# Building a space elevator would stimulate the economy **URL:** \ **Category:** Great Debates\ **Created:** [March 4, 2009, 6:13pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299 "2009-03-04T18:13:56Z")\ **Posts on this page:** 13\ **Page:** 6
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 8, 2009, 7:51pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/101 "2009-03-08T19:51:28Z")
Quoth **Sam Stone** : > [@](#): > > If we could build large quantities of nanotube sheets, I think I’d rather see something like an Orbital Balloon. > > First, you build a balloon big enough and light enough that it can climb to 140,000 feet. There, you assemble a much bigger one, which isn’t affected by weather and turbulence and which stays up all the time. It’s basically a floating waypoint. Then at this one, you build a truly humongous balloon (over a mile long) that is so light it can climb even in the rarified atmosphere above 140,000 ft. You put an ion drive on this one so that as it climbs it very slowly accelerates until it’s eventually in orbit. To come down, you just decelerate, and let it float back down slowly through the atmosphere. I’ve been thinking a bit about this, and the biggest objection I can see is that if the balloon is big enough to get non-negligible lift at whatever height it operates at, then it’ll also be big enough to get non-negligible drag at that height, too, which would be a big problem at orbital speeds. You could still use the balloon itself as a replacement for satellites for some purposes, and you could potentially use it as a launch platform for semi-conventional rockets which would be freed from the burden of punching through most of the atmosphere. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [March 8, 2009, 11:48pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/102 "2009-03-08T23:48:28Z")
The balloon doesn’t just get static lift - it gets dynamic lift through its own propulsion. Think of it slowly ‘skipping’ across the top of the atmosphere as it accelerates over a period of 5 days. Because it gets dynamic lift, it goes higher as it goes faster, and needs fewer molecules to keep it ‘flying’. The key to it is it’s gigantic size coupled with very low weight. You don’t need that many molecules to keep it flying. I think the math on this actually works out. This isn’t pie-in-the-sky - these guys are building these balloons today. Did you follow the link to their web site? Their facilities are quite large and impressive. There are some identified problems. One is actually building the balloon at what they call ‘dark sky station’, a gigantic floating factory 2 miles across and at 140,000 feet. The problem is that the environment is damned close to outer space, requiring full pressure suits and all that, and yet they’re still at full gravity since they’re just floating above the earth like a hot air balloon. That’s a challenging environment to do construction in. Another problem is that since the ‘ascender’ balloon takes 5 days to reach orbit, it’s going to be subjected to a lot of radiation. It’ll need some serious shielding for the astronauts. But compared to the difficulty of building a space elevator, this is nothing. Just extensions of known engineering. No exotic unobtanium required - just money and effort. And if you could get the system working well, it would be incredibly cheap to get to orbit - probably as cheap as your space elevator. Nothing is subjected to re-entry heat. Nothing is under any kind of radical acceleration. you just float up your payload or people to the way station, move them into another balloon, and gently fly up into orbit. The risk goes way down as well, and there are no catastrophic failure modes that threaten people on the ground in any large way. All in all, it’s a pretty cool concept, and one I give much more credence to than a space elevator for having a chance to actually be functional within my lifetime. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 9, 2009, 1:57am UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/103 "2009-03-09T01:57:02Z")
> [@](#): > > And if you could get the system working well, it would be incredibly cheap to get to orbit - probably as cheap as your space elevator. I’ve no doubt that something like this could lead to costs radically lower than chemical rockets, but you can operate a space elevator at an arbitrarily low energy cost per mass lifted. If this giant balloon can work (and I’d want to work through the math myself), then they can almost certainly get it going sooner than a space elevator, though, and there’s no sense putting all of our eggs in one conceptual basket. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [March 9, 2009, 2:27am UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/104 "2009-03-09T02:27:53Z")
