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

[Kerbart]

On 2/6/2016 at 4:06 PM, SomeGuy123 said:

Anyways, TLDR, I don't see why anyone ever wasted any time on the space elevator as a concept.  It fails the most basic analysis of feasibility.  There are other ways to reach space, and some of those ways could be potentially made very cheap with advanced technology.

Your arguments have merit. Do keep in mind, that similar rationale was used about steel ships, heavier-than-air-aircraft, steam trains, the tunnel under the English channel, etc, etc. What are limitations for one, are challenges and inspiration for out-of-the-box thinking for others.

Whenever a bunch of academics declare that it's impossible, not just economic, but also physically, to build something, there's usually a guy who shows up saying "I just built one." Not that I'm optimistic enough to bet on this one though. I agree that it seems improbable. But that never stops the dreamers, and sometimes they succeed.

 

[kerbiloid]

Those academics said: "A flying carriage drown by the eagles is impossible!"

And... er... yeah, it's impossible.

[Bill Phil]

54 minutes ago, Kerbart said:

Your arguments have merit. Do keep in mind, that similar rationale was used about steel ships, heavier-than-air-aircraft, steam trains, the tunnel under the English channel, etc, etc. What are limitations for one, are challenges and inspiration for out-of-the-box thinking for others.

Whenever a bunch of academics declare that it's impossible, not just economic, but also physically, to build something, there's usually a guy who shows up saying "I just built one." Not that I'm optimistic enough to bet on this one though. I agree that it seems improbable. But that never stops the dreamers, and sometimes they succeed.

 

Except, most academics knew that flight was possible, and the steam train, and the other examples. It was mostly the loud critics who said it was impossible. Many gliders were flown in the 1800s, and engines were getting more powerful. It was inevitable.

[sgt_flyer]

6 hours ago, Stargate525 said:

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?

at the moment you catch the incoming spacecraft, both vehicles are supposed to move at the same speed. at this point, the orbital curvature is low enough than an adjustable deployable system from the maglev can match the orbital curvature (especially if the section of the maglev track where you catch spacecrafts has a curve parallel to the orbital curvature) would give you more time to catch the incoming spacecraft. when you know the inbound spacecraft velocities and how much time you need for your maglev to accelerate to match the speed, timing it down for rendez-vous is not an extraordinary feat

Edited February 8, 2016 by sgt_flyer

[magnemoe]

6 hours ago, Orc said:

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 

Agree, here the problem is the strength of perfect carbon nanotube rope who is not known yet, some estimates says its too weak for this to be practical but current nanotubes has weaknesses. 
And yes high quality nanotubes has lots of other uses so it will be developed anyway so we wait and see how practical an space elevator is. 

[YNM]

I think people missed a point : basically, you're going to build a single bridge on one (or, depends on how you think about it, two) piers, the length of Earth's circumference.

If we don't do Gibraltar bridge, Bering bridge, and Atlantic bridge yet, don't tell me it's viable.

 

Edited February 8, 2016 by YNM

[peadar1987]

1 hour ago, YNM said:

I think people missed a point : basically, you're going to build a single bridge on one (or, depends on how you think about it, two) piers, the length of Earth's circumference.

If we don't do Gibraltar bridge, Bering bridge, and Atlantic bridge yet, don't tell me it's viable.

 

Not really. A bridge like that would be primarily loaded by bending moments. A space elevator would be loaded in tension. If you're going to have a big structure, tension is pretty much the best loading mode to have. That's why the space elevator is hovering around the edges of possibility, while a single-span Atlantic bridge is outright impossible.

[sgt_flyer]

29 minutes ago, peadar1987 said:

Not really. A bridge like that would be primarily loaded by bending moments. A space elevator would be loaded in tension. If you're going to have a big structure, tension is pretty much the best loading mode to have. That's why the space elevator is hovering around the edges of possibility, while a single-span Atlantic bridge is outright impossible.

