Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Space Elevator

neal.fun

Post reply on HN
Print view View original

101–110 of 414 posts

Re: Space Elevator

#101

Post by sixQuarks »

Yizahi wrote: post #97
pbmonster wrote: post #41

Earlier quoted context omitted.

I don't see it. Why worry about a weaponized space elevator when stealth bombers, cruise missiles and ICBMs exist? If the power building the space elevator wants to bomb you, you're going to get bombed.

Russia, China, Iran etc. are throwing a hissy fit whenever even a small weapons are deployed in the neighboring countries. USA too if we are being fair. They won't even wait for that opportunity.

The US throws the biggest hissy fit AND is the biggest hypocrite about it as well.

Re: Space Elevator

#102

Post by matheusmoreira »

ta1243 wrote: post #48

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 scroll…

How much delta V would be needed to reach, say, a circular orbit from GEO altitude?

Re: Space Elevator

#103

Post by pfdietz »

dpq wrote: post #61

Amazing work! One minor correction: > As particles from the sun hit the atmosphere, they excite the atoms in the air. These excited atoms start to glow, creating brilliant displays of light called auroras. The process is a bit more nuanced than that. The modern mainstream understanding is that the growing pressure of the solar wind makes the tail of the magnetosphere "contract" (sort of pushing it inwards from the si…

Right. So the solar wind provides the energy that drives the aurora, but it's more indirect than just "solar wind particles hit the atmosphere". Instead, the solar wind is injecting energy into the magnetic field of the magnetosphere, and when reconnection occurs some of this magnetic energy is dumped into particles in the magnetosphere, some of which can then strike the atmosphere.

Re: Space Elevator

#105

Post by iberator »

pbmonster wrote: post #63
tsimionescu wrote: post #54

Earlier quoted context omitted.

The bigger problem I think is the elevator itself. Cutting it and letting it fall would be far more destructive than any weapon ever fired or even conceived.

Probably no easy task. Snipping off just the first few kilometers is not catastrophically destructive yet, and cutting it down further up would require multistage rocket designs, sophisticated steering/targeting and potentially significant yield (you'd need to cut unobtainium, after all...). If you can build a space elevator, you can defend against those. You better thoroughly inspect what cargo you put on the elevat…

Easy. You just blow the elevator FROM INSIDE. Plant some bomb into the elevator itself and while in half way BOOM!

Re: Space Elevator

#106

Post by xrd »

My 8 and 10 year old daughters love this site, often choosing it over Roblox during screen time.

This is stunning and perfect.

Re: Space Elevator

#108

Post by pfdietz »

icetank wrote: post #77
tsimionescu wrote: post #58

Earlier quoted context omitted.

While a space elevator doesn't contradict any fundamental limits of physics, that doesn't mean it's actually possible to build one. There is no reason to be certain that it's actually possible to create a material that has the required characteristics in terms of tensile strength to support it's own weight, plus the weight of the elevator, plus the weight of all the additional cabling. It also has to endure the huge…

The issue of the line falling back to earth is solved by putting the base of the elevator on water. If the top part of the elevator was cut of you could even detonate charges along the line to make sure all pieces fall into water.

There's also the issue of the vehicle on the space elevator falling back to Earth if it detaches from the space elevator (accidentally or deliberately in case of malfunction that stops it from moving up). This means each vehicle will need rockets on it. At low altitude, the rockets are fired to keep the vehicle from reentering the atmosphere too fast at a steep angle, killing the passengers. At high altitude, the rockets fire to raise the perigee enough that the vehicle misses the atmosphere entirely (or enters at a very shallow survivable angle). There's a cross over point that dictates the delta V the rocket must be able to deliver. which if I vaguely recall correctly is greater than 4 km/s.

Pure payload capsules with no passengers wouldn't need this.

The argument for space elevators is that there's a pretty strong limit on how much payload can be launched by rockets due to injection of water into the upper atmosphere. Starship could arguably reach this limit with plausible projected growth rates in traffic.

Re: Space Elevator

#109

Post by pfdietz »

pbmonster wrote: post #39
tempestn wrote: post #8

TIL it's estimated that over 48 tons of meteors hit the atmosphere every day. Regarding actual space elevators though, while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible - they're still pretty firmly in the realm of sci-fi. We don't have anything close to a cable that could sustain its own weight, let alone that of whatever is being elevated. Plus,…

> A space elevator on the moon is much more feasible: less gravity, slow rotation The slow rotation is a minus, it means you've got to string the tether up to L1 instead of "just" up to geo/luna-stationary orbit. A lunar space elevator needs to be at least 56000 km long, more than 20000 km longer than the one to earth. > But it's also much less useful. Yeah, especially because all the things that make lunar space ele…

A space elevator is kind of like a vertical mass driver, so just build one of those along the surface of the moon with modest acceleration, survivable by passengers.

Rotating cables ("rotavators") on the moon seem much more practical than full space elevators.

https://en.wikipedia.org/wiki/Momentum_exchange_tether#Rotov...

Re: Space Elevator

#110

Post by tetris11 »

> Temperatures can reach but the molecules are spread sobfar apart you wouldn't feel it.

Conceptually I get, it's like being in a cold room that showers hot sparks on you from above occasionally...

...but I feel that the definition of temperature has been abused here slightly

Post reply on HN