Why are Space Elevators not a horrible idea, as bad as gunpowder cannons to space?

[magnemoe]

8 hours ago, Val said:

Edit: @cantab ninjaed some of my points. I need to learn to write faster.

That sounds a bit ludicrous.

I'm pretty sure most modern proposals suggest launching a factory and materials to GEO. The cable is then produced there and lowered towards the earth while a counterweight is raised above GEO, so the whole structure retains a CoM at GEO.

It'll eventually become a geo-satellite that touches the ground. Then the counterweight is pushed further out to pull the cable tight.

Yes, if they ever build it, it must have at least 4 separate cables. 2 for up traffic and 2 for down, so there can be several climbers on each cable. Climbers are then unhooked at the ends and moved to a reverse direction cable. And to maintain at least half capacity if a climber breaks down midway.

No, it can't hide and probably not dodge a missile, but it can move little.

 

You also have the option to reinforce the cable with an climber during construction, And yes having 2-4 linked cables is an good idea. 

If the base is mobile like an ship its easy to move it to avoid junk in LEO.

Finally its an cable not an tower, if it fall down it will likely burn up in the atmosphere, high surface area for weight and probably made of carbon nanotubes of some type. 
 

[GoSlash27]

6 hours ago, Camacha said:

You people seem to forget everything seems impossibly hard and impractical before it is implemented on a reasonable scale. Tell people 150 years ago that they need to move hundreds of thousand of people and equal amounts of goods each day by air. Impossible, they would tell you. Ships are simpler and do the trick. Yet it happens. Tell people 50 years ago any person needs to be able to share cat pictures with any other person in the street. They would not only tell you it is impossible and unnecessary, but that telegrams and mail work perfectly fine. Yet today we can, because we built a massive infrastructure. Before hand, it seems not practical, unreasonable even. Until we do it.

The difference being that both of these examples were economically viable and self- sustaining. A space elevator isn't.

[JamesGoblin]

I'm noob to all this, but it certainly is very interesting to compare it with the only other "source" I was aware of - Clarke's fantasies =)

[SomeGuy123]

I'm actually surprised by how many people agree with me.  Apparently, I was wrong about deployment.  Naturally, it sounds even harder to get into orbit a spool of elevator cable.  The cable has to be thick enough that a very small climber car can traverse it bringing another cable, and there are other issues such as it needing a coating to protect the nanotubes inside against oxidation, etc.  So a single reel of elevator cable might be extremely heavy.

[Nibb31]

1 hour ago, SomeGuy123 said:

I'm actually surprised by how many people agree with me. 

I'm not. Nobody is seriously considering space elevators.

[Rakaydos]

1 hour ago, Nibb31 said:

I'm not. Nobody is seriously considering space elevators.

Not for Earth, anyway.

[Val]

 

5 hours ago, SomeGuy123 said:

I'm actually surprised by how many people agree with me.  Apparently, I was wrong about deployment.  Naturally, it sounds even harder to get into orbit a spool of elevator cable.  The cable has to be thick enough that a very small climber car can traverse it bringing another cable, and there are other issues such as it needing a coating to protect the nanotubes inside against oxidation, etc.  So a single reel of elevator cable might be extremely heavy.

It can't be done that way. The cable is only able to bear its own weight plus some fraction for margin, it wouldn't be strong enough to carry a second cable up.

You have to consider, these cables are gonna weigh in at thousands of tons.

The cables would have no problem carrying climbers adding up to several hundred ton, which only amounts to a few percent of cables total strength, but it wouldn't be able to carry twice it's own weight. Plus the climber would have to be insanely strong to lift that up.

The cables will be produced and assembled in orbit. Materials for additional cables could be lifted by climbers, once the first cable has been established, though.

[SomeGuy123]

21 minutes ago, Val said:

 

It can't be done that way. The cable is only able to bear its own weight plus some fraction for margin, it wouldn't be strong enough to carry a second cable up.