Yup, a passive structure like a bridge would be impossible over such spans.

An active structure, that's another story though  (You basically have a giant maglev continuously accelerating mass so it has a ballistic trajectory 'higher' than the track's curve - so such a structure would be held through tension too (as the accelerated mass would tend to 'press' upwards onto the magnetic track). You'll just need tethers on the side of the track to prevent sideway movements - that's the launch loop concept. (Because a launch loop could be also used as a bridge as well as an orbital launch system  - start acceleratng on a separate track, match the speed and 'latch' onto one of the outgoing maglev elements - the maglev element would transport you at very high speeds towards the other end - where you 'unlatch' the maglev to get onto a slow down separate track.

(in the meantime, on each extremity of tehe launch loop you have a looped track to send back maglev elements back in the launch loop with limited impact on their speeds)

Note, in the concept, the launch loop is meant to span over oceans anyway - in case of failure

however, of course, the permanent energy requirements to keep such a structure afloat would be quite tremendeous  - have a power failure, and the thing would break apart under it's own weight. 

An interesting concept, but building the 'starter' track onto which you build the rest to increase the loop's capacity would be hard  - not including the constant energy requirements to keep such a structure in the air.

Edited February 8, 2016 by sgt_flyer

[Stargate525]

4 hours ago, sgt_flyer said:

at the moment you catch the incoming spacecraft, both vehicles are supposed to move at the same speed. at this point, the orbital curvature is low enough than an adjustable deployable system from the maglev can match the orbital curvature (especially if the section of the maglev track where you catch spacecrafts has a curve parallel to the orbital curvature) would give you more time to catch the incoming spacecraft. when you know the inbound spacecraft velocities and how much time you need for your maglev to accelerate to match the speed, timing it down for rendez-vous is not an extraordinary feat

I get that. But you're moving at around 1-2 kilometers a second at orbit that low. Either your maglev structure is absolutely MASSIVE (talking total length 30-50km) or your window to adjust speed, match, and lock is measured in tenths or hundreths of seconds. If your orbit is off by a fraction of a percent, you either miss the platform completely or, worse, turn your shipment into a multi-ton connonball that's blown your maglev to smithereens.

[SomeGuy123]

11 hours ago, magnemoe said:

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.

Why would the elevator be cheaper than a quench gun?  The rail gun, yes, because the rails will erode and need to be replaced every so often.  A quench gun doesn't have this problem (it's a gauss gun using superconducting magnets).  A quench gun, you could in principle launch a payload every few minutes, day in and day out, until something breaks or you run out of payloads lined up.

The advantage there is if you can launch every 5 minutes 1 ton, say, you can launch 105,000 tons a year.  An elevator, if it only can carry 100 tons in transit and the transit takes a week of climbing, has a yearly launch volume 1/20 of that.  

It's also vastly easier to work on the quench gun.  It's a big set of separate modules, and everything is inside some gigantic set of tunnels in a mountain or something, readily accessible.  A good design for one would include maintenance access equipment to let you rapidly swap any piece of equipment with a spare to get the system online as fast as possible.  

If elevator cables start to fail, I'm not even sure what you can do.  Dunno what kind of spackle can patch a cable under this kind of tension...

[Stargate525]

23 minutes ago, SomeGuy123 said:

The advantage there is if you can launch every 5 minutes 1 ton, say, you can launch 105,000 tons a year.  An elevator, if it only can carry 100 tons in transit and the transit takes a week of climbing, has a yearly launch volume 1/20 of that. 

So what happens if you want to launch a payload larger than a ton? Don't forget that you're going to be losing a lot of that to guidance, crew space (if it's manned) and fuel for the circularization burn.

Sure, the payload volume is less, but you can do it in bigger chunks, and don't waste space on non-payload support.

[SomeGuy123]

2 hours ago, Stargate525 said:

So what happens if you want to launch a payload larger than a ton? Don't forget that you're going to be losing a lot of that to guidance, crew space (if it's manned) and fuel for the circularization burn.

