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Are there big differences in the amount of radiation if you would put the crew compartment (on the journey to Mars) inside the LOX/LH2 fuel tank? I know that there are similarities with other question, but this is only meant with its own rocket fuel.

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  • $\begingroup$ I don't know what kind of fuel you're thinking of, but I know I wouldn't want to ride in the fuel tank. $\endgroup$ – called2voyage Oct 12 '15 at 17:55
  • $\begingroup$ LOX/LH2.. I only wonder, if this Could be possible... $\endgroup$ – mars72 Oct 12 '15 at 18:01
  • $\begingroup$ So your habitat would have to be designed to prevent implosion instead of rupture. $\endgroup$ – called2voyage Oct 12 '15 at 18:16
  • $\begingroup$ But would LOX or LH2 prevent it from radiation?....nearly as good as water? $\endgroup$ – mars72 Oct 12 '15 at 18:26
  • $\begingroup$ @called2voyage if your in space and there is an explosion in your fuel tank does it really matter where you are in relationship to the tank? $\endgroup$ – James Jenkins Oct 13 '15 at 14:42
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Yes, low-Z shield would work (generally, water or polyethylene). However, LH2 is famously prone to seeping through seemingly solid walls, and making habitable space fit inside the fuel tank would put you at a disadvantage:

  • Crew habitat has to be at room temperature (293K).
  • LH2 has to be kept at the temperature of 20K.
  • You would have to increase insulation between the habitat and the tank to reduce thermal losses (and correspondingly, hydrogen boil-off which is mass wasted, pure and simple). Instead of a cylinder with hemispherical ends, you'd have to produce a less efficient and more expensive vessel.
  • Even then, the crew would be freezing cold, and thermal design would be unnecessarily bulky and risky.
  • If you spend the last drops of fuel on Trans-Earth injection you'll have no protection from cosmic rays during the return voyage.
  • Another important part of that disadvantage is LH2's low density: 70.85 $kg/m^3$ instead of water's 1000 or ice's 917.
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    $\begingroup$ LH2 is not used in deep space, only in first stages because of all mentioned disadvantages. So, instead of LH2 there will be hydrazine which is better for this purpose $\endgroup$ – MadBender Oct 13 '15 at 9:24
  • $\begingroup$ @MadBender - the OP explicitly asked about LOX/LH2. Hydrazine has lower Isp, and there may come a day of zero-boiloff cryo storage. $\endgroup$ – Deer Hunter Oct 13 '15 at 9:44

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