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Sticks
2009-Jan-06, 09:39 AM
No this is not about Harry Potter, but Space Elevators again

From BBC News Online (http://news.bbc.co.uk/1/hi/sci/tech/7792297.stm)


The prospects for the space elevator have been shaken up with a simple prototype using a broomstick.

Age-Raymond Riise of the European Space Agency demonstrated the device at a space elevator conference in December.

Nicolas
2009-Jan-06, 11:20 AM
That is so cool. I don't mean just the idea, but also the way of showing it in the meeting. Low cost, high impact.

NEOWatcher
2009-Jan-06, 02:02 PM
I applaud that it is a remarkably simple idea, and a new way to look at it, but it looks like a bigger hurdle than other ones.


While the novel idea could greatly simplify the provision of climbing power to the space elevator, a number of considerable technical challenges remain, namely in the makeup of the cable on which the climber ascends.

The talk about the cable needing to be stronger, but I wonder by how much, or if/how stiffness is a factor. I would have liked to see a demonstration with a wire, or rope or something like that.

I also wonder if they worked out any projections of power requirements. It has the advantage of being ground based, but it seems to me that there would be a lot of loss along the length of the cable.

aquitaine
2009-Jan-06, 02:05 PM
I think a loftsrom loop would be more sensible, since we can do it with our current technology.

NEOWatcher
2009-Jan-06, 02:15 PM
I think a loftsrom loop would be more sensible, since we can do it with our current technology.
I beg that we don't follow the "x would be better" route. It seems like every thread about possible technologies goes down that road, and sometimes gets rather opinionated.

I dont see a problem with discussing rival technologies. It's not that I agree or disagree, but I like to see some things discussed on their own merits or faults.

Trakar
2009-Jan-06, 02:55 PM
I beg that we don't follow the "x would be better" route. It seems like every thread about possible technologies goes down that road, and sometimes gets rather opinionated.

I dont see a problem with discussing rival technologies. It's not that I agree or disagree, but I like to see some things discussed on their own merits or faults.

Sensible, as it keeps the focus specificaly on the currently mentioned idea, and produces a list of pros and cons for later comparison with other concepts rather than leaping into a situation where people will immediately begin advocating their own pet concept and the thread veers off into predictable and non-topical discussions!

I worry about mechanical interlinks with any proposed tether system, primarily because of induced point loads and stresses that are inherent to such systems, and any system that depends upon inducing rapid vibrations into the tether just seems very problematic from the get-go. A broomstick model is very different from what one might expect if that broomstick were extended to 50 feet long (much less the distances involved in an actual tether).

How are they going to induce vibrations into the tether?
How are they going to deal with the stresses and stress fractures that will be induced into the tether by this system?
How are they going to dampen the induced and magnified oscillations at the outer anchor end?

More, but that would be a good start on my list issues to deal with in regards to this system. Too bad we don't have more direct access to the system designer(s).

Sticks
2009-Jan-06, 04:14 PM
My concern about any space tether is weather

Hey they rhymes!!

What I mean is things like what would the effect of wind pressure be, at ground level and higher up where you get jet streams and CAT

NEOWatcher
2009-Jan-06, 05:23 PM
My concern about any space tether is weather
Me too, but I would think that the weather could induce an additional type of vibrational energy which actually would assist.

Yes; weather is a major issue (as has been discussed before), but for it to be strong enough for that type of energy transfer, I would think it would have the added benefit of solving some of the weather issues.

samkent
2009-Jan-06, 05:34 PM
Transportation via broom stick method has been around for a long time. In fact one of our female office staff have been using it!

Ara Pacis
2009-Jan-06, 08:28 PM
I think a rocketship would be more sensible, since we can do it with our current technology.

Forget carbon nanotubes, maybe if we made it out of arbitrarily large carbon megacubes... :-)


sorry. could. not. resist.

On topic, I wonder if the bristles would damage the ribbon, especially once weight is applied. Maybe it would need a large surface area compared to the surface area needed between presure rollers. Also, I wonder if the ribbon would dampen the vibrations or if it would start a resonance and whip apart.

NEOWatcher
2009-Jan-06, 08:39 PM
On topic, I wonder if the bristles would damage the ribbon, especially once weight is applied. Maybe it would need a large surface area compared to the surface area needed between presure rollers.
I think that's going to be a function of the tether technology. But my guesses are... you can minimize damage by increasing area (and thus less force per bristle), or you can stiffen the bristles to hold on better (and probably lose some sensitivity in the process)

Also, I wonder if the ribbon would dampen the vibrations or if it would start a resonance and whip apart.
That's another reason I would have liked to see the demo with a more flexible technology (other than a broomstick)

Samkent: my experience is that those types of people can fly all thier own, and the broomstick is there to aggravate thier condition. :whistle:

KaiYeves
2009-Jan-06, 11:28 PM
No this is not about Harry Potter, but Space Elevators again
Darn, that was my first thought!

