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Will we be able to take the amount of water that will be needed for this 18 month trip, or will they have to recycle the water that they take with them? I imagine that this will be quite a challenge because water is very heavy?

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It's likely that a Mars mission will take a total of 32 months, not 18; the launch window for a fuel-efficient return journey requires a wait of over a year after arrival.

Humans need 2-4 liters of water per day. Assume a crew of 5; that works out to about 10-20 tons of water if you don't recycle it. That's a significant chunk of the overall mass requirement of the mission (NASA thinks the crew habitat and command module for a Mars mission will mass about 50 tons), so it's obviously attractive to consider a small water supply and a good recycling system.

However, one of the major concerns for a manned Mars mission is radiation exposure over the journey, and water makes a decent radiation shield. If you have to carry 20 tons of shielding anyway, you could do worse than carrying it in the form of water.

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  • $\begingroup$ One year ??? I always thought that they would only be on Mars for a few days and then return here.So they will have to take a tremendous amount of food and water and probably even medicine. What about air, can they take a three year supply of that ? How will their body react to the lower gravity and also the radiation on Mars ? What is the longest period of time that humans have spent in space before this and did they suffer any ill effects from it ? $\endgroup$ – Peter U Dec 13 '14 at 22:27
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    $\begingroup$ @PeterU That's a whole bunch of questions, most of which are probably on Space Exploration. $\endgroup$ – HDE 226868 Dec 14 '14 at 16:53
  • $\begingroup$ Several humans have spent hundreds of days in space in a single stretch (en.wikipedia.org/wiki/…) with minor ill effects -- bone loss and muscular atrophy. Radiation exposure is definitely the biggest concern. $\endgroup$ – Russell Borogove Dec 14 '14 at 17:28
  • $\begingroup$ Hmmm. NASA's asteroid redirect mission could perhaps be reconfigured. Redirect a comet instead to impact Mars, or put it in Mars orbit (+: Then the intrepid explorers to Mars would only need to meet dV in Mars' orbit instead - with the necessary purification/filtration facility. Easier said than done, I know. But it's a thought. $\endgroup$ – Everyone Dec 15 '14 at 6:13
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    $\begingroup$ Another issue I think is how to deal with fatalities and manage corpses. What about ethics envolved? And relationships? And stress? The negative impact on humans are huge but still are worth to try. Nevertheless, it is a one way trip. And to protect from radiation water barrier and a litte artificial magnetosphere would be a good start... $\endgroup$ – Claudia Dec 15 '14 at 19:05

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