Space elevator ? How can it work?

[Gfellow]

...huge man power commitment (and money). With the bean stalk we are talking about using materials that have not been invented yet, and building techniques that do not exist.

I put it to you that we have emerged into a new paradigm. The adept control of manpower and resources was the great triumph of the past two centuries, a tool we now take for granted. The flower of our epoch is the additional thrust of efficient research towards a given end.
When Kennedy told the world the US was going to put a man on the moon in a decade, the NASA science staff were gobsmacked. Although it is what they wanted, they had not really taken the time to sweat the details. However, it turned out to be a confirmation that this paradigm was upon us.

The REAL issue comes down to, 'is it worth it?'.

As a rule, nation-state military systems tend to be conservative and usually remain complacent unless there is an imminent and obvious threat. Seen in this light, the space elevator can be dealt with in three ways:
1. A space elevator race could ensue between nation-states.
2. An agreement might be forged to share costs and build an international space elevator, the advantage being that no individual nation-state gains an overall advantage.
3. Agreeing amongst themselves not to build it at all, which would suggest a conspiratorial component historically uncharacteristic of such entities.

 

[mugaliens]

OK, we make the cable, how are we supposed to get it to the earth.

You build the geosynchronous location, along with the counterweight, then slowly lower the cable while simultaneously extending the counterweight further out. Once the cable is anchored on Earth, you can extent the counterweight further in order to apply tension along the length of the cable.

 

[DaveC426913]

You build the geosynchronous location, along with the counterweight, then slowly lower the cable while simultaneously extending the counterweight further out. Once the cable is anchored on Earth, you can extent the counterweight further in order to apply tension along the length of the cable.

You stopped reading halfway through his sentence. He explains why he thinks getting it to Earth might be problematic.

 

[Phrak]

There are about 400 satellites in geosynchronous orbit. At present, launch costs run from $4K to $40K per kilogram dependent upon dependability of launch. Taking $10K/kilogram cost as a near-future cost for rocket launches, how much will the cost equivalent of a space elevator be to amortize 4000 satellites to break even with rocket lauch profits? (Hint: you need to know the average mass of a satellite.)

 

[Phrak]

The folks I work for make boxes that cost the customers x dollars apiece. At the premium launch dependability demanded, the customer pays 0.2x to get it to orbit. For this particular component, launch cost is only 1/5 of payload cost. I don't see any significant economic advantage for a marginal price break to develop this technology.

 

[mugaliens]

Agreed, Phrak - Not in the case of your customer and their product, no.

Before anyone, private or government, begins to work in ernest on the space elevator, there will have to be demonstrable economic benefit over current Earth to LEO launch platforms.

It's not necessarily a pipe dream, but it's both a long way off, and may never be economically viable.

One principle tenet of management is to ensure technology is developed in support of business goals, principles, and practices, and never becomes a driver of those business rules. This holds as true for the space program as it does for Company X looking to upgrade aging computer systems. Define the need, then find the best solution.

Occasionally, it'll be something as exotic as the space elevator! Given the fact my alma mater's entire computing storage across all university and student-owned storage passed the 1 TB hurdle in 1986, I agree that a 1 TB external hard sitting on my desk is ridiculous! Yet I have two of them. Go figure.

But I didn't buy them because they existed. I bought them because I do daily incremental, and weekly full backups of my computer's 120 GB hard drive, of which about 80 GB is full of user data. I swap out the TB drives weekly, storing them off-site, as I've literally decades of data on them.

I bought them because my needs were such that I needed two 1 TB drives, not because 1 TB drives were "cool," or that I had money to blow. They're simply a safe and effective tool to ensure my computing requires would continue relatively unabated in the event of theft or fire.

Given that my off-site storage is only a mile away, however, I think I'm pretty susceptible to nuclear holocaust...

...but I'm hoping and praying against all hope that will never be the case! LoL!

Back to the space elevator concept: Noteworthy concept! Proponents must learn that technology doesn't drive adoption. Econonomics drive adoption. If it's cheaper in the long run, and only well-proven to be so, it will be adopted. Otherwise, it will remain a "gee whiz" technology, neat, but not economically useful.

 

[dr dodge]

an elevator space race...could you imagine
the satelites would have to be swerving around like a race at sears point.
the Earth would look like a daisy from space.

can a geosat have an eliptical orbit, or will they always be a (somewhat) perfect circle?
what linear distance is the actual wobble of the earth?
we'd need to handle that slack, and keep a constant even tension

dr

 

[mgb_phys]

Proponents must learn that technology doesn't drive adoption. Econonomics drive adoption.

