wrote: post #143

Very cool. One thing I wish was better shown: space is close, it's just hard to go up. Our liveable breathable atmosphere is razor thin compared to the size of earth. In most cases, 100km is less than the distance between sizeable metropolitan areas. It's a day long bike ride. Air runs out less than a bus ride across town. A 15k jog/hike would put you in the stratosphere. Those jet aircraft that seem so high are clos…

For a standard globe that you might see in a classroom, the Earth's atmosphere is about as thick as the paper glued to the outside that displays the map.

That didn't sound right to me, and so I checked it as follows:

Estimate for a standard classroom globe at 13" in diameter (I'm seeing a rnage of 12-14 inches as typical). I'm reporting in inches because that is what came up first and most of the globes are for sale in the US. Mixing units here, but, it works out.

But, in meters, the diameter of the Earth is 12,742,000 m on average. if we use the 'Karman line' as defining the edge of what the atmosphere is, that is 100,000 meters. Solving for X ... (13" / 12742000 m)=(X / 100,000 m). gives us an atmosphere thickness of approximately 0.1". -----

Paper glued to the globe would have a thickness of maybe, 0.004" (thin paper) to 0.012" (like a card stock paper).... so that analogy is off by an order of magnitude or more.

Even if you use the mesosphere as the definition for the top of the atmosphere, that is still 85,000 meters and thus similar.

People can check the numbers I used.

* Perhaps the analogy should go more like: the thickness of the cardboard sphere the globe is made out of is about the thickness of the atmosphere. Because, having completely destroyed a globe once in my youth, I remember the cardboard shell being approximately a tenth of an inch thick. But, that's maybe not a great reference for the analogy because not everyone has cut apart a classroom globe....

Re: Space Elevator

#294

Post by gertlex »

amflare wrote: post #248
jvanderbot wrote: post #143

Very cool. One thing I wish was better shown: space is close, it's just hard to go up. Our liveable breathable atmosphere is razor thin compared to the size of earth. In most cases, 100km is less than the distance between sizeable metropolitan areas. It's a day long bike ride. Air runs out less than a bus ride across town. A 15k jog/hike would put you in the stratosphere. Those jet aircraft that seem so high are clos…

For a standard globe that you might see in a classroom, the Earth's atmosphere is about as thick as the paper glued to the outside that displays the map.

I wonder how standard this globe size is. My mental one is the one we had at home that was about 15" in diameter I'd guess.

Another comment talks about atmosphere being a 1 mm layer on a grapefruit... so definition of atmosphere extents might be different in these two anecdotes.

(edit: I submitted this comment two minutes after another comment did the math on the globe/paper layer version...)

Re: Space Elevator

#295

Post by aDyslecticCrow »

advisedwang wrote: post #240
aDyslecticCrow wrote: post #166

Earlier quoted context omitted.

> Going fast enough sideways so you stay up there is the tricky bit. nah, thats the simple part. getting up there efficiently is the difficulty. once we're up, its just a matter of force over time to create a nice orbit. The faster you go, the more friction you face, and the more heat and vibration your equipment must endure. Going slower reduce friction and stress but use more energy just negating gravity. Slow rock…

Energy for 1kg to reach LEO (800km * 1kg * 9.8m/s2) ~ 8MJ Energy to reach LEO velocity ~ (1/2 * 1kg * (8km/s)^2) ~ 32MJ

But the energy needed is not an indicator of what is difficult or dangerous. Leaving the atmosphere intact is the most difficult part of launching a rocket going by failure rate. Of those that reach space, those that still fail often took damage from the launch.

Once you're in space, force over distance until your fuel runs out.

Re: Space Elevator

#296

Post by kakacik »

icetank wrote: post #77
tsimionescu wrote: post #58

Earlier quoted context omitted.

While a space elevator doesn't contradict any fundamental limits of physics, that doesn't mean it's actually possible to build one. There is no reason to be certain that it's actually possible to create a material that has the required characteristics in terms of tensile strength to support it's own weight, plus the weight of the elevator, plus the weight of all the additional cabling. It also has to endure the huge…

The issue of the line falling back to earth is solved by putting the base of the elevator on water. If the top part of the elevator was cut of you could even detonate charges along the line to make sure all pieces fall into water.

What would be the wnergy delivered by 35k km of ultra strong thick cable falling down with possibly supersonic speed? A small bit not much, but such length adds up.

Re: Space Elevator

#298

Post by shagie »

mk_stjames wrote: post #293
amflare wrote: post #248

Earlier quoted context omitted.

For a standard globe that you might see in a classroom, the Earth's atmosphere is about as thick as the paper glued to the outside that displays the map.

That didn't sound right to me, and so I checked it as follows: Estimate for a standard classroom globe at 13" in diameter (I'm seeing a rnage of 12-14 inches as typical). I'm reporting in inches because that is what came up first and most of the globes are for sale in the US. Mixing units here, but, it works out. But, in meters, the diameter of the Earth is 12,742,000 m on average. if we use the 'Karman line' as defi…

https://en.wikipedia.org/wiki/Atmosphere_of_Earth#Pressure_a...

90% of the atmosphere is below 16 km.

16 km * (12" / Earth diameter) :: https://www.wolframalpha.com/input?i=16+km+*+%2812%22+%2F+Ea...

0.015 inches, 0.38 mm

... and tossing sheets of paper into that ( https://www.wolframalpha.com/input?i=thickness+of+paper ) ...

16 km * (12" / Earth diameter) / thickness of paper :: https://www.wolframalpha.com/input?i=16+km+*+%2812%22+%2F+Ea...

4

Note that that's copy paper rather than card stock...

Adjusting this to 5.6km (the 50% atmosphere amount) ...

5.6 km * (12" / Earth diameter) / thickness of paper :: https://www.wolframalpha.com/input?i=5.6+km+*+%2812%22+%2F+E...

1

So it's a matter of selecting the proper globe, proper paper, and proper threshold for the atmosphere.

Re: Space Elevator

#299

Post by hinkley »

jvanderbot wrote: post #143

Very cool. One thing I wish was better shown: space is close, it's just hard to go up. Our liveable breathable atmosphere is razor thin compared to the size of earth. In most cases, 100km is less than the distance between sizeable metropolitan areas. It's a day long bike ride. Air runs out less than a bus ride across town. A 15k jog/hike would put you in the stratosphere. Those jet aircraft that seem so high are clos…

In a parallel universe where Africa is covered by world powers, Mount Kilimanjaro would make a pretty good launch facility. Reduced rocket equation needs for being nearly 3 miles high. If you start in thinner atmosphere you need less fuel to punch through it. You’re also higher when you hit Max Q.

This is essentially what Scaled Composites and Virgin Galactic were trying to do with their cargo plane system, only you don’t have to worry about the ignition timing because you’re not in free fall.

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