A Lunar Space Elevator Is Actually Feasible & Inexpensive, Scientists Find

From NASA and ESA (the European Space Agency) to Jeff Bezos and Elon Musk, it’s every space institute’s and tech billionaire’s dream to take return to the moon during this century.

more…

Tau.Neutrino said:

A Lunar Space Elevator Is Actually Feasible & Inexpensive, Scientists Find

From NASA and ESA (the European Space Agency) to Jeff Bezos and Elon Musk, it’s every space institute’s and tech billionaire’s dream to take return to the moon during this century.

more…

These are astronomers, not engineers.

dv said:

Tau.Neutrino said:

A Lunar Space Elevator Is Actually Feasible & Inexpensive, Scientists Find

From NASA and ESA (the European Space Agency) to Jeff Bezos and Elon Musk, it’s every space institute’s and tech billionaire’s dream to take return to the moon during this century.

more…

These are astronomers, not engineers.

My thoughts exactly.

Nice idea, but they should get someone to check their numbers.

dv said:

Tau.Neutrino said:

A Lunar Space Elevator Is Actually Feasible & Inexpensive, Scientists Find

From NASA and ESA (the European Space Agency) to Jeff Bezos and Elon Musk, it’s every space institute’s and tech billionaire’s dream to take return to the moon during this century.

more…

These are astronomers, not engineers.

The whole project may cost a few billion dollars, which is “within the whim of one particularly motivated billionaire,” said Penoyre.

ROFL

So it’s a 40 tonnes, stretched over 320000 km.

That’s 0.125 grams per metre.

“the lunar elevator would be a cable thinner than a pencil “

Well you’re fuckin’ right about that. They haven’t specified any materials but if it is steel, it will be about a tenth of a millimetre across, a mere filament. It won’t have the tensile strength to support its own weight even in lunar gravity.

I think they’ve made very serious order of magnitude errors.

Maybe they are engineers…

dv said:

So it’s a 40 tonnes, stretched over 320000 km.

That’s 0.125 grams per metre.

“the lunar elevator would be a cable thinner than a pencil “

Well you’re fuckin’ right about that. They haven’t specified any materials but if it is steel, it will be about a tenth of a millimetre across, a mere filament. It won’t have the tensile strength to support its own weight even in lunar gravity.

I think they’ve made very serious order of magnitude errors.

Maybe they are engineers…

Hey…

dv said:

So it’s a 40 tonnes, stretched over 320000 km.

That’s 0.125 grams per metre.

“the lunar elevator would be a cable thinner than a pencil “

Well you’re fuckin’ right about that. They haven’t specified any materials but if it is steel, it will be about a tenth of a millimetre across, a mere filament. It won’t have the tensile strength to support its own weight even in lunar gravity.

I think they’ve made very serious order of magnitude errors.

Maybe they are engineers…

They must have specified naterials somewhere. If they’ve assumed continuous carbon nanotubes then that might work (it’s a long time since i checked the math).

So far, continuous carbon nanotubes have only bern made ten or so metres long, but there’s no fundamental reason why they couldn’t be made more than km long.

Rope made from short sections of nanotube in resin haven’t a hope in hell of working. CSIRO was getting steength drops of a factor of 100 on a good day.

mollwollfumble said:

dv said:

So it’s a 40 tonnes, stretched over 320000 km.

That’s 0.125 grams per metre.

“the lunar elevator would be a cable thinner than a pencil “

Well you’re fuckin’ right about that. They haven’t specified any materials but if it is steel, it will be about a tenth of a millimetre across, a mere filament. It won’t have the tensile strength to support its own weight even in lunar gravity.

I think they’ve made very serious order of magnitude errors.

Maybe they are engineers…

They must have specified naterials somewhere. If they’ve assumed continuous carbon nanotubes then that might work (it’s a long time since i checked the math).

So far, continuous carbon nanotubes have only bern made ten or so metres long, but there’s no fundamental reason why they couldn’t be made more than km long.

Rope made from short sections of nanotube in resin haven’t a hope in hell of working. CSIRO was getting steength drops of a factor of 100 on a good day.

The top end of experimental tensile strength of carbon nanotubes is about 60 GPa.
Density is about 1500 kg/m^3.

So if you were somehow able to manufacture a long cable of this stuff (and that’s probably not on the cards for the foreseeable future), then IF it managed to keep those bulk specs, then under lunar gravity it would be able to support about 25000 km of its own weight.

Which is fucking amazing but it’s not even a tenth of the way from the Earth to the Moon.

Jesus knows what it would cost but it’s not a “few billion dollars”.

dv said:

So it’s a 40 tonnes, stretched over 320000 km.

That’s 0.125 grams per metre.

