Carefully Timed Jerks Could Power Space Elevator

Hugh Pickens writes "BBC has an interesting article on the long-standing issue of how to power the 'climber' that would ascend a space elevator into space. Previous ideas have included delivering microwave or laser power to the climber beamed from the Earth's surface, but now European Space Agency ground station engineer Age-Raymond Riise has demonstrated a device that could provide a "lift into space" for cheaper space missions along a 100,000-km long tether anchored to the Earth. Riise demonstrated sending power mechanically by providing carefully timed jerks of the cable at its base with a broomstick to represent the cable held in tension, an electric sander to provide a rhythmic vibration to the bottom of the stick, and three brushes representing the climber with their bristles pointing downwards allowing the climber assembly to slide upward along the broomstick as it moved slightly downward, but grip it as it moved slightly upward. 'It would be possible to make a suspension system that completely decouples the cabin where the passengers are,' says Riise. 'For them it would be a linear movement with very little disturbance.' Riise says that he has been approached by commercial elevator companies, who are researching new ideas for elevators in superscrapers where the simplicity of the approach makes it attractive when compared to other ideas for powering lifts, such as compressed air."

Comments

I call bullshit

[deft]

"Why is everyone so obsessed with this terrible idea? Even if we got it to work, there's no way we'd be able to afford the maintenance and energy costs. It just isn't viable."

This guy just copied and pasted his post. I found this same post about plane flight, the space shuttle, the hubble, the mars rover, and the lightbulb.

ok, i lied, but you get the point :)

Re:"jerks"

[biryokumaru]

Actually, this is something the average person can see at home. The idea he's describing is a ratcheting mechanism, and is an excellent idea easily seen to be of use in any amateur environment.

My only concern is what happens when those bristles get a little worn out after all that high intensity cyclic stress and an elevator load of passengers plummet to their doom from 100 km up. Gonna need a really good preventative maintenance regimen, not something commercial operations are typically known for in the industrial sector.

I don't think this will work

[Cthefuture]

Consider how much energy it would take to move this massively long cable. There is no way in hell that is going to be efficient. You're going to be wasting a massive amount of energy as you move the entire cable the whole time the thing is climbing.

To the naive this approach seems workable because it looks simple. The fact is that it takes a certain amount of energy to do things and this is probably a very poor method that will become quite obvious at the scale we are talking about. In this house we obey the laws of thermodynamics and all that...

Then you have to consider the wear and tear on the mechanical parts, especially that really expensive long cable into space. This just seems like a bad idea all around.

Re:I don't think this will work

[SethJohnson]

Your point about the energy is spot-on. Additionally, this concept totally ignores the orbiting anchor for the space elevator. For every 'yank' performed on the cable, you pull the anchor lower in orbit. The anchor then has to reposition itself USING ENERGY. Probably rocket fuel, I'd imagine. Either that, or the anchor releases the cable to allow it to go downwards, then has to pull it up again. That's the "lift" for the elevator- the pulling up of the cable.

Seth

Re:I don't think this will work

[seanadams.com]

Consider how much energy it would take to move this massively long cable. There is no way in hell that is going to be efficient. You're going to be wasting a massive amount of energy as you move the entire cable the whole time the thing is climbing.

That was my initial reaction too, but then I thought about it for a minute and it occurred to me that this is probably analogous to an electrical/RF transmission line. The cable has some (very low) impedance in the sense that it is quite rigid, but it's not zero. You're not "moving the whole cable" by jerking on it, what you're really doing is transmitting a wavefront along a medium. Provided the whole system is impedance matched, nearly all the power could be delivered to the vehicle.

I'm not sure how well this holds up when you consider internal friction of the cable and other inefficiencies, but I wouldn't dismiss it off hand. The simplicity of it in that it works purely on kinetic energy makes it pretty intriguing. It may even have applications besides a space elevator.

Re:I don't think this will work

[seanadams.com]

Your assuming that the cable is rigid... most designs for this that I have seen are usually a ribbon/cable that can flex in either one or two dimensions. This would mean that you could not push it, only pull.

Actually I'm assuming precisely the opposite - nothing could be considered rigid at this scale. I'm further assuming that the wavelength of the vibrations is vastly shorter than the length of the cable. The cable has very high tensile strength and is under constant tension by centripetal force - this gives it a low enough mechanical impedance to be able to transmit meaningful force.

Also, we are having enough trouble creating a cable that can withstand the incredible force required for a simple tether... now they want to add vibration on purpose? This has disaster written all over it.

This does not necessarily introduce transverse oscillation, which would indeed be a problem. The net added tension on the cable would be zero, we're only talking an incredibly tiny variance in comparison.

I think you need to give this some more consideration before dismissing it. We don't know much from TFA how much research has gone into this, but I'd venture a guess that the inventor spent more time thinking about this than the few minutes you've had to noodle the idea since it made slashdot.