Why Space Elevators Could Be the Future of Space Travel | Hacker News Reader

Why Space Elevators Could Be the Future of Space Travel

futurism.com

39 pointsdaredave38 comments

As long as a major component of space elevators is unobtanium any kind of discussion about them in a terrestrial context should focus on materials science and how to advance it to the point that it becomes feasible. Anything else is not productive, akin to deciding on how to spend your first billion when you have $50 in the bank.

Maybe it's the daydreams of life in a futuristic loading dock in space that inspires Kate Miller, age eight today, to become the scientist inventing unobtanium :)

Firstly, the tether of a space elevator could be tethered (EDIT: tapered), which reduces the required tensile strength a bit.

Secondly, there are some intermediate space elevator-like constructs that have similar ideas but are much more feasible. For example the skyhook (https://en.wikipedia.org/wiki/Skyhook_(structure)). Rather than tethering to the ground it would 'hook' into the air at high altitude, and rotate the earth at high but airplane achievable speeds. There are a lot of engineering challenges, but its theoretically possible with existing materials.

> Firstly, the tether of a space elevator could be tethered

Uh... Aren't connectors already supposed to be connected?

Oops, typo. I meant tapered. As in varying in width. You could imagine a tether that has a 5mm diameter at the surface (in a sort of ribbon shape), but has a diameter of 500mm at the geostationary orbit.

According to this (http://sustainable-nano.com/2014/04/01/space-elevator-a-last...) a carbon nanotube has a factor between ground and orbit of 1.6 or so, and for steel it's something crazy like 1.6e33.

A whole article about why space elevators would be better than rockets with only the slight problem that we don't know of any way to build one with any materials we have.

If we are allowed to do that, I think we should use star trek transporters. They would be even cheaper and even better. We don't know how to build those either...

Well we can already build them on the moon or mars, but there's not much use to do that at this point. The physics of a space elevator our completely understood, it's "just" finding a strong enough material to build the tether. A star trek transporter is still far out of reach.

The physics of rockets is completely understood, too, and several applications have already been debugged. It's "just" a matter of finding a better propellent.

I would rather go from point A to B than be murdered and have a copy of myself assembled at point B.

Why? Unless there will be an accident where there are 2 of you why does this even bothers you?

If it's as safe or safer than any other mode of transport then who cares if technically one copy gets destroyed, your body is doing that every few years anyhow.

"Why does this even bothers you?"

Because he's human and despite every fibre of his wit possibly thinking otherwise, he has some unshakeable suspicion that he has a spirit or is at least more than a mere golem?

I dunno, that's what puts me off the idea.

> I think we should use star trek transporters. They would be even cheaper and even better.

Most of the energy of a spaceship in star trek is provided by anti-matter annihilation. Those are stupendous amounts of energy that they have available. Transporters may not be cheaper or better than space elevators. They're just far more convenient.

For lifting gigatons of raw material into space you probably still want an elevator or other more "conventional" launch systems (anti-grav, impulse engines, etc.). Or just tow asteroids from outside the gravity well to your manufacturing site.

Starting construction without having the needed materials is the approach followed at ITER. This way of working is based in a very reasonable idea: available materials have been improving since ever, there is no reason to think this progress will stop now.

But it's hard to even imagine what something stronger than carbon nanutubes would look like. How much stronger than diamond-like molecular bonds can you get?

According to simulations, 58% [1]. Experimental confirmation is still needed. Although we are still far from it, it is something that we could see in our life times.

[1] https://www.newscientist.com/article/dn16610-diamond-no-long...

Hardness is not the same as tensile strength.

I know. From the linked article: "The simulation showed that wurtzide boron nitride would withstand 18 per cent more stress than diamond, and lonsdaleite 58 per cent more." The title of the article is misleading.

The title of that article is accurate, where it says "stress" they are really referring to hardness and not tensile strength. The quoted 58% comes from this paper, it talks about "hardness" and "indentation strength" in the abstract:

http://sci-hub.cc/10.1103/physrevlett.102.055503

You are right, I stand corrected. They actually talk about tensile strength in the PRL article:

"It is noted that lonsdaleite exhibits almost identical ideal tensile strength and only slightly larger pure ideal shear strength compared to diamond. The significant enhancement in its indentation strength occurs under biaxial stress loading conditions. The situation in w-BN versus c-BN is similar. All past calculations have shown that diamond exhibits the highest strength under various loading conditions compared to other materials, which was consistent with all available measurements. Here we show for the first time that w-BN and lonsdaleite exhibit higher strength than diamond under indentation."

So, indeed, diamond is still the winner here.

we could start by getting an asteroid into orbit, this could be used as orbital station, construction site and counterweight for a future elevator

While a space elevator is constructable on the moon or mars, making one for earth would needs exotic high tensile strength materials that we don't know how to build.