“the lunar elevator would be a cable thinner than a pencil “

Well you’re fuckin’ right about that. They haven’t specified any materials but if it is steel, it will be about a tenth of a millimetre across, a mere filament. It won’t have the tensile strength to support its own weight even in lunar gravity.

I think they’ve made very serious order of magnitude errors.

Maybe they are engineers…

Ooooh!

The text says:

We now have two conditions on η(h), both of which must be satisfied for a uniform-area spaceline to be possible. We can rearrange these to a condition on the strength of the material, α > η(1 −rD ) − η(l) ∼ 2.6. Thus a constant area spaceline can exist for any material with a relative strength of ∼ 3 or greater, which, with reference to Table 2, a number of currently manufacturable materials satisfy.

Okay so I’ll choose one of the materials from their table that has r.s. >3. Dyneema is probably the strongest that is commercially available, and has r.s. = 3.5.

According to the article, it has density 970 kg/m^3, and strength 3.6 GPa.

By my calcs, a constant area line of density 970 kg/m^3 from the height of geostationary orbit to the lunar surface would have a maximum tension of 7.0 GPa, about twice the strength of Dyneema.

I think I’ve found the booboo. Pages 5 and 6,

α > η(1 −r/D) − η(l) ∼ 2.6.

They’ve plugged in the lunar surface there (1-r/D) instead of the hanging end.

I’ll email them.

Scrub that.

They’ve done a bit of a bait and switch …

In the lede they are talking about a line from lunar surface to the height of a geostationary orbit (about .11 D), but they later show that the maximum height of the end of the line is 0.24 D, and they’ve proceeded with that. Given their list of materials, Zylon could get you to about 0.2 D.

(shrugs)

So using the strongest bulk produced substance known to man right now, you could set a constant area line from the moon to a point about 70000 km above the Earth’s surface, which is way above geostrationary.

I mean I guess it’s better than nothing, but you still have to launch the materials to a 70000 km orbit.

The news article says “ would be a cable thinner than a pencil “

The arxiv article says “only a little more than a pencil lead”. That’s pretty different. a pencil might be 8 mm across. A pencil lead is less than a millimetre.

It uses a reference width for its “hybrid line” as 10 ^−7 m^2 of Zylon. That corresponds to about 0.4 mm thickness.

I was going to ask about micrometeors but I see they have a footnote suggesting that multiple strands be used and segments repaired systematically.

How are we going to manufacture a filament 200 000 km long? How are we going to deploy it or prevent it from becoming tangled?

dv said:

mollwollfumble said:

dv said:

So it’s a 40 tonnes, stretched over 320000 km.

That’s 0.125 grams per metre.

“the lunar elevator would be a cable thinner than a pencil “

Well you’re fuckin’ right about that. They haven’t specified any materials but if it is steel, it will be about a tenth of a millimetre across, a mere filament. It won’t have the tensile strength to support its own weight even in lunar gravity.

I think they’ve made very serious order of magnitude errors.

Maybe they are engineers…

They must have specified naterials somewhere. If they’ve assumed continuous carbon nanotubes then that might work (it’s a long time since i checked the math).

So far, continuous carbon nanotubes have only bern made ten or so metres long, but there’s no fundamental reason why they couldn’t be made more than km long.

Rope made from short sections of nanotube in resin haven’t a hope in hell of working. CSIRO was getting steength drops of a factor of 100 on a good day.

The top end of experimental tensile strength of carbon nanotubes is about 60 GPa.
Density is about 1500 kg/m^3.

So if you were somehow able to manufacture a long cable of this stuff (and that’s probably not on the cards for the foreseeable future), then IF it managed to keep those bulk specs, then under lunar gravity it would be able to support about 25000 km of its own weight.

Which is fucking amazing but it’s not even a tenth of the way from the Earth to the Moon.

Jesus knows what it would cost but it’s not a “few billion dollars”.

> Which is fucking amazing but it’s not even a tenth of the way from the Earth to the Moon.

Oh. Did you take into account cross section change, it can be thinner when the stress on it is smaller, near the end, in order to reduce self-weight. Say if it has a payload of 500 kg in addition to self weight.

> it’s not a “few billion dollars”

Perhaps it is. Costs are high now only because demand is low. I keep in mind the Golden Gate bridge. Before construction of the Golden Gate, the cost of steel wire was enormous. The bridge could never have been built at that cost. But because demand was so huge during construction, the cost of steel wire plummeted.

There are two main classes of manufacturing method. One is by using methane decomposition at high temperature on a nanotube-metal interface. The other is by carbonising a linear polymer such as polyacrylonitrile or rayon.

Neither process is particularly intrinsically expensive. Or to put it another way, In bulk, nanotube wire could be made for ballpark the same cost (give or take a factor of ten) as steel wire.