Light Propulsion...Is this for REAL??

reply to post by Lethil


Sounds like your talking about Quantum teleportation, using the quantum entanglement theory and it is very intersting, consider this along with an electrical universe, everything being powered from the core of the universe, to the galaxies, to the stars, to the planets and then to us, as I said, very interesting.

[edit on 24-7-2008 by ElectroMagnetic Multivers]

Originally posted by amantine
Yes, these vehicles do work. Light from a laser is directed at a reflective surface. The light has momentum and transfers that momentum to the reflective surface. It seems like they are already working on a commercial application of this technology.

I highly doubt there will be commercial applications for a photon drive. It's just too inefficient. It has an infinite specific impulse, but it takes something like 3 megajoules per newton of thrust. That is simply untenable.

You could, perhaps, use a laser on the ground to vaporize part of a target on a vehicle, and use that for thrust, but that's kind of a different idea. (the target could even be air, if it were still in atmosphere.)


reply to post by robertfenix


Uh, no. They're nothing like each other. An ion drive works simply by firing ions as reaction mass. This is convenient because they can be manipulated by electric fields. Ions are massive particles, so Ion drives have a limited but still rather high specific impulse, with a tiny amount of thrust, for relatively low power.

Photon drives work but either emitting or reflecting photons, which are massless particles (the key here is that they have momentum, based on their frequency). photon drives have an infinite specific impulse, but a truly ridiculously low thrust and energy efficiency.

reply to post by Viendin


It IS an ion drive. Just a high power one. Since ion drives use so little propellant in the first place, engineers find that it's better to use much lighter, smaller power sources and accelerators to fire a higher volume of particles. There's a good scientific reason for this: The equation for momentum is p=mv. The equation for kinetic energy is Ke=1/2 mv^2. So the energy required to accelerate something goes up with the square of the velocity you intend to get it up to. The momentum only goes up with the first power. Ion drives use very little propellant, so all that really matters is the mass of the power source supplying it. Most spacecraft have to make do with solar panels, which are far to weak in reasonable amounts to run a real linear particle accelerator as an engine.

It's an elegant idea, but not yet practical.

Light is massless but not energyless. E=mc^2

Photons are massless, yes. In a vacuum the principle works on radiation pressure.

There is an old idea to use radiation pressure to fuse a pellet with lasers in fusion plans. Same pressure is applicable as applied to propulsion.

edit to add as a second thought the explosive isothermic expansion of the shell around a fusion pellet contributes to fusion reaction. However this does not disqualify radiation as pressure.

For a truer example, look to the Casimir effect. Even though it deals with vacuum fluctuations, in my opinion the principle would hold true for radiation.

Whether or not the glass is viewed as half full or empty has no bearing on the presence of potential.

[edit on 11/17/2008 by Matyas]

Originally posted by amantine
Yes, these vehicles do work. Light from a laser is directed at a reflective surface. The light has momentum and transfers that momentum to the reflective surface. It seems like they are already working on a commercial application of this technology.

While this would work most light propulsion vehicles work by heating the air in a chamber to increase pressure in the chamber producing thrust. Basically it's a jet without fuel. The reason that light isn't bounced off like you suggest is because it has very little mass e/c^2 to be precise. The amount of energy you need to produce a change in momentum is the momentum times the speed of light. So to give a kilogram 1 meter a second extra velocity you need to produce 150,000,000 joules of energy. Even if you can get a 99% efficient mirror that's still 1,500 kilojoules of waste heat to produce a very small change in momentum. Photon drives like this have one advantage, they don't throw away mass. They are far too low powered to use in earth's gravity field.