Long-time lurker, first-time poster here. Hello everyone!
volrath77 wrote:Krulle wrote:(And who wants a wager that they won't have enough water for Alex to rehydrate his rations?)
Well, Jardin can certainly pee on his rations. Current MREs can be rehydrated using any water including urine, right? I'd like to think that future rations would likely retain that bit as a contingency. If his own is not enough, well...
No, you can't.
"Rehydrate" is what you do to dried (
freeze-dried aka
lyophilised,
spray-dried being the less-popular method) foodstuff.
Your instant coffee is a good example of a freeze-dried foodstuff that needs rehydrating. Well... I don't think I'd try doing it with urine under any circumstances! And yes, in all the military ration packs I've tried or seen tried, there was usually standard, off-the shelf freeze-dried coffee included.
However, since freeze-drying is a costly process and you'd still need water to rehydrate the food, it is used mainly for drinkable components of a military ration pack (aforementioned instant coffee, and instant beverages). Entirely freeze-dried food rations do exist (like the French RIL ration), but they are rare.
Some field rations contain water purification tablets, either iodine (that's the older technology) or some other stuff. It is meant to disinfect water (killing bacteria, funghi and other nasty stuff) and make impurities fall to the bottom, making top layer safe to drink, if usually foul-tasting and not especially good for your health.
I guess it wouldn't improve urine's potability much. Also, I don't think it would work well in microgravity.
Again, not all the military rations do contain these - some armies assume that all the potable water will be brought by the logistic services, as it is a more foolproof way of making sure your troops won't get sick due to bad local water (keep in mind: diarrhea caused way more casualties in the history of warfare on Earth than any enemy action ever did!)
A filtering apparatus (some kind of membrane, allowing only water molecules through, and keeping impurities on the other side) could be a solution, and in a high-tech setting, a workable one. If Bellarmine had such filters (personal-use ones can be as small as a bulky felt-tip pen) in her emergency supplies / crash packs, there is a chance Beryl scavenged such equipment along with the rations. But I digress.
What you could- theoretically - with your urine and some modern ration packs, is reheat them: a number of modern field rations rely on flameless ration heaters to heat the main course. Put a hermetically sealed food package in a plastic bag with the heater, add a little water, and a chemical reaction will start, producing enough heat to get you a warm meal in a couple of minutes. Quality of the water is of little consequence, remember however you'll be tearing that food packet open, once it is heated.
A side effect of the reaction, however, is release of gaseous hydrogen (and a few other gases). Not important in the field, it is however highly volatile - and therefore unadvisable in enclosed spaces. The FRH bags are actually maked with waringns to keep troops from heating up their food packets indoors, and especially inside their vehicles. For exactly that reason, I believe it would be highly inadvisable to try it on board of the shuttle.
Also, it wouldn't be necessary: the food can be eaten cold, it is simply less appealing, although ready and fit for consumption as-is in most cases.
Since Bellarmine didn't seemed to be designed with atmospheric flight in mind, I assume it didn't carried conventional military field rations as emergency food, more likely something like RL lifeboat & life raft food supplies (which tend to include canned potable water, in addition to water purification methods like solar stills... but those would be totally useless in space).