4 ms·

Non-starter. The whole point of ordinance is its cheap. What's wrong with ye olde ground based x-ray laser and a mirror on a satellite?

ben_w 7y ago
I thought the mean free path of x-rays in air would limit you to, effectively, “radiation mines”? (Or short-range death-rays, robot-mounted because the backscatter would kill a human operative)?
- TeMPOraL 7y ago
  If I'm reading this chart correctly[0], visible light has much worse mean free path than x-rays, so wouldn't x-ray lasers work even better than visible ones? As for backscatter, that's only an argument for a shell instead of a ground installation - you pulse the laser high up, where the backscatter is of no concern to you. -- [0] - https://en.wikipedia.org/wiki/Mean_free_path#/media/File:Photon_Mean_Free_Path.png https://en.wikipedia.org/wiki/Mean_free_path#/media/File:Pho...
  - ben_w 7y ago
    I saw the same chart, but I thought it’s only showing down to 1 keV photons? Whereas blue light is about 2.6 eV?
    - TeMPOraL 7y ago
      My mistake, I confused the scales when reading the chart. Indeed it doesn't extend below 1keV.
TeMPOraL 7y ago
How do you make an x-ray mirror that won't ablate and burn up when trying to reflect that kind of energy? Also, I said "pumped x-ray laser" for a reason; this type of design usually involves blowing up the energy source and/or the laser medium. Fits the missile or shell use cases. > The whole point of ordinance is its cheap Not in the US, with how much missiles cost.
mftrhu 7y ago
> Non-starter. The whole point of ordinance is its cheap. What's wrong with ye olde ground based x-ray laser and a mirror on a satellite? Mostly the fact that 1. as someone mentioned already, x-ray lasers are not easy to generate, with designs sometimes using nukes to pump them [see https://en.wikipedia.org/wiki/Project_Excalibur https://en.wikipedia.org/wiki/Project_Excalibur ]; 2. while x-rays can be reflected, x-ray mirrors don't behave like optical mirrors because the wavelength of an x-ray is in the same ballpark as the size of atoms (10 nm to 0.1 nm, with atomic radii being in the 0.1-0.01 nm range), and they only reflect 100% of incident radiation when it hits them at very shallow angles ("For gold at 1 keV, the critical reflection angle is 2.4 degrees") [see https://physics.stackexchange.com/questions/128247/how-would-an-x-ray-mirror-work https://physics.stackexchange.com/questions/128247/how-would... http://henke.lbl.gov/optical_constants/ http://henke.lbl.gov/optical_constants/ https://en.wikipedia.org/wiki/X-ray_optics https://en.wikipedia.org/wiki/X-ray_optics ]. When talking about lasers pumping out enough energy to be usable as weapons over distances of hundreds of kilometers - to bounce them off a satellite - you will need a mirror that can reflect that ray almost perfectly, or you'll just blast your own satellite out of the sky. And to do that, that mirror will only be able to reflect your ray at a shallow angle, which pretty much rules out bouncing an X-ray off it (unless your target is in orbit or, I suppose, if you have a fleet of such satellites, and coordinated enough to bounce the ray down 2° at a time). [Also see http://www.projectrho.com/public_html/rocket/spacegunconvent.php http://www.projectrho.com/public_html/rocket/spacegunconvent... , C-s for "X-ray" and "grazing", but that whole website is a goldmine]

ben_w 7y ago

I thought the mean free path of x-rays in air would limit you to, effectively, “radiation mines”? (Or short-range death-rays, robot-mounted because the backscatter would kill a human operative)?

TeMPOraL 7y ago
If I'm reading this chart correctly[0], visible light has much worse mean free path than x-rays, so wouldn't x-ray lasers work even better than visible ones? As for backscatter, that's only an argument for a shell instead of a ground installation - you pulse the laser high up, where the backscatter is of no concern to you. -- [0] - https://en.wikipedia.org/wiki/Mean_free_path#/media/File:Photon_Mean_Free_Path.png https://en.wikipedia.org/wiki/Mean_free_path#/media/File:Pho...
- ben_w 7y ago
  I saw the same chart, but I thought it’s only showing down to 1 keV photons? Whereas blue light is about 2.6 eV?
  - TeMPOraL 7y ago
    My mistake, I confused the scales when reading the chart. Indeed it doesn't extend below 1keV.

TeMPOraL 7y ago

How do you make an x-ray mirror that won't ablate and burn up when trying to reflect that kind of energy? Also, I said "pumped x-ray laser" for a reason; this type of design usually involves blowing up the energy source and/or the laser medium. Fits the missile or shell use cases. > The whole point of ordinance is its cheap Not in the US, with how much missiles cost.

mftrhu 7y ago

> Non-starter. The whole point of ordinance is its cheap. What's wrong with ye olde ground based x-ray laser and a mirror on a satellite? Mostly the fact that 1. as someone mentioned already, x-ray lasers are not easy to generate, with designs sometimes using nukes to pump them [see https://en.wikipedia.org/wiki/Project_Excalibur https://en.wikipedia.org/wiki/Project_Excalibur ]; 2. while x-rays can be reflected, x-ray mirrors don't behave like optical mirrors because the wavelength of an x-ray is in the same ballpark as the size of atoms (10 nm to 0.1 nm, with atomic radii being in the 0.1-0.01 nm range), and they only reflect 100% of incident radiation when it hits them at very shallow angles ("For gold at 1 keV, the critical reflection angle is 2.4 degrees") [see https://physics.stackexchange.com/questions/128247/how-would-an-x-ray-mirror-work https://physics.stackexchange.com/questions/128247/how-would... http://henke.lbl.gov/optical_constants/ http://henke.lbl.gov/optical_constants/ https://en.wikipedia.org/wiki/X-ray_optics https://en.wikipedia.org/wiki/X-ray_optics ]. When talking about lasers pumping out enough energy to be usable as weapons over distances of hundreds of kilometers - to bounce them off a satellite - you will need a mirror that can reflect that ray almost perfectly, or you'll just blast your own satellite out of the sky. And to do that, that mirror will only be able to reflect your ray at a shallow angle, which pretty much rules out bouncing an X-ray off it (unless your target is in orbit or, I suppose, if you have a fleet of such satellites, and coordinated enough to bounce the ray down 2° at a time). [Also see http://www.projectrho.com/public_html/rocket/spacegunconvent.php http://www.projectrho.com/public_html/rocket/spacegunconvent... , C-s for "X-ray" and "grazing", but that whole website is a goldmine]