BFS for construction of a Lunar Elevator?

[RDoc]

The numbers I've seen for a Lunar Elevator require something less than 1000T of material, so about 10 BFS launches, with LEO refueling. I haven't worked out any numbers, but if we assume $30M per launch, 5 launches per mission, 100T per mission that's about $150M per mission, about $1.5B to get the material for the elevator in place.

That doesn't seem too crazy, especially if it were done as an international effort, which I'd think would be a requirement anyway. There are a very limited number of simultaneous elevators possible I believe.

If that were done, a lot of other things get easier and cheaper since the cost of getting stuff on and off the lunar surface would be so much easier.

[Nomadd]

The numbers I've seen for a Lunar Elevator require something less than 1000T of material, so about 10 BFS launches, with LEO refueling. I haven't worked out any numbers, but if we assume $30M per launch, 5 launches per mission, 100T per mission that's about $150M per mission, about $1.5B to get the material for the elevator in place.

That doesn't seem too crazy, especially if it were done as an international effort, which I'd think would be a requirement anyway. There are a very limited number of simultaneous elevators possible I believe.

If that were done, a lot of other things get easier and cheaper since the cost of getting stuff on and off the lunar surface would be so much easier.

No telling where you saw numbers, but you might have noticed that the moon doesn't spin very fast. I think you'd have to build an elevator out past L1 or L2, meaning more that 60,000 kilometers long.

[Asteroza]

The Liftport guys were busy putting papers out 3 or 4 years ago regarding a lunar space elevator through L1, and I think they had a single beginner tether supporting very light payloads as one launch (but that probably needs a tug for delivery...) that didn't look totally insane and did not use unobtanium. Liftport has gone real quiet though, especially after the rolling trainwreck that was their kickstarter campaign...

[Tuna-Fish]

No telling where you saw numbers, but you might have noticed that the moon doesn't spin very fast. I think you'd have to build an elevator out past L1 or L2, meaning more that 60,000 kilometers long.

That is correct. It needs to be even longer than that, as you need to put your counterweight far past L1 to have any real lifting ability at lunar surface. However, it could still be built because the cable would not have to be all that strong. A ribbon made of kevlar is strong enough.

The seminal study on the subject was done by niac. (pdf) While a lunar elevator is still pretty out there, it has the massive advantage over a terrestrial one in that it can be built from materials that already exist and are in mass production, and still have reasonable amount of engineering margin, allowing things like multi-ribbon structures where loss of a ribbon does not mean loss of the elevator, and a repair vehicle could still climb up on a surviving one to hang a new one.

[Keldor]

You could in theory make a lunar elevator at whatever weight you wanted by making it thinner or thicker.  But of course, this directly affects how much payload can be transported up or down it at a time.  A very long strand of nylon fishing line secured at both ends would technically be a lunar elevator, but it would be of limited utility.

Keep in mind that it will take something on the order of a month for your cab to travel from one end of the elevator to the other.  For it to provide a useful throughput, it needs a decent capacity.

Does anyone have any elevator mass vs. throughput numbers floating around?

[Tuna-Fish]

Does anyone have any elevator mass vs. throughput numbers floating around?

Read the paper I linked, it's all there.

[RDoc]

You could in theory make a lunar elevator at whatever weight you wanted by making it thinner or thicker.  But of course, this directly affects how much payload can be transported up or down it at a time.  A very long strand of nylon fishing line secured at both ends would technically be a lunar elevator, but it would be of limited utility.

Keep in mind that it will take something on the order of a month for your cab to travel from one end of the elevator to the other.  For it to provide a useful throughput, it needs a decent capacity.

Does anyone have any elevator mass vs. throughput numbers floating around?

Actually, you need very strong materials because the link has to support itself. Things like Kevlar work, Nylon wouldn't, it can't even support its own weight. The weight of the payload certainly is an issue with the design, but the weight of the cable plus any counterweight dominates by a lot.

[RDoc]

No telling where you saw numbers, but you might have noticed that the moon doesn't spin very fast. I think you'd have to build an elevator out past L1 or L2, meaning more that 60,000 kilometers long.

Lunar elevator designs don't work by centrifugal force. They are based on a balance of Lunar and Earth gravity. That is, the elevator extends straight towards the Earth, well past L1, and is tensioned by Earth's gravity, not centrifugal force as a Martian or Earth elevator. Many designs use a counterweight at the end which is attracted by the Earth to tension the cable. It's also possible to build one on the other side of the Moon, but that's not very useful. That also means that it's not possible to build lots of independent ones. They all have to aim pretty much at the Earth.