You have to consider, these cables are gonna weigh in at thousands of tons.

The cables would have no problem carrying climbers adding up to several hundred ton, which only amounts to a few percent of cables total strength, but it wouldn't be able to carry twice it's own weight. Plus the climber would have to be insanely strong to lift that up.

The cables will be produced and assembled in orbit. Materials for additional cables could be lifted by climbers, once the first cable has been established, though.

Then this really is just straight up science fiction.  Being able to produce something this complex and fragile in orbit, building a facility that needs thousands of tons of raw materials in a station in geosync, etc.

It kind of defeats the purpose of a space elevator if you have to launch more payload than the total launched in the history of orbital spaceflight to build a space elevator.  You pretty much would need to first develop cheap rocket flight first which then makes the relative advantage of an elevator smaller.

 

 

[Val]

4 minutes ago, SomeGuy123 said:

Then this really is just straight up science fiction.  Being able to produce something this complex and fragile in orbit, building a facility that needs thousands of tons of raw materials in a station in geosync, etc.

It kind of defeats the purpose of a space elevator if you have to launch more payload than the total launched in the history of orbital spaceflight to build a space elevator.  You pretty much would need to first develop cheap rocket flight first which then makes the relative advantage of an elevator smaller.

Pretty much, yeah!

[Rakaydos]

For earth, yes. However, for exploiting the Moon or Mars, you can loft a 100 ton spool of Kevlar ribbon, and string it from EML1 to the lunar surface. That's enough for a 1 ton self-powered elevator car. More ribbons give more capacity.

[tater]

Yeah, it's an interesting idea, but once you really look at the details it's not terribly sensible, even if it were possible. Even the lunar version doesn't work well, though the forces are much lower. The climbers would take a LONG time given the longer cable required to L1 or L2. Who wants a week-long elevator ride?

 

[Stargate525]

51 minutes ago, tater said:

Yeah, it's an interesting idea, but once you really look at the details it's not terribly sensible, even if it were possible. Even the lunar version doesn't work well, though the forces are much lower. The climbers would take a LONG time given the longer cable required to L1 or L2. Who wants a week-long elevator ride?

 

Ore and Helium 3 won't care if it takes a week or a month. There's a reason cargo ships don't go at fifty knots, even though it's possible.

[GoSlash27]

2 hours ago, Rakaydos said:

For earth, yes. However, for exploiting the Moon or Mars, you can loft a 100 ton spool of Kevlar ribbon, and string it from EML1 to the lunar surface. That's enough for a 1 ton self-powered elevator car. More ribbons give more capacity.

But OTOH you can use a rail gun on the lunar surface to propel payloads into an orbital Hohmann transfer for essentially nothing, with a tiny kick at apoapsis to circularize. Cheaper in the long run.

Best,

-Slashy

Edited February 8, 2016 by GoSlash27

[Laie]

On 2/6/2016 at 10:06 PM, SomeGuy123 said:

Why are Space Elevators not a horrible idea, as bad as gunpowder cannons to space?

Allow me to reply not to your post, but to the title: Because if you had suitable materials, and were able to marshal the necessary resources, it would work. Whereas the gunpowder cannon couldn't possibly.

[GeneralVeers]

On 2/6/2016 at 2:06 PM, SomeGuy123 said:

Anyways, TLDR, I don't see why anyone ever wasted any time on the space elevator as a concept.

For two reasons.

#1: Because if it could be made to work, you could send stuff to space much more easily than by putting it at the top of a huge and highly explosive stack of boosters.

#2: Because, just because it's a bad idea won't stop people from entertaining it as a purely theoretical possibility. Or sometimes not theoretical. There are a whole bunch of things in history that were bad ideas (or that appeared to be!) but happened anyway.

[Bill Phil]

2 minutes ago, GeneralVeers said:

For two reasons.

#1: Because if it could be made to work, you could send stuff to space much more easily than by putting it at the top of a huge and highly explosive stack of boosters.