Wouldn’t shooting a rocket off of a hydrogen balloon generally be referred to as a “bad thing”? 😉 But more seriously, exactly how big would this thing need to be to support the weight of a full rocket? How much does shooting from a higher point save us in terms of weight? If you’re that far above most of the atmosphere, does that mean that the balloon would be stable enough to support something like this? I would be worried that without much atmosphere, even if there was no wind, that any change in weight on any point on the surface would cause the whole thing to bobble and lean. There just wouldn’t be much stabilizing it. I wouldn’t want to shoot a rocket off of something where the lightest touch on one corner caused it to do cartwheels. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [March 9, 2009, 4:40am UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/105 "2009-03-09T04:40:43Z")
> [@Sage\_Rat](#): > > Wouldn’t shooting a rocket off of a hydrogen balloon generally be referred to as a “bad thing”? 😉 > > But more seriously, exactly how big would this thing need to be to support the weight of a full rocket? > > How much does shooting from a higher point save us in terms of weight? > > If you’re that far above most of the atmosphere, does that mean that the balloon would be stable enough to support something like this? I would be worried that without much atmosphere, even if there was no wind, that any change in weight on any point on the surface would cause the whole thing to bobble and lean. There just wouldn’t be much stabilizing it. I wouldn’t want to shoot a rocket off of something where the lightest touch on one corner caused it to do cartwheels. You’re not shooting off a rocket. That’s the whole point. You’re floating your way to orbit. You create a balloon that looks kind of like a big V. It’s miles across, and must be assembled at 140,000 feet because it wouldn’t be strong enough to withstand weather. You put an ion engine on this. You get aboard from your floating space station, and cast off. It starts to rise very slowly in the rarified atmosphere, but it does rise - to about 200,000 ft. As it rises, you light your ion engine, and start it moving forwards. As it goes faster, lift from the few molecules it encounters push it higher. You keep accelerating, and as you go faster and faster, the balloon goes higher and higher. Eventually, you are going fast enough to reach orbital velocity, and voila, you’re in orbit. To come back, you decelerate very gradually. The thing slowly sinks, and as it does it starts to encounter the tenuous atmosphere. Now you use a balance between drag and your engine to slowly transition from orbital speeds to ‘flying’ speeds, and then float back down to the station hovering at 140,000 ft. The thing encounters the atmosphere so slowly and decelerates so gradually (days instead of minutes) that it never gets hot. It needs no heat shield, and is not subjected to any real stress. As an astronaut, you’d simply see the earth gradually getting larger, and over a period of five days you’d gradually feel gravity building until eventually you were just a guy floating down in a balloon. Very safe. Almost cost-free. And only a tiny fraction of the fuel is required because you’re leveraging the atmosphere to buoy/skip you into space. There are still lots of questions to answer about this, having to do with how much payload it could carry, whether it could carry the weight of the engines it would need, whether it can handle static building and other stuff like that. But compared to the problems of building and maintaining a space elevator, this is nothing. ---
**Author:** ![\_Undecided\_Adrian](https://avatars.discourse-cdn.com/v4/letter/_/eada6e/32.png) [@\_Undecided\_Adrian](https://boards.straightdope.com/u/_Undecided_Adrian)\ **Post date:** [March 9, 2009, 11:08am UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/106 "2009-03-09T11:08:03Z")
How do you want to accelerate a huge balloon with an engine that [develops only 5 N of thrust continuously with an enourmous power requirement](http://en.wikipedia.org/wiki/Ion_thruster)? ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [March 9, 2009, 3:35pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/107 "2009-03-09T15:35:58Z")
I’ve always heard that the orbital balloon concept would use plasma engines, not ion. I still couldn’t tell you what sort of thrust/weight ratio they have. ---
**Author:** ![smiling\_bandit](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@smiling\_bandit](https://boards.straightdope.com/u/smiling_bandit)\ **Post date:** [March 9, 2009, 5:46pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/108 "2009-03-09T17:46:59Z")
If you really wanted to get into space cheap, build a nuke plant, an extremely powerful laser fed off of it, and use laser-confinement acceleration to shoot a spaceplane up. It can come down under its own power. Or build a giant magnetic-accelerated railgun, with the added benefit that you can do it anywhere and not just at the equator, and do the same thing. ---
**Author:** ![BrainGlutton](https://avatars.discourse-cdn.com/v4/letter/b/82dd89/32.png) [@BrainGlutton](https://boards.straightdope.com/u/BrainGlutton)\ **Post date:** [March 11, 2009, 1:39am UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/109 "2009-03-11T01:39:30Z")
> [@smiling\_bandit](#): > > . . . laser-confinement acceleration . . . How does that work? ---