Sure, the payload volume is less, but you can do it in bigger chunks, and don't waste space on non-payload support.

These were example numbers of why you get more out of your capital.  You can make the quench gun bigger.

[sgt_flyer]

2 hours ago, Stargate525 said:

I get that. But you're moving at around 1-2 kilometers a second at orbit that low. Either your maglev structure is absolutely MASSIVE (talking total length 30-50km) or your window to adjust speed, match, and lock is measured in tenths or hundreths of seconds. If your orbit is off by a fraction of a percent, you either miss the platform completely or, worse, turn your shipment into a multi-ton connonball that's blown your maglev to smithereens.

you'll need a quite long maglev structure / railgun in any case - simply to limit the G forces during acceleration and deceleration  - the automated maglev car alone could sustain much higher G forces, but when you have to accelerate / decelerate a manned payload , you don't want the crew to sustain too much G forces.

now, such structure will be long for sure, but on the moon it should be within the realm of feasability with today's materials - if you pick the right spot to have things as flat as possible. now, as for precision, you'll of course need several observation systems all along the orbital path on the moon's surface, capable of precisely determining the spacecraft's orbital parameters,then use a feedback loop system to adjust. if we can determine and track orbital trajectories of passive debris threatening ISS, a spacecraft with active comms systems would be much easier to track

Edited February 8, 2016 by sgt_flyer

[cantab]

8 hours ago, sgt_flyer said:

at the moment you catch the incoming spacecraft, both vehicles are supposed to move at the same speed. at this point, the orbital curvature is low enough than an adjustable deployable system from the maglev can match the orbital curvature (especially if the section of the maglev track where you catch spacecrafts has a curve parallel to the orbital curvature) would give you more time to catch the incoming spacecraft. when you know the inbound spacecraft velocities and how much time you need for your maglev to accelerate to match the speed, timing it down for rendez-vous is not an extraordinary feat

Using something like a launch loop or railgun for landing is possible, but to me it sounds incredibly demanding and risky. I think it would be better to do atmospheric re-entry or propulsive landing, taking advantage of the launch megastructure to maintain orbital infrastructure to support that.

[sgt_flyer]

5 hours ago, cantab said:

Using something like a launch loop or railgun for landing is possible, but to me it sounds incredibly demanding and risky. I think it would be better to do atmospheric re-entry or propulsive landing, taking advantage of the launch megastructure to maintain orbital infrastructure to support that.

oh, the idea i was talking about was for something akin to a reduced size launch loop on the moon, where you can't aerobrake for landing  - depending on the size, with the moon's reduced gravity and no atmospheric perturbation, it might even be feasible to build without needing 'active' power hungry support components like those a launch loop or a space fountain would need on earth.

 

 

Edited February 9, 2016 by sgt_flyer

[fredinno]

On February 7, 2016 at 2:02 PM, 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.

How would you make a lunar space elevator, though? You can't go in GEO around The Moon.

22 hours 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.

Way too risky to use a railgun track to land. If you f**k up, you could destroy the entire thing.

[Rakaydos]

11 minutes ago, fredinno said:

How would you make a lunar space elevator, though? You can't go in GEO around The Moon.

Earth-Moon Lagrange 1 (EML1) is furthur from the moon than geosynch is from earth, but the moon's gravity is low enough that even the longer cable can be made of conventional materals. Like an earth space elevator, the lunar elevator hangs a counterweight out past the balance point, where it gets pulled toward Earth just hard enough to suspend the weight of the elevator cable toward luna.

[cantab]

16 minutes ago, fredinno said:

How would you make a lunar space elevator, though? You can't go in GEO around The Moon.

