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Ten Millionth Floor, Please

By kuran42 in Technology
Fri Mar 15, 2002 at 02:52:04 PM EST
Tags: Science (all tags)
Science

The Norse called it the Yggdrasil and represented it with an ash tree; to the Kabbala and others, it was the Tree of Life; for the Mayans, the ceiba tree was its embodiment. Since man first looked up at the stars, he has been driven to travel amongst them and more than any other, the "world tree", a mythical bridge between the Earth and the Heavens has been his means. The 20th century brought an update to this myth. Will the 21st see it made real?


In 1960 Yuri Artsutanov, a young engineer living in Leningrad, published a paper on what he termed a "heavenly funicular". This was the first modern description of what is now often referred to as a "space elevator". What is a space elevator, you ask? It's quite simple: first put a space station in geosynchronous orbit (GEO), preferably above an ocean or very tall mountain; next, extend equal lengths of tether down towards Earth and in the opposite direction, out into space; when you have extended the tether all the way down to your ocean platform or the top of your mountain, you have a space elevator. The equal lengths of tether extended in opposite directions keep the station's center of gravity in GEO and you have, literally, a rope hanging from the heavens.

Once you have your heavenly funicular, it is a relatively simple matter to attach an elevator car to it. Electromagnetic (EM) propulsion is preferable because it removes the need for moving parts that can wear out or require repair. EM propulsion also allows you to reach the fantastic speeds needed to make the trip bearable. It is more than 35,000 kilometers from the Earth's surface to GEO. Using mechanical propulsion, the best car speed we can expect is a couple hundred kilometers per hour; with EM propulsion, a car speed of ten to twenty times that is possible. The trip each way will last between 12 and 16 hours and be devoid of the traumatic acceleration today's astronauts must endure. Using an EM propulsion system also allows the car to be extremely efficient. Solar panels can collect enough energy to power them, and you can even design systems which recapture most of energy used to accelerate the cars when they are decelerated at their destination.

Does all this sound impossible? Until very recently, it has been. The problem is an obvious one: your tether will break under its own weight long before it reaches the Earth's surface. One way to combat this is to taper your tether - make it thicker at the top than at the bottom. Unfortunately, even one of the strongest materials available - steel - would have to be several billion kilometers thick at the top to support its own weight. In fact, it would have a mass many times greater than that of the entire solar system put together. If you use Kevlar, a material roughly three times stronger, matters improve, but not much. Can we do better? Some people think yes, and experiments may have demonstrated so already.

Enter carbon nanotubes. Carbon is abundant on Earth. It varies in form from the common graphite, soft and fragile, in your pencil, to diamond lattices that make up one of the strongest materials known to man. Nanotubes are another form, one that doesn't occur in nature. A carbon nanotube is made up of carbon atoms arranged into a cylindrical shape, with walls a single atom thick, and ends capped with half-soccer balls. Scientists make them in a variety of ways. One way involves blasting graphite with a high power laser and letting the resulting carbon vapor arrange itself around various substrates; another mixes carbon with oxygen under high pressure and then slowly deposits the vapors to build up nanotubes.

But all existing methods are expensive. It costs about $500 USD to make a single gram of carbon nanotubes, and it will take nearly 15 million kilograms of the stuff to build a space elevator. For reference, that's about 7,700 shuttle payloads, or 154 years worth of dedicated launches. Several companies think they can bring the cost down to as little as $0.05 USD per gram in the next 5 to 10 years. But how can we carry so much material into space?

The answer lies in a modification of the design of the space elevator. Remember, equal weights must be extended from each side of the station or its center of gravity will change and it will fall to Earth or tumble out into space. There is an alternative to weighing the space-end of the station with tether, though. A counter-weight asteroid with the right mass can be used in place of the tether. This asteroid can also be mined for the carbon to make nanotubes, even the most average of carbonaceous asteroids has enough carbon to spare for such a task. Such asteroids are readily available and waiting in the Earth-Sun LaGrange points.

There are plenty of reasons for us to build a space elevator. Today, space flight is extremely expensive; it costs about $20,000 USD to launch a single kilogram into orbit. Most existing launch programs have a narrow focus for which they work well: launching comsats, launching unmanned probes, or carrying people into orbit. While the systems are adaptable to other uses, such adaptation is expensive. With a space elevator, any mission you can think of can be launched without the least bit of trouble. Unmanned probes? Trivial, just fling them off the outer end of the tether. Their tangential velocity will be great enough to send them on unpowered trips all the way to Saturn. The situation is similar with comsats; just drop them off the tether a bit sooner, and put them in an orbit that won't later collide with the space elevators. Manned missions are a cinch - being able to lift consumables and equipment at a miniscule fraction of the cost (estimates range from $0.50 to $2.50 USD per kilogram, or 0.001% of current costs) opens up a world of possibilities. What about a manned mission to Mars? Easy. A fully equipped moon base, complete with the latest state of the art astronomical equipment? Piece of cake.

There are some problems to overcome before a space elevator can be made a reality. Within the decade we will be able to make cheap nanotubes on Earth, but what about in space? Can they be synthesized from carbon extracted from an asteroid? Speaking of asteroids, moving one from a LaGrange point into orbit will be no small task. While we possess the technology now - a combination of light sails, ion propulsion, and good old fashion chemical rockets could do it - the cost will be great, and the precision required fantastic. Missing Earth orbit could have disastrous results, and is not an option. Arthur C. Clarke wrote, "the space elevator will be built about fifty years after everyone stops laughing." Are we ready to stop laughing and turn this age-old myth into reality?

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Ten Millionth Floor, Please | 179 comments (176 topical, 3 editorial, 0 hidden)
An easier way (4.33 / 15) (#1)
by dennis on Fri Mar 15, 2002 at 02:21:37 PM EST

Actually, as reported on that other site, it's even more feasible than you describe. NASA recently completed a study (15MB pdf) that concluded if we start directed research now, we could start building in 10 years, and complete in another 2 or 3 at a cost of $40 billion for the first one, $15 billion for the next.

With their scheme, instead of using an asteroid, they make the cable on the ground, and just start with a very thin cable - so thin it only takes seven shuttle flights to get the material to space. Once you have that, you use it to drag up more cable, and continue until you've reached the size you want.

Are NASA's timeline/cost.. (none / 0) (#38)
by RandomAction on Fri Mar 15, 2002 at 03:29:22 PM EST

..know for being accurate? Think 20 years, $100 billion is more likely?

[ Parent ]
Nope (2.00 / 1) (#42)
by kuran42 on Fri Mar 15, 2002 at 03:36:01 PM EST

NASA isn't historically very accurate, but you might be surprised that they don't always underestimate the costs. For example, their (admittedly brief) analysis of a program to put astronauts on Mars suggested a price tag of $490 billion. More recent plans suggest $20 billion is a more accurate number.

Or maybe that's how much it really would cost NASA. Private space program, anyone?

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]

Time to start writing to Bill Gates... (none / 0) (#77)
by leifb on Fri Mar 15, 2002 at 05:03:00 PM EST



[ Parent ]
I take that back... (4.00 / 4) (#81)
by leifb on Fri Mar 15, 2002 at 05:04:16 PM EST

we can't afford for this thing to crash.

[ Parent ]
Yep (4.00 / 4) (#51)
by conraduno on Fri Mar 15, 2002 at 03:53:00 PM EST

Actually they would have a small robot which would climb this initial (incredibly thin and weak) tether, winding more line around it. Each pass up the tether it would get stronger and stronger, after a couple of years we would have a true tether which would be capable of carrying vehicles.

Rather interesting, I wouldn't be surprised if I see this in the next 20 years.
non.
[ Parent ]
That's what I meant... (4.00 / 1) (#58)
by dennis on Fri Mar 15, 2002 at 04:16:13 PM EST

...but now that you mention it, I can see how what I wrote could be misinterpreted. Thanks.

[ Parent ]
What about wind? (none / 0) (#52)
by speek on Fri Mar 15, 2002 at 03:58:58 PM EST

That sounds good, but wouldn't a thin cable be more affected by wind at the surface? How thin are we talking here?

--
al queda is kicking themsleves for not knowing about the levees
[ Parent ]

look at a spider's strand (none / 0) (#87)
by rebelcool on Fri Mar 15, 2002 at 06:09:31 PM EST

They're very very thin. Yet they seem to brave even the strongest of winds right?

Nanotubes are an order of magnitude stronger than those. And if you make it slightly thicker, the kind of winds the earth sees wont affect it that much.

COG. Build your own community. Free, easy, powerful. Demo site
[ Parent ]

Spiderwebs survive tornados? (3.00 / 2) (#119)
by Double Dave Deluxe on Sat Mar 16, 2002 at 04:31:41 AM EST

Wow!

[ Parent ]
Don't be silly.. (none / 0) (#146)
by RandomAction on Sat Mar 16, 2002 at 07:09:40 PM EST



[ Parent ]
Not on the equator (4.00 / 1) (#138)
by John Milton on Sat Mar 16, 2002 at 06:26:07 PM EST

Such a cable would most likely be constructed near the equator anyways. The region 5 North and South of the equator is known as the doldrums and is characterized by very weak winds.


"When we consider that woman are treated as property, it is degrading to women that we should Treat our children as property to be disposed of as we see fit." -Elizabeth Cady Stanton


[ Parent ]
Can't use shuttles (5.00 / 2) (#95)
by cyberformer on Fri Mar 15, 2002 at 07:34:32 PM EST

A space elevator would be wonderful, and perhaps feasible, but shuttles won't be much use in contructing it.

The GEO orbit is a lot higher than the shuttle can reach (35,000 miles comapred to about 500). The only people who have been that far away from Earth were the Apollo astronauts. Even at the lower orbtis, the shuttle couldn't help build the initial stages. Relative to the ground, it (and the space-station) move at about mach 25, whereas the beanstalk would be standing still.

[ Parent ]

That's okay (none / 0) (#160)
by dennis on Sun Mar 17, 2002 at 09:34:35 PM EST

The shuttles are just for launch, the cost estimate includes orbital transfer vehicles that can be carried in the shuttle cargo bay.

[ Parent ]
Great science story! (3.50 / 4) (#2)
by DesiredUsername on Fri Mar 15, 2002 at 02:22:07 PM EST

You neglected to mention how strong carbon nanotubes are, though. Also, presumably you'd still need a tether that was half as long as the original proposal which is still a lot of Space Shuttle trips (mining an asteroid still require equipment, people and supplies so you may not save much there).

Play 囲碁
Nanotubes... (5.00 / 2) (#9)
by kuran42 on Fri Mar 15, 2002 at 02:33:58 PM EST

They have a theoretical strength of about a TeraPascal. The Pascal is a unit of elasticity, relating how much a material will stretch - and eventually break - to how much tension is placed on it. Nanotubes produced in lab experiments have tested at about 200 GigaPascals. It's hard for me to relate to this particular unit of measure, so I just like to think "they're really, really, really damn strong" :) For comparison, kevlar is about 20 GigaPascals and steel is a third of that. The "magic number" of a space elevator is 62 GigaPascals - stronger than that and it will work, less strong and it goes <snap>.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
Bringing down the cost (none / 0) (#16)
by DesiredUsername on Fri Mar 15, 2002 at 02:40:48 PM EST

Presumably they'd like to bring down the cost for reasons unrelated to space elevation, then. Like nanotube bullet-proof vests. Or re-constructing the WTC. Though I suppose neither of those is really a linear tension issue...

