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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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isgb ◴[20 Oct 25 12:46 UTC] No.45643283[source]▶
> Space elevators are actually a possible idea being considered by scientists. > The hard part is making a strong enough cable. And finding enough elevator music...

Most engineers would bring up a lot more issues than just finding a strong cable. Also, most attempts with e.g. carbon nanotubes have been abandoned ages ago https://www.newscientist.com/article/2093356-carbon-nanotube....

- We don't have a good ascent mechanism other than rockets - and then we might just use rockets without building an elevator. - We don't have a good (and safe) descent mechanism. - Maintenance? Protection from space debris? Protection from oscillations? Ground-protection if the elevator collapses?

This is dyson-sphere level of fiction. We can do back-of-the-napkin calcualtions on how things would work, but the practicalities make it completely impossible or impractical.

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gizmo686 ◴[20 Oct 25 14:38 UTC] No.45644414[source]▶
Isn't the entire point of the space elevator to be the ascent/descent mechanism?

Once you have the cable up, you can grab onto it and pull yourself up.

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bisby ◴[20 Oct 25 15:17 UTC] No.45644930[source]▶
A space elevator doesnt just take you to the karman line (like in the OP website), to get to orbit, you'd need to get up to geostationary height. That's 22,000 miles.

What's the best way to pull yourself directly vertical along a cable for 22,000 miles?

What's the best way to descend 22,000 miles quickly, but also with a braking mechanism that isn't going to require a heat shield?

Some sort of slow cable car going at 10mph even is going to take 2200 hours... 1000mph is going to take 22 hours still. That's a full day to orbit even going REALLY fast. And getting up to 1000mph vertically, for a sustained 22 hours... that's not an easy feat.

And if the goal is just to get up past the karman line and use the elevator as a stage 1 for a rocket launch and detaching from the elevator while suborbital is fine, then it's a one way trip, and still need to re-enter the old fashion way.

The scale of space makes all of the problems far more complicated (edit: not just the cable strength issue, but traversing the cable)

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1. notahacker ◴[20 Oct 25 16:17 UTC] No.45645632[source]▶
Unless we're using it for humans the transit time isn't that big a deal; "last mile" orbital transfer times are often measured in days anyway.

That "last mile" bit is going to entail independent propulsion anyway. Getting to the altitude if the ISS is a mere 10 hour trip at a sedately 40kph which isn't unpleasant even for humans, but the ISS orbits at nearly 29000kph (as will you if you let go of the space elevator at that altitude) and the velocities are only half as scary at the far end, so your rendezvous anywhere other than one specific point in geo is going to be complicated. But you've saved the fuel costs of escaping the earth's atmosphere that's rather significantly more than the fuel costs of other bits of your satellite mission, including reentry. (At least until the costs of building and maintaining and protecting the elevator are factored in, but who knows what unobtanium costs?)

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2. gizmo686 ◴[20 Oct 25 22:54 UTC] No.45650458[source]▶
> as will you if you let go of the space elevator at that altitude)

Doesn't the teather have a constant (24 hour) rotational period at every elevation? That is significantly slower than the ISS

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3. notahacker ◴[21 Oct 25 19:22 UTC] No.45660413[source]▶
fair point, you'd need to be orbiting at that speed to stay in that orbit, but you'd need propulsion to get the delta v to get there after letting go of the tether, but a lot less than to launch from ground level through the atmosphere. Or you could figure out the point higher up the tether to release where your orbital decay would intersect the IS orbits, but given the precision involved in that rendezvous you'd still want propulsion. You'd want propulsion for the last mile bit for pretty much anything other than building a station attached to the tether was kind of my whole point :)