It works (on paper) if you take it to either the L1 or L2 Lagrange points, the latter demanding a slightly longer elevator but both are doable with current materials. It's also possible to curve the elevator to reach points away from directly under the counterweight, at the cost of less payload or needing stronger material. In fact that's theoretically possible on Earth too, but considering no current material can handle even a vertical elevator, a curved one may be over-ambitious.

http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf

[magnemoe]

11 hours ago, SomeGuy123 said:

Why would the elevator be cheaper than a quench gun?  The rail gun, yes, because the rails will erode and need to be replaced every so often.  A quench gun doesn't have this problem (it's a gauss gun using superconducting magnets).  A quench gun, you could in principle launch a payload every few minutes, day in and day out, until something breaks or you run out of payloads lined up.

The advantage there is if you can launch every 5 minutes 1 ton, say, you can launch 105,000 tons a year.  An elevator, if it only can carry 100 tons in transit and the transit takes a week of climbing, has a yearly launch volume 1/20 of that.  

It's also vastly easier to work on the quench gun.  It's a big set of separate modules, and everything is inside some gigantic set of tunnels in a mountain or something, readily accessible.  A good design for one would include maintenance access equipment to let you rapidly swap any piece of equipment with a spare to get the system online as fast as possible.  

If elevator cables start to fail, I'm not even sure what you can do.  Dunno what kind of spackle can patch a cable under this kind of tension...

Yes, coil, not rail, and I agree that an lunar space elevator has so many issues its even less practical than an earth based one. For one the poles are most interesting and the elevator has to be close to equator. 
And as you say an single coil fail would not be an issue and can easy be swapped. 
No you can not use it to land realistically however main export would be water, H2, O2, rocks and ore, import would be ready made stuff who is fragile and lighter. 

[Rakaydos]

14 minutes ago, magnemoe said:

 I agree that an lunar space elevator has so many issues its even less practical than an earth based one. For one the poles are most interesting and the elevator has to be close to equator.

Less practical than an earth based elevator? What problems does an earth elevator NOT have, that a lunar elevator has, that makes up for material tech difficulties and space trash around earth?

[Bill Phil]

13 minutes ago, Rakaydos said:

Less practical than an earth based elevator? What problems does an earth elevator NOT have, that a lunar elevator has, that makes up for material tech difficulties and space trash around earth?

The fact that you have to get to the moon.... Albeit, that's a chronic problem for a lot of things.

[Rakaydos]

Just now, Bill Phil said:

The fact that you have to get to the moon.... Albeit, that's a chronic problem for a lot of things.

Not really worse than having to get to geosynchronus orbit...

[Bill Phil]

6 minutes ago, Rakaydos said:

Not really worse than having to get to geosynchronus orbit...

The moon takes more energy to get to... And I wasn't saying GEO is any easier.

[cantab]

12 hours ago, SomeGuy123 said:

The advantage there is if you can launch every 5 minutes 1 ton, say, you can launch 105,000 tons a year.  An elevator, if it only can carry 100 tons in transit and the transit takes a week of climbing, has a yearly launch volume 1/20 of that.  

So quick calculation here. It's about 1.5 km/s to put a payload in low lunar orbit (plus a little rocket delta-V to circularise), and more to send it to further places. So that's about 1 GJ of energy per ton of mass. If you want a launch every 5 minutes you need a 4 Megawatt power station, and that's assuming near-perfect efficiency.

Heh, that's actually not a whole lot. Even if it was to escape speed it still wouldn't be much. The railgun might draw higher peak power but it could easily be charged up by a small nuclear reactor or a few football pitches of solar panels. I was expecting much bigger requirements.

[juanml82]

On 7/2/2016 at 9:36 PM, vger said:

As for whether or not there's any point: we're quickly approaching the commercial age of space. People want to go up. A space vator would make space accessible to a lot more people, not just those with optimal health. And corporations are now seriously looking into space mining. If we can make a space elevator work, it's by far the most cost-effective to ferry equipment and harvested resources between orbit and Earth.

Equipment sure. But you can't carry people: it's too slow, so people would expend too much time in the Van Allen belts.

 

Or at least I've read that somewhere