Play 囲碁
[ Parent ]
Wait, I have another question (none / 0) (#18)
by DesiredUsername on Fri Mar 15, 2002 at 02:42:59 PM EST

The "magic number" of a space elevator is 62 GigaPascals...

Wouldn't the magic number depend on the weight of the material you were building from?

Play 囲碁
[ Parent ]

Hmm (none / 0) (#43)
by kuran42 on Fri Mar 15, 2002 at 03:38:30 PM EST

Tentatively, I'll say that the pascal is already adjusted for weight. I could be wrong though, it's been a while since I took a physics course :) Anyone know for sure?

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
Magic number (2.50 / 2) (#111)
by marx on Fri Mar 15, 2002 at 11:52:44 PM EST

Tentatively, I'll say that the pascal is already adjusted for weight.

No, the tensile strength just tells you how much you can pull at a material before it breaks. Pascal is N / m^2, so the tensile strength works the same as pressure.

My guess is that the magic number was only for carbon nanotube. Steel has ~1 GPa tensile strength, but is ~10 times as dense as carbon nanotube.

Join me in the War on Torture: help eradicate torture from the world by holding torturers accountable.
[ Parent ]

Addendum (3.00 / 2) (#118)
by marx on Sat Mar 16, 2002 at 04:00:34 AM EST

BTW, I saw you mentioned elasticity above. That's a different quantity from tensile strength. They both have the same unit though, Pascal.

Join me in the War on Torture: help eradicate torture from the world by holding torturers accountable.
[ Parent ]

I was reminded (none / 0) (#12)
by davidduncanscott on Fri Mar 15, 2002 at 02:35:09 PM EST

of Niven's comment that the Ringworld, "comes after solutions" -- it occurs to me that by the time we've launched that much of whatever into orbit, we'll have solved the problem of cheap launches.

Ever read "A Rocket A Day"?

[ Parent ]

Moving Asteroids (1.83 / 6) (#3)
by Jehreg on Fri Mar 15, 2002 at 02:26:09 PM EST

We can easily use our current nuclear arsenal to move any asteroid we want. That's the least of our problems.

Care to back that up? (none / 0) (#26)
by Bwah on Fri Mar 15, 2002 at 02:57:49 PM EST

How do you propose to do that? Just detonate on the surface to generate delta-vee? Pull fissionables out of the warhead to create something more efficient?? Genuinely curious ...

--
To redesign an infinite ensemble of universes: what terrible responsibility, what arrogance ... It sounds just like the type of thing your average Homo sap would do for a dare. -- Stephen Baxter
[ Parent ]

The Orion Project (4.50 / 2) (#33)
by yostinso on Fri Mar 15, 2002 at 03:16:27 PM EST

I keep running across mention of the Orion Project, and that seems perfectly applicable here. Dig a hole in said asteroid, fill it full of nukes and put a serious door at the end. Chuck a bomb out the back, close the door, repeat as necessary.

--E.O.

I fight for truth. I fight for glory. I fight for love. I fight for beauty. I am Hero.
[ Parent ]
Nuke Rockets (4.00 / 1) (#34)
by shaftus on Fri Mar 15, 2002 at 03:17:54 PM EST

There has been a lot of research into using a nuclear reactor to vaporize hydrogen and produce thrust. Though on this scale I'm not sure it would be as cost effective as a detonation.....

[ Parent ]
NERVA (4.00 / 1) (#39)
by kuran42 on Fri Mar 15, 2002 at 03:30:32 PM EST

Nuclear Engine for Rocket Vehicle Application. Not as much research in the field as there used to be. Probably a combination of nobody caring about long-distance space flight and people being afraid of anything with "Nuclear" in its name. A few big NERVAs strapped to an asteroid could work, given a reasonable time frame - several years, maybe a decade (Don't quote me, I haven't done the math. Maybe later ;). Things might be weightless in space, but they still have inertia. Detonating nukes directly might be faster, but I'd hate to think what would happen if you pushed a little too hard...

Solar sails are still my favorite option.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]

What about radioactivity? (3.00 / 1) (#45)
by RandomAction on Fri Mar 15, 2002 at 03:38:42 PM EST

How 'contaminated' would the asteroid be? Would it even matter?

[ Parent ]
Given a clean nuke, probably not (3.00 / 1) (#103)
by bgalehouse on Fri Mar 15, 2002 at 08:39:59 PM EST

At least half of the nuke's leftover reaction material will end up floating away at high speed. Anything in outer space, especially for any length of time needs basic rad shielding anyway.

And it is possible to make a fairly clean nuke if you have time and the ability to test. Gamma radiation does damage, but doesn't make things radioactive. I think alpha particles only do a little. Thermal neutrons are the big activator, but you want the thing to use up all those neutrons for a big explosion anyway.

[ Parent ]

Most nukes are pretty darn clean (3.50 / 2) (#129)
by rebelcool on Sat Mar 16, 2002 at 12:29:44 PM EST

Virtually all the stuff that can be radioactive is (hopefully) used up in the reaction. People sometimes confuse cobalt-jacketed weapons (which leaves things VERY radioactive and uninhabitable) with normal weapons.

COG. Build your own community. Free, easy, powerful. Demo site
[ Parent ]

space elevator == target (3.60 / 10) (#4)
by speek on Fri Mar 15, 2002 at 02:26:48 PM EST

If you thought the WTC was an unresistable target, think again. This thing has to be protected absolutely. How do you do that? Would you tolerate countries like Iraq and North Korea with a space elevator ripe for taking down? Just how hard would it be to bring it down, anyway?

The more our technology takes us to places where global destruction is possible, the fewer freedoms each of us will be allowed.

--
al queda is kicking themsleves for not knowing about the levees

Already been approached. (4.00 / 2) (#5)
by Jehreg on Fri Mar 15, 2002 at 02:28:56 PM EST

There is a sci-fi story that describes what would happen if a Mars-based space elevator was blown up by terrorists. One of the these books has it, I do not remember which one: Blue Mars, or Green Mars.

[ Parent ]
Depends (5.00 / 1) (#15)
by dennis on Fri Mar 15, 2002 at 02:39:53 PM EST

Depends on how you build it. The recent NASA study proposed using low-melting-point epoxy to glue a bunch of short (something like 1 cm, I forget) nanotubes together. If the whole thing comes down, it disintegrates on reentry.

This does make the thing vulnerable to lightning, but they deal with that by putting it on a movable sea platform in an area with very little storm activity. And it makes your worst case just the loss of your $15 billion cable, instead of global disaster.

[ Parent ]

The book (none / 0) (#19)
by ucblockhead on Fri Mar 15, 2002 at 02:43:29 PM EST

In the book, it isn't the tube itself that is attacked, but the mooring of the tube to the orbiting asteroid it is attached to.
-----------------------
This is k5. We're all tools - duxup
[ Parent ]
Still works (4.00 / 1) (#23)
by dennis on Fri Mar 15, 2002 at 02:46:22 PM EST

Still works as I described, the study examined possible breaks at any point in the cable. Even with a high break, the energy release as the cable disintegrates is diffuse enough to not be a problem.

[ Parent ]
Yeah Red Mars is the book (4.00 / 1) (#84)
by JahToasted on Fri Mar 15, 2002 at 06:03:12 PM EST

but they don't blow it up... don't forget the tether is really strong. and damaging it at the base is useless since it would just hang there if you did. What they did in the book is detach the tether from the asteroid. this sent the asteroid flying into outer space, and the cable crashing into the planet.... it actaully wraped around the equater 4 times. I don't know how long it would be for Earth, but I'm guessing it would wrap around at least once.

the point is that the elevator is only really vulnerable at the top where it connects to the asteroid. Of course if someone was able to carry out such an attack, the collateral damage would be huge to equatorial areas, and coastal areas (think of the tsunamis).
______
"I wanna have my kicks before the whole shithouse goes up in flames" -- Jim Morrison
[ Parent ]

It wouldn't wrap once (4.00 / 1) (#105)
by schrotie on Fri Mar 15, 2002 at 08:56:30 PM EST

Geostationary orbit is about 35,787 km above sea level. The equator is 40,075.16 km long.

[ Parent ]
also (none / 0) (#125)
by Acous on Sat Mar 16, 2002 at 06:25:21 AM EST

the earth rotates far too slow for it to wrap, most of it would fall near the base... at least, thats what i've read.

[ Parent ]
Give me the link? (none / 0) (#145)
by RandomAction on Sat Mar 16, 2002 at 07:05:25 PM EST

How fast would it fall, it would depend on the break point.

[ Parent ]
Too slow? (none / 0) (#172)
by Dyolf Knip on Tue Mar 19, 2002 at 11:15:08 AM EST

Earth rotates at Mach 1.5 at the equator. I don't know what planet you come from, but around here that's pretty fast. And that isn't even the whole story. The top of the cable is moving at orbital velocities, usually measured in kilometers per second, and as it comes down, gaining speed all the way, there's nothing to slow it down except the ground.

---
If you can't learn to do something well, learn to enjoy doing it poorly.

Dyolf Knip
[ Parent ]

Your right but.. (1.00 / 1) (#144)
by RandomAction on Sat Mar 16, 2002 at 07:04:06 PM EST

The length of the whole thing is around twice that needed for Geostationary orbit. If the cut were above that point, then everything beyond it would be shoot off tangentially into space. The rest would fall to earth possibly quite slowly, think months. A low cut would result in less material falling faster, and any burn up being less effective. The maths for creating the most damage to Earth is pretty complex, I guess.

[ Parent ]
Bollocks ;-) (none / 0) (#148)
by schrotie on Sat Mar 16, 2002 at 11:11:57 PM EST

If it fell rather slowly it would be emergency cut by an elevator or whatever. Whatever the fiber will be, it won't be uncuttable. And elevators installed will have cutters on a thing like that. So they'd be able to cut it in 10 kilometer long bits or longer/shorter to prevent massive damage.

The whole idea of a space elevator is pretty much science fiction. The technic is not available (yet?) and not even the need or volition of society to build such an amazing monument is clearly established (yet?). But I think one thing can be assumed. If society, or a mega corp. or the evil empire of america ;-) decides to build that writing on the wall, then whoever manages to finance something like that will take security masures to ensure that it does not destroy earth.
If you don't make that assumption, it's just bad science fiction ;-)

[ Parent ]

That depends (4.00 / 1) (#6)
by DesiredUsername on Fri Mar 15, 2002 at 02:29:17 PM EST

If these carbon nanotubes can withstand the tidal forces produced by the admittedly relatively weak gravitational field of Earth then presumably a 747 won't do much damage. Also, you could build it in "strands" do give it redundancy.