But sometimes technology drives economics.
Just like your Tb harddrives and fast internet connection chnages the economics of selling movies container ships change the economics of where you build stuff.

If you can put somethign into orbit for the same price as airmail it's likely to have some unforseen economic effects beyond what we currently use space for.

 

[mugaliens]

But sometimes technology drives economics.
Just like your Tb harddrives and fast internet connection chnages the economics of selling movies container ships change the economics of where you build stuff.

Oh, I agree! I wouldn't be working from home without it! However, technology is an enabler, not a driver. As an enabler, it's certainly changed the variables in the economnic equation of whether to work from home or sit in a corporate office.

If you can put something into orbit for the same price as airmail it's likely to have some unforseen economic effects beyond what we currently use space for.

Absolutely. Currently, space elevators are not technologically feasible. If/when they become technologically feasible, they may or may not ever become economically feasible.

Given unlimited funds we might accomplish all sorts of technical feats! However, our funds are limited, so we follow (more or less) the most economical approach.

As for our use of space, communication satellites were once considered the heat, but advances in fiber optics (the ocean floors are littered with them) have resulted in fiber carrying nearly all global communication traffic. NASA would love to sell you space, but aside from exploring, there's exceedingly little space offers at economically more favorable rates than we can achieve here on Earth. As for manned exploration, those unmanned Martian rovers are still kicking!

 

[Phrak]

Otherwise, it will remain a "gee whiz" technology, neat, but not economically useful.

It's pretty 'gee whiz' to me, otherwise I wouldn't be posting to see if someone can show me wrong.

But I still want to see the equations for things like required tensile strength and things like that (this is, after all a physics forum) so I don't have to derive them.

(And what would the unloaded diameter of the cable be as a function of height such that each element of the cable is under the same tension, anyway?)

 

[mgb_phys]

but aside from exploring, there's exceedingly little space offers at economically more favorable rates than we can achieve here on Earth.

If transport was cheap enough there a bunch of alloys and materials that would be easier to make in zero G, access to infinite vacuum and cold might also be handy industrially.

It's going to have to get a lot cheaper than the Shuttle though !

 

[Gfellow]

there will have to be demonstrable economic benefit...
Proponents must learn that technology doesn't drive adoption. Econonomics drive adoption. If it's cheaper in the long run, and only well-proven to be so, it will be adopted. Otherwise, it will remain a "gee whiz" technology, neat, but not economically useful.

Finding an immediate economic reason would be nice and I'm sure that there are SE proponents who might expand on that, but as unpopular as my comment might be, the foremost priority is tactical. If it is not an international effort, some nation state - US, China, Japan, will make the move. Whoever does it will insist it is economic in nature, but the fact is that the owner of the SE gets to decide what goes up.

 

[LURCH]

This is an area of lively study. The cable is heap big flexible and can be maneuvered. Simulations have been done that show the cable can be moved out of the way of any satellites. (Don't assume that it is as simplistic as I describe. There's a lot more to it.)

I do believe it is possible, and even probable, that the materials to build a space elevator will soon be developed. However, the simple construction of an inanimate tether would be a gargantuan engineering challenge. The idea that we could ever build one that spends its entire operational life performing a combination of dodge ball and hula dance is beyond the limits of mike credulity.

At this point putting a space elevator on Mars is the equivilent to putting a Starbucks there. When it does become possible it will probably be ancient technology.

The beanstalk on Mars would have the same problem I'm concerned about with an Earth based system, but on steroids: the satellite it would have to dodge is Phobos!

 

[DaveC426913]

The idea that we could ever build one that spends its entire operational life performing a combination of dodge ball and hula dance is beyond the limits of mike credulity.

Based on what? Your intuition?

How many satellites is the cable actually likely to encounter?

Consider that, with all the satellites we currently have in orbit, we almost never have collisions. We almost never worry about the ISS colliding with anything.

Granted, the cable is a line instead of a point, which multiplies the odds. But what do you get when my multiply "very-nearly zero" by even a largish value? You get "something a little more than zero".

Your intuition is not a reliable yardstick in this case.

 

[mugaliens]

If transport was cheap enough...

Aye, there's the rub.

It's going to have to get a lot cheaper than the Shuttle though !

