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Space Elevator

(neal.fun)
1773 points kaonwarb | 1 comments | 20 Oct 25 04:42 UTC | HN request time: 0s | source
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ta1243 ◴[20 Oct 25 08:51 UTC] No.45641466[source]▶
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 scrolling there was to get to 100km.

To get to the ISS you'd need to scroll 4 times further. Starlink and Hubble are another 100km beyond that.

You start having radiation problems if you spend too much time above 600km.

Aside from Apollo, the highest a human has been is about 1400km - 14 times more scrolling than this page.

To get to GEO would require scrolling over 25 times further than even that.

replies(1): >>45642813 #
matheusmoreira ◴[20 Oct 25 11:44 UTC] No.45642813[source]▶
How much delta V would be needed to reach, say, a circular orbit from GEO altitude?
replies(1): >>45646741 #
1. ta1243 ◴[20 Oct 25 17:39 UTC] No.45646741[source]▶
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.