Play 囲碁
[ Parent ]
Except... (4.00 / 2) (#25)
by vefoxus on Fri Mar 15, 2002 at 02:51:28 PM EST

that the tidal forces are scattered on all parts of the elevator (which can move/girate without significant problems). Whereas the plane would apply a force very locally and suddenly. Plus, the force would be applied perpendicularly to the tubes, along a direction where they are much less resistant.

[ Parent ]
I doubt an aircraft could.. (none / 0) (#48)
by RandomAction on Fri Mar 15, 2002 at 03:46:44 PM EST

..get close, any terrorist would have to use a much less obvious strategy.

[ Parent ]
I got it (5.00 / 4) (#91)
by Wah on Fri Mar 15, 2002 at 06:44:46 PM EST

Giant, nanocarbon scissors.
--
Choas and order, flowing down the drain of time. Ain't it purdy? | SSP
[ Parent ]
an interesting factoid ive read.. (none / 0) (#85)
by rebelcool on Fri Mar 15, 2002 at 06:04:24 PM EST

cant quite recall, but it stated that a 747 could be stopped in midflight by a centimeter thick strand of spider silk. Nanotubes are a tad stronger.

A 747 wouldnt do much to it.

COG. Build your own community. Free, easy, powerful. Demo site
[ Parent ]

Red Mars (none / 0) (#7)
by ucblockhead on Fri Mar 15, 2002 at 02:29:26 PM EST

The Kim Stanley Robinson book "Red Mars" (or maybe it was in "Blue Mars") has a pretty harrowing account of what happens when a space elevator falls down. It ain't pretty!
-----------------------
This is k5. We're all tools - duxup
[ Parent ]
I hate books (1.60 / 5) (#8)
by Ken Pompadour on Fri Mar 15, 2002 at 02:31:21 PM EST

So tell me what happens when a space elevator falls down :)

...The target is countrymen, friends and family... they have to die too. - candid trhurler
[ Parent ]
Welll... (none / 0) (#13)
by Jehreg on Fri Mar 15, 2002 at 02:35:15 PM EST

Imagine the longest whip you can think of....

Now imagine that whip cracking against the longest table you can think of...

Now protect your ears.... It will all happen in slow motion while most of the cable is still in partial orbit, but the last part of the "crack" will be quite spectacular.

[ Parent ]

Ok (none / 0) (#17)
by ucblockhead on Fri Mar 15, 2002 at 02:42:08 PM EST

Imagine a 100 megaton nuclear explosion occuring at every single point on the equator.
-----------------------
This is k5. We're all tools - duxup
[ Parent ]
Every point on the equator? (none / 0) (#24)
by DesiredUsername on Fri Mar 15, 2002 at 02:47:31 PM EST

Why so far? Above a certain height presumably the cable would burn up on reentry. That is, unless nanotubes are fireproof. Wouldn't that be ironic.

Play 囲碁
[ Parent ]
Doesn't completely burn up (4.00 / 1) (#47)
by EricLivingston on Fri Mar 15, 2002 at 03:43:32 PM EST

The portrayal of the falling space elevator in the Mars books is one of those images I'll keep around for a while - it was well done. The upper parts of the elevator do burn as they fall through the atmosphere, but don't burn UP - there's plenty left to hit the ground. I don't know whether a "real" space elevator would burn up completely or not, but at least in the book the cable was thick enough and tough enough to remain at least partially intact when it hit - along its entire length, which, of course, wrapped around the planet a few times. So, you had this huge, fiery, constant-sonic-boom generating cable bisecting the entire sky as seen from below, coming down around the equator, and generating (big) nuclear-warhead scale impact force around the entire planet as it hit the ground - several times as it wrapped itself up on the planet. Really quite a vision, I'd imagine, for those far enough away not to be obliterated by it.

[ Parent ]
Yes, great writing (none / 0) (#76)
by ucblockhead on Fri Mar 15, 2002 at 05:01:40 PM EST

I've no idea how accurate it was, though, and the Mars of the book had a much thinner atmosphere than Earth's.
-----------------------
This is k5. We're all tools - duxup
[ Parent ]
It came down in Red Mars,... (none / 0) (#40)
by nefertari on Fri Mar 15, 2002 at 03:31:42 PM EST

in Green Mars they start to remove it, and build a new one.

[ Parent ]
Atmospheric and gravity difference between.. (none / 0) (#49)
by RandomAction on Fri Mar 15, 2002 at 03:51:33 PM EST

..Earth and Mars would make any burn on re-entry much more effective.

[ Parent ]
you think i just made this up myself? (none / 0) (#50)
by speek on Fri Mar 15, 2002 at 03:52:36 PM EST

:-)

--
al queda is kicking themsleves for not knowing about the levees
[ Parent ]

Yes thats a great reason not to build great things (none / 0) (#86)
by rebelcool on Fri Mar 15, 2002 at 06:06:35 PM EST

'Cause some maniac might blow it up.

Come to think of it, some maniac might blow ME up. I'm never leaving the house again.

COG. Build your own community. Free, easy, powerful. Demo site
[ Parent ]

FUD (1.00 / 1) (#92)
by Prophet themusicgod1 on Fri Mar 15, 2002 at 06:51:04 PM EST

oh we cant make a fire by rubbing two sticks together because, someone might light us on fire!
fire is ev0l
"I suspect the best way to deal with procrastination is to put off the procrastination itself until later. I've been meaning to try this, but haven't gotten around to it yet."swr
[ Parent ]
Red, Blue Green Mars... & Need for an elevator (4.16 / 12) (#10)
by vefoxus on Fri Mar 15, 2002 at 02:34:43 PM EST

You could also encourage people to read the Mars books by K.S. Robinson, in which there is a space elevator which IIRC is made of carbon nanotubes.

However, there still is not enough need to build such a space elevator, because we are still at the level of manned space experimentation, and not yet at the level of manned space exploitation.

This may change if(when) a permanent, large manned station existed (large meaning > 1000 people), either in space or on the moon, requiring frequent coming and going. A space elevator which would be used every 2-3 months (since no more is needed right now) would be a waste. It's a nice idea, though, if you are not afraid of ever having this elevator falling on earth...

There's a reason for that (none / 0) (#20)
by dennis on Fri Mar 15, 2002 at 02:44:41 PM EST

The reason we're still at the experimental stage is that it's really freakin' expensive to get anything to orbit. A space elevate would reduce that cost by roughly a factor of a thousand. If it only costs a couple bucks a pound to get to orbit, we'll find reasons to do it pretty quickly.

[ Parent ]
Reasons? (none / 0) (#27)
by vefoxus on Fri Mar 15, 2002 at 03:03:06 PM EST

The reasons to build it will have to come before, not after. A settlement on the moon would have been possible a long time ago, but no man has set foot on it for 20 years. Why? because there is nothing we could do on the moon that we cannot do on Earth for less... Except an astronomy lab on the hidden face of the moon, but that's not enough...

I'm still waiting to hear about what can be done in space that we cannot do on Earth and requires frequent (daily) coming and going.

[ Parent ]

Reasons (none / 0) (#30)
by yostinso on Fri Mar 15, 2002 at 03:13:31 PM EST

The reasons aren't hard to come by. Saving money putting each new satellite into orbit, crystal growth and alloy synthesis, tourism (heh), starting point for manned (or otherwise) spaceflight to other planets (it costs a <u>lot</u> to get off this planet with a rocket), etc.

--E.O.

I fight for truth. I fight for glory. I fight for love. I fight for beauty. I am Hero.
[ Parent ]
Not to mention... (4.00 / 1) (#37)
by dennis on Fri Mar 15, 2002 at 03:29:13 PM EST

...if access is that cheap, we could move all our strip mining and nasty chemical industries to places where there's no biosphere to screw up.

[ Parent ]
Chicken? (5.00 / 1) (#32)
by J'raxis on Fri Mar 15, 2002 at 03:15:38 PM EST

Egg.

Ȕ The Raxis

[ J’raxis·Com | Liberty in your lifetime ]
[ Parent ]

Reasons, sure (none / 0) (#35)
by dennis on Fri Mar 15, 2002 at 03:20:51 PM EST

We can figure out worthwhile things to do in space pretty easily, if we assume a launch cost of $2 per pound. What we can't do is implement those things, when the launch cost is $10,000 per pound as it is now.

We need cheap launch before we can have a large presence in space, just as we needed rockets before we could have any presence in space.

[ Parent ]

Well.... (none / 0) (#44)
by carbon on Fri Mar 15, 2002 at 03:38:30 PM EST

On the moon, self-powered flight (under air pressure and with wing assemblies, btw) is at least theoretically possible. That would be very cool, IMO. I'd be willing to shell out some dough for a vacation centering around actual flight.

In fact, I even wrote an article about this, but right before going front page (94 points!) it was eaten by kuro5hin during the ad implementation, and help@k5 hasn't responsded to my email about it. Rusty, if you're reading this, what happened?


Wasn't Dr. Claus the bad guy on Inspector Gadget? - dirvish
[ Parent ]
There is no reason ... (none / 0) (#98)
by schrotie on Fri Mar 15, 2002 at 07:55:58 PM EST

... anybody would want to have a computer at home.

It's not that long since this stratement has been made (with out too much objection BTW). As processing power got cheaper and cheaper we found that computers are essential for almost every imaginable application from toasters to your desktop PC, from cars to space stations. The technology has been there first, than the need for it.
This is true for many advanced technologies. 'I don't assume it will be the other way round for space exploitation - if we find it useful once the technology is available.

[ Parent ]

a few major problems with this idea (4.73 / 15) (#21)
by demi on Fri Mar 15, 2002 at 02:44:46 PM EST

While I have nothing but enthusiasm for the prospect of economical space travel, this proposal vastly simplifies some of the major problems with maintaining an orbiting elevator system.

Nanotubes, for instance, aren't made as perfect long-range monofilaments (here at Rice there is a lot of work done with carbon nanotubes). At least as of now they aren't. If they are made in bulk they come in bundles of ropes of tube material, with very little long range order (imagine a wad of steel wool). Although the tensile strength of a perfect nanotube cable would undoubtedly be high, nobody has figured out how to align the tubes and thread them together at length scales beyond microscopic resolution. To make a good cable exclusively out of spun nanotubes is not within the capability of current technology, although the price of bulk material is rapidly coming down and will continue that way for some time.

Another problem is with the lift vehicle, which would climb up the rope somehow without destroying it. Remember that to keep the tensile stresses realistic, such a long filament would need to be as light (per unit length) as possible, but able to support the force of multiple large payloads moving against gravity. To keep the center of gravity dynamically stable, the mass of the tether system would have to greatly exceed the combined masses of all of the payloads climbing and descending, or else the station would just be pulled down to earth by the lift vehicles.

And as for the station itself, being attached to the earth by a moderately conductive bundle of nanotubes would constitute a gigantic electrostatic potential difference. The tether might act as a huge lightning rod unless measures were taken to dissipate the potential drops along its length. Additionally, the dynamic stability of geosynchronous orbit may not be sufficient to allow for safe transport from the earth's surface (probably a lot of severe cable lash at various points along the journey).

