How expensive would a Lunar Elevator be? (approx 1.8 billion)

[Rakaydos]

A lunar space elevator is a proposed piece of infrastructure to make space exploitation easier. Unlike most plans, it has nothing to do with decreasing costs from earth's surface to low earth orbit. Instead, it reduces payload mass by making missions to the moon (and potentially beyond) easier and less Dv intensive.

So how expensive would one be to create, with current technoligy?

Based on this pdf (http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf) building an elevator who's counterweight is entirely cable, assuming a constant-stress exponential taper (it gets wider closer to L1 because it's holding more weight), is on the order of 300,000 km. (edit: fixed an order of magnatude error) That is also the minimum mass that would need to be launched from earth to bring the system online.

However, once the system is online, you can build a counterweight out of lunar rocks, reducing the amount of cable needed to keep the system functional. This lets you repurpse those strands to reinforce the main cable, allowing the tram to carry more mass to orbit on each trip. So the initial Tether needs only to have enough strength to bring the tram down with a small excavation bot and back up with a load of lunar rubble- it can be reinforced after construction.

The existing math assumes modern high strength composits, such as Carbon Fiber, Kevlar, or M5 Fiber. Page 21 of the PDF posted earlier shows the densities of canidate materials, and their stress limit. I have not been able to find costs per KG for these materials, but we can estimate the mass of cable needed, and calculate the number of launches needed- however mind boggling 300 km of rope is, the launch vehicals are still probably going to be the majority of the price.

On page 15 of the linked pdf there's an estimate of the mass of an entirely cable lift, presumably made from M5 Fiber, the selection that is givin the most weight in that paper, somewhat shy of 1,000,000 kg, or one thousand metric tons. (rounding up to include spools and such to manage the fibers)

A Falcon Heavy has a promised price of $90mil for 6.4 tons to GTO. lets round that down to 5 tons to L1, so the elevator will need on the order of 200 Falcon Heavy (or equivilant) launches to build. That works out to 1.8 billion dollars to launch the elevator, plus bulk material costs.

Of course, rockets get cheaper the more they're flown, and a lunar elevator would be buying launches in bulk. it's concevable that the effort to build a Lunar elevator would itself drive the launch prices down. And once it is in place, it would help stimulate demand for lunar missions, including surface mining, refining, and production of space-rated equiment that would be far cheaper to "launch" than anything bade earthside.

Edited May 20, 2015 by Rakaydos

[NFUN]

How heavy is 300km? Or did you mean the 300km of cable provides the minimum mass?

Edited May 19, 2015 by NFUN

[Rakaydos]

How heavy is 300km?

Of M5 fiber, with a constant-stress exponential taper? According to the PDF I linked (I assume they did the math correctly), a bit shy of 1,000 tons.

It's on Page 15

[kStrout]

if you just want to get off the moon, you can build a giant railgun on the surface.

[Rakaydos]

if you just want to get off the moon, you can build a giant railgun on the surface.

How heavy of a railgun? how many launches to assemble, what kind of lander are you using to put it on the moon?

I'm trying to put a pessimistic price tag on assembling the elevator, so there's a good price comparison to other space efforts.

[vger]

Are you factoring in labor costs and machinery, or JUST the cost of flying the raw materials and the cost of the materials themselves?

Either way, 1.8bil is a pretty good price for such an ambitious project.

[Rakaydos]

Are you factoring in labor costs and machinery, or JUST the cost of flying the raw materials and the cost of the materials themselves?

Either way, 1.8bil is a pretty good price for such an ambitious project.

Actually it's just the costs of flying the materials, rounded up multiple times to allow for other expenses. I couldnt find raw material prices for any of the candidate materials, but I'm assuming the materials costs are going to be lost in the launch costs... though I could be wrong. Labor and machinery I left off entirely- I have n idea where to begin for that kind of expense.

[NuclearNut]

That seems... a tad cheap for anything that ambitious. So I did the calculations myself:

(1000/5)90x10^6

Which gives us 18x10^9, or 18 billion dollars. Can someone confirm if that is correct?

