Space Elevator vs Wildlife

An anonymous reader writes "The longest test yet of the technology that might one day lead to space elevators has revealed some unusual problems. From the article: "There were several unexpected encounters with wildlife. More than a dozen insect egg colonies had been laid on the tether and curious bats flew around the balloons, apparently attracted by the sound made by the tether's vibrations. Late in the test, swallows were also seen swooping down on the balloons, possibly to sip the morning dew on their surfaces." Maybe all the critters just want to go to space too."

Comments

It's Probably a Valid Concern

[eldavojohn]

From an industry report I found sometime ago on Slashdot:

Among the small wonders produced by nanotechnology are carbon nanotubes, an advanced material as strong as diamond. These amazing carbon cylinders possess 100 times the tensile strength of steel and are 10,000 times finer than human hair. They are believed to conduct heat better than any other material, and they can also conduct electricity or function as semiconductors.

"Nanotubes are astonishingly promising, and I'm a realist, not an optimist," says Rod Ruoff, a mechanical engineering professor at Northwestern University. "It's a question of making the technology cheap enough." In 2001, only 3 kilograms of the highest quality carbon nanotubes--the single-walled variety--were produced worldwide, each gram worth $300, or 30 times as expensive as gold.

Now, full-scale production of carbon nanotubes is underway at the world's first ever large-scale nanotube factory, built outside Tokyo by the Carbon Nanotech Research Institute, a subsidiary of Japan's Mitsui & Co. The new facility is expected to churn out 10 tons of carbon nanotubes--albeit the lesser quality multi-walled type--a month, and CNRI anticipates the price will be a much more reasonable $80 a kilogram.

These multi-walled carbon nanotubes may not possess all the impressive properties of their single-walled brethren, but mixed with plastics, they make ultrastrong composites or microscale precision parts. Such carbon nanotube-filled plastics are already being used by automakers in fuel lines because they are conductive and can thus be grounded to release static electricity, which can ignite flammable gasoline.

But this LiftPort PDF states:

One issue brought up is the possibility of discharging the ionosphere. Our calculations based on the size and conductivity of the ribbon and the electrical properties exhibited in our upper atmosphere illustrate that a small area (square meters) around the ribbon could become discharged in the worst conditions. The magnitude of this discharging makes us believe with high confidence that no adverse local or global phenomenon will occur. It also shows that it is unlikely, without considerable effort, that any kind of usable power may be generated by this same method.

I think your concern is valid though for conduction through the ionoshpere or even on the surface of the nano tube/wire -- what would this huge antenna/conducter do to our atmosphere (if anything)?

Re:It's Probably a Valid Concern

[Anonymous Coward]

Only in the upper atmosphere. Ozone is actually toxic.

Re:It's Probably a Valid Concern

[Orange Crush]

Didn't NASA conduct (hah) an experiment that used a microsatelite attached via a tether to the shuttle and as one was placed in a higher orbit than the other it travelled faster and produced an electrical charge ?

They've conducted several experiments on electrodynamic tethers, but they work on different principles than a space elevator would. An orbiting tether generates its charge by its motion through the earth's magnetic field the same way a spinning magnet generates electricity in a coil of wire in a generator. The space elevator would be geostationary (kind of important to tie it down at the bottom) so it won't be moving relative to the earth's magnetic field.

Tethered satellites are still a neat trick, tho, since (like a generator/electric motor) it works both ways--trading velocity for electricity . . . or electricity for velocity. This can allow some orbital manuevers without burning any fuel.

Re:It's Probably a Valid Concern

[Rei]

Well, yes, but there's still the inner Van Allen belt to contend with, where it will encounter a radiation flux of highly energetic protons (some > 100MeV). In addition to being damaging, they'll positively charge the elevator. That doesn't mean that they'll be a problem, though.

My big gripe about these experiments? They're working on ironing the kinks out of a climber on a tether, and ignoring the 800lb gorilla in the room: namely, that a space elevator from Earth needs to be built out of unobtainium to be realistic.

Most serious proposals (ones that actually consider the economics) require a tether strength the density of graphite with a tensile strength > 100GPa. Many want higher -- > 120GPa. The reason is the taper factor. You get much lower and the taper factor becomes huge. A huge taper factor means a vastly increased launch weight, pushing the costs into fantasyland. They'll often cite studies showing that SWNTs (Single-Walled Nanotubes) have 100, 120, sometimes even more GPa predicted tensile strength. There's a big problem with that: they don't have that sort of strength. Measured strengths of SWNTs have capped out at just over 60GPa. Now, this could be from imperfections in the tubes, but it's quite possible, due to the way that the tubes form (extruded from a tiny ball of molten carbon -- this sometime even leads to them looking like "strings of pearls" in places) that imperfections are, for the forseable future, an inherent part of SWNTs. It's also possible that even perfect SWNTs just aren't that strong. Either way, this is a huge roadblock -- one that's not going to be solved, commercially, any time soon. Possibly never.