It's a good idea, and a lot of people are quite seriously working on it, but there is a lot more to putting it all into practice than most people realize.



Already a potential difference (4.00 / 1) (#28)
by epepke on Fri Mar 15, 2002 at 03:10:25 PM EST

There's already a fairly smooth potential difference up through the atmosphere, at least. There is a potential difference of about 200 volts between your head and your feet. You can actually measure this with a good IGFET-based voltmeter. The problem is that the current is so slow that it takes a while to charge the probe. You can accelerate this by waving a propane torch near the probe to ionize the air. I've done this, and it's way cool.

So, I doubt that lightning strikes would be too much of a problem. On the other hand, most of the designs seem to have the bottom be much thicker, which means lower resistance, so they might be. But still, the presence of the ribbon throughout the atmosphere would probably make any discharge fairly steady and easy to deal with. More problematic is that this steady discharge might significantly affect local weather patterns.


The truth may be out there, but lies are inside your head.--Terry Pratchett


[ Parent ]
Actually.. (none / 0) (#36)
by RandomAction on Fri Mar 15, 2002 at 03:20:56 PM EST

..the cable tapers as it drops to Earth, the thickest point is at the center of gravity.

On the other hand, most of the designs seem to have the bottom be much thicker

Could provide a link to the designs you mention?

[ Parent ]
No, you're right (none / 0) (#75)
by epepke on Fri Mar 15, 2002 at 05:01:00 PM EST

I got it backward. It still might be a problem, though, as it's a nonlinear in resistance--basically a big voltage divider.


The truth may be out there, but lies are inside your head.--Terry Pratchett


[ Parent ]
dynamically stable (4.00 / 2) (#29)
by DesiredUsername on Fri Mar 15, 2002 at 03:12:35 PM EST

Actually the mass wouldn't have to exceed the payloads all that much. First, you could send a vehicle down at the same time one comes up (although most returns would be empty--then again maybe not if we are mining the asteroid). Also, from other comments here, it sounds like nanotubes have plenty of extra tension to play with--why not adjust the asteroid end with a rocket to balance the center of mass?

Play 囲碁
[ Parent ]
more questions about the tether. (5.00 / 1) (#57)
by demi on Fri Mar 15, 2002 at 04:14:03 PM EST

If the LV (lift vehicle) climbs the nanotubes, how would it grip the tether? The nanotube bundle would be very thin and probably very low-friction (fullerene is, in some circumstances, a superb lubricant). If the LV's were self-propelled, how would they get their power? And about the mass system, geosynchronous orbit is the point where the centripetal force equals the gravitational (downward force). If you had a number of massive objects traveling up the tether (and using it for traction), that would increase the downward force on the station as they accelerate. I don't think that could be counterbalanced by another downward traveling payload because that wouldn't add an equal and opposite force. Anyway, I'm not sure about this 'cuz I don't have paper handy to do the calculations and draw a picture.



[ Parent ]

Linear motors. (2.50 / 2) (#143)
by RandomAction on Sat Mar 16, 2002 at 06:55:57 PM EST

Basically magnets pull it up. The good thing about linear motors is that, on the way down they can be used as generators, to slow the LV as gravity pulls it back to earth.

[ Parent ]
Dynamic stability and energy conservation. (5.00 / 1) (#106)
by bgalehouse on Fri Mar 15, 2002 at 09:03:30 PM EST

If there is no tension at the bottom of the cable, then every bit of mass which goes up the cable pulls the cable (and asteroid) down a touch. Simple center of gravity argument. Most of the energy still has to come from the car's climbing action, but a little does come from the asteroid. This could be put back with rockets on the asteroid.

But, consider when the cable has a bit of tension. In particular, suppose that the asteroid is let out a bit from the 'natural' geosynchronous orbit. The rock would be in a slower than geo orbit, but the tether of the elevator will keep it geosynchronous.

Now when you haul mass up the elevater, the rock will still loose some energy, but it will be put back by pull of the tether, slowing earth's rotation slightly. Then you don't need the rockets, which makes the system more foolproof.

[ Parent ]

RE: Dynamic stability and energy conservation. (none / 0) (#142)
by RandomAction on Sat Mar 16, 2002 at 06:49:51 PM EST

If there is no tension at the bottom of the cable, then every bit of mass which goes up the cable pulls the cable (and asteroid) down a touch. This is all very nice but there is tension at the bottom. Tension is a needed for this to work.

[ Parent ]
Wow.. (1.66 / 3) (#31)
by RandomAction on Fri Mar 15, 2002 at 03:13:53 PM EST

..from your link 'Right now, 99.5 percent pure C60 fullerenes sell for $40 per gram' Cool cheaper than cocaine.. I wonder what the effect would be if one were to snort it, not much I guess, I don't suppose it's all that reactive.

[ Parent ]
Dirty lungs. (3.50 / 2) (#66)
by Kaki Nix Sain on Fri Mar 15, 2002 at 04:35:22 PM EST

I wonder what the effect would be if one were to snort it, not much I guess, I don't suppose it's all that reactive.
You would most likely just dirty up your alveoli. I've got some C60/70 here on my desk and I can't really tell it apart from graffite dust. I imagine little clumps of carbon nanotubes would look pretty much the same.



[ Parent ]

For answers... (none / 0) (#60)
by dennis on Fri Mar 15, 2002 at 04:18:51 PM EST

Pretty much all of the issues you mention are addressed in the paper I cited.

[ Parent ]
Elevator or no, we still have problems.... (2.30 / 10) (#41)
by shaftus on Fri Mar 15, 2002 at 03:34:10 PM EST

Why build an elevator before even having the technology to master our own gravity?(And No, I don't consider a trilion dollar elevator mastering gravity) What happens when we land on another planet? Start building an elevator so we can leave? It's a great project, but one which should be attempted later on in our development.... I think we're jumping off the high dive with our water wings deflated.

"Master our own gravity" (5.00 / 1) (#46)
by kuran42 on Fri Mar 15, 2002 at 03:40:44 PM EST

What do you mean by that, exactly? We've had chemical rockets for decades, and hot air balloons for centuries. If you're looking for an anti-gravity ray, I would suggest not holding your breath. All you can do against gravity is push, and we've been doing that for a long time...

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
Cost and repeatability. (none / 0) (#53)
by shaftus on Fri Mar 15, 2002 at 03:59:37 PM EST

When I think of mastering a given task, I imagine being able to accomplish it at will, with minimal effort, and maximized safety. I'm thinking more along an evolutionary path here. We need a technology that will enable an adaptable route into space for more than just governments. A space elevator is fine for minimizing future lauch cost, but impractical for a near term goal. No gravuity rays required. I just want to see us being able to enter orbit from anywhere before investing our efforts into something this big.

[ Parent ]
To be honest.. (none / 0) (#54)
by RandomAction on Fri Mar 15, 2002 at 04:03:24 PM EST

..I'm having trouble following your logic. Is it just me?

[ Parent ]
Ok, let me try again. (none / 0) (#61)
by shaftus on Fri Mar 15, 2002 at 04:23:22 PM EST

I think our efforts are better spent on gaining more experience with launch vehicles than on building a space elevator. That knowledge will be something we need for moving out into the universe. Without a way to enter and exit other gravity wells, our ability to expolore will be limited to drifting in between the planets.

[ Parent ]
Nuclear Rockets (4.00 / 1) (#67)
by kuran42 on Fri Mar 15, 2002 at 04:35:25 PM EST

Chemical propulsion has come a long way. Some would say as far as it can come. 450 Isp is about as good as most people think you can get, and while it'd be great if they were wrong, they probably aren't. Moving to completely new technologies is one way of doing things better. Look at computers: people didn't just keep throwing in more and more vacuum tubes after the transistor was invented, nor did they continue to use transistors after the integrated circuit came along. I'm not saying the space elevator is inherently better and obviously the next logical step any more than nuclear rockets or rockoons or linear accelerators are, but it is a possible next step, so why not research it until we find something better? The main point is chemical rockets will get us nowhere fast.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
NERVA within the atmosphere? (2.50 / 2) (#70)
by shaftus on Fri Mar 15, 2002 at 04:47:30 PM EST

Do you think we'll ever have a NERVA system that could opperate within the atmosphere and not produce unacceptable amounts of radiation? I think the research being done along "scramjet" lines look interesting as a possible alternative. Something just dosent seem right about a brute force approach to getting into space.

[ Parent ]
Your right this approach has a lot of.. (none / 0) (#72)
by RandomAction on Fri Mar 15, 2002 at 04:52:45 PM EST

..possibilities, check this. From sciam.com

[ Parent ]
Well... (4.00 / 2) (#73)
by kuran42 on Fri Mar 15, 2002 at 04:54:36 PM EST

Technically, a NERVA needn't expel any radioactive material into the environment. The nuclear reactor is used only to heat a propellant, and it is the propellant that is expelled. Hydrogen gives you a much nicer Isp than plutonium or uranium anyway :) In practice this turns into an engineering nightmare, but seems like it should be solvable if we didn't just give up (but we did). SCRAM-jets are nice, probably nicer than NERVA for atmospheric flight, but it looks like we're about to give up on them, too. The test flights NASA was conducting (earlier this year? last year? I can't remember) went into the ocean, and funding was immediately "reapportioned". I'm not aware of any other large organizations attempting to make SCRAM-jets work.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
That unquenchable font of research dollars... (none / 0) (#114)
by physicsgod on Sat Mar 16, 2002 at 12:34:26 AM EST

The DOD is working on a project called hypersoar which is basically a cross between a rocket, a bomber, and a skipping stone. Given the current political climate in the US it shouldn't be hard to get money for a system where you could take off after lunch, bomb the fuck out of Afghanistan, and be home in time for dinner (though turning around at Mach 10 might produce some...issues).

--- "Those not wearing body armor are hereby advised to keep their arguments on-topic" Schlock Mercenary
[ Parent ]
Re: That unquenchable font of research dollars... (4.00 / 2) (#122)
by khallow on Sat Mar 16, 2002 at 05:06:22 AM EST

The DOD is working on a project called hypersoar which is basically a cross between a rocket, a bomber, and a skipping stone. Given the current political climate in the US it shouldn't be hard to get money for a system where you could take off after lunch, bomb the fuck out of Afghanistan, and be home in time for dinner (though turning around at Mach 10 might produce some...issues).

Is this the bomb-anywhere-in-90-minutes plane? Pretty soon, it's just going to be the prez and a couple of techinical people calling the shots.

Tech #1: Ok, Mr. President. The system is point and click. Hover your mouse over the target that you want to select.

Prez: You mean like this. (presses a button).

Tech #2: Oh no, he right clicked England!

Tech #1: Well, I'm sure England is pretty understanding about these things. After all he's learning the system. They're allies, right?

Prez: What does that message mean? Whoa fifty thousand confirmed badguys killed! That's pretty cool.

