4 ms·

One thing that I have been wondering, if the atmosphere is so thin, then how does the RTG cool? I seem to have nerd-sniped myself. It needs a temperature diffe

One thing that I have been wondering, if the atmosphere is so thin, then how does the RTG cool? I seem to have nerd-sniped myself. It needs a temperature differential to generate electric current and it looks to have fins for convective cooling but the atmospheric pressure is a few % of that of sea level Earth.

gbrown 6y ago
I believe the fins are primarily radiators. Conduction, convection, radiation.
pengaru 6y ago
mars is freezing cold, it's like dust covered ice ball.
- iso1631 6y ago
  But the heat still needs to leak into the environment, and a thin atmosphere means little convection, so it's still just radiation - same problem as in a vacuum.
- nkrisc 6y ago
  Space is cold and yet getting rid of waste heat is a challenge for any spacecraft. The ISS has giant radiators to dissipate heat. It doesn't matter how cold Mars is if it's difficult to transfer the heat away, such as in a very thin atmosphere which has less capability to carry away heat than Earth's atmosphere. There needs to be some kind of medium for the heat to transfer away (aside from radiation), regardless of ambient temperature. It's why a vacuum-walled thermos can keep things warm even in a cold environment. That's what they were asking about. Heat can be conducted away by contact with another object, probably not what you want if you're using an RTG to power your spacecraft, you don't want your RTG to heat it too much. It can be convected away, which is more difficult in a thin atmosphere like Mars has. Or it can be radiated away by blackbody radiation, which some certainly is, but that is limited and isn't much.
  - trhway 6y ago
    > blackbody radiation, which some certainly is, but that is limited and isn't much. Boltzman equation has temperature in the 4th power, so it is quickly becomes a lot. https://en.wikipedia.org/wiki/Thermal_radiation https://en.wikipedia.org/wiki/Thermal_radiation "Using the formulas below shows a human, having roughly 2 square meter in surface area, and a temperature of about 307 K, continuously radiates approximately 1000 watts." At the temperature that you can keep your electronics at, say 60C, it would be 700W/m2. So, for example a GPU mining ethereum in space (where i think we're ultimately heading toward with the crypto) would need a heat radiator only 3-5 times the size of the GPU.
joshvm 6y ago
You can read a bit about this in quite some detail in this pre-print from the 80s: https://www.osti.gov/servlets/purl/1033420 https://www.osti.gov/servlets/purl/1033420 ".. radiation, diurnal and seasonal temperature". "Convective cooling by the Martian atmopshere, even on a cold windy day makes only a relatively minor contribution to heat rejection"

gbrown 6y ago

I believe the fins are primarily radiators. Conduction, convection, radiation.

pengaru 6y ago

mars is freezing cold, it's like dust covered ice ball.

iso1631 6y ago
But the heat still needs to leak into the environment, and a thin atmosphere means little convection, so it's still just radiation - same problem as in a vacuum.
nkrisc 6y ago
Space is cold and yet getting rid of waste heat is a challenge for any spacecraft. The ISS has giant radiators to dissipate heat. It doesn't matter how cold Mars is if it's difficult to transfer the heat away, such as in a very thin atmosphere which has less capability to carry away heat than Earth's atmosphere. There needs to be some kind of medium for the heat to transfer away (aside from radiation), regardless of ambient temperature. It's why a vacuum-walled thermos can keep things warm even in a cold environment. That's what they were asking about. Heat can be conducted away by contact with another object, probably not what you want if you're using an RTG to power your spacecraft, you don't want your RTG to heat it too much. It can be convected away, which is more difficult in a thin atmosphere like Mars has. Or it can be radiated away by blackbody radiation, which some certainly is, but that is limited and isn't much.
- trhway 6y ago
  > blackbody radiation, which some certainly is, but that is limited and isn't much. Boltzman equation has temperature in the 4th power, so it is quickly becomes a lot. https://en.wikipedia.org/wiki/Thermal_radiation https://en.wikipedia.org/wiki/Thermal_radiation "Using the formulas below shows a human, having roughly 2 square meter in surface area, and a temperature of about 307 K, continuously radiates approximately 1000 watts." At the temperature that you can keep your electronics at, say 60C, it would be 700W/m2. So, for example a GPU mining ethereum in space (where i think we're ultimately heading toward with the crypto) would need a heat radiator only 3-5 times the size of the GPU.

joshvm 6y ago

You can read a bit about this in quite some detail in this pre-print from the 80s: https://www.osti.gov/servlets/purl/1033420 https://www.osti.gov/servlets/purl/1033420 ".. radiation, diurnal and seasonal temperature". "Convective cooling by the Martian atmopshere, even on a cold windy day makes only a relatively minor contribution to heat rejection"