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" you can just make it from the ice" I always read this but do we really have the tech to this without needing big and heavy equipment and a lot of energy? Why

" you can just make it from the ice" I always read this but do we really have the tech to this without needing big and heavy equipment and a lot of energy? Why don't we "just" do this on the South Pole?

Sharlin 8y ago
Because there’s no pressing need for hydrogen and oxygen on the South Pole. On Mars we’d need both. A serious Mars mission would almost certainly include a small nuclear reactor for power.
- maxxxxx 8y ago
  You also need to cool down and liquify the hydrogen. That doesn't seem simple.
  - Sharlin 8y ago
    Not if you feed it to a Sabatier [1] reactor to produce methane, which is what most ISRU-based mission designs call for. A LH2 based return vehicle would indeed make things considerably trickier. [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction
  - arijun 8y ago
    Most plans that use water to make fuel on Mars don't use liquid hydrogen at all. The two most well known plans are the BFR/SSH and Zubrin's Mars Direct, both of which use liquid methane. You still have to cool it, but not nearly as much, and it doesn't come with the other problems of hydrogen like embrittlement.
    - trhway 8y ago
      Methane can also be used to make food https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/ https://www.newscientist.com/article/2112298-food-made-from-... Thus no need to grow potatoes :)
Tuna-Fish 8y ago
> I always read this but do we really have the tech to this without needing big and heavy equipment Sure, the chemistry is simple and well understood and the equipment needed isn't that heavy. > and (without) a lot of energy Nope. Splitting water is heavily endothermic. The SpaceX BFR Mars mission plan would require ~3MW continous for two years for the energy required for CO2 capture and chemistry to make enough CH4+O2 to return to earth. This is a massive amount of energy, basically requiring either a quite respectable fission reactor or ~10ish MW of solar panels, which take about a single BFS cargo hold by themselves. The reason these kinds of plans are floated regardless of the energy costs are simply that carrying that much power production down there is still much easier than taking enough fuel with you to return home.
- ddingus 8y ago
  >that carrying that much power production down there is still much easier than taking enough fuel with you to return home. Rationally, yes. This sentence makes sense. But, I find it amazing and difficult to visualize just how EXPENSIVE FUEL is.

Sharlin 8y ago

Because there’s no pressing need for hydrogen and oxygen on the South Pole. On Mars we’d need both. A serious Mars mission would almost certainly include a small nuclear reactor for power.

maxxxxx 8y ago
You also need to cool down and liquify the hydrogen. That doesn't seem simple.
- Sharlin 8y ago
  Not if you feed it to a Sabatier [1] reactor to produce methane, which is what most ISRU-based mission designs call for. A LH2 based return vehicle would indeed make things considerably trickier. [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction
- arijun 8y ago
  Most plans that use water to make fuel on Mars don't use liquid hydrogen at all. The two most well known plans are the BFR/SSH and Zubrin's Mars Direct, both of which use liquid methane. You still have to cool it, but not nearly as much, and it doesn't come with the other problems of hydrogen like embrittlement.
  - trhway 8y ago
    Methane can also be used to make food https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/ https://www.newscientist.com/article/2112298-food-made-from-... Thus no need to grow potatoes :)

Tuna-Fish 8y ago

> I always read this but do we really have the tech to this without needing big and heavy equipment Sure, the chemistry is simple and well understood and the equipment needed isn't that heavy. > and (without) a lot of energy Nope. Splitting water is heavily endothermic. The SpaceX BFR Mars mission plan would require ~3MW continous for two years for the energy required for CO2 capture and chemistry to make enough CH4+O2 to return to earth. This is a massive amount of energy, basically requiring either a quite respectable fission reactor or ~10ish MW of solar panels, which take about a single BFS cargo hold by themselves. The reason these kinds of plans are floated regardless of the energy costs are simply that carrying that much power production down there is still much easier than taking enough fuel with you to return home.

ddingus 8y ago
>that carrying that much power production down there is still much easier than taking enough fuel with you to return home. Rationally, yes. This sentence makes sense. But, I find it amazing and difficult to visualize just how EXPENSIVE FUEL is.