Tech #1: It'll be even better if you hover your mouse over that spot on the screen... Yes, the spot marked "EVIL AXIS".

Prez: And right click? (he right-clicks again)

Tech #2: Er, congratulations. That's another ten thousand confirmed terrorist kills!

Prez: Huh, that's less than the first time.

Tech #1: Yeah, but we'll want to save a few terrorists for for the English! Yes, we do!

Tech #2: You can kill some more terrorists later. Over here is your spy satellite cam. We've targeted Malibu for your viewing pleasure...

Prez: (drool)

[ Parent ]

I guess we had better thank OBL. (none / 0) (#140)
by RandomAction on Sat Mar 16, 2002 at 06:37:20 PM EST

IRONY

[ Parent ]
You haven't heard about HyShot then. (none / 0) (#117)
by Quixato on Sat Mar 16, 2002 at 03:21:39 AM EST

NASA isn't the only organization investigating SCRAM-jet technology. The Aussies have their own project. I think I remember hearing about their test flight, which had mixed results. Something about sensors malfunctioning, but a partial success. Anybody else know anything?

"People are like smarties - all different colours on the outside, but exactly the same on the inside." - Me
"Learn to question, question to learn." - Sl8r
[ Parent ]

Where is the gutsy space science (none / 0) (#123)
by minra on Sat Mar 16, 2002 at 05:11:49 AM EST

Does it seem to anyone else that by commercialising NASA, the USA is undercutting its' long-term technological goals?



[ Parent ]
Getting into and out of.. (5.00 / 1) (#71)
by RandomAction on Fri Mar 15, 2002 at 04:48:07 PM EST

..other gravity wells would be made cheaper/easier if exiting our own was cheap. Our current vehicles aren't there to simply explore the universe, for the most they exist to provide direct benefits to the military, governments, corporations and other consumers.

Moreover there are other benefits to easy access to earth orbit, such as manufacturing or research. Waiting till we gain some 'experience' in launch vehicles ain't logical, I just can't see the benefit. This isn't an approach used elsewhere in industry or human exploration so why is logical now?

Though I agree we don't have technology for manned exploration. But 'exploration' from here is good enough for now e.g. the hubble telescope.

[ Parent ]
Why go to another planet? (4.00 / 1) (#151)
by A Trickster Imp on Sun Mar 17, 2002 at 06:19:26 AM EST

> What happens when we land on another planet? Start building an elevator so
> we can leave?

It was pointed out many decades ago that, resources aside, there really isn't a reason to go to other planets. Once you leave Earth, you move into space, not to other planets. Sure, other colonies on planets will outstrip space as far as manufacturing goes, but the ultimate goal is a space society, not other planets.




[ Parent ]
If my physics do not fail me, you're wrong (3.57 / 7) (#55)
by Trickster on Fri Mar 15, 2002 at 04:03:37 PM EST

"you can even design systems which recapture most of energy used to accelerate the cars when they are decelerated at their destination"

That energy is converted to potential energy which would be equal to the work you've done against Earth's force of gravity to get up so the only way to get that energy back is to drop the elevetor back and even then you won't recover the energy wasted on heat, sound waves, etc.

No the elevator is not in.. (none / 0) (#56)
by RandomAction on Fri Mar 15, 2002 at 04:06:53 PM EST

..freefall, the linear motor used to get it up, is used as 'dynamo' on the way down, extracting energy as the elevator is decelerated.

[ Parent ]
Its been a while (none / 0) (#59)
by japhar81 on Fri Mar 15, 2002 at 04:17:33 PM EST

since I studied physics, but I'm pretty sure you can't get anywhere near 100% of that energy back anyway. Last I checked the best you could do was something like 25%. Sorta the same concept as the hybrid-electric hondas are, while youre moving, the electric motor is acting as a generator and using the rotation of the wheels.

<H6>Rome is always burning, and the younger generation never respects its elders. The time of your second coming, japhar81, is no exception. -- Aphasia</H6&gt
[ Parent ]
Motor? (5.00 / 1) (#62)
by kuran42 on Fri Mar 15, 2002 at 04:26:49 PM EST

Most EM elevator designs don't employ any motor, or anything else with moving parts. Think of it as a maglev pointed at the sky. The work done in raising you is converted to gravitational potential which you use to get back to the ground on your return trip ("freefall", but with some breaking to prevent overspeed). The breaking on the way down is done electromagnetically as well, and so generates a current, which can be used to raise the next car, etc... Of course it isn't 100% efficient, and the early versions probably wouldn't be anything close to it, either. But eventually practice approaches theory, and I wouldn't be surprised to see 85% - 95% efficiency levels after a decade or so of operation.

But then, with free energy from the sun, who cares :)

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]

A linear motor.. (4.50 / 2) (#65)
by RandomAction on Fri Mar 15, 2002 at 04:34:25 PM EST

..does have moving parts, if you consider the elevator as part of it. Uses energy on the way up, extracts it on the way down.

[ Parent ]
Something from nothing? (4.00 / 1) (#68)
by japhar81 on Fri Mar 15, 2002 at 04:39:04 PM EST

If you're using electromagnetic braking on the way down, youre using energy for that, even if you gather some while moving down, some law that I cant remember now says that youll expend more than you'll collect. If not, we just invented the perpetual motion machine.

Or I might be talking out my ass, its been a while since I've done any real physics.

<H6>Rome is always burning, and the younger generation never respects its elders. The time of your second coming, japhar81, is no exception. -- Aphasia</H6&gt
[ Parent ]
Second Law of Thermodynamics (2.00 / 1) (#69)
by kuran42 on Fri Mar 15, 2002 at 04:40:42 PM EST

or some corollary thereof. But that only applies to 100% efficient systems. Nothing says you can't have a system that is 99.9999% (or however many 9's you want) efficient.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
entropy (3.00 / 2) (#113)
by Subtillus on Sat Mar 16, 2002 at 12:33:14 AM EST

I'm a biologist who's taken his share of chemistry classes. skeptically speaking, I think it would be interesting to see any system that doesn't lose a VERY significant portion of it's intake to entropy.

more productively, metabolism is as far as i know one of the most efficient ways of harvesting energy and it does this in a kind of quantized leap frog fashion. Getting out the energy of a "fuel" molecule in smaller bursts approaches a "thermodynamically reversible" process.
maybe that would help things along somewhere.

but as others stated THERES NO FREE ENERGY, whether you pay for it in building materials, maintaining ion or temperature gradients or whatever, you're GOING to lose lots of energy.

there's just no way to get around that.

[ Parent ]
Free Energy? (none / 0) (#139)
by RandomAction on Sat Mar 16, 2002 at 06:34:39 PM EST

Don't confuse physics with economics. I find a load of coal on my property, it costs me a little time and some cash, and bang I barter it for loads of others time and cash. I'm getting a lot for very little. Of course it's not free, millions of years ago, the sun shone, and generations of trees grew and died, their remains get buried, and compressed and eventually we get coal. No of course it ain't free.

[ Parent ]
giving me a one is in poor taste. (none / 0) (#132)
by Subtillus on Sat Mar 16, 2002 at 03:28:08 PM EST



[ Parent ]
It's not different to a generator. (none / 0) (#74)
by RandomAction on Fri Mar 15, 2002 at 05:00:40 PM EST

E.G. A hydro dam uses gravity to shift water passed a generator(dynamo). This system uses gravity to shift the elevator passed a generator(dynamo).

The difference:
Instead of being circular the generator is un-coiled and forms a line.
Of course it will always cost more energy to get to the top than can be extracted from the drop to the bottom.

[ Parent ]
The hybrid cars.. (none / 0) (#63)
by RandomAction on Fri Mar 15, 2002 at 04:30:48 PM EST

..use the normal engine to charge the batteries, not wheel rotation. Using the batteries for initial acceleration, and low ratio driving which can be very polluting for normal engines, but the gas engine for highway driving. Some systems use a flywheel to store energy from braking, which in most vehicles is wasted as a lot of heat. Your fundamental point though is correct; these systems are nothing like 100% efficient.

[ Parent ]
Let's get dirty (physics) (none / 0) (#90)
by Trickster on Fri Mar 15, 2002 at 06:35:17 PM EST

For starters, let's ignore real-world things like air and the fact that the Earth rotates. On the way up the forces acting on the elevetor (mass M) are:
  • Force applied by the propulsion system (don't care what it is) Fp and it's acting up
  • Force of gravity = M*g, acting down
So at the final point H, the total energy, would be equal to the potential energy,
M*g*H = Fp*H - M*g*H;
Fp*H = 2*M*g*H.
Already you've lost a half of your applied energy to fight work done by the gravity.
The most efficient way to get the elevator back is to let it fall. The moment before it hits the ground all that potential energy it had would be converted into kinetic energy. And you can't recover even that part fully. So no, no matter how hard you try you can't get all of your energy back.

[ Parent ]
Sorry what is your point.. (none / 0) (#100)
by RandomAction on Fri Mar 15, 2002 at 08:23:25 PM EST

..no one says you can recover all the energy, according my understanding of nature that's impossible. The idea that The most efficient way to get the elevator back is to let it fall is simply bollocks. X gets the elevator up, energy expended getting it down also = X. (Of course if we don't use it we lose it.) No one here has denied that. However you can extract energy from the downward part without breaking any physics that I know of. If you know something we don't please.. PLEASE post it. However I'm now on my last beer.. so facts are getting hazzyee . ..Oups where was I.

[ Parent ]
That was exactly my point (none / 0) (#104)
by Trickster on Fri Mar 15, 2002 at 08:49:32 PM EST

I need beer.

That and that the original post was inaccurate. From the original: "you can even design systems which recapture most of energy used to accelerate the cars when they are decelerated at their destination."

My point was that you won't come even close, especially at the destination.

But I guess we agree on this one.

[ Parent ]
No way... (none / 0) (#127)
by Hatoyama on Sat Mar 16, 2002 at 09:05:05 AM EST

I think you missed out on the physics lesson about conservation of energy... Let's put it this way instead (with your exceptions, i.e. no friction and no rotation of the Earth): At the Earth's surface, your potential energy is E = m*g*0 = 0. At the endpoint, i.e. at the space station, your potential energy will be E = m*a*h, where a is whatever your gravitational acceleration is up there. Disregarding friction, i.e. saying that we can have electrical motors/generators with 100% efficiency, you will have to spend an energy amounting to W = m*a*h to climb up the tether, and will regain the exact same amount on the way down. I'm not quite sure that I understand what it is you're trying to show in your example...? And, as a matter of fact, noone claimed to be able to get all the energy back...only *close* to all the energy

[ Parent ]
You're forgetting something (none / 0) (#171)
by dasunt on Tue Mar 19, 2002 at 11:14:03 AM EST

What about the idea that the elevator is running the entire length of an electrically charged atmosphere?



[ Parent ]
space elevator, huh? (3.50 / 8) (#64)
by sja8rd on Fri Mar 15, 2002 at 04:31:16 PM EST

...i would much rather have escalator to space.

