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Space Elevator

neal.fun

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Re: Space Elevator

#251

Post by nroets »

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

The rocket fuel needed to produce that 40 MJ weighs close to 1 kg, especially when you include the oxidiser. So the energy needed to accelerate 1kg of payload to LEO velocity is much more.

Re: Space Elevator

#252

Post by simpaticoder »

Given the title "Space Elevator" I was expecting some more information on a hypothetical space elevator cable. Assuming humans can manufacture defect-free nanotubes at any length and can combine them into thicker cables, you could specify at every height a) the cumulative mass of the cable, b) the thickness of the cable at that point, and c) the stress experienced by the cable at that point. You could further break c down into the gravitational vs centripetal forces on the cable at that point.

Re: Space Elevator

#253

Post by kmacdough »

Super fun!

I do always have to object to comments like "space elevators are possible," "scientists have studied" and "would save money".

It's a fun thought experiment, nothing more (for now). You can do some calculus to estimate the necessary strength-to-weight ratio based on centripetal and gravitational forces. Single carbon fibers seem to meet this optimistic criteria.

But there are many forces left out. Many practicalitites left unconsidered. Why? Because there is no scientific community that believes it's vaguely achievable with near-future technology. It's simply not worth investing the outrageous resources required to do a vaguely useful viability analysis.

Re: Space Elevator

#254

Post by kmacdough »

GMoromisato wrote: post #232

I love this page and I donated, but I was (naively) expecting it to get to geosynchronous altitude, which is the actual top of a space elevator. Of course, that would require a page 420 times longer, and I don't know if a browser would even support it.

I mean the idea isn't actually real or practical. It's a thought experiment that makes for some fun calculus. No one's actually going to try and build one.

Re: Space Elevator

#255

Post by andersa »

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's a fascinating comparison, never seen it visualized like that before.

Re: Space Elevator

#258

Post by kmacdough »

bentt wrote: post #172

Seems like even before we do an elevator, we should get _something_ tethered to the ground to be in space. Like... anything! That'd be a huge accomplishment.

No engineer actually thinks a space elevator is possible. It would be a silly waste of resources.

Re: Space Elevator

#259

Post by sharkjacobs »

anticrymactic wrote: post #79
daniel_iversen wrote: post #4

This was incredible! Couldn't stop scrolling and reading. For a kid of a certain age and curiosity it'll blow their mind! I'm so grateful the creator made this, shame that his "buy me a coffee" isn't a simple PayPal or Apple Pay but you have to put in credit card or bank details!!

PayPal and Apple pay take a significant cut of the transaction. CC is a lot less and bank is mostly free of TX fees. Most users don't know/don't care, so given the option, they will likely take it and funnel their donations to conglomerates.

> Apple Pay take a significant cut of the transaction

I don't think this is true

> Apple Pay does not cause additional fees for users and merchants.[1]

[1]https://en.wikipedia.org/wiki/Apple_Pay#Cost

Re: Space Elevator

#260

Post by ta1243 »

matheusmoreira wrote: post #102
ta1243 wrote: post #48

What's really interesting is that a space elevator goes to Geostationary orbit by necessity. Getting to 100km vertically doesn't save as much as you might think when it comes to getting into orbit. To get into a very low earth orbit from an equatorial launch pad at sea level you need about 9.2km/s of Delta-V To get there from a 100km tall tower, you need about 8km/s of delta-V - about 85%. Think about how much scroll…

How much delta V would be needed to reach, say, a circular orbit from GEO altitude?

Zero. By the time you get to GEO your are connected to a station which is in Geostationary orbit. Your 35 hour ascent at say 1000km/h will have accelerated you sideways to the required 3km/second with a sidewards acceleration of 0.002g throughout the trip.

Of course you would be looking at a constant acceleration, not just a 1000km/hour trip. You'd probably be able to do the journey in a couple of hours with a reasonable acceleration and a rotating cabin (say 1.1g, meaning acceleration would slowly increase from about 0.1g at the surface, then after the flip point you'd decelerate at 1.1g). Even then sideways acceleration wouldn't be noticable (and your cabin could gimbal to just add it to vertical acceleration)

That's the other crazy thing. A space elevator takes forever at elevator, or car, or even plane speeds. But with constant acceleration/decelleration you can have a trip in airplane style seats with cabin crew serving you caviar // scratchcards (depending on class of cabin). Your peak vertical speed would be in the region of 8km/second - way above Earth's escape velocity, but you wouldn't even notice the acceleration/deceleration. You'd slow down in under 15 minutes.

Or you wouldn't and you'd depart Earth at 8km/s, twice the escape velocity.

(If you really wanted a fast departure you'd accelerate at say 1.2g and get upto 30km/s, twice the speed of New Horizons. 1.2g would probably mean you'd have the seatbelt on for the whole 40 minute trip)

You could launch cargo to Mars at say 5G, which would get it there in between 10 and 45 days depending where it is. Obviously you'd have a problem slowing down when you got there.

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