From: schillin@spock.usc.edu   
      
   "Carey Sublette"  writes:   
      
   >"John Schilling"  wrote in message   
   >news:d0fm47$iu8$1@spock.usc.edu...   
   >> "Allen Thomson"  writes:   
      
   >>>However, the viewgraph that started this seemed to say that   
   >>>the state of the art isn't here for preserving nutritionally   
   >>>adequate food for multi-year Mars missions.  So is there some   
   >>>ingredient of a multi-year nutritionally complete diet that   
   >>>can't be preserved by chilling or freezing or dehydration or   
   >>>whatever?  If so, what might it be?   
   >>   
   >> Don't know; I can't find the original references at my local   
   >> library or online, just abstracts and summaries.  What I can   
   >> find suggests it isn't anything as simple as a missing vitamin   
   >> or amino acid or whatnot.  But in the course of developing the   
   >> MRE, the Army did *something* to the mix that resulted in a   
   >> food that would last indefinitely if kept cold, but will lead   
   >> to unexplained weight loss and mental deterioration if used   
   >> exclusively for more than a few weeks.   
      
   >I think the "cherry box" on the viewgraph:   
   >" Improvements in food storage technology or production technology are also   
   >needed to reduce overall mass and ensure crew health."   
   >states the issue accurate, but the other sentence on the slide:   
   > "Current food preservation technology is not capable of providing   
   >nutritionally viable food for the longer mission durations under study"   
   >is a bit of a misstatement.   
      
   >Ensuring crew health requires a diet that is varied and palatable so that   
   >the crew eats properly, and the food itself is not a source of stress on the   
   >mission (psychological health).   
      
   >And the trick is to do it with low mass foods (i.e. dehydrated).   
      
   >Also, nutrition science is far beyond the RDA stage - finding the essential   
   >individual components in a diet required for health.   
      
   Right, and the failures of known long-term stored-food diets are not at   
   the RDA, individual-componet level either.   
      
      
   >I think it is the combined problem of satisfying all of these together, and   
   >quite clearly no one has ever developed a food system like this before.   
      
   >The whole viewgraph presentation is about design trade-offs, and the dietary   
   >aspect of a mission is going to involve trade-offs of its own. For a   
   >palatable, optimally healthy, indefinitely storable diet a solution is at   
   >hand right now - just prepare thousands of excellent meals and freeze them   
   >in ready-to-eat form. But this is quite heavy with all that water.   
      
   It's not that easy, alas.  Not all foods retain everything that used to   
   make them nutritious and palatable through a freeze/thaw cycle, at least   
   using known freezing and thawing processes, and I'm not aware of any   
   successful attempt at providing a healthy long-term diet using only those   
   foods known to freeze well.   
      
      
   >Maintaining the good qualities of those meals but getting rid of the water   
   >mass, not so easy.   
      
   Getting rid of most of the water would be a plus, but *all* of the known   
   preservation methods - freezing, canning, dehydrating, and the rest - have   
   limits.  The early arctic and antarctic expeditions were not seriously   
   mass-limited, at least for their base camps, and certainly did not lack   
   for refrigeration.  They could and did carry their choice of canned and   
   frozen food, all fully hydrated, and yet found that a full overwinter   
   stay was testing the limits of endurance on such a diet.   
      
   Again, I don't think this is likely to be a major problem.  We know more   
   about food preservation than we did in the early 20th century, and we   
   know from their experience what doesn't work and what the problems are.   
   But we also know more about transport logistics than we did in the early   
   20th century, and have used that to ensure that we never had to test our   
   presumed ability to have people live for years without any resupply.   
      
   That's something we are going to have to test before we sent people to   
   Mars with an assortment of canned, frozen, and dehydrated food.  Tweaking   
   the diet to increase the fraction of dehydrated food is a secondary goal.   
      
      
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