A launch loop, on the other hand, has many of the benefits of a space elevator; but the nicest feature is that it can be constructed from conventional materials. https://en.wikipedia.org/wiki/Launch_loop

How about a active structure, like a space fountain?

rockets connected to each other ascending and descending constantly?

Iirc, Robert L Forward's variant was an electromagnetic cannon launching metal pellets, which were slowed down at the top and fired back down.

The pellets would go up and down like a juggler's balls was thrown.

Since you'd regain much of the energy when you slowed them down, it wouldn't be so energy expensive as it seems. And yes, you need vacuum pipes. And a stop in electricity would have side effects ("Timber!"). :-)

some kind of ubend, and the "pellets" are magnetised?

say we drop a rocket into this ubend and it redirects the energy back up into space?

and in orbit there are rockets that lift them the rest of the way, remove the passengers and then drop them again.

I was clumsily trying to explain Space fountains. :-) This do discuss the Forward thing and so on:

https://en.wikipedia.org/wiki/Space_fountain#History

What is the heaviest planet where we could build a space elevator with current technology? Would it work on Mars? The Moon?

The moon, yes:

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

Mars, edge case?:

http://physics.stackexchange.com/questions/33547/space-eleva...

Good post on the subject:

http://tsanad.blogspot.nl/2011/03/space-elevators-where-to-p...

With the U.S. Navy having working railguns, we already have the tech to launch unmanned cargo into orbit quite cheaply. All we need is a standardized shell casing that can hold the cargo and provide the horizontal thrust once the package reaches apogee.

Space elevators are cool, but why chase something with so much missing tech when we have a solution in front of us?

I agree with you, although I should note that the current Navy railguns are not capable of putting shots in orbit. However, the logic behind choosing guns over elevators is simple:

I. Actively supported towers are easier/more likely to be built than a space elevator made of unobtainium. II. The technology to build a space fountain or actively supported tower is more difficult than a gun, because you first have to have a gun which can shoot objects faster than orbital speed, and then add the recirculation plus the momentum transfer to the tower. So, an orbital gun is a subset of the technology needed for an active tower.

One other thing which is often overlooked when discussing shooting stuff into orbit, is that the size and cost of the gun is proportional to the size of the projectile. If shooting from very high in the atmosphere, very small projectiles could work without significant atmospheric losses. A railgun or light gas gun on an airplane could easily shoot literal tons of small projectiles, machine gun style, then land and reload (and with current tech, replace barrels).

If a target in orbit was shot at, you wouldn't even need to have a rocket in each projectile to provide thrust at apogee. Instead, you hit the target and embed into it. By hitting the target at different parts of its orbit, you avoid substantially changing the shape of its orbit, balancing out the momentum change to keep the orbit how you want it.

This wouldn't work for anything besides bulk materials which can be broken down into small pieces and shot like tiny bullets out of a hypersonic machine gun. But the cost per kg for bulk materials could be very low.

Bore a hole inside a mountain in Peru right on the Equator two meters in diameter and two kilometers long. Put the electric rail gun in that.

They're probably not jumping to give away the plans for a treaty-compliant superweapon.

It seems that getting information out of a gravity well is much easier than mass. There's a bit of a bootstrapping problem to to develop the initial infrastructure, but once in place it would be much simpler to just build in space.

The problem with that of course is that terrestrial refineries and factories are highly soecialized to their products, which means multiplies the amount of base inf needed to construct even simple materials. If orbital manufacturing emerges, I think it would need to adopt a new paradigm of custom fabrication such as with 3d printing and similar technologies.

Not even carbon nanotubes are strong enough to make a space elevator on Earth. Individual CNTs (the molecules) are just barely strong enough, but you cannot make a macroscale fabric out of them that's just as strong as the individual molecules. And even if you did, there's no safety margin.

It's never going to happen on Earth.

However we could make an elevator today on the Moon or Mars with already existing fabrics like Kevlar.

This article mentions a study saying CNTs are too weak. Here's a New Scientist summary of the flaws in CNTs: https://www.newscientist.com/article/2093356-carbon-nanotube...

hum... silly thought of the day. Why we still launch rockets from sea level and not from some high mountain? Wouldn't be less expensive and more safe that building 3-5km extra of space elevator?

If the mountain is higher enough, zero probability of birds crashing against your structure, Neither clouds nor hurricanes, high visibility, free solar energy all year around...

funny that they mentioned 2009's “Gundam 00”, but haven's said a word about Authur C Clarke's 1979 novel "Fountains of Paradise", the whole novel is about this.

Could a space elevator be warp based?

the early versions of warp would have to be huge anyways, so why not take advantage of that by creating a space elevator using warp?

With warp you could technically send things through the earth's core as a form of teleportation too.

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