COMMENT ⊗   VALID 00003 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002		One often proposed source of food in space is algae.  SP-374
C00009 00003		It may not be worthwhile to discuss a design for a lunar
C00013 ENDMK
C⊗;
	One often proposed source of food in space is algae.  SP-374
is rather negative about it, but LLW has experience that explicitly
contradicts the claim (if I remember it correctly) that eating
algae makes you sick after a short time.

	New Scientist (24 September 1981) has an article by
Orio Ciferri, Professor of microbiology at the Universita di Pavia
Italy, discussing the algae Spirulina.  His main points are:

1. It was used by the Aztecs who skimmed it from Lake Texcoco.  It
is presently used the region of Kanem in Chad.

2. It likes very alkaline lakes (pH = 11), which it therefore has
to itself.

3. Up to 70 percent of the dry weight is protein.  The protein is
of high quality, being somewhat short of lysine, however.
Analyses were done at the Insitut Francais du Petrol.  It is
a prokaryote and has no cellulose and therefore is completely
digestible.  It contains only 6 percent nucleic acids, the latter
cause some worry about gout.

4. There have been no controlled studies of Spirulina as a human
nutrient although "the literature contains a few reports of human
feeding trials".  In a variety of whole life trials in animals it
produced normal growth rates and no abnormalities at autopsy.

5. Its requirements are water, CO2, sunlight and minerals.  The
strongly alkaline medium it requires keeps away competitors.

6. Yields up to 20 grams per day dry-weight per square meter have been
reported.  The table in the article also refers to 50 tonnes/ha/year.

	All this suggests that Spirulina be considered a candidate
for Shackleton food.  If the colony succeeds in enlarging the growing
area sufficiently, it could be fed to chickens in addition to direct
use.  This reduces the yield of protein to improve the variety.

	We need to find literature on proposals to grow plants on
the moon in order to see what pressurization schemes have been
proposed.

	General remark: In so far as SP374 assume a continuation
of present space exploration practices, they tend to assume diets
appropriate to test pilots and military aviators, i.e. acceptance
of danger is compensated by luxury.  The diets traditionally accepted
by explorers who have to eat what the natives eat and mountain climbers
who have to eat what they can carry provide better analogies to what
we should plan.

PROBLEMS

1. If we want a kilogram per day per man, this suggests 50 square meters
per man growing area assuming that perpetual sunlight for 14 days
makes up for the 14 days darkness.  If the water is one centimeter
deep, this amounts to 500 kilograms of water per person, a non-trivial
part of a payload.

2. There is a problem with temperature control.  If the water is allowed
to heat up during the lunar day, it will probably boil unless we can
arrange to admit only the radiation optimal for photsynthesis or unless
we reradiate heat.  The latter can be done by circulating the water
through a radiator that sees black sky,e.g. the radiator sees only Southern and nNorthern
sky.  In this case we need more water, and we have
to worry about how to circulate the water and still keep the Spirulina
growing.  Perhaps different water circulates, and there is a heat exchanger.

3. Spirulina is grown locally and sold in health food stores.

4. With all these problems, maybe there is a better way of using
solar energy to generate food than photosynthesis.  We could grow
protein with Spirulina, but get pure carbohydrate from exhaled
CO2 by a purely chemical process.  Alternatively,
we could use electrochemical energy to produce compounds usable
by non-photosynthetic plants like mushrooms.

5. It isn't obvious whether one centimeter is deep enough or
whether less depth would do.  It also isn't clear what is the
best way of mixing the exhaled CO2 with the water.  Presumably it
would be optimal to allow a considerably higher concentration
of CO2 in the air than the .03 percent in the earth's atmosphere.
It is my impression that humans tolerate up to one percent without
difficulty and this would ease the mixing problem and make the
plants grow faster.
	It may not be worthwhile to discuss a design for a lunar
agriculture system before reading the literature on the subject,
but it may be best to write these ideas in their pure form
before they get lost.

	For the Shackleton Project, weight transported from Earth
is a key factor. The second key factor is labor on the moon.  At
20 grams/day Spirulina production and one cm depth of water we
need 500kg of water per person for the Spirulina to grow in.

	Therefore, we must try to get by with one mm depth of water.
We propose the following design for consideration.

	1. Spirulina is grown in flat units each having a base and 
cover.  The bases and covers are stackable separately for transportation.
They are fastened together by bolts to hold the pressure.
They might be one meter by two and should weigh (say) one kilogram.

	2. The water in each unit is as shallow as possible (say 1 mm).
The CO2 is supplied by an attached unit that has been charged with
exhaled  CO2 that has somehow been concentrated chemically.

	3. The units are self contained and are placed carefully on
the surface of the moon.  They are harvested by being taken into the shelter
and disassembled.  Then they are reloaded with fresh CO2, water and
minerals,re-assembeled and set out again.

	4. Temperature control is a key problem.  We suppose the
units can tolerate freezing at night.  If not we suppose they are
taken into a shelter or conceivably, they could be covered with
blankets.

	During the day, anything getting the full heat of the sun
will reach a temperature above the boiling point of water.
However, a system can be used in which some area sees sun for
the photosynthesis, but an appropriate very close area sees black
sky to the north or south.  The areas are adjusted so that the
correct temperature is maintained.  It should be possible to
adjust the geometry of reflectors and absorbers so that the
right temperature is maintained as the sun moves through the
sky during the 14 day lday (lunar day).  Ideally this could
be done without having to adjust the reflectors.  If nature is
less favorable, an active though slow servomechanism may be
required.

	In space and on the moon, high and low temperatures are
available in close proximity depending on whether a black body
can see the sun or is looking at space.  This suggests running
heat engines or at least convection between these temperatures.