It should also be noted that these things tend to get mired in what most will pass off as "mere technical details" as those details tend to be a significant problem in construction (eg. corrosion in early nuclear reactors). Thus it would be reasonable to double the cost of the hardware construction to include the reactor or transmission equipment needed to power the elevator, the R&D costs for the elevator, and the inevitable unexpected costs.

But it is still impressive, only four times as expensive as an AP 1000 in the US. Though the question now is, how safe would it be, and how long would the cable last, and then we can see how much it would cost compared to conventional launch..

[Nibb31]

How expensive is this compared to, for example, a reusable SSTO lander infrastructure? By the time we need regular access to the lunar surface, multiple reusable landers would offer more redundancy, more flexibility, and would not be limited to a single liftport, which might not be where you want to go.

In the end, there are too many unknowns at this stage.

Also, your cost figure only factors the launch cost, which is silly. The R&D and manufacturing alone would be orders of magnitude more expensive than that.

[Silver_Swift]

Cool idea, I hadn't heard/thought of putting space elevators on the place you want to go, rather than on earth.

I assume it being in a fixed location isn't that big of a deal since a project like this is basically only ever going to pay off if we have a functional permanently occupied lunar colony. In which case that is very likely where you want to go.

[drake000666]

They could not even build something like this with today's tech let alone build it for this cheap. I would say 100 billion on the low end and more then likely 500 billion when done , just think how expensive it is to build a bridge on earth let alone what it would cost for every mile of this cable would cast after construction costs.

[Rakaydos]

They could not even build something like this with today's tech let alone build it for this cheap. I would say 100 billion on the low end and more then likely 500 billion when done , just think how expensive it is to build a bridge on earth let alone what it would cost for every mile of this cable would cast after construction costs.

It is entirely possible with todays tech- that's the whole point. The price I list is strictly the transportation cost, not materials or labor, but two orders of magnatude difference is a bit much, ever for goverment pork.

[drake000666]

It is entirely possible with todays tech- that's the whole point. The price I list is strictly the transportation cost, not materials or labor, but two orders of magnatude difference is a bit much, ever for goverment pork.

How is it possible, your talking about holding a 300km cable in a geostationary orbit around the moon as the moons and earths gravity acts on it and what do you think will happen when this cable moves true the earths magnetic field and how to you think you can get a 300km cable in place to begin with

[Rakaydos]

Actually, it's not geostationary orbit. (there isnt a geostatinary orbit around the moon) It passes through the L1 Lagrange point instead. Because the moon is tidelocked, it remains effectively stationary, pointed directly toward earth the entire month, and the earth's gravity is what holds the structure up.

As for putting it in place, I'd imagine you get all the cable in big spools to the L1 point, then start reeling it out in both directions until the moonside spool hits dirt.

[moronwrocket]

300km is the characteristic height of the cable - the maximum length it can be under a 1g field before it rips itself off. 300 km does not hit the L1 Lagrange point for the Earth/Moon system.

http://www.ottisoft.com/Activities/Lagrange%20point%20L1.htm

L1 is a-x-Rmoon above the surface, or about 384,044 km - 326,054 km - 1,737 km = 56,253km

Also, since you start at L1 and go up and down, how do you use regolith to counterbalance your cable?

I suppose you could start with a half-thickness cable going up beyond L1 and down to the surface, and once you reach the surface and can send loads up, you fill up L1 with your counterweight, then send up a special robot with the bottom end back up to the top, while at the top you spool out your counterweight while bringing down your cable.

And you want to do this over 112,000 km?

Just doesn't seem reasonable.

[Requia]

That seems... a tad cheap for anything that ambitious. So I did the calculations myself:

(1000/5)90x10^6

Which gives us 18x10^9, or 18 billion dollars. Can someone confirm if that is correct?

It should also be noted that these things tend to get mired in what most will pass off as "mere technical details" as those details tend to be a significant problem in construction (eg. corrosion in early nuclear reactors). Thus it would be reasonable to double the cost of the hardware construction to include the reactor or transmission equipment needed to power the elevator, the R&D costs for the elevator, and the inevitable unexpected costs.

