4 ms·

Nukes produce lots of gamma and x-rays. On Earth, those are absorbed to produce the fireball. In LEO, some are absorbed by upper atmosphere to make EMP. In spac

Nukes produce lots of gamma and x-rays. On Earth, those are absorbed to produce the fireball. In LEO, some are absorbed by upper atmosphere to make EMP. In space, they are radiation. Except for military satellites like GPS, most satellites aren't hardened to deal with that much radiation. My guess is that the range would be thousands of miles.

oskarkk 1y ago
I wondered how much energy could pass through some area 1000 miles away from the explosion, so I made some rough calculations. Assumption: all energy of the nuclear explosion is radiation uniform in every direction. The energy E would be spreading in a sphere with area 4*pi*R^2. Area A being a part of that sphere would capture E*A/(4*pi*R^2) of energy. So with: energy E = 209 PJ (Tsar bomba for an extreme example) area A = 1 m^2 radius of the sphere R = 1000 miles (1609 km) That would give: 2.09 * 10^17 J * 1 m^2 / (4 * pi * (1.609 * 10^6 m) ^ 2) = 6.4 kJ So at the distance of 1000 miles an 1 m^2 object would be exposed to 6.4 kJ of radiation. I don't know how destructive would that be. That energy would be equivalent to 6 seconds of sun irradiating a 1 m^2 area above the Earth's atmosphere, but of course sun's radiation is less dangerous (very little gamma/x-ray), and all of that radiation would be almost instant. From what I'm reading about high-altitude nuclear testing, it can cause artificial radiation belts around the Earth (composed of high-energy electrons). I think that may be more dangerous to satellites at distances like 1000 miles (or at any distance) than the immediate gamma/x-ray radiation.
- ianburrell 1y ago
  Radiation is measured in gray, which is 1 J absorbed by 1 kg. I can't find the conversion between flux to absorbed dose. 5 gray is fatal. If even a fraction of that energy is absorbed, it would be fatal. I found that satellites get 100-1000 rad per year. Getting that much in a moment would cause problems.
  - oskarkk 1y ago
    So, given that human body area viewed from the front is around 0.5 m^2, then a 70 kg human in space 1000 miles from the explosion would get 6.4 kJ * 0.5 / 70 kg = 45 gray. That would mean that even being a couple thousand miles away could be fatal. But that's assuming 100% of Tsar Bomba energy would be ionizing radiation, I don't know what % would that be in reality.
  - ben_w 1y ago
    > Radiation is measured in gray, which is 1 J absorbed by 1 kg. I can't find the conversion between flux to absorbed dose. 5 gray is fatal. If even a fraction of that energy is absorbed, it would be fatal. It's measured in a lot of different ways depending on the need, and the unit "sievert" is Gy times a conversion factor that depends on the kind of radiation (for equivalent dose) and which body parts (for effective dose): https://en.wikipedia.org/wiki/Sievert#Radiation_type_weighting_factor_WR https://en.wikipedia.org/wiki/Sievert#Radiation_type_weighti... But also, beta radiation (electrons) will be stopped by a thin sheet of tinfoil, while alpha radiation (helium-4 nuclei) by paper or the outer layer of dead skin on your body and therefore only matters if you eat a source of it, and a significant fraction of any gamma radiation you're exposed to will pass right through you without getting absorbed.

oskarkk 1y ago

I wondered how much energy could pass through some area 1000 miles away from the explosion, so I made some rough calculations. Assumption: all energy of the nuclear explosion is radiation uniform in every direction. The energy E would be spreading in a sphere with area 4*pi*R^2. Area A being a part of that sphere would capture E*A/(4*pi*R^2) of energy. So with: energy E = 209 PJ (Tsar bomba for an extreme example) area A = 1 m^2 radius of the sphere R = 1000 miles (1609 km) That would give: 2.09 * 10^17 J * 1 m^2 / (4 * pi * (1.609 * 10^6 m) ^ 2) = 6.4 kJ So at the distance of 1000 miles an 1 m^2 object would be exposed to 6.4 kJ of radiation. I don't know how destructive would that be. That energy would be equivalent to 6 seconds of sun irradiating a 1 m^2 area above the Earth's atmosphere, but of course sun's radiation is less dangerous (very little gamma/x-ray), and all of that radiation would be almost instant. From what I'm reading about high-altitude nuclear testing, it can cause artificial radiation belts around the Earth (composed of high-energy electrons). I think that may be more dangerous to satellites at distances like 1000 miles (or at any distance) than the immediate gamma/x-ray radiation.

ianburrell 1y ago
Radiation is measured in gray, which is 1 J absorbed by 1 kg. I can't find the conversion between flux to absorbed dose. 5 gray is fatal. If even a fraction of that energy is absorbed, it would be fatal. I found that satellites get 100-1000 rad per year. Getting that much in a moment would cause problems.
- oskarkk 1y ago
  So, given that human body area viewed from the front is around 0.5 m^2, then a 70 kg human in space 1000 miles from the explosion would get 6.4 kJ * 0.5 / 70 kg = 45 gray. That would mean that even being a couple thousand miles away could be fatal. But that's assuming 100% of Tsar Bomba energy would be ionizing radiation, I don't know what % would that be in reality.
- ben_w 1y ago
  > Radiation is measured in gray, which is 1 J absorbed by 1 kg. I can't find the conversion between flux to absorbed dose. 5 gray is fatal. If even a fraction of that energy is absorbed, it would be fatal. It's measured in a lot of different ways depending on the need, and the unit "sievert" is Gy times a conversion factor that depends on the kind of radiation (for equivalent dose) and which body parts (for effective dose): https://en.wikipedia.org/wiki/Sievert#Radiation_type_weighting_factor_WR https://en.wikipedia.org/wiki/Sievert#Radiation_type_weighti... But also, beta radiation (electrons) will be stopped by a thin sheet of tinfoil, while alpha radiation (helium-4 nuclei) by paper or the outer layer of dead skin on your body and therefore only matters if you eat a source of it, and a significant fraction of any gamma radiation you're exposed to will pass right through you without getting absorbed.