**Author:** ![ENugent](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@ENugent](https://boards.straightdope.com/u/ENugent)\ **Post date:** [March 12, 2009, 8:42pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/110 "2009-03-12T20:42:14Z")
> [@Tenebras](#): > > Look, here’s an [incredibly optimistic paper](http://www.liftport.com/papers/2005Nov_LP-Ribbon_Mass.pdf) (pdf) written by a guy who works for a Space Elevator Booster corporation. (Get it, booster?) Check out Figure 2. CNTs have a density of between 1.3 and 1.4 g/cm[sup]3[/sup], which puts us between the yellow and the green curves. (If we build it out of water, we can use the red curve.) According to wikipedia, in 2000, somebody built a nanotube that measured a tensile strength of 63 GPa. This seems to be a reference to [this paper](http://www.sciencemag.org/cgi/content/abstract/287/5453/637). (abstract only) You’ll note that the tubes ranged in tensile strength from 11 to 63 GPa, although 63 GPa is the figure which seems to be cited as the “tensile strength of CNTs”. You will also notice that this was not a test on a macroscopic scale. The entire testing apparatus fit into the imaging chamber of a scanning electron microscope. (That is, it 'tweren’t very big.) > > Back to the point, referencing figure 2 of the incredible optimistic paper, we see that if we have a tensile strength of 50 GPa we’re talking about a mass of between 400 and 700 metric tons. (I’m estimating the green curve, obviously, but it looks to be a bit larger than 1.5 times the yellow curve, and both curves ought to be exponential.) That’s if the cable can uniformly withstand 50 GPa and we accept a factor of safety of 1. If the cable is weaker, the situation only gets worse, of course. (Remember, this is the graph which gives bare minimum masses supplied by the true believers who think the whole thing can be put into operation for only $1B.) The author no longer believes that a space elevator will be built on Earth any time soon, as I understand it from dinner table conversation. (He’s my husband.) He gave a presentation at the last [Space Elevator conference](http://www.spaceelevatorblog.com/?p=1005) on the reasons why not. I think he does think that it is still feasible for other planets when we get to the point of permanent bases there - the numbers work out much better for a lighter planet. I tried to get him to join the discussion here, but he’s [way too busy](http://www.lasermotive.com/blog/) right now. ---
**Author:** ![ENugent](https://avatars.discourse-cdn.com/v4/letter/e/4af34b/32.png) [@ENugent](https://boards.straightdope.com/u/ENugent)\ **Post date:** [March 12, 2009, 8:45pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/111 "2009-03-12T20:45:37Z")
Oh, he was also amused by the “incredibly optimistic” characterization, since he was being so much more pessimistic than most of the space elevator community when he wrote that paper. ---
**Author:** ![smiling\_bandit](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@smiling\_bandit](https://boards.straightdope.com/u/smiling_bandit)\ **Post date:** [March 12, 2009, 11:28pm UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/112 "2009-03-12T23:28:36Z")
> [@BrainGlutton](#): > > How does that work? It’s actually quite ingenious, and coiuld probably be built with modern materials. You create a “bottle” on the hind-end of your spaceship. The bottle can be made to self-stabilize, so the ship automatically stays in line with the laser. The energy does heat the sucker, but most of the energy actually floods back out, shoving it forward. The downside is that you need a monster power plant and a laser with a lot of juice running through it … but that will come in handy when the Evil Asteroid of Doom comes to Sprinkle Zombie Powder and Harbinge Our Alien Overlords. More seriously, there are big engineering challenges, but they are a lot more practical than building a space elevator. I favor the magnetic-acceleration launcher system more, though. Another issue with the “space elevetaor” is that the sucker with resonate. At two freqeuncies. Get it slightly wrong, and you’ll rip the thing to pieces just running a shuttle up and down. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 13, 2009, 2:50am UTC](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299/113 "2009-03-13T02:50:58Z")
> [@](#): > > Another issue with the “space elevetaor” is that the sucker with resonate. At two freqeuncies. Get it slightly wrong, and you’ll rip the thing to pieces just running a shuttle up and down. Only two? A taut string has an infinite number of different resonant frequencies. Still, though, it’s the narrow resonances you’re trying to avoid, not the broad spaces between the resonances. So if you plan to be off resonance, and get it slightly wrong, you’ll almost certainly still be off resonance. [Previous page](https://boards.straightdope.com/t/building-a-space-elevator-would-stimulate-the-economy/488299.md?page=5)