3 ms·

And that megawatt will be absorbed in a tiny surface area, no? Given that it's a laser? So even though the sail has plenty of surface area to reject heat, it wo

And that megawatt will be absorbed in a tiny surface area, no? Given that it's a laser? So even though the sail has plenty of surface area to reject heat, it won't be able to conduct it faster than it vaporizes. But maybe you could use 500x 1GW lasers distributed around the sail, or use the plume of vaporized material as your propulsion, or have a sacrificial layer of material. I don't have relevant expertise, to be clear, I'm spit balling.

bufferoverflow 2y ago
1 megawatt of continuously absorbed power would require a lot of mass to dissipate without melting. But since we're talking about gram-sized objects, there's no chance. Even kilowatt would be a problem for object that small.
- marcosdumay 2y ago
  > 1 megawatt of continuously absorbed power would require a lot of mass to dissipate without melting Hum... I would require a lot of surface area, that's certain. There's no constraint at all at the mass.
  - bufferoverflow 2y ago
    Yes, there's a constraint on mass. Surface area is for dissipation. Mass will have to store the absorbed energy until it's dissipated. Mass determines the temperature. And every material has a limit on that temperature.
- EthanHeilman 2y ago
  Starshot which is the above proposal is likely based uses 10 meter square solar sails that are 100 atoms thick. > In order to reach relativistic speeds, the Starshot lightsail should have an area of ~10 m2 and be kept to a mass of under ~1 gram, which translates into an equivalent thickness of approximately 100 atomic layers ... With radiative cooling being the sole mechanism for passive thermal management in space, we quantify stringent requirements on material absorptivity that enable the lightsail to withstand high laser intensity and prevent excessive heating and mechanical failure. They seem to think that heat dissipating is within the realm of plausibility Materials challenges for the Starshot lightsail, Nature Materials, 2018, https://daedalus.caltech.edu/files/2018/05/Materials-challneges-for-Starshot-lightsail.pdf https://daedalus.caltech.edu/files/2018/05/Materials-challne...
  - barbegal 2y ago
    It's a nice idea but surely any variation in mass of the lightsail will result in significant forces which will literally pull the sail apart. And with a thickness of 100 atoms that variation might be just a few atoms. I can't see how this can be manufactured to take such high forces and be so light and thin.
    - EthanHeilman 2y ago
      That's why it is a research project, it is hard to do.
rocqua 2y ago
No, lasers are rather inaccurate over large distances. So it would be very uniformly spread.
jerf 2y ago
"Laser" actually refers only to the generation technique and the resulting phase coherence of the resulting photons. Lasers don't have to be particularly tightly focused. In fact if you've got a laser pointer at home, there's may be a lens on it you can take off, and there will be quite a spread on it. It is focused down by a lens and if you look carefully at the resulting spot you can see interference speckles from the focusing lens. Without the lens the laser will lack those speckles and you'll get a uniform, much larger spot from the raw laser.

bufferoverflow 2y ago

1 megawatt of continuously absorbed power would require a lot of mass to dissipate without melting. But since we're talking about gram-sized objects, there's no chance. Even kilowatt would be a problem for object that small.

marcosdumay 2y ago
> 1 megawatt of continuously absorbed power would require a lot of mass to dissipate without melting Hum... I would require a lot of surface area, that's certain. There's no constraint at all at the mass.
- bufferoverflow 2y ago
  Yes, there's a constraint on mass. Surface area is for dissipation. Mass will have to store the absorbed energy until it's dissipated. Mass determines the temperature. And every material has a limit on that temperature.
EthanHeilman 2y ago
Starshot which is the above proposal is likely based uses 10 meter square solar sails that are 100 atoms thick. > In order to reach relativistic speeds, the Starshot lightsail should have an area of ~10 m2 and be kept to a mass of under ~1 gram, which translates into an equivalent thickness of approximately 100 atomic layers ... With radiative cooling being the sole mechanism for passive thermal management in space, we quantify stringent requirements on material absorptivity that enable the lightsail to withstand high laser intensity and prevent excessive heating and mechanical failure. They seem to think that heat dissipating is within the realm of plausibility Materials challenges for the Starshot lightsail, Nature Materials, 2018, https://daedalus.caltech.edu/files/2018/05/Materials-challneges-for-Starshot-lightsail.pdf https://daedalus.caltech.edu/files/2018/05/Materials-challne...
- barbegal 2y ago
  It's a nice idea but surely any variation in mass of the lightsail will result in significant forces which will literally pull the sail apart. And with a thickness of 100 atoms that variation might be just a few atoms. I can't see how this can be manufactured to take such high forces and be so light and thin.
  - EthanHeilman 2y ago
    That's why it is a research project, it is hard to do.

rocqua 2y ago

No, lasers are rather inaccurate over large distances. So it would be very uniformly spread.

jerf 2y ago

"Laser" actually refers only to the generation technique and the resulting phase coherence of the resulting photons. Lasers don't have to be particularly tightly focused. In fact if you've got a laser pointer at home, there's may be a lens on it you can take off, and there will be quite a spread on it. It is focused down by a lens and if you look carefully at the resulting spot you can see interference speckles from the focusing lens. Without the lens the laser will lack those speckles and you'll get a uniform, much larger spot from the raw laser.