Some of the interesting designs are aimed at the Earth and have side links to the poles (or other locations).

[RobLynn]

Slinging stuff from ~5km tall Malapert mountain at the lunar south pole (near likely shaded water deposits) using a rotating tether several hundred km long is probably much cheaper, can probably be done with a few hundred tonnes of payload, and can launch at low enough acceleration for humans.  Most valuable real estate on the moon (IMHO)
https://forum.nasaspaceflight.com/index.php?topic=5420.msg1865335#msg1865335

[raketa]

Slinging stuff from ~5km tall Malapert mountain at the lunar south pole (near likely shaded water deposits) using a rotating tether several hundred km long is probably much cheaper, can probably be done with a few hundred tonnes of payload, and can launch at low enough acceleration for humans.  Most valuable real estate on the moon (IMHO)
https://forum.nasaspaceflight.com/index.php?topic=5420.msg1865335#msg1865335

interesting idea

[Lar]

I think Jon Goff posted something about this on Selenian Boondocks a few years back. It's a crazy sounding idea that might work well!

[Tulse]

Many designs use a counterweight at the end which is attracted by the Earth to tension the cable.

How big a counterweight?  It might be problematic if the cable broke...

[rakaydos]

Many designs use a counterweight at the end which is attracted by the Earth to tension the cable.

How big a counterweight?  It might be problematic if the cable broke...

How far from L1 do you want your cable to stretch? if you stretch it halfway to geosynch, you don't need a counterweight at all- the weight of the cable in earth's gravity is enough to keep the cable in luna's gravity aloft. But the shorter you make the cable, the more counterweight you need at the tip to make up for it.

Generally, though, the counterweight is in a stable, elliptical orbit that shouldn't cause any problems at earth,

[Lampyridae]

Many designs use a counterweight at the end which is attracted by the Earth to tension the cable.

How big a counterweight?  It might be problematic if the cable broke...

Make it out of something that won't be a hazard. Eg a water-filled balloon. Unzip a side and let the contents spew into space and boil away.

[ZChris13]

Many designs use a counterweight at the end which is attracted by the Earth to tension the cable.

How big a counterweight?  It might be problematic if the cable broke...

Counterweight in this case, among the kinds of people who suggest space elevators, typically means "propellant depot"
When you're putting that much mass up, at least make it useful.

Hmmmm, how much gravity would the counterweight feel? Maybe enough for a farm or other preposterous ideas

[speedevil]

The numbers I've seen for a Lunar Elevator require something less than 1000T of material, so about 10 BFS launches, with LEO refueling. I haven't worked out any numbers, but if we assume $30M per launch, 5 launches per mission, 100T per mission that's about $150M per mission, about $1.5B to get the material for the elevator in place.
<snip>
If that were done, a lot of other things get easier and cheaper since the cost of getting stuff on and off the lunar surface would be so much easier.

This is directly competing against lunar ISRU - pretty much.
Even only doing lunar oxygen slashes costs hard.

The moon is nice in that (with a depot in lunar orbit), you aren't really in the deeply exponential part of the rocket equation, especially for downmass.

A 1100 ton wet ~starkicker class lander can drop nearly 550 tons of cargo on the surface and return to LLO.

Try this in LEO and ...

A tether for earth would have lots more benefit than for the moon, as SSTO on earth makes all of your payload vanish.

[hkultala]

Many designs use a counterweight at the end which is attracted by the Earth to tension the cable.

How big a counterweight?  It might be problematic if the cable broke...

Counterweight in this case, among the kinds of people who suggest space elevators, typically means "propellant depot"
When you're putting that much mass up, at least make it useful.

Propellant depot would not work, as the weight of the counterweight would change too much and the system would become unstable considerable amount of the propellant would be used. The weight of the counterweight has to stay relatively constant.

But the counterweight could consist of living spaces of astronauts, and lots of solar cells.

[Tuna-Fish]

Many designs use a counterweight at the end which is attracted by the Earth to tension the cable.

How big a counterweight?  It might be problematic if the cable broke...

The counterweight would be in a stable orbit* even if the cable broke.

(* relatively stable. The apogee would be so high it would get perturbed by the moon on every pass, and over long timescales would probably crash down or get flung out or something. Realistically, in case the cable snapped, it would be brought back into place and a new one fitted before any funny business happened.)

[RoboGoofers]

How is this related to Starship, again?

[rakaydos]

How is this related to Starship, again?

"Things Starship makes possible on a single nation's budget or less."