From: niklas.holsti@tidorum.invalid   
      
   On 2020-06-29 0:03, Niklas Holsti wrote:   
   > On 2020-06-28 22:12, JF Mezei wrote:   
   >> Did some reading (danger will robinson, danger !)   
   >   
   >   
   >     [snip]   
   >   
   >> I also know from the specs that O2 will liquify at -183°C at a presusre   
   >> of 1 atm (14.7 psi).   
   >>   
   >>   
   >> So if you have a good refrigirator, you could keep your liqiud oxygen in   
   >> a plastic bottle without any pressure at -183.   
   >   
   >   
   >     [snip]   
   >   
   >> So in the context of going to Mars where you need to keep that O2 for 6   
   >> months without venting, what sort of strategies are possible?   
   >   
   >   
   > Who says "no venting"? Of course you can vent some of it, if it is   
   > included in your propellant calculations. The amount of venting is about   
   > proportional to the amount of heat you let into the tanks -- no heat, no   
   > venting; a little heat, a little venting.   
   >   
   >   
   >> On the trip to Mars, won't the ship be constantly exposed to the   
   >> sun?   
   >   
   > In the SpaceX videos of Mars trips (quite old already...) the Starship   
   > points its rear end (rocket end) at the Sun, and moreover deploys from   
   > that rear end a large solar-electric array that seems to shadow most of   
   > the ship, even if there is some deviation from the rear-end-to-Sun   
   > attitude. Most of the surface of the propellant tanks therefore sees   
   > only deep space, at a few degrees K.   
      
      
   That was not quite accurate -- the propellant tanks see the thermal   
   radiation from the shadow side of the solar array. That side might be   
   quite warm, so its thermal radiation may be quite large. However, that   
   radiation mostly strikes the tank walls at an almost glancing angle, so   
   most of it is perhaps reflected and not absorbed. Then again, the   
   thermal protection tiles are very black visually, so perhaps they absorb   
   a large part of infrared light too, even at glancing angles. An   
   interesting thermal-balance calculation for SpaceX.   
      
   --   
   Niklas Holsti   
   niklas holsti tidorum fi   
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