#2: Because, just because it's a bad idea won't stop people from entertaining it as a purely theoretical possibility. Or sometimes not theoretical. There are a whole bunch of things in history that were bad ideas (or that appeared to be!) but happened anyway.

The problem with it is even if you decide to build it, other projects could effectively do the same thing sans elevator, for less...

[Rakaydos]

56 minutes ago, GoSlash27 said:

But OTOH you can use a rail gun on the lunar surface to propel payloads into an orbital Hohmann transfer for essentially nothing, with a tiny kick at apoapsis to circularize. Cheaper in the long run.

Best,

-Slashy

That works for launch, but not for landing. You have to get the railgun to luna in the first place, after all.

[Bill Phil]

12 minutes ago, Rakaydos said:

That works for launch, but not for landing. You have to get the railgun to luna in the first place, after all.

Landing isn't all that hard, actually.   Neither is taking off, but it can be a limitation. It's the "getting the lander there" part.

[SomeGuy123]

2 hours ago, Laie said:

Allow me to reply not to your post, but to the title: Because if you had suitable materials, and were able to marshal the necessary resources, it would work. Whereas the gunpowder cannon couldn't possibly.

Actually...if you used the gunpowder to drive a piston and hydrogen gas as an intermediate...

[sgt_flyer]

1 hour ago, Rakaydos said:

That works for launch, but not for landing. You have to get the railgun to luna in the first place, after all.

with a good spacecraft guidance, you could also use the railgun track (more like a maglev track in fact;)) to decelerate for moon landing. The structure's shape would be quite similar to a launch loop which is another proposed orbital launch system) (ramps on both ends with a high altitude flattened curve section in the middle) . - high enough above the surrounding natural formations that you can lower your periapsis down to the maglev track without risking impacting the moon's surface.

for landing an inbound spacecraft, you time and accelerate a maglev car on the track until it matches the spacecraft speed and position, the maglev car then use a deployable system to bridge the gap between the track and the spacecraft at it's periapsis, catch the spacecraft then the maglev car slows down the spacecraft on the remaining of the track. in case of problem with the maglev car / the track during the spacecraft approach, the spacecraft would simply continue it's orbit.

of course, you can also launch with such a track - accelerate the maglev car with the spacecraft attached to it, deploy the spacecraft, and release it when you reached your desired orbital speed. the maglev car then slows down on the rest of the track.

Edited February 8, 2016 by sgt_flyer

[Stargate525]

30 minutes ago, sgt_flyer said:

with a good spacecraft guidance, you could also use the railgun track (more like a maglev track in fact;)) to decelerate for moon landing. The structure's shape would be quite similar to a launch loop which is another proposed orbital launch system) (ramps on both ends with a high altitude flattened curve section in the middle) . - high enough above the surrounding natural formations that you can lower your periapsis down to the maglev track without risking impacting the moon's surface.

for landing an inbound spacecraft, you time and accelerate a maglev car on the track until it matches the spacecraft speed and position, the maglev car then use a deployable system to bridge the gap between the track and the spacecraft at it's periapsis, catch the spacecraft then the maglev car slows down the spacecraft on the remaining of the track. in case of problem with the maglev car / the track during the spacecraft approach, the spacecraft would simply continue it's orbit.

of course, you can also launch with such a track - accelerate the maglev car with the spacecraft attached to it, deploy the spacecraft, and release it when you reached your desired orbital speed. the maglev car then slows down on the rest of the track.

So... Docking a landbound object and an orbiting spacecraft moving at a kilometer a second with a (if we're being generous) tenth of a second window is easier to you than building a cable a few thousand kilometers long?

[magnemoe]

2 hours ago, GoSlash27 said:

But OTOH you can use a rail gun on the lunar surface to propel payloads into an orbital Hohmann transfer for essentially nothing, with a tiny kick at apoapsis to circularize. Cheaper in the long run.