Siguy
2009-Jan-07, 01:18 AM
I hate the space elevator. Such a stupid, stupid, stupid idea and a waste of intellectual thought on a fantasy when we could already building the far, far superior, cheaper, more feasible, and practical Lofstrom Loop. The Loop doesn't require Harry Potter to conjur some 40,000 KM LONG CABLE OF FRIGGIN CARBON NANOTUBES. The cost of the Loop would actually be something governments would consider. The Loop could actually save a significant amount of money over rockets. It wouldn't have to take months to launch a payload. No irradiation, not limited to geostationary orbit, no having to fetch trillions of dollars from somewhere.

Gemini
2009-Jan-07, 03:53 AM
I first read Broomstick as Boomstick (Jules Verne?)

cjameshuff
2009-Jan-07, 05:02 AM
I hate the space elevator. Such a stupid, stupid, stupid idea and a waste of intellectual thought on a fantasy when we could already building the far, far superior, cheaper, more feasible, and practical Lofstrom Loop. The Loop doesn't require Harry Potter to conjur some 40,000 KM LONG CABLE OF FRIGGIN CARBON NANOTUBES. The cost of the Loop would actually be something governments would consider. The Loop could actually save a significant amount of money over rockets. It wouldn't have to take months to launch a payload. No irradiation, not limited to geostationary orbit, no having to fetch trillions of dollars from somewhere.

The loop has its own issues. It would not necessarily be cheaper. It requires a power plant that can power a few cities, maglev and linear motor systems that can operate at extreme speeds, and involves active stabilization of a complex system with a variety of instabilities, and a whole new set of engineering difficulties involved in construction and startup. No, we can't build one now, and the issues with powering and controlling the thing make the space elevator look trivial.

The technologies developed for the space elevator also have multiple applications. Tether and climber systems would be useful for spacecraft, space stations, and asteroids. The tether materials will find countless uses here on Earth. Development into the concept has immediate gains, and benefits us even if a space elevator is never built on Earth. The loop itself is more flexible, but its technologies are less widely applicable. The situation is nowhere near as clear-cut as you make it out to be.

Siguy
2009-Jan-07, 05:14 PM
True, we can't build one now, but we're closer to the motor systems and little issues with the loop than the massive scale carbon nanotubes for the space elevator. Your right though, it isn't a complete waste of energy, I wasn't being very rational. Yes, the technologies from space elevator materials research could be invaluable.

I highly doubt it would be more expensive than the elevator, the massive scale alone of the elevator would make it cost trillions no matter what the material. I believe Lofstrom's estimate was $30 billion for an efficient space elevator, even assuming that's optimistic, a loop would probably cost less than $100 billion. Plus the cost per launch is much lower and the annual launch capacity is much higher than the space elevator.

JohnD
2009-Jan-09, 01:07 PM
siguy,
I hadn't heard of the Loop, so I had a look. I went as far as the Wiki article, which suggests, among other concepts, that 'elevator cables' are hung from the rotor, that at altitude would be travelling at 14 kilometers a second. Is the technology to achieve a trolley that can stay on a track at that speed in existance or even in theoretical existance, any more than a space tether?


And the 'broomstick'. A stiff wooden broomstick will have harmonic frequencies many times higher than the vibrating sander, so no problem. An elastic tether, thousands of miles long will be able to vibrate in almost any frequency that you wish. The resulting nodes, or rather antinodes, will throw off anything riding it.
I thought that the pay-back for the elevator was in the return. Imported mass will balance anything coming up, so that only a small amount of power will move the elevator. This return will be delayed until mining etc. can provide the return.
John

Nicolas
2009-Jan-10, 09:39 AM
And the 'broomstick'. A stiff wooden broomstick will have harmonic frequencies many times higher than the vibrating sander, so no problem. An elastic tether, thousands of miles long will be able to vibrate in almost any frequency that you wish. The resulting nodes, or rather antinodes, will throw off anything riding it.

Would it help in this case to make it vibrate using white noise or filtered noise instead of a single frequency? My gut feeling says that the tether would still be vibrating, but would have less pronunciated nodes.