But it is still impressive, only four times as expensive as an AP 1000 in the US. Though the question now is, how safe would it be, and how long would the cable last, and then we can see how much it would cost compared to conventional launch..

I think the real question isn't necessarily 'can we afford this' but 'is an LEO to mun reusable barge cheaper'. The whole reason that infographic has it attached to the south pole is there's apparently water down there, one of the mere technical details you mention is building a real ISRU and mining system, without that there's not really a reason to go so often that this is cost effective. But once we've done that, the cost of fuel in space goes way way down (or this turns out the equipment and R&D is so expensive it's not worthwhile and the moonvator isn't worthwhile either), and now we don't really need the moon elevator... it's a cool long term science fiction concept in that I'm pretty sure this will actually work given carbon nano-tube ribbon, but there's no reason for it unless travel there is incredibly frequent.

[Rakaydos]

300km is the characteristic height of the cable - the maximum length it can be under a 1g field before it rips itself off. 300 km does not hit the L1 Lagrange point for the Earth/Moon system.

http://www.ottisoft.com/Activities/Lagrange%20point%20L1.htm

L1 is a-x-Rmoon above the surface, or about 384,044 km - 326,054 km - 1,737 km = 56,253km

Also, since you start at L1 and go up and down, how do you use regolith to counterbalance your cable?

I suppose you could start with a half-thickness cable going up beyond L1 and down to the surface, and once you reach the surface and can send loads up, you fill up L1 with your counterweight, then send up a special robot with the bottom end back up to the top, while at the top you spool out your counterweight while bringing down your cable.

And you want to do this over 112,000 km?

Just doesn't seem reasonable.

...you're right, I misread the scale of the graph on page 15. it's 300 thousand KM, not 300 km, for an entirely cable based counterweight (the lightest option, requiring the least earth based lift)

Fortunately I'm taking my mass numbers from the same document, instead of calculating it myself- so my error doesnt reflect on my lift cost calculation.

As for replacing the extra cable with a regolith counterweight, its not nessisary, but it would be cheaper than sending another full set of cables from earth to the moon if you wanted to expand the system capacity.

Edited May 20, 2015 by Rakaydos

[Findthepin1]

If it were not to have "weight" on the Moon it would need to be balanced with the Moon's spin. The Moon is tidally locked to Earth. Any lunar elevator with no apparent weight on the Moon's surface would have to be as long as the distance between the Moon and Earth, so it would need to be anchored to the Earth in order not to collapse onto the Moon. Of course the Earth spins nearly thirty times too quickly for this falsifying my design. If I am incorrect please let me know.

[KSK]

Wikipedia has a decent looking summary of this. It seems that high tensile polymers such as ultra high molecular weight polyethylene (Spectra) will do the job. Granted, spinning out thousands of kilometres of plastic isn't at all trivial but it beats the heck out of doing the same thing with any kind of composite.

[Rakaydos]

If it were not to have "weight" on the Moon it would need to be balanced with the Moon's spin. The Moon is tidally locked to Earth. Any lunar elevator with no apparent weight on the Moon's surface would have to be as long as the distance between the Moon and Earth, so it would need to be anchored to the Earth in order not to collapse onto the Moon. Of course the Earth spins nearly thirty times too quickly for this falsifying my design. If I am incorrect please let me know.

Earths gravity well is deeper than the moon's. The earth moon balance point (lagrange point) is only 50-60 thousand km from the lunar surface. Depending on the counterweight the cable cpuld stop there (huge counterweight just barely in the earths SoI) or trail on for another 240 thousand km,which is still well short of earth, if it had no counterweight at all.

[-Velocity-]

Assuming the Earth-Moon L1 is around 60,000 km from the surface of the Moon (too lazy to calculate it right now), then you're looking at a pretty long trek down to the lunar surface. Assuming your crawler or crank/pulley operates at 200 km/h, that's a 12.5 day trip. If it's manned, it better have a beefy shelter in case the Sun flares up.