Best,

-Slashy

No the elevator is cheaper in the long run, however the rail gun is cheaper to build. The rail gun is also usable from the poles where its most ice.

Another issue is that by the time an space elevator on earth make sense we will have so much stuff in LEO it will be hard to use it.
At this time most will be using LEO as an staging area, SSTO to orbit dock and transfer at space station over to tug or spaceship. 
You will have stuff at GEO too but not so much. 

 

[GeneralVeers]

3 hours ago, Bill Phil said:

The problem with it is even if you decide to build it, other projects could effectively do the same thing sans elevator, for less...

Less what?

Even if a space elevator costs a lot more to build, the point of a space elevator is you only build it once. And then (theoretically) it costs a lot less to use, once it's done being built, than it currently costs to put stuff in orbit using huge tanks full of stuff that goes kaboom.

[Orc]

Hi all

 

The objections to the space elevator mentioned above all apply to the 1980s concept of an elevator. The visions of death and destruction raining down are right out of Kim Stanley Robinson's Red Mars. Spectacular, awesome, fun but not up-to=date with modern thinking.

 

Modern think calls for slight better carbon materials, nanotubes in the length of a couple of meters rather than the millimeters currently available.

 

The 'cable' would in fact be a 'ribbon' composed of dozens of individual strands, held together by epoxies and by a series amount of criss-crossing reinforcement. The initial seed mass of the elevator was projected to be around 7 tons. The ribbon is slowly lowered (over the course of a couple of years) till it meets the ground station (an equatorial floating platform). In the meanwhile addition ribbon has been delivered to the satellite and crawlers start down the cable with the next ribbon, welding, gluing and spinning the reinforcements cross-overs as they go. Over a few of these mission cycles the cable is finally strengthened to the point were a single climber from the ground station can climb the elevator, deploying more cable as it goes. The entire construction period would take more than 10 years. Once it was done the cable would remain in a constant of maintainence and repair. This is not a product that is ever 'finished' - just like long steel suspension bridges are permanently being repainted with anti-rust paint. 

 

In the event of a cable failure the lower portion of the cable does fall to earth, but because it's mass is only kilograms for kilometres and not the tons described by KSR it falls to earth as so much black confetti, not a death dealing planet slicing blade of destruction. With the criss crossing reinforcement compromised and the tension gone the cable will quickly come apart. 

 

Obviously problems remain. The long term nature of the project is well beyond the scope of politicians and corporations who are worried about opinion polls and profits in the next quarter, let alone decades. 

 

The structure is also less capable than traditional elevator concepts, meaning lower tonnage, but then again it can also spawn addition elevators instead of relying on one vulnerable thraed.

 

The materials don't yet exist. We are a lot closer to them than we were in the 90s, and a hell of a lot closer than we were in the 80s when the only material imaginable was a super double diamond helix thingie that was infinitely strong and infinitely expensive.

 

The crawler tech would require some major work. Powering the damn things is still an issue.

 

But mostly it needs people to stop laughing.

 

The biggest thing elevator supporters and detractors don't get is that the materials that make the elevator possible automatically make OTHER launch concepts MUCH cheaper and safer. Why bother with an elevator when your regular space plane design is now 25% stronger and 50% lighter, or your standard disposable rocket stage is now light enough and strong enough (and empty enough) to fly itself back to the launch site? Building the elevator MIGHT JUST MAKE IT OBSOLETE.

 

Anyways, YMMV, its all future tech, future fantasy right now, we can't even get reusuable rockets to land successful every time.

 

Regards

ORc 

[Bill Phil]

1 hour ago, GeneralVeers said:

Less what?

Even if a space elevator costs a lot more to build, the point of a space elevator is you only build it once. And then (theoretically) it costs a lot less to use, once it's done being built, than it currently costs to put stuff in orbit using huge tanks full of stuff that goes kaboom.

But you still have to amortize the delivery service over a long time. All that Dev cost could've gone into developing a cheaper rocket.