Higher thrust from light than photon sails?
Not sure how they’d solve the charge build up problem, though.
9 thoughts on “Graphene”
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Higher thrust from light than photon sails?
Not sure how they’d solve the charge build up problem, though.
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Who needs conservation of momentum?
Which is to say, fine, maybe graphene can be a more efficient reflector, but there is a limit, and current reflectors aren’t all that far from the limit.
If it were easier to fabricate, stow, and deploy a graphene sail, that would be a plus, too. But, “Spacecraft built from graphene could run on nothing but sunlight”? Meh. So what else is new?
Something’s not properly explained there. But solar sails are our best hope for doing cheap deep space probes right now.
It’s nice to something else other than bombastic claims about the S.China Sea coming out of China.
The explanation they give makes no sense. You can’t add up incident photon energy in a substance until an electron is ejected. That was the whole reason Einstein revolutionized physics by establishing that energy was quantized, and his example was the photoelectric effect. But commercially available graphene can be had in sheets weighing 0.1 mg/cm^2. If you do the math, you’ll see that focused sunlight will accelerate that at 45 m/s^2. This is a solar sail, and is actually half as efficient as the idea (which reflects photons, doubling the momentum transfer). Nevertheless, it is worth looking at, because it will reduce the overall mass.
idea = ideal .
You can’t add up incident photon energy in a substance until an electron is ejected.
While true in general, this is not -strictly- true. The short version of the wall of math is: You have a decent chance of ‘adding’ if the two incident photons add to precisely the right amount and impact close enough together to be considered simultaneous. Two red photons can be excite a molecule -as-if- they were one blue(er) photon. The trick is “simultaneous”, or “vaguely-plausible that considering the Heisenberg… they -might- be simultaneous”.
But this is basically something only relevant for high-intensity laser games, I don’t see it being what is actually going on.
I wonder more along the lines of unrecognized ablation. (That’s not actually -hot- enough to vaporize in general, but something about the structure and vibrational modes expelling an atom.)
Enough charge buildup would stop electron emission. Before that point is reaches the sail will start collecting ambient electrons, from both sides. But this collection is rate limited, and comes at the expense of emitted electrons. Accepting their estimate of 70eV electron energy, there’s not going to be a lot of voltage to collect new electrons.
Just what I was about to say! Basically, if the effect is real and works because electrons are thrown off the surface then, sooner or later, the thrust will stop because the positively-charged sail will attract all the electrons back.
However, this can be corrected for. Simply use a relatively small amount of energy throwing protons away in the same direction. Of course, this means use of a small amount of reaction mass.