Henry Spencer wrote:

The simplest way to address the food loop is not to try,
given that freeze-dried food weighs less than half a ton
per man-year. Generally, much the simplest and most
reliable way to tackle a lot of the smaller recycling/
repair issues is brute force: more mass, and more fuel
to push it, is cheaper than major engineering R&D.

Of course, trying to sell that approach to R&D-oriented
organizations is a bit of a challenge. "Anything which
they do not wish to do is always lacking in technology.
Whether single stage to orbit or Mars missions,
the technology is never quite ready..." (Jim French)


I don't know enough about long-term nutrition and related
matters to have an opinion, but note that the manned-Mars
presentation at the recent Mars roadmap meeting contains
the following assertions at slide 21:

http://www.hq.nasa.gov/office/apio/p...an_studies.ppt

Closing the life-support air and water loops with low
expendables is a key leveraging technology for long
duration human exploration missions

Current food preservation technology is not capable of
providing nutritionally viable food for the longer
mission durations under study. Food production
technologies under the environmental conditions of these
missions is not developed to the point of being the
primary source of food.

Power requirements for both closed loop life support and
food production can be significant, indicating that
advanced life support and advanced power systems are
closely coupled.


[Boxed summary]

Closing the air and water loops is essential to reduce the
total mass of long duration missions to a reasonable level.

Improvements in food storage technology or production
technology are also needed to reduce overall mass and ensure
crew health.