What about... (4.00 / 1) (#83)
by rebelcool on Fri Mar 15, 2002 at 05:57:46 PM EST

...a stairway to heaven?

Oh yes, I am the master of bad jokes.

COG. Build your own community. Free, easy, powerful. Demo site
[ Parent ]

that is an evil pun... (n/t) (none / 0) (#110)
by tenpo on Fri Mar 15, 2002 at 11:24:19 PM EST



[ Parent ]
How bout (5.00 / 1) (#108)
by Tachys on Fri Mar 15, 2002 at 10:19:55 PM EST

How about a really big cannon?

Any game that gets banned by the Austrailian govt can't be all bad... - Armaphine


[ Parent ]
Earth-Trojan asteroids? (3.80 / 5) (#78)
by madsci on Fri Mar 15, 2002 at 05:03:17 PM EST

Just a nitpick... but I wasn't aware of any known asteroids at the Earth-Sun Lagrange points... only L4 and L5 (the Trojan points) are stable orbits, and I don't think anyone's seen anything there besides dust.

http://www.seds.org/nineplanets/nineplanets/hypo.html#moon2

Is it one way? (3.25 / 4) (#79)
by Prophet themusicgod1 on Fri Mar 15, 2002 at 05:03:34 PM EST

i'd pay 300$ for a one way, but there's no way that i'd pay 300$ to leave this hicktown and have to come back!!!
"I suspect the best way to deal with procrastination is to put off the procrastination itself until later. I've been meaning to try this, but haven't gotten around to it yet."swr
Asteroids at Earth's LaGrange points? (4.00 / 5) (#80)
by eemeli on Fri Mar 15, 2002 at 05:03:50 PM EST

[C]arbonaceous asteroids ... are readily available and waiting in the Earth-Sun LaGrange points.

Are there? I was under the impression that at least Earth's LaGrange points are pretty much empty. However, do you mean near-earth asteroids (Atens, Apollos & Amors)?



there is another... (none / 0) (#121)
by khallow on Sat Mar 16, 2002 at 04:42:59 AM EST

As I recall, there is a pile of gravel that thinks it's an asteroid orbiting around the Earth-Sun L5 point in a really screwy orbit. Maybe it's carbonaceous. I dunno. You still need to move it to L5 before you could use it there.

[ Parent ]
Do you mean 3753 Cruithne? (none / 0) (#159)
by Wayfarer on Sun Mar 17, 2002 at 06:17:10 PM EST

Although (IIRC) 3753 Cruithne doesn't orbit the Earth's L5 specifically (more like the L4 and L5--if it can even be said to 'orbit' them), it's still something of a companion to Earth. I also recall an article on faint splotches-that-might-be-gravel near the L5, but I can't remember whether those observations have been corroborated.

I don't recall any composition studies being done on Cruithne. Hell, I don't even know its albedo. However, it's pretty big. There's a FAQ, if you're interested.



-W-

"Is it all journey, or is there landfall?"
-Ellison & van Vogt, "The Human Operators"


[ Parent ]
Yes, this is the beast (none / 0) (#177)
by khallow on Wed Mar 20, 2002 at 03:48:49 AM EST

That's a really weird orbit. Don't think it has much to do with either L4 or L5 (except it probably comes close every once in a while). My guess is that it would take a lot of energy to park it in one of those points.

[ Parent ]
Cool... just don't build one on mars (4.42 / 7) (#82)
by JahToasted on Fri Mar 15, 2002 at 05:42:51 PM EST

The damn revolutionaries will just disconnect the asteriod, sending it flying into outer space and the cable will crash down to the planet.

But that'll probably never happen on Earth...
______
"I wanna have my kicks before the whole shithouse goes up in flames" -- Jim Morrison

Considerations besides weight/mass (3.87 / 8) (#88)
by Rahyl on Fri Mar 15, 2002 at 06:11:07 PM EST

Changing weather conditions would prevent such a system from remaining stable for long periods of time. Electrical discharge from storm clouds could also pose a problem. Although building the elevator to have the same weight/mass on each end of the station would theoretically keep it in place, maintaining this state of equilibrium is, in all likelihood, impossible.

The coefficient of linear expansion also poses an interesting dilemma. As the materials changed in temperature, they would expand and contract. Although I don't have the numbers in front of me, single degree C change in a nanotube 35,000 km in length would create a major problem for a space elevator. Could the temperature of the elevator be kept constant? Probably, but a cost so enormous, it probably isn't worth the time to consider.

An interesting idea, but one that probably won't see the light of day.


Why so expensive? (none / 0) (#137)
by RandomAction on Sat Mar 16, 2002 at 06:18:52 PM EST

Could the temperature of the elevator be kept constant? Probably, but a cost so enormous, it probably isn't worth the time to consider.
Why so expensive? Lots of solar enery up there.

[ Parent ]
Unfortunately, In Physics Nothing is Free (3.09 / 11) (#89)
by ikeaboy on Fri Mar 15, 2002 at 06:18:49 PM EST

The space tether works on the principle that you can "pull yourself" into space. You're not "pushing off" the Earth, but being pulled up into space.

The problem with a tether is that all the force is exerted on the space station. You're adding mass to the space station, and as you drag mass up on the tether you drag the space station down from orbit bit by bit. So with every bit of mass you add the entire space station will be pulled into a lower and lower orbit. SpaceLab and MIR were bad enough, let alone a station with a massive asteroid coming crashing out of orbit.

Adding the mass of the Asteroid would help a little, but the tolerances of a stable orbit aren't that high. Raise more than a certain amount of mass and the whole platform will come out of orbit (I say mass rather than weight, the Asteroid will have a much lower gravitational force exerted on it).

Of course, you could use rockets or whatever you like to stabilize the station orbit, but you can always blast yourself into orbit anyway. That is the kind of thing the tether is trying to avoid. You could also do a exchange for the mass, say mined from the asteroid, to Earth to equalise the balance, but then it's all getting quite complex and expensive. You could increase the energy gained this by "launching" mass at Earth. This seems like a bit of a bad idea because (a) you're firing stuff at Earth and that energy has to go somewhere, and (b) the tether was trying to avoid using launching in the first place, you might as well have launched the original payload.

So in terms of allowing a massive lift into space, there are limitations. For human travel; experiments and tourism it may be possible. There are also some nifty things you can manufacture in zero-g, but I doubt the economics are there.

Oh yeah (none / 0) (#94)
by merchant on Fri Mar 15, 2002 at 07:20:50 PM EST

Actually, didnt think of that at all, but I think thats right.

There is no wsy it will be rigid so the force will be on the space station.

[ Parent ]
Rigid elevator (none / 0) (#96)
by ikeaboy on Fri Mar 15, 2002 at 07:35:59 PM EST

Correct. A rigid "pole" would move the force onto the Earth, so you would climb up to the space platform.

However, you're never going to make something that long and thin rigid, no matter what material you use. A tether has to bend otherwise it's simply not practical.

The station itself isn't anchored in space, it's suspended there. Drag a mass X up into space requires creating a potential energy. That energy has to come from somewhere, and that's the energy of the platform orbit...

[ Parent ]
Or... (none / 0) (#97)
by kuran42 on Fri Mar 15, 2002 at 07:45:56 PM EST

...another elevator coming down. While I doubt it would be worth it to match masses and velocities exactly, getting them pretty close and working the rest off with low-thrust, high-Isp NTRs or directed solar sails seems pretty workable. At GEO, you have the luxury of time. You can afford to take an hour or six to correct your position, so low-thrust works.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]
and.. Microwave launches (none / 0) (#99)
by ikeaboy on Fri Mar 15, 2002 at 08:21:22 PM EST

True. But you'd have to launch the downward mass towards earth, just dropping it is not enough. In fact, if you did drop it it would just stay in orbit. Just as you "pulled" up to the station, you'd need to "push off" to equalise the forces.

You couldn't use the elevator on the downward journey, since the tether would still act as a downward force on the station as gravity increased.

There is one other solution. You could move mass further out into orbit to balance the effect. However, moving the mass further out takes work as well. You're just shifting the work from the launch pad to the platform.

In the end, and even if you use low thrust, this balancing act is real just using up a lot of energy. You don't get energy for nothing, and putting a mass X into space will always cost energy. I'm sure a tether would not really help make this process more efficient, in fact I'm sure it would take less energy just to do an Earth launch.

I like the Solar Sail idea. Still not sold on it though. The sail would have to be quite large (enormous really) because the Earth's magnetic field deflects quite a bit of solar radiation. Additionally, to get the force of the sail acting in the right direction it would have to absorb the radiation (too much heat created and very low force) or reflect it all at Earth... Sure there are some places that could do with some more sun, but this would be a little too much I think :)

[ Parent ]
Some good points... (3.00 / 1) (#112)
by kuran42 on Sat Mar 16, 2002 at 12:08:54 AM EST

Elevators going down push in the opposite direction as elevators going up. This doesn't help by itself, because if you "push" on a tether, it just crinkles. But if you have elevators pushing in the opposite direction at the same time, the effects are roughly cancelled out. The relevant pairs are accelerating an elevator car going from Earth to the station (pushes "down" on the cable) and an elevator car going from the station to Earth (pushes "up" on the cable), and vice versa. This scenario requires that you actively push yourself down the tether, rather than just succumbing to gravity (Not that you would - it's GEO, after all).

But even if you do need to use rockets to maintain orbit, consider this: the most important number in rocket science is Isp. Isp is the number of seconds a single pound of propellant will accelerate a kilogram of payload at one meter per second. Chemical rockets have an Isp of around 300 to 450, whereas electric-ion engines can have an Isp of 900. For the cost of putting "mass X" into space, you get twice the work. But you can't use such a system for ground based launches because they are too low thrust - you'd never get off the ground.

Lastly, I think if we ever do manage to construct a tether 35,000 kilometers long, building a solar sail with a surface area of a couple hundred square kilometers won't pose us much of a problem. Also keep in mind there are a couple different kinds of sails. One depends on solar ejecta, protons and the like, to push it like a real wind does on Earth; the other is based on light pressure, and photons aren't deflected by the Earth's magnetic field. The later is the kind that can be steered, because it reflects photons, whereas solar ejecta gradually build up on the sail and only thrust directly away from the sun.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]

This is not a problem, people (5.00 / 1) (#150)
by A Trickster Imp on Sun Mar 17, 2002 at 06:15:24 AM EST

If the thing is farther out than geosynchronous orbit, the earth will pull it around much the same way you swing a rock around your head at the end of a string.

Anything that passes the point where the earth's gravity is cancelled by the centripital force will then "fall" out to the station. The "cord" will thus tighten back up, the energy coming from the earth.

I thought the math was worked out a long time ago, and that this was the design, not that the thing would literally be in an orbit. It would not be in an orbit.




[ Parent ]
You only need to use energy to get.. (none / 0) (#136)
by RandomAction on Sat Mar 16, 2002 at 06:16:09 PM EST

the 'to earth' elevator some small distance from the station from there gravity takes over. From being in a free fall, to being in what would be without the strand, a decaying orbit, .

