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My first thought was that they should paint them with Vantablack, but then I wondered if that might be too dark? Do they need to aim for a specific reflectivit

My first thought was that they should paint them with Vantablack, but then I wondered if that might be too dark? Do they need to aim for a specific reflectivity or just aim for the lowest possible value?

wongarsu 7y ago
I think the lowest possible reflectivity is desirable. Space isn't perfectly black but very close to it. Any reflectivity means you sometimes reflect something very bright like the sun and sometimes nothing, so you have the wrong brightness no matter what you do. Black dots are at least fairly unambiguous.
MojoDwarf 7y ago
I was thinking about this also but wonder if it would collect too much heat while in direct sun light.
SEJeff 7y ago
That is often considered, but the light is absorbed and turns into heat. Where does that heat go? It would fry the electronics with no way to get rid of it.
- kevingadd 7y ago
  You could use some mechanisms to convert and dissipate the heat, though that doesn't come for free. Though the atmospheric pressure at that altitude is pretty low, you might be able to rig up some sort of peltier cooler setup to dissipate heat. Alternately if you can convert enough of the heat to electricity some other way, you could convert the heat back to light using LEDs or something and only turn on the ones facing away from earth, perhaps? Plenty of other orbital devices have to deal with heat so I'm sure this is something that has existing solutions.
  - rtkwe 7y ago
    Peltier coolers won't do anything but draw power and create more heat you have to dissipate, they're not magic you have to remove the heat from the hot side too which means you need radiators for them too plus more than you'd need originally because peltier coolers are quite inefficient. Same thing with the LED idea converting that heat into electricity requires some heat differential which requires... a radiator.
  - DuskStar 7y ago
    > Alternately if you can convert enough of the heat to electricity some other way Thermodynamics says "lolnope", I'm afraid. You need a temperature differential to convert heat to power.
the8472 7y ago
reflectivity/aborbtion is more than a percentage value. it's also a hemispherical distribution. if you glued retroreflectors to the surface most of the light would go back in the direction of the sun and thus never hit the surface. Those are probably too costly or bulk for satellites. If specular reflections are the problem they might just apply a more diffuse coating.

wongarsu 7y ago

I think the lowest possible reflectivity is desirable. Space isn't perfectly black but very close to it. Any reflectivity means you sometimes reflect something very bright like the sun and sometimes nothing, so you have the wrong brightness no matter what you do. Black dots are at least fairly unambiguous.

MojoDwarf 7y ago

I was thinking about this also but wonder if it would collect too much heat while in direct sun light.

SEJeff 7y ago

That is often considered, but the light is absorbed and turns into heat. Where does that heat go? It would fry the electronics with no way to get rid of it.

kevingadd 7y ago
You could use some mechanisms to convert and dissipate the heat, though that doesn't come for free. Though the atmospheric pressure at that altitude is pretty low, you might be able to rig up some sort of peltier cooler setup to dissipate heat. Alternately if you can convert enough of the heat to electricity some other way, you could convert the heat back to light using LEDs or something and only turn on the ones facing away from earth, perhaps? Plenty of other orbital devices have to deal with heat so I'm sure this is something that has existing solutions.
- rtkwe 7y ago
  Peltier coolers won't do anything but draw power and create more heat you have to dissipate, they're not magic you have to remove the heat from the hot side too which means you need radiators for them too plus more than you'd need originally because peltier coolers are quite inefficient. Same thing with the LED idea converting that heat into electricity requires some heat differential which requires... a radiator.
- DuskStar 7y ago
  > Alternately if you can convert enough of the heat to electricity some other way Thermodynamics says "lolnope", I'm afraid. You need a temperature differential to convert heat to power.

the8472 7y ago

reflectivity/aborbtion is more than a percentage value. it's also a hemispherical distribution. if you glued retroreflectors to the surface most of the light would go back in the direction of the sun and thus never hit the surface. Those are probably too costly or bulk for satellites. If specular reflections are the problem they might just apply a more diffuse coating.