Free-propellant space propulsion using graphene and light

[Jesrad]

An unexpected discovery about graphene's weird properties: it can "turn" photons into electrons (turn the photons into pure momentum for its electrons, more accurately), and it can emit those electrons coherently, in one direction. This makes it possible to get useful amounts of momentum by shining a laser or even raw sunlight (that was tested successfully) at graphene sheets. I mean "useful" as in "orders of magnitude more than a conventional solar sail". The boffins were able to physically push a graphene sponge around with mere sunlight.

Simply said, this is a totally-OP form of solar sail. We live in exciting times.

[monophonic]

This smells of cold fusion. Even if this was true, it would soon exhaust the electron supply in the spacecraft and leave it as a brick-in-space with a strong positive charge. I think some other phenomenon must be what caused the material to move.

[K^2]

This smells of cold fusion. Even if this was true, it would soon exhaust the electron supply in the spacecraft and leave it as a brick-in-space with a strong positive charge. I think some other phenomenon must be what caused the material to move.

In LEO, you can pick up pretty decent supply of matter to use as reaction mass in that manner. Even in interplanetary space, solar wind has enough intensity for this to outperform a solar sail, which relies on light pressure almost exclusively.

Mind, the thrust obtained in this manner is still minuscule. This won't compete even with current generation of ion thrusters. But if you are limited purely by reaction mass, and your only other option is a light sail, this can do way, way better in theory. Whether it ever becomes practical is another question.

[vitekc45c]

So, a photon drive? What exactly is new about this?

[Perry Apsis]

So, a photon drive? What exactly is new about this?

I think you must not have read the summary, much less the article. It doesn't emit photons, it absorbs them and emits electrons.

(Although they didn't seem very confident that they actually knew what was happening.)

[Jesrad]

Yeah it's a solar-powered electron cannon which happens to be extremely lightweight and simple (two very desirable qualities for a space drive).

[K^2]

(Although they didn't seem very confident that they actually knew what was happening.)

It's not like anyone famous ever got a Nobel Prize for discovering something like a photoelectric effect over a century ago, or anything.

Yeah, I'm being facetious. But it's basically the same thing. The main difference is that electrons are thoroughly delocalized in graphene, so if you excite them with coherent light source, such as, say, a laser, you end up with the same coherence on the emitted electrons. And because electrons act as a wave here, you end up with a directed beam. Neat stuff, but it's honestly not rocket science. More like undergraduate level solid state physics in any decent university.

[AngelLestat]

I wonder how big is the propulsion against simple photons boucing. They talk about orders of magnitud higher, I will like to know a more accurate measure.

It seems that graphene sponge can only resist 900c degress, but if the force is much higher, then I am interested.

One problem is that even if the graphene sponge is very light, is not as light as few graphene layers, so this affect the acceleration.

So we end with lightmass/lowforce vs heavymass/highforce ratio. It seems interesting.. I want to know more.