Unfortunately, it will require several hundred heavy lifts simply to construct it! That doesn't seem to daunt http://www.liftport.com/" , however. Their FAQs page addresses most of the concerns raised here.

 

[LURCH]

Based on what? Your intuition?

Based on the rarity of any extremely complex system operating perfectly 100% of the time.

How many satellites is the cable actually likely to encounter?

A few thousand (nearly every satellite that isn't in geosynchronous orbit), and each one repeating over and over, ad nausium.

Consider that, with all the satellites we currently have in orbit, we almost never have collisions. We almost never worry about the ISS colliding with anything.

Granted, the cable is a line instead of a point, which multiplies the odds. But what do you get when my multiply "very-nearly zero" by even a largish value? You get "something a little more than zero".

It's not the geometry of the cable that makes the biggest difference, but the fact that it is stationary. Every satellite that is below geosynch (and not in some orbital period that is a factor of 24hr) must eventually pass through the space occupied by the cable. That's somewhere around 3,000 to 5,000 satellites (at a rough guess), each one repeating the encounter thousands of times. That's millions of encounters that must be avoided, and a single failure would spell disaster.

Your intuition is not a reliable yardstick in this case.

No-one's intuition, whether based on pecimism or wishfull thinking, is a reliable yardstick in this case.

 

[ShotmanMaslo]

All space elevator concepts don't require currently unfeasible high tensile strenght materials. The Launch Loop substitutes tensile strenght with kinetic energy of moving belt, so no new materials need to be developed.

I think the best alternative would be either the launch loop, electromagnetic mass drivers, or heavy lifters (150 tons or more). Of course I am not talking about satellite lifts, current rockets are enough for them, but things like space stations, tourism, moon colony, asteroid mining.. cannot be feasibly acomplished with current rocket technology.

 

[FredGarvin]

The Launch Loop topic has really injected a dose of reality to this thread

 

[DaveC426913]

Every satellite that is below geosynch (and not in some orbital period that is a factor of 24hr) must eventually pass through the space occupied by the cable.

That's not true.

 

[Phrak]

Um. How about every satellite or orbital debree that is below geosynchronous orbit, whose period is irrational with respect to a sidereal day, will eventually thread the space occupied by the cable?

Of course it could take good a while to sweep out enough area, and other collisions, solar wind, and perturbations have been ignored in the argument.

What's the diameter of the cable?

 

[DaveC426913]

What's the diameter of the cable?

A couple of metres.


[ EDIT: No idea. ]

 

[wolfkeeper]

The Launch Loop topic has really injected a dose of reality to this thread

Space elevators currently are impossible to build; the carbon nanotube *cable* doesn't exist to do this right now; not even 6 inches of it. The strongest engineering materials available can't build the space elevator.

So far as anyone has been able to show, launch loops are actually possible right now, and fairly economic as well.

Basically, space elevators are a very elegant idea; but elegance isn't enough.

With space elevators if you get past the materials problem, there's the space radiation problem lurking- space elevators are only good for cargo because the van Allen belts are like experiencing continuous dental x-rays for several days; you wouldn't *quite* get radiation sickness unless the elevator car broke down, but it's far, far above permitted limits. The materials or techniques to shield humans better don't exist either (until you get to very, very big and very, very expensive space elevators), existing materials would be too heavy.

Launch loops have the same problem to some degree; the radiation is annoyingly high; but launch loops payloads traverse the belts *very* fast and the radiation limits aren't exceeded.

 

[ShotmanMaslo]

Space elevators currently are impossible to build; the carbon nanotube *cable* doesn't exist to do this right now; not even 6 inches of it. The strongest engineering materials available can't build the space elevator.

So far as anyone has been able to show, launch loops are actually possible right now, and fairly economic as well.

Basically, space elevators are a very elegant idea; but elegance isn't enough.

With space elevators if you get past the materials problem, there's the space radiation problem lurking- space elevators are only good for cargo because the van Allen belts are like experiencing continuous dental x-rays for several days; you wouldn't *quite* get radiation sickness unless the elevator car broke down, but it's far, far above permitted limits. The materials or techniques to shield humans better don't exist either (until you get to very, very big and very, very expensive space elevators), existing materials would be too heavy.

Launch loops have the same problem to some degree; the radiation is annoyingly high; but launch loops payloads traverse the belts *very* fast and the radiation limits aren't exceeded.