[ Parent ]
Geosynchronous orbit (none / 0) (#179)
by linca on Mon Mar 25, 2002 at 03:48:26 AM EST

is high enough that the earth's magnetic field is nonexistant, I think. That would be the problem of that kind of space station : no pretection from radiations.

[ Parent ]
Hmmm... (none / 0) (#128)
by awakening rage on Sat Mar 16, 2002 at 09:46:47 AM EST

Since there's no way for the cable to be rigid, why not use it's movement to our advantage. The Earth has a magnetic field, right? Anybody remember what happens when you move a conductor in a magnetic field? Sounds close enough to "free energy" to me.

[ Parent ]
Re: Hmmm... (none / 0) (#130)
by danceswithcrows on Sat Mar 16, 2002 at 01:24:35 PM EST

The Earth has a magnetic field, right? Anybody remember what happens when you move a conductor in a magnetic field?

David Brin wrote a story called "Tank Farm Dynamo" that discusses this; it's part of his book _The River of Time_. I'll summarize:

This is not a good idea, because there is no such thing as free energy. The electricity you're extracting using the tether has to come from somewhere--specifically, in this case, it comes from the orbital momentum of the station. This isn't good because if the station loses too much orbital momentum, it tends to fall to Earth.

Conversely, if you have a tether or even a long wire that extends into the Earth's magnetic field, you can put energy (obtained from solar panels, most likely) into the wire/tether, and oppose the magnetic field, either keeping the station's momentum constant or raising it. Conceivably, you could use this to raise the station to a higher orbit.

(I don't know if things would work out this way in the Real World, but Brin has a Ph.D in astrophysics and may know what he's talking about.)

Matt G (aka Dances With Crows) There is no Darkness in Eternity/But only Light too dim for us to see
[ Parent ]

Hmmm, cont'd (none / 0) (#147)
by awakening rage on Sat Mar 16, 2002 at 10:13:06 PM EST

True, a PhD in astrophysics does trump a MS in Math (and I barely remember physics from college), but I was thinking along somewhat tangenital lines from the discussion. Well, "perpendicular" to be precise.

Since there's this enormously long non-rigid body, you'd expect some sort of harmonic motion along its length. We damp that motion converting it to electricity and use that to help keep the cable in place. Or maybe built the cable with some piezo-electric properites...

As for the cable falling to Earth, it doesn't look likely, as long as we don't overload the system.

I admit, it's not a simple problem (nor as simple as I present it), but I think a solution exists. Let's instead assume that the cable has no mass... um... never mind that, let's assume that the mass of the calbe is accounted for. Since in geosynchronous orbit the accelleration due to angular velocity [A] (orbital velocity [V] squared divided by the radius [R] or the orbit) is equal in magnitude and opposite in direction to the accelleration due to gravity [G] an object will stay up. If a force is applied to the object that is in the same direction as G or that decreases V, and nothing ballances that force, the object will fall. If, like the scientists said, the object is extended away from the earth, past geosynchronous orbit, then the cable will be pulled taut as |A| > |G|. If a mass [M] is tacked onto the end of the cable, somewhere further out from the earth from geosynchronous orbit, it's generating a force [F] somewhere around F=(A-G)M. If we don't haul things up the cable with a greater force than that, the cable should snap back into place.

[ Parent ]

Oh come on (none / 0) (#156)
by flikx on Sun Mar 17, 2002 at 04:03:34 PM EST

I get massless cables all the time from the physics stockroom at my university.

This should have been built ages ago!


--
One future, two choices. Oppose them or let them destroy us.
[ Parent ]
It's pretty simple: (none / 0) (#102)
by schrotie on Fri Mar 15, 2002 at 08:38:14 PM EST

What goes up must come down - sooner or later. Humans that go up, will hopefully come down again eventually using the same elevator. As does any garbage and waste. If you want to get things up that should not come down the same way (e.g. sattelites) you have to supply extra lift.

Apart from getting fuel or fusion material up, could one not somehow utilize the gravitaional force of moon? If you used a cable that extended as far into space as the distance earth-stationary orbit you'd already have more than 1/5 of the distance moon-earth covered. Gravitational effects of the moon might matter then. If you adjusted the mass relations properly, you might be able to get all the lift you need for free.
And that would be an unlimited energy source, since moon is receding anyway (not that it would really matter considering the masses involved).

[ Parent ]

It is mostly.. (2.00 / 1) (#107)
by bgalehouse on Fri Mar 15, 2002 at 09:50:43 PM EST

As described in the NASA report, and in another of my responses, if you tension the cable, and set the weight out past the geo orbit, you avoid these issues through centripital force.

[ Parent ]
A Balancing Act (none / 0) (#124)
by ikeaboy on Sat Mar 16, 2002 at 05:37:24 AM EST

Just because NASA have a report on it doesn't make is feasible. NASA has a lot of think-tanks and they chuck up tons of ideas to either have them expire or inspire.

Consider this; Could you have the tether connected to a 1kg mass in space? If you pulled on the tether it would come crashing out of space. The fact that the platform would be several hundred tons only changes the scale.

When you have a geosynch orbit the forces of gravity and centripetal force are in balance. As
is the velocity of the object and the rotation of the earth. Centripetal force for geosynchronous orbit is not infinite, it a balance. Hence, any energy you use pulling something up is going to have to come from somewhere. It's not advanced physics, it all comes down to Newton's 3rd law... Any force you use pulling something into space must go somewhere, and in this case it's the platform (through the tensioned cable you mentioned). This must ultimately effect the balance of the orbit, there is nowhere else for this force to go. Unless you use some clever countermeasures, which kuran42 and I discussed in the other thread, the orbit will fail.

The end result will always be a lower orbit, proportional to the platform mass and the raised mass. The only way to counter this is to move the position of the platform, and this will take the same energy.

[ Parent ]
Orbit? (none / 0) (#149)
by A Trickster Imp on Sun Mar 17, 2002 at 06:08:32 AM EST

1. If it was in orbit, that would be a problem. If it was not in orbit, i.e. swinging at the end of a rope such that it had its own centrifugal force pulling away from the earth, then any weight that climbed up there would be added to the ability of the object to stay up there, like adding another washer to the weight you're swinging around your head.

2. A few hundred tons, or a few hundred million tons?

3. Either way, you've got to guide it into orbit in the first place, which means sending a huge rock at the earth with a very narrow tolerance. Then, once there and connected, if 1. is to take place, you'd have to rocket into higher orbit, where the tug will start the centripital force.

[ Parent ]
The math at least, I trust (5.00 / 1) (#155)
by bgalehouse on Sun Mar 17, 2002 at 01:47:59 PM EST

I'm not at all sure that I'd trust the cable engineering, the ability to avoid lightning strikes, etc.

But you are criticizing feasability from an orbital mechanics point of view? That I trust NASA to get right. That it matches my physics knowledge doesn't hurt.

When you have a geosynch orbit the forces of gravity and centripetal force are in balance. As is the velocity of the object and the rotation of the earth. Centripetal force for geosynchronous orbit is not infinite, it a balance. Hence, any energy you use pulling something up is going to have to come from somewhere.
The cg of the elevator isn't in geosynch. It is in something slightly higher than geosynch, making the centripital force stronger than gravity. It is gravity plus cable tension which keep the cable in place, not just gravity. The excess centripital force still isn't infinite, but it is higher than needed to keep the system cg above geostationary for a sufficiently small climber. When the climber finishes, it has added mass to the system evenly, and the system will go back to equilibrium with the cg where it was before. The excess centriptial force is higher though, so the next climber can be larger.

This is implicit in the NASA report, but maybe it isn't argued through completely. I would guess that they assume that the uneducated won't question and the real physicists won't have trouble seeing what is happening.

Most of the energy to climb comes from the motor on the climber. However, a very slight bit comes out of the rotation of the earth.

[ Parent ]

NASA? (none / 0) (#158)
by ikeaboy on Sun Mar 17, 2002 at 05:48:54 PM EST

I was commenting (originally) about the story, which I don't think mentions NASA at all. In fact the story mentions putting and keeping the station in "GEO".

The story details a matched countermeasured system, something that is not required (as it's described anyway) if you're planning for a cable under tension...



[ Parent ]
OK (none / 0) (#162)
by bgalehouse on Mon Mar 18, 2002 at 01:28:21 AM EST

The NASA study was the first comment posted, I guess I may have gotten the two confused. It is so much better than the main posting.

Letting out cable in both directions is an alternative to deployment - untill you have ahold of the cable on the ground you need to keep the cable-station system in geo orbit. The main posting itself doesn't seem to say anything about what you do to the orbit once the tether is on the ground.

[ Parent ]

Well, look down to (5.00 / 1) (#131)
by bjlhct on Sat Mar 16, 2002 at 01:38:43 PM EST

the comment below, and say: Depending on the temperature of teh cable, it would be longer or shorter. Then the orbit would we larger or smaller. Going out to a larger orbit tension decreases, in it it increases. Opposite for a smaller orbit. So, sent stuff up or down at the right times to cancel this. (?)i

*
[kur0(or)5hin http://www.kuro5hin.org/intelligence] - drowning your sorrows in intellectualism
[ Parent ]
No the elevator is under tension. (none / 0) (#135)
by RandomAction on Sat Mar 16, 2002 at 06:01:55 PM EST

It's being swung around the Earth, climbing up it slows the spinning of the Earth, the energy that keeps it up comes from the spinning of the Earth. Get over it.

[ Parent ]
Tension (none / 0) (#152)
by ikeaboy on Sun Mar 17, 2002 at 06:22:16 AM EST

It's doesn't really matter if the cable is under tension (and if it is under tension, why do you need the asteroid on the other side?). Perhaps if you put your message in bold I would get it.

Putting the platform in orbit, with tension on the cable, takes a certain amount of energy. When you move a mass up the tether you take from this energy. The same amount of work is done, you're just changing where the energy is stored -- and adding a whole lot of complexity. e.g. How do you anchor this tether, can you anchor that amount of force to make the amount you can lift worthwhile?

[ Parent ]
Center of mass needs to be in geosynchronous orbit (none / 0) (#174)
by raygundan on Tue Mar 19, 2002 at 04:44:25 PM EST

The center of mass of the whole system needs to be in geosynchronous orbit to prevent it from moving in relation to the earth. So just building the cable up to geosync is a really, really bad idea, since you'll end up with a whole lot of expensive stuff crashing into earth. The cable either needs to be built twice as long as the distance to geosynchronous orbit, or to save the unnecessary work of making more exotic materials than we really need, we can just tie a big rock on the far end to add the necessary mass. The cable really is under tension. You really can ride up and down it without pulling it down. (although I think you are probably slowing the earth slightly)

[ Parent ]
Or past it, rather. (none / 0) (#175)
by raygundan on Tue Mar 19, 2002 at 04:49:26 PM EST

My mistake-- just at geosync would be your balance point. You want to move your cg past geosync to put tension on the cable. NOW you can move stuff up and down it, as long as the force of the earth's gravity pulling on that stuff doesn't exceed the tension force.

