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Space Elevator

(neal.fun)
1773 points kaonwarb | 4 comments | 20 Oct 25 04:42 UTC | HN request time: 0s | source
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jvanderbot ◴[20 Oct 25 13:03 UTC] No.45643427[source]▶
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 closer than that. Closer than your friends house or the local stadium probably.

Look at a map or globe with that in mind and everything feels so thin!

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messe ◴[20 Oct 25 13:28 UTC] No.45643658[source]▶
> it's just hard to go up

Going up is the comparatively easy part, it's not exactly rocket science. Going fast enough sideways so you stay up there is the tricky bit.

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aDyslecticCrow ◴[20 Oct 25 13:54 UTC] No.45643965[source]▶
> 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 rocket is inefficient rocket.

So we wanna leave the atmosphere as soon as possible, but not so fast that the rocket melts or engines collapse. Prefferably just below the sound barrier.

once we're up, its pretty chill... until you wanna go down again. Slow rocket is alive rocket.

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1. raducu ◴[20 Oct 25 14:36 UTC] No.45644389{3}[source]▶
> once we're up, its just a matter of force over time to create a nice orbit.

It depends what you mean by "up there". ChatGpt tells me you'd free fall from 1000 km to 100km in about 8 minutes. It also did the math that you'd need 1.65G of sideways thrust to reach orbital speed. That's quite a bit of force for spacecraft sized objects.

If you have an actual space elevator, sure, you can go to close to geosynchronous altitude and by that time you'd have enormous sideways velocity just by being dragged sideways by space elevator and indeed it would be easy to propel yourself to orbit (above a certain altitude my intuition tells me you could let go of the rope and while you'd end up on an eliptise you'd still be in orbit)

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2. hermitcrab ◴[20 Oct 25 15:26 UTC] No.45645021[source]▶
>ChatGpt tells me you'd free fall from 1000 km to 100km in about 8 minutes

You trusted an LLM to do the maths when it is just s = 5t^2?

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3. kaonwarb ◴[22 Oct 25 05:56 UTC] No.45665340[source]▶
Not quite; g drops materially between 100 km and 1000 km. 8 minutes I believe is quite close, whereas 5t^2 (or even 4.9t^2) will lead to underestimating time.
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4. hermitcrab ◴[22 Oct 25 14:46 UTC] No.45669928{3}[source]▶
The radius of the earth is around 6300km. The difference in g at the start (between 6400km and 7400km) is 25%. But gets less as you fall. So it might make somewhere around a 10-15% difference overall? So s=5t^2 is fine unless you need a super accurate figure, in which case you need to do some calculus. I would trust an LLM with calculus even less.