Tractor Beams

[ydoaPs]

http://arxiv.org/pdf/1102.4905v1

 

How feasible would it be to make a large scale tractor beam? Would it be useful as a propulsion mechanism(pulling the moon toward it, but the moon has enough inertia to not really move) to sort of slingshot rocket payloads into space to ease the fuel needed to attain orbit?

[Xittenn]

I don't see how you could tractor the moon with this. If the beam was emitted at the moons surface it would at best kick up a lot of dust. If a harness was developed to pull the moon and the device was made ready for such a tractoring configuration, then maybe. This would be one really big harness though!

[ydoaPs]

I don't see how you could tractor the moon with this. If the beam was emitted at the moons surface it would at best kick up a lot of dust. If a harness was developed to pull the moon and the device was made ready for such a tractoring configuration, then maybe. This would be one really big harness though!

How about tractor beam powered bumper cars?

[Xittenn]

 

The big issue here is coupling. If the object being towed is not readily coupled by a device such as this, to achieve enough backwards scattering force to tow it will result in vaporization. The coupling device will have to be specialized and not just a surface to shoot at, whatever the object may be. My opinion ...

[Schrödinger's hat]

Yes, even laser tweezers will tend to vaporise anything macroscopic before they push it around much, as you increase the momentum you're trying to impart, you vastly increase the amount of energy the object is increasing, and cube-squared will mean that energy dissipation will become an issue before very long.

The maths these things are based on also tend to assume non-magnetic materials, there's also the difficulty of making exact -- or close to exact -- solutions for something as large and inhomogeneous as the moon so you know what type of beam geometry to use. This paper suggests that we can barely pull something of a specific size, with specific, homogeneous materials, as long as it doesn't absorb too much light (quite transparent), not a large hunk of rock.

While I wouldn't rule it out, it's certainly out of the range of our current science, let alone our current engineering.

[swansont]

The paper uses grazing incidence light and forward bias scattering (Mie scattering) to get this result. Mie scattering occurs for particles roughly the size of the wavelength of the light hitting them. http://en.wikipedia.org/wiki/Mie_theory

[Mr Skeptic]

From the description it sounds like it would be slightly better than laser propulsion, and would push you away from the object you're pulling toward you.