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Space Elevator

(neal.fun)
1773 points kaonwarb | 3 comments | 20 Oct 25 04:42 UTC | HN request time: 0.001s | 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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1. ianburrell ◴[20 Oct 25 20:43 UTC] No.45649090{4}[source]▶
There isn't enough air at high altitudes for jets to reach space even if you count 100km as space.

The highest jet record is 37km in MiG-25. The scramjet record is 33km. I found source that says the limit is 40km at Mach 15.

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2. Retric ◴[20 Oct 25 21:11 UTC] No.45649443[source]▶
The MiG didn’t reach 37km in level flight, which is probably where Mach 15 @40km comes from. Instead the MiG was doing a nearly parabolic trajectory starting with Mach ~3 worth of kinetic energy.

The NASA X-43A hit Mach 9.6 as an air breathing engine (test used a rocket at lower speeds for cost reasons) which in theory should be capable of ~65 km assuming it could survive a similar maneuver. Actual limits are heavily influenced by how much thrust you can generate while slowing down etc not just max velocity.

So yea no actually built air breathing aircraft can hit space, but it’s within the realm of possibility.

3. LorenPechtel ◴[21 Oct 25 04:24 UTC] No.45652459[source]▶
Nobody has been able to build one, but I'm not aware of any proof that it's impossible. You need some way to build an engine that doesn't appreciably slow the air that's passing through it.