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Space Elevator

(neal.fun)
1773 points kaonwarb | 3 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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block_dagger ◴[20 Oct 25 16:59 UTC] No.45646224[source]▶
It's NOT rocket science?
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Retric ◴[20 Oct 25 17:01 UTC] No.45646256{3}[source]▶
You can reach space using air breathing jets. You can’t stay in space using air breathing jets.
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CobrastanJorji ◴[20 Oct 25 17:39 UTC] No.45646750{4}[source]▶
I don't think there are any physics reasons why it'd be impossible, but certainly we can't do it with existing technology. You'd need an air breathing jet that could get a vehicle to go about five or six times faster than any current such engine has ever achieved (i.e. around mach 20-30), which is perhaps ridiculous, but I don't think it's necessarily impossible, just something we don't know how to do. There have been some (failed) efforts to get there, like the X-30.
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1. estimator7292 ◴[20 Oct 25 18:07 UTC] No.45647113{5}[source]▶
Can an air breathing jet actually attain those velocities? I thought most supersonic aircraft use rockets after a certain point
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2. LeifCarrotson ◴[20 Oct 25 18:54 UTC] No.45647706[source]▶
"Most" supersonic aircraft are fighter jets and other military aircraft that use jet engines, not rockets. They may have afterburners that are much like a rocket that just injects jet fuel in the exhaust stream, but that's still using atmospheric oxygen.

The issue, I think, is more about balancing drag and air intake at appropriate atmospheric densities for different speeds. An SR-71 Blackbird could fly at 85,000 feet continuously, and a MiG-25 set what I believe is still the air-breathing record max altitude by pulling a "zoom climb" (accelerating in higher-density air that the engines could use effectively, then pulling the stick back and coasting up through rarefied air too thin for the engines) to 38km or 123,000 feet.

Most experimental hypersonic aircraft use rockets because that's what works.

3. marcosdumay ◴[20 Oct 25 21:09 UTC] No.45649426[source]▶
> Can an air breathing jet actually attain those velocities?

There's no theoretical limitation on how fast an air breathing jet can move. You just have to redesign everything every few mach numbers, and deal with the atmospheric drag.