How close are we to a feasible space elevator? Once we have something that can withstand the forces involved, we can just ride up to space for a fraction of the energy and cost, and start our propulsion from orbit instead of the surface.

> How close are we to a feasible space elevator?

Perhaps infinitely far - at least I suspect the law against elevator on the grounds of danger to orbital assets will get passed as soon as somebody will get too close to the ideas to actually build it.

As I understand it, very far. The materials science isn't there, we have yet to conceive of a material that would be able to carry it's own weight let alone move a useful load.

No, the problem isn't in the material, that's relatively easy part, we already have good prototypes in carbon nanotubes.

My source:

> "No current material exists with sufficiently high tensile strength and sufficiently low density out of which we could construct the cable," he told me. "There's nothing in sight that's strong enough to do it — not even carbon nanotubes."

"The best that theorists can do right now is come up with a material that's about two-thirds the strength needed to make a practical elevator," Henson told me. "And that's a very, very short tiny tube."[0]

[0]https://io9.gizmodo.com/why-well-probably-never-build-a-spac...

The title should have mentioned the measure was diameter, rather than mass or volume. They give wildly different outcomes.

Anyone think this is an additional factor in the Fermi paradox? i.e planets that are too small can’t support a strong atmosphere and life. Planets that are too big make space travel too uneconomical.

I've often considered an alien planet with an atmosphere so thick that one couldn't see the night sky. Would inhabitants of this world even be interested in space travel? How much longer would it take for them to discover space, or even effective navigation of their own sphere? Maybe these people just wouldn't be explorers.

Then there is the Krikkit response to discovering a universe beyond the clouds: "It'll have to go."

Yes, but what about only 49% larger?

My question is what if we were unconcerned about the risks of nuclear powered rockets, could we get off a larger planet then?

The article doesn't seem to consider non-conventional launch strategies. With things like Project Orion, mid-air launches (by either balloon or plane), and space elevators all being theoretically possible, it seems unlikely that any given civilization would never be able achieve spaceflight, given enough time.

It's my impression that ideas for carbon nanotube space elevators would just barely be able to theoretically support their weight, even for earth, so there might not be any way at all for a larger planet, and we might never be able to make a practical one except for a smaller body with no atmosphere.

Right? A balloon first stage seems like an obvious work-around...

Insert xkcd about how the difficulty in getting to orbit is speed not altitude.

This is all the more true about a larger planet than earth.

Sure, you might have a thicker atmosphere, but that's an additional challenge. Needing a balloon (if it made sense, I couldn't do the calculation) would be a reflection of the difficulty above and beyond the increased orbital velocity that is the basic problem.

Well sure, but the majority of your energy spent is fighting to get up to speed while in the atmosphere. A balloon or dirigible or some buoyancy play should be able to get you to a certain atmospheric density regardless of planetary gravity. That cuts the bottom off of the rocket equation pyramid and reduces drag immensely at your 'starting' point.

Of course we could: https://xkcd.com/1162/