[ Parent ]
scratch that last one. change the cable length. (none / 0) (#176)
by raygundan on Tue Mar 19, 2002 at 05:17:31 PM EST

I am out of it today. Past geo has the same problem as under geo. The cable would smack the earth silly. You have to change the *length* of the cable to move the center of mass while you're moving things up and down it. But the cm must stay in geo. Lengthen the cable when you move towards GEO and shorten it while you're moving above GEO.

[ Parent ]
not a problem (none / 0) (#141)
by fourseven on Sat Mar 16, 2002 at 06:44:35 PM EST

one could use a ... counterweight ;-) when sending a mass up, send another, equal mass down. there's a bit of a problem at the point where the two masses meet on the single tether, but i'm sure the clever scientists can think of a workaround..

[ Parent ]
Where the energy comes from (none / 0) (#166)
by dennis on Mon Mar 18, 2002 at 10:34:02 AM EST

The asteroid is way out past geosynchronous, pulling the cable upwards. With slack in the cable, the asteroid will start to fly straight, until the cable is tight again. The energy comes from slowing down the rotation of the Earth, very slightly.

If you want, you can even send the cablecars out to the end of the cable with some cargo, and use the Earth's rotational energy to fling them out into space.

[ Parent ]

Space Elevator (4.07 / 13) (#93)
by slick willie on Fri Mar 15, 2002 at 07:05:13 PM EST

Prereq: Super Tensile Solids
  • Doubles ECONOMY energy reserve production at THIS base
  • Doubles MINERAL production rate at all your bases while producing Orbital improvements
  • Your units equipped with DROP PODS may make Orbital Insertions anywhere on Planet
  • Eliminates Aerospace Complex restrictions on Orbital improvements
Oh, never mind. It's probably not near as funny as I think it is...

"...there is no limit to what a man can do or where he can go if he doesn't mind who gets the credit."
--Ronald Reagan, First Inaugural Address

SMAC play by email (none / 0) (#116)
by drbrain on Sat Mar 16, 2002 at 03:13:11 AM EST

I've been looking for people to play SMAC with, anybody up for a game?

[ Parent ]
Don't play it, shoot it... (1.50 / 2) (#126)
by dipipanone on Sat Mar 16, 2002 at 08:58:56 AM EST

I don't know anything about playing it, but I'd be happy to shoot it with you if you happened to have a bag.

--
Suck my .sig
[ Parent ]
what happens when it crashes. (2.33 / 3) (#101)
by turmeric on Fri Mar 15, 2002 at 08:26:29 PM EST

or when space debris crashes into it?

Well... (1.50 / 2) (#109)
by tenpo on Fri Mar 15, 2002 at 11:18:06 PM EST

A mass somewhere near the total mass of our solar system crashes into our planet and we are flung out of control most likely out into the cold void of space, or more humanely into one of the other planets or our sun. A sacrifice i'm willing to make (assuming i'm living safely on our moon base with plenty of coke and skittles).

[ Parent ]
Risk is consumate with rewards (none / 0) (#170)
by Dyolf Knip on Tue Mar 19, 2002 at 11:01:01 AM EST

A lot of the problem with space debris is not the debris itself, but rather the current requirements set for space construction. Satellites and vehicles have to be as light as possible, which means the walls are as thin as they dare make them. If launch costs drop to the level of mail postage, you can afford to armor everything to the hilt or use other means to deflect incoming debris.

Junk hitting the tethered asteroid isn't a big deal; it's massive enough that only something really large could possibly move it and we'd see it coming a million miles away. Something hitting the cable itself might be a problem, but carbon nanotubes is pretty tough stuff.

As for a crashing beanstalk; well, it's not pretty. To do it you'd have to move the whole assembly into a decaying orbit or cut it in two at some point along it. Either way, it's going to come down like the fist of god. Pretty much anything on or near the equator is going to be obliterated, in some areas twice since the thing will wrap around earth with length to spare. Towards the end it would be like a line of nuclear weapons detonating around the globe.

But the advantages to having such a construct are extreme. And emergency safeguards could be installed, like rockets placed along the length of the cable so that if the orbit starts to fail catastrophically they'll help shift it back.

---
If you can't learn to do something well, learn to enjoy doing it poorly.

Dyolf Knip
[ Parent ]

What was the name of the book... (1.66 / 3) (#115)
by wintermute204 on Sat Mar 16, 2002 at 02:49:05 AM EST

I see you read the same Arthur C Clark book I did. I read it some time ago though and can't recall the name...

The Fountains of Paradise (5.00 / 2) (#120)
by khallow on Sat Mar 16, 2002 at 04:34:14 AM EST

Charles Sheffield also wrote a book (independently) on space elevators at the same time, "The Web Between the Worlds", but he loses on the cool book title. :-) As mentioned in the main story, the idea has been around a number of years before either story.

[ Parent ]
Also described in 3001: A Final Odyssey (none / 0) (#134)
by Lethyos on Sat Mar 16, 2002 at 04:50:30 PM EST

In 3001, much of the human population lived on a "ring around the world", as Clarke calls it. It is basically a giant loop-shaped space-station in geosyncronous orbit with the earth. Connected to the ring and the earth are space elevators that are made out of C60 gotten from giagantic chunks of diamond. The source of this carbon came from the detonation of Jupiter (becoming "Lucifer", or "Light Bringer", the second sun to warm Europa).

earth, my body; water, my blood; air, my breath; fire, my spirit
[ Parent ]
The Songs of Distant Earth (none / 0) (#157)
by Booj on Sun Mar 17, 2002 at 04:15:03 PM EST

I'm not sure about other books in which he might of written about, but there is a space elevator in "The Songs of Distant Earth." Interestingly that book also discusses the possibility of the quantum vacuum as an energy source. (Albiet without most of the kookiness associated with the free-energy, zero-point-energy camps that seem enamoured of the idea.)

[ Parent ]
The Foutains of Paradise? (none / 0) (#165)
by Freaky on Mon Mar 18, 2002 at 10:23:55 AM EST

I've got an old (1979) edition, and I'm yet to actually get around to finishing it, but it does revolve around the contruction of a space elevator. Others:
  • 3001, which includes a ring in GEO attached to the ground by things more akin to skyscrapers than anything else.
  • The Songs of Distant Earth, where a temporary one is made to lift ice.


[ Parent ]
But what about that 50 km tower they're planning? (4.00 / 1) (#133)
by anansi on Sat Mar 16, 2002 at 03:30:35 PM EST

Here is a link to more information about the technological testbeds they're discussing, the 'murcury and gemini' aspects of the 'apollo' that a functioning space elevator represents.

On a crazy paranoid side note... I've heard all kinds of reasons for the US being involved in plan columbia. One of the nuttier was "to build another canal in the region". But when I looked at how the equator crosses mountanous territory in Columbia, it made me wonder if the grey men in washington are maybe thinking ahead, farther ahead than anyone could imagine...? Maybe it's not another canal, but an engineering project that's analogous in many ways to the panama canal in its day?</paranoid rant>

Don't call it Fascism. Use Musollini's term: "Corporatism"

another use for a space tether (4.00 / 1) (#153)
by pelican on Sun Mar 17, 2002 at 11:49:43 AM EST

posting a link to a nasa story. Discusses using a tether to generate electricity. This was actually tested but failed due to stress on the cable.

here is the link (none / 0) (#154)
by pelican on Sun Mar 17, 2002 at 11:54:42 AM EST

Sorry folks forgot to include the link http://www-istp.gsfc.nasa.gov/Education/wtether.html

[ Parent ]
BUZZZ. (none / 0) (#161)
by rszasz on Mon Mar 18, 2002 at 12:51:55 AM EST

It was a short caused by air trapped in the insulation becoming an ionized plasma and shorting the tether to the shuttle. See article

[ Parent ]
Building infrastructure in space is a better way. (none / 0) (#163)
by CitAnon on Mon Mar 18, 2002 at 05:54:22 AM EST

Space elevator upside: cheap way to space Space elevator downside: big asteroid crashes out of the sky, vaporizing several million people. A better way, imo, would be to design self perpetuating robotic systems to mine and build infrastructure in space, then build cool things like space elevators around other planets.

Why would the asteroid... (none / 0) (#164)
by RandomAction on Mon Mar 18, 2002 at 09:07:05 AM EST

..crash out of the sky? If your talking about the one attached to the elevator then that would be flung out into space.

[ Parent ]
Asteroids crashing out of the sky (none / 0) (#178)
by CitAnon on Wed Mar 20, 2002 at 03:07:06 PM EST

I'd imagine that it would be a rather delicate operation to move the asteroid into orbit around the earth. If the asteroid does something unexpected, such as break apart, pieces could very well get inot a spiraling orbit that take it into the earth. -cit

[ Parent ]
Am I the only one (5.00 / 1) (#169)
by tabris on Mon Mar 18, 2002 at 11:28:13 PM EST

thinking of the computer (and PlayStation) game Descent?

Admittedly, I know that it isn't a very popular game anymore, but it does make an interesting question. I am all for AI development, but am wary of computers/AI's that do not interact w/ humans very much, which could lead to undesired consequences..........

[ Parent ]

So how much is this all going to cost? (none / 0) (#167)
by LQ on Mon Mar 18, 2002 at 12:19:45 PM EST

Will we ever be able to afford to take space exploration much beyond a few guys in orbit and the occassional uncrewed probe to the outer planets? Pessimistically, I don't think so. There is not enough prospect of profits to made by the corporations. What return would they expect on G$ over 50 years?

Some ideas... (none / 0) (#168)
by kuran42 on Mon Mar 18, 2002 at 12:47:01 PM EST

Asteroid mining could turn into a trillion dollar per year industry, easily. Metallic asteroids are generally believed (and we've got fragments to study, so we're probably right) to contain significant quanities of platinum-group metals. That translates directly into profit. Big profit. Assume the space elevator costs $500 billion to build, and the first asteroid retrieval and mining operation costs another $500 billion. By conservative estimates, you still make back costs and net about a trillion dollars on your first mining operation. And that's just considering platinum group metals.

Of course a huge influx of supply drives down the price, but many industries on earth use platinum due to its highly non-reactive nature. A company could easily capitalize on a low cost source of platinum to make high-quality, inexpensive replacements for many current-day devices, making further profits in a secondary market.

--
kuran42? genius? Nary a difference betwixt the two. -- Defect
[ Parent ]

Asteroid mining (none / 0) (#173)
by LQ on Tue Mar 19, 2002 at 01:16:24 PM EST

There's a good SciAm article on the subject which includes the telling quote "The bottleneck in such plans is the need to obtain detailed mineral characterization of near-earth asteroids and the lunar poles. Although funding for the discovery of near-earth asteroids and for small lunar and asteroidal spacecraft missions has recently been on the upswing, the level of funding is still 100 to 1,000 times smaller than that lavished on a single large military or civilian spacecraft"

[ Parent ]
Ten Millionth Floor, Please | 179 comments (176 topical, 3 editorial, 0 hidden)
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