NASA Power Beaming Challenge is On For November 2nd

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."

Comments

Why not just use wires?

[slifox]

Why must we beam the power to a space elevator?

Wouldn't it be reasonable to use wire conductors? If we will be able to build the support lines that can span from the earth to orbit, why couldn't we also make a couple of smaller ones inside the main one for carrying power? Or why not just use the support lines themselves to provide power (assuming there are multiple support lines for redundancy)?

Can anyone provide some more insight into this? I haven't been able to find a decent explanation

Re:Why not just use wires?

[beefnog]

The tensile strength of an eventual space elevator material is not related to its electrical conductivity or resistance. 10,000 miles of a conductor will (currently) weigh more than its own tensile strength could support.

Re:Why not just use wires?

[fred fleenblat]

aside from the weight issue, shouldn't the cable specifically be designed to be an insulator anyway? Shorting out the fair weather return current and/or tapping into particle storms in the upper atmosphere seems like it could lead to some nasty little electrical issues.

Re:Why not just use wires?

[Rei]

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. No nonexistent (and possibly even impossible) materials required.

Re:Why not just use wires?

[Rei]

"a few extra tonnes"? First off, space elevators aren't exactly high payload devices; the margins in most designs are generally tiny compared to the elevator's mass. But the big problem with what you wrote is that geosynchronous orbit is 26,199 miles up; a space elevator must be *at least* that long. You're looking at something like one ton per 10,000 miles, or one pound per five miles, or 17 milligrams of conductor per foot. Do you really think that's going to power anything? Even if you only provide power for part of the way up, it's still just not going to happen.

Re:Why not just use wires?

[Rei]

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?

[gurps_npc]

It is totally correct that we can't make a space elevator right now.

But we could make a space elevator.

1. Take a particle accelerator, preferably one built at a high altitude. You should be able to start at least 4000 meters above sea level (China's Qinghai-Tibet Plateau averages 4,500 meters.

2. Put a bend in the output - straight up.

3. Detach the final u turn that bends the particle stream down again.

4. Add some magnets to recover power from the particle stream. Use it to power the magnets in the final U bend, that is now detached.

5. Focus the energy so that the it is self-centers the now detached final U.

6. Up the power. The detached U bend now floats.

7. Keep raising the power. U bend keeps going up.

8. At low altitudes, the atmosphere will drain massive energy. So build an air-tight 2000 meter tower around the particle stream. At the very least this should take you 6000 meters above sea level. Air pressure is now 50% sea level. This will reduce power consumption

Problems: 1. Power requirements will be HIGH. We will need to build a Nuclear power plant (probably a 2nd on as a backup). 2. We will building the tallest man made structure on Earth, at one of the highest points on Earth. 3. A lot of untested engineering, although the physics is known.

In other news....

[snspdaarf]

High-powered laser shoots down helicopter. Film at eleven.

Re:Why a helicopter?

[jimbolauski]

1 m^3 of helium has about 1kg of buoyancy, to lift 1km cable along with the elevator would require a very large balloon, the winds at 1KM are much stronger then on the surface so the giant balloon would be blown all over the place with a laser pointed at it I'm sure you can figure out the rest.