NASA Power Beaming Challenge is On For November 2nd 81
carstene writes "The NASA Centennial Challenge Powered Beaming competition, to develop technology for uses such as a space elevator, or to power a rover in a shadowed crater on the moon, was delayed indefinitely due to trouble setting up the kilometer-high race track. It has now had the kinks worked out and is rescheduled for the week of November 2nd. The competition involves using a high-power laser to beam power to a robot that climbs a kilometer-high cable attached to a helicopter. The competition was previously covered on Slashdot."
Re:Why not just use wires? (Score:4, Informative)
Re:Why not just use wires? (Score:5, Informative)
Yeah, even if you use ridiculous voltages, it's just not going to happen.
Plus, these competitions always seem like putting the cart before the horse. The elephant in the room is that we have no material close in terms of properties to what is needed to make a remotely feasible space elevator on Earth (at least 100GPa at the density of graphite), and it may not even be physically possible. Some people have theorized that SWNTs could be that strong, but the strongest SWNTs measured so far are about 60GPa -- and that's for *individual nanotubes*, let alone nanotube bundles, let alone composites made out of nanotube bundles many thousands of miles long. MWNTs have been measured somewhat stronger, but they're a lot denser, so that doesn't help. I mean, even if you ignore the other issues that have been shown to be huge stumbling blocks with space elevators, such as oscillations, that's really a killer.
These competitions come across as though someone started promoting their new "Levitation Shoes" with the following exciting announcement:
"Good news, Levitation Shoe engineers! We will be hosing a Levitation Shoe shoelace-development contest. As you all know, we need to solve the issue of shoelaces being able to withstand the wearer getting buffeted around by high altitude winds without breaking or becoming untied, so we've reserved a site with a huge fan that you can test your shoelace prototypes on! This will bring us one step closer to the dream of Levitation Shoes."
Honestly, much more realistic than a space elevator appears to be a Launch Loop [wikipedia.org]. No nonexistent (and possibly even impossible) materials required.
Re:Why not just use wires? (Score:4, Informative)
Let's say you're looking at a 100GPa cable (I can show you why you need a cable this strong later if you need me to). That's 14.5 million pounds per square inch. Let's give it a two-fold safety margin, so we have 7.25 million psi to work with. Let's say we want to carry a payload of 10 tons. That means we need a cross-section of 0.00275790291 square inches. Don't think that makes our cable super-light, mind you -- it must thicken as you go up, and will weigh hundreds or thousands of tons in net weight.
I don't know the resistivity of 5,5 armchair CNTs, but let's just go with copper for now. As we all know:
Resistivity = (Resistance * Cross-Sectional Area ) / Length
If we only care about the craft climbing up to GEO (42,164km), that means we have:
0.0000000168 = Resistance * 0.0000017792886414156 / 42164000
Resistance = ~400,000 ohms
Good luck with that. :P
Re:Why not just use wires? (Score:3, Informative)
Agreed but beamed power does have other very real and current day uses so the competition isn't entirely moot.
Re:Why not just use wires? (Score:3, Informative)
Oh, and a couple more things:
1) I was generous and assumed a cylinder for the cable rather than a ribbon, as most designs call for, for easier climbing. If you go with a ribbon, you'll get a lot more resistance.
2) If your solution is "superconductors", that'll help, but they break down at high currents, so it's still not a solution.
3) If your solution is "extremely high voltages", you get coronal discharge (which occurs even in the partial vacuum of near-space).
Finally! (Score:3, Informative)
You can watch a sweet (if cheesy) video about the team on their website [usask.ca].