Then there's the next potentially fatal flaw to the problem: nanotube ropes. CNTs naturally align into ropes (they can be hard to get separated in fact). Unfortunately, they naturally align into haphazard ropes, weakening them. Even a flawless rope, however, faces some serious fundamental problems. The ropes are held together by VdW and pi bonding -- not nearly as strong as the orderly CNT sp2 bonds. With the ability to make flawless, extremely long CNTs, and align them perfectly into ropes, the long individual tube length could supply enough force in the VdW and pi bonding to hold the ropes together under the sort of pressures that cause the tubes to break. In the real world, however, we're typically limited to about 20GPa.

However, CNT ropes are only part of the problem in themselves. You need to make a fiber or fabric out of them. Once again, imperfect bonding and manufacturing problems step in the way, reducing your strength by a significant factor yet again.

See the problem? They quote the *theoretical* strength of *unlimited length* *individual tubes*, and pretend that we're right around the corner from being able to produce a tether like that. We're not even close. This is *The* challenge with a space elevator. The amount of engineering to achieve such strengths, if they're even possible (a very big if), vastly exceeds the engineering needed to make a photovoltaic-powered machine climb a rope. They want to be seen as making progress, but really, they're spinning their wheels unless a (quite possibly impossible) material to make the tether out of, affordably, is discovered.

Re:Nature

[jimstapleton]

actually, it's not a complete vacuum. The concept most use as "vacuum" is relative - simlpy a system with less pressure than another.

Re:Time.....

[jimstapleton]

actually, they'd be able to travel faster because there would be more accelleration time. It would take just over ten seconds at 1G (2G force on the passangers) to get to a velocity of 100meters per second, at which point you have 360,000 seconds, or 100 hours. Now with a lower accelleration, but a longer acceleration, that could be cut down significantly. Once acceleration stops, you are back to 1G (minus the effects of your distance from earth).

Re:robot tests are dumb

[Anonymous Coward]

We are within 100 orders of magnitude. 100 orders of magnitude is 10^100 or a Googol. My tennis shoe laces are this close as well.

Thanks.

Re:Other issues and possible resolution

[painQuin]

telephone wires are no problem... it's the power lines you're thinking of, and the reason they can sit on them is because they only sit on one. If something touches both parts of a pair of power cables, zap.

Re:Other issues and possible resolution

[Tim C]

Strictly, you don't need to be grounded in order to recieve a shock, you need to have one part of your body (eg a hand) touching an area of high voltage, while another (eg a foot) touches an area of low(er) potential. That creates a potential difference between the two points, which enables current to flow; it is this current that causes the shock. Birds can sit on power lines because the potential difference between their feet is tiny, and so any current that does flow is insignificant.

Now the situation is a little different if the object is charged. Then, when you touch it, charge will tend to flow from it to you (as you are uncharged). If you're touching an area of lower potential, you'll get a shock, just as the GP mentions. If not, then you'll simply become charged. What happens then depends on a number of factors; perhaps you'll bleed the charge off naturally, perhaps you'll retain some of it until you ground yourself and get a delayed shock (just as you do when touching metal after charging yourself on carpet, etc).

I suppose if the thing is charged enough, then the short-lived flow of charge into the body could deliver enough of a shock to be problematic, but I'm an (ex-)physicist, not a physician, so I don't know for sure.

Re:robot tests are dumb

[dfenstrate]

I think you mean two orders of magnitude off, not 100.

That being said, how far off were we when this idea was first concieved, or practical work began? A factor of 1000? 10,000 ?

Anyway, we do stuff like this because it's fun and achievable. Most people who follow this sort of thing know that material strength of tether is the current limiting factor, and there is ongoing research in this field.

But there are plenty of people who don't have the expertise to contribute to the material strength problem, but they can sure have fun screwing around with climbers, can't they? The work has to be done sometime anyway.

Very promising concept

[Rankiri]

Here's a quote from an IEEE Spectrum article (Aug, 2005):

"It now costs about US $20 000 per kilogram to put objects into orbit. Contrast that rate with the results of a study I recently performed for NASA, which concluded that a single space elevator could reduce the cost of orbiting payloads to a remarkably low $200 a kilogram and that multiple elevators could ultimately push costs down below $10 a kilogram. With space elevators we could eventually make putting people and cargo into space as cheap, kilogram for kilogram, as airlifting them across the Pacific."

The article answers many space elevator-related questions. Those who want to know more about the project can read it here:

http://spectrum.ieee.org/aug05/1690

There are some technical problems (mainly related to construction of the cable) to be solved first, but the space elevator idea is definitely worth serious consideration, as it could provide humanity with extremely cheap and easy access to space.

Re:Very promising concept

[khallow]

The IEEE article is off by almost an order of magnitude. Russia puts stuff into space for $3,000 to $4,000 per kg, maybe less these days. I think both the Atlas V and the Ariane V are well under $10,000 per kg. In fact, the only commonly used launch system that costs $20,000 per kg is the Space Shuttle and it certainly is disingenuous to compare your phatom project to one of the most expensive launch vehicles ever.