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Comment by moloch-hai | Hacker News Reader

SpaceX's Starship+Superheavy ("can+kicker", informally) promises $100/kg to orbit. (Musk is on record lying that it might be $20/kg.) So, the space elevator would need to do much better than $50/kg.

Anyway there are better alternatives than the space elevator that have the advantage of being, y'know, possible. The orbiting, rotating "skyhook" concept, that dips down to snatch a payload from the upper atmosphere and fling it to space, is one. A ring-shaped version, rolling, might be more structurally practical.

None of the ideas cited in the article originate from Liu. He riffs on them. What would make them more interesting would be knowing how to achieve them. But we don't. People are working on some of them. Some are just bad ideas, the Neptune one spectacularly so.

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Thanks! Will add an edit mentioning your points on the elevator.

As for the Neptune idea, assuming 200+ years of technological progress in chemistry and physics, isn't there something that could be remotely viable about the idea? (Not fixating on Neptune in particular, but as in using materials from other planets.)

An advantage of alternatives to rockets would be that they do not contribute to destroying the ozone layer.

Restoring the ozone layer by dispersing ozone could be a useful idea, but all it requires of material is oxygen, which we have plenty of right here. Neptune has nothing extra we need. The sun turns oxygen into ozone by the gigaton, today. To really address the problem, you would need to remove the fluorine compounds that consume the ozone. Nobody seems to have a better idea than not to vent more.

The space elevator notion relies on discovering a material strong enough to build it of. Other schemes seem possible with existing materials.

Neptune has helium-3 that might someday be useful as fuel for aneutronic fusion, if we can get that to work. Hardly anybody is trying. Getting to Neptune and collecting it seems even harder than getting aneutronic fusion working.

It sounds like Skyhooks still need lots of rockets to reach the hook, just much less fuel needed to burn per trip.

> A skyhook differs from a geostationary orbit space elevator in that a skyhook would be much shorter and would not come in contact with the surface of the Earth. A skyhook would require a suborbital launch vehicle to reach its lower end, while a space elevator would not.

https://en.wikipedia.org/wiki/Skyhook_(structure)?oldformat=...

Almost all the fuel needed to reach orbit is used getting to 5 miles per second. Catching the skyhook needs none of that fuel, but only whatever is needed to get to altitude.

I.e., Blue Origin's pogo stick, or Virgin Atlantic's tour bus, would suffice. The requirements on such a vehicle are massively less than for an orbital launcher.

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