Comment by curtis | Hacker News Reader

Comment by curtis | Hacker News Reader

Geoffrey Landis made a proposal for a polar landing site for the first manned mission to Mars back in the 90s. One of the clear advantages is that you don't need to bring hydrogen with you for the return trip, but instead you can just make it from the ice. Landis proposed the mission for northern hemisphere summer so that solar power would be constantly (or nearly constantly) available. One thing Landis didn't mention but is worth considering is that ice could be used for radiation shielding, either by tunneling into it or by melting it and reforming it into a surface structure.

However, landing on the polar ice cap has some downsides, not least of which is it would be the most boring place on the whole planet to land.

Korolev crater might make a good alternative site since you could conceivably land near a substantial amount of easily accessible water ice while still retaining easy access to terrain that is not ice-covered.

[1] http://www.geoffreylandis.com/pole.html

Back when Landis made his proposal, he proposed the poles because that was the only place we knew to contain water.

Since then, we've found a lot more. For example, this recent paper about the million cubic km of ice in Valles Marineris[1] (which are near the equator), or this presentation about kilometer-thick glaciers on Mars at mid-latitudes[2] from the recent Mars society convention.

We don't have to go to really cold and annoying for return flights locations near the poles to find water -- there's plenty of it on Mars in better places.

[1] http://www.dmzone.org/papers/Gourroncetal2014_VM.pdf [2] https://www.youtube.com/watch?v=m2ERsEXAq_s

" 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?

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.

You also need to cool down and liquify the hydrogen. That doesn't seem simple.

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

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.

Methane can also be used to make food

https://www.newscientist.com/article/2112298-food-made-from-...

Thus no need to grow potatoes :)

> 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.

>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.

"it would be the most boring place on the whole planet to land."

Would it? Wouldn't the ice preserve certain things (e.g. any microorganisms which might have lived there) better than if they were left out in the open?

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