I agree, Launch Loops are more possible now because they don't require sci-fi materials. Engineering problems can be overcomed, but if you don't have material with enough tensile strenght, cable approach is just a no go...

Why would you want to go through van Allen belts? LEO is almost completely under them. And Launch Loop will certainly not be higher than 80 km..

 

[wolfkeeper]

I agree, Launch Loops are more possible now because they don't require sci-fi materials.
Why would you want to go through van Allen belts?

You don't particularly, but you don't have *that* much choice.

LEO is almost completely under them.

Yes, there's no way to get directly to LEO from a space elevator of course, you have to go to GEO first. Well, you can, you can go up an elevator with a rocket ~1000km and then go from there, single stage. It's quite a small rocket actually, because of the height and lack of atmosphere.

And Launch Loop will certainly not be higher than 80 km..

Yup. But Lofstrom's launch loops are sized to throw to escape velocity. You can use them to reach LEO as well, but you really want to go to escape because that allows you to reach the moon, Mars etc. LLs also don't like being off the equator that much due to coriolis effects, but it's probably not a show-stopper to put them elsewhere, it just costs a bit more.

 

[dr dodge]

I just researched the launch loop.
again, all I can say is...
how is that any more do-able than the elevator?

1200 miles long and hanging 50 miles in the air

rockets and aerospace investment is still way more cost effective

dr

 

[wolfkeeper]

Launch loops scale much better than rockets.

If you want to build a bigger rocket, you pretty much need a clean sheet of paper; rockets scale badly, you have to redesign *everything*.

If you want a bigger launch loop, you just build more cable; the same design of cable.

And launch loops are not currently impossible (so far as anyone knows, space elevators ARE currently impossible).

Magnetic bearings have no known upper speed limit, so launch loops have a much higher rotor velocity than rockets' exhaust- a launch loop is fully reusable and single stage to escape velocity; rockets are 3 stages to escape, and expendable.

 

[ShotmanMaslo]

rockets and aerospace investment is still way more cost effective

dr

For launching satelittes, yes. But for space colonisation and tourism, it is not enough. I don't think it will ever achieve few dollars per kg launch cost like space elevator (launch loop) approaches. Even with huge 200+ t rockets, it may be far more expensive.

 

[wolfkeeper]

For launching satelittes, yes. But for space colonisation and tourism, it is not enough. I don't think it will ever achieve few dollars per kg launch cost like space elevator approaches. Even with huge 200+ t rockets, it may be far more expensive.

Don't believe the hype; space elevators won't realistically reach those numbers for a long, long time, if ever.

Most of the costs are infrastructure. The space elevator is only cheap at really *enormous* launch rates, after operating at maximum capacity for years. Launch loops can handle higher launch rates, are probably cheaper to make in the first place and the energy cost is pretty similar (a bit higher, the space elevator steals energy from the Earth's rotation as it launches).

Incidentally, unlike space elevators, launch loops can be made subscale; they can be used as a first stage for rockets. Rockets get a *lot* more efficient if you give them initial altitude and lots of speed; when they take off from the ground they're horribly inefficient until they reach about Mach 3 or so.

That also makes launch loops advantageous; because you can start small.

 

[ShotmanMaslo]

Don't believe the hype; space elevators won't realistically reach those numbers for a long, long time, if ever.

Most of the costs are infrastructure. The space elevator is only cheap at really *enormous* launch rates, after operating at maximum capacity for years. Launch loops can handle higher launch rates, are probably cheaper to make in the first place and the energy cost is pretty similar (a bit higher, the space elevator steals energy from the Earth's rotation as it launches).

Incidentally, unlike space elevators, launch loops can be made subscale; they can be used as a first stage for rockets. Rockets get a *lot* more efficient if you give them initial altitude and lots of speed; when they take off from the ground they're horribly inefficient until they reach about Mach 3 or so.

That also makes launch loops advantageous; because you can start small.

By "space elevator" I meant launch loop too, which is a type of space elevator (I had misquoted dr dodge, edited now..). Yes, they are the best and only realistic choice now, compared to other designs. :)

 

[wolfkeeper]

By "space elevator" I meant launch loop too, which is a type of space elevator (I had misquoted dr dodge, edited now..). Yes, they are the best and only realistic choice now, compared to other designs. :)

Hopefully.

Still, nobody has even built a launch loop a few feet across yet, never mind thousands of miles.