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Comment by CryoLogic | Hacker News Reader

These are all rockets. What happened to attempts and more permanent space launch fixtures like: https://en.wikipedia.org/wiki/Space_elevator

I am under the impression many other methods of getting into space have been hypothesized but never attempted.

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A space elevator is a long ways off - assuming that human interest in space continues and technology develops at similar rates to today, I wouldn't expect something like that to be constructed for at least a couple centuries. Hopefully I'm wrong, I'd love to see something like that, but a project of that sort would make the space station look like a dinky house-boat in terms of scale and complexity. As crappy as rockets are, I expect we will continue to be using them for the duration of our lifespans.

What do you think about space elevators for asteroid mining? A large asteroid has a non-negligible escape velocity (e.g. for Ceres it's 500m/s), so taking stuff from them via regular rockets requires a significant amount of fuel. On the other hand, a space elevator could just be possible with our current materials and technology.

I think a mass driver in most cases would be simpler and more economical. We would use them on earth if we didn't need to worry about the atmosphere.

A Space elevator would require that the body spins fast enough that the centripetal acceleration would equal the gravitational acceleration. Ceres spins roughly every 9 hours - I haven't done the math but that seems like it could work in that case, but even so I would still vote mass driver.

At least for the space elevator, we do not have the necessary materials to create it. There's been some hypotheses that carbon nanotubes could have the required strength, but we cannot produce strands long enough.

And there are other challenges, including:

- Wind: variable speed & direction, can be high.

- Ionosphere charges: the sapce elevator would essentially be a giant ground rod in the ionosphere… that might attract a few bolts of lightning.

You don't need to attach a space elevator to the ground. Keeping one end of the tether at 100,000 feet still makes access to space cheap without many of the security issues of a ground based tether.

Interesting. How do you get stuff to 100,000 feet? I'm imagining some sort of cargo helicopter but that is probably not at all the right idea.

We used a balloon to lift Felix Baumgartner 135,000 feet for his record jump [1]. Could this be scaled up for larger payloads?

[1] https://en.wikipedia.org/wiki/Felix_Baumgartner

Rockets or balloons can get to that altitude fairly easily. You could even build a second elevator that gets to 100,000 feet hanging off a balloons.

But, really it's just a security precaution to prevent terrorists or whatnot just flying into the thing.

Forget terrorist, an accident is more likely including earth quakes, tsunamis and storms and one of the biggest problems is that while building it might just be the easy part maintaining it and decommissioning it when the material fatigue sets in is a much more complicated mess.

Depending on the failure you might have a cable with a length greater than the earth’s circumference if we are putting it to a geostationary orbit falling down to earth.

For a space elevator to work it’s center of mass needs to be at or above geostationary orbit, depending on the counterweight at the end of the tether it will likely be at least 50,000KM long.

So what we need to do is start building down towards Earth from an anchor point

Other means of launching would be massive infrastructure projects, have huge power requirements, or simply might not be practical with current technology (as with a space elevator). I would guess that the most practical would be some sort of EM launch system + rocket/ramjet, if you could figure out how to transition from the first part to the second, but who knows.

While the materials don't quite exist for a tether that can survive the forces needed to escape Earth gravity, the wiki you linked mentions the moon as a place where current materials could be used.

Makes me wonder about the near-term viability of an elevator on Mars, which IIRC has 2/3rd Earth's gravity...

The WP page describes the viability of a Martian in the paragraph before the Lunar one.

A launch loop is perhaps a better solution (meaning no material breakthrough needed):

https://en.wikipedia.org/wiki/Launch_loop

How exactly are you going to build a 50 mile tall structure? Current world record is Burj Khalifa, which is 828 meters tall, which is 0.51 miles. We're not even close.

Actually the answer is very interesting. The launch loop is a so-called active structure. The momentum of the rotor is raising the structure (notice that there are cables stays, but they are to hold it down, not to support it). In this way active structures can be made to any height, taller than material properties that limit static buildings.

At some point this technique will have to be used to make the next world's tallest building. Disadvantage is that the power must be kept on or the building collapses.

Relevant Isaac Arthur video:

https://www.youtube.com/watch?v=zSimYARyL2w&index=15&list=PL...

https://www.youtube.com/watch?v=5QLOAQmZbZs

Isn't the idea with the launch loop that it suspends itself by electrical force? The downside being that when it looses power it comes crashing down.

On the ground.

Getting into space isn't hard. It's STAYING there that's difficult.

Relevant XKCD What If: https://what-if.xkcd.com/58/

This is why a space elevator needs to go much higher than low-earth orbit. Reach all the way to geostationary orbit, and then you are already going fast enough to stay in space.

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