h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Are fremen stillsuits feasable?
Can they really be made?

The important thing about still suits was that they extracted the moisture from the air you breathe out before expelling it into the atmosphere. I don't see why this shouldn't be possible, but wouldn't know the details.

They also processed urine and sweat (and maybe extracted the moisture from poop?) and turned it into water fit for drinking if I remember rightly. I guess that would require some kind of chemical process, and I remember something about the movement of the body providing some kind of pumping action within the suit.

Not only did they process the sweat, they did it while still allowing the cooling effect of evaporation. That always struck me as the most difficult part: the heat would have to be removed from the sweat as part of the processing and radiated away somehow into the already hot atmosphere -- perhaps some sort of evaporative cooling system could do it.

Heel-pump powered refrigeration coils?

The stillsuit extracted moisture from, as I recall, exhaled moisture from the nostrils, urine and sweat. It made mention of extracting the moisture from faeces, but probably shied away from the details for reasons of taste, but also possibly feasability.

We have existing technologies which could do all of the above except the drying poop one - to dewater sludge is a difficult job, partly because your colon has already done as much as is reasonably feasible. The only way to reliably dewater further is to incinerate - not something you want happening close to your skin.

One massive leap in technology that we've made since the stillsuit was postulated is Goretex. Stillsuits would be mostly made of supergoretex type materials. You could condense collected sweat under pressure generated from heel pumps, and generate cooling by the Joule Thomson effect. You could do everything a stillsuit does with just some goretex and pumps.

being an astronaut isn't all fun and games:
http://www.space.com/missionlaunches/090520-space-urine.html

you have to test drink wee as well!

Well don't we do that from our taps all the time anyway.

This always annoys me when I go on holiday when holiday reps tell you that the dirty dago water is desalted water from a desalination plant or whatever.
Well ours is, lets face it, recycled sewage...

Some UK water smells like swimming pools, it has so much chlorine in it - some smells like pondwater (maybe it is?) Desalinated seawater smells fishy even if it's not so salty

The human nose can detect minute particles, so what would this recycled sweat/urine be like to drink? At least it would be your 'own' vintage?

Traveller in Times looking at the nostril cap
"I guess you would smell nothing wearing those pipes in your nose.

(water escaping from your system)

Hmm, the technique could be to inhale through your mouth and exhale through your nose. More or less the wrong way around "

It's specifically described in the book as something the Fremen have had to learn to do, which Paul does instinctively as soon as he puts on the suit.

the suit would have to have reseviours full of water to start with, if they just recycled water you would loose too much before you had a propper drink,

the face piece would have to be very close fitting, similar to a breathing mask, to be as efficient as possible, this would do away with the wrong way breathing tecnique

if the outter layer of the suit were fitted with photo voltaic cells it might generate enough power to run a small refrieration unit to cool the ocupant and aid the condensation of water vapour back into liquid

one problem that troops in respirators found in the first gulf war was, you could be loosing water faster than you could replace it using the respirators drinking tube.

so a working stillsuit might not be a viable dessert working suit but a usefull survival tool

It's implied in the books that the Fremen in stillsuits can outfight Sardaukar. This is either indicative of the badassery of Fremen, the help that a stillsuit gives, or both. If a stillsuit actively cooled the wearer, it could be a big help to desert infantry.

The problem that I had with the Fremen suits was that I couldn't understand the thermal cycle. Sweat evaporates at body temperature and then only if the air in your suit isn't saturated. Body heat can evaporate the water in urine and faeces at the same temperature. To condense it would require an environmental temperature lower than that.

Dune couldn't have been a hot desert planet, it must have been a cold desert planet. At the very least the Fremen couldn't move about in the daytime and expect the suits to work. It's been too long since I've read it so I can't remember what the description was.