Food Mass numbers text

[kgstar@most.fw.hac.com (Kelly Starks x7066 MS 10-39)]

Heres some more text to look over.  Attack at will.  This is what I
consider the baseline drive system for my Explorer class design.

Kelly

Oh, if anyone wants.  I can send set of the graphics and HTML files for
this and the others.  Let me know.


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Food Mass Numbers


Normally people assume that food supplies in space will need to come from
onboard farms, or some other intricate recycling system. This may be an
unjustified assumption. The farms discussed in the "Space Settlements: A
design study" (the book I reference frequently, and STRONGLY recommend)
lists the farm mass per person at about 36 tons of which 22 tons is soil.
The farm includes everything from farm animals to fish, and all normal
grains and vegetables. The idea was to make it capable of providing all
normal food needed for a standard North American diet for a population of
10,000. Said diet according to their numbers weighed about 1.67 tons
per-person per year. They also assumed that with intensive care this farm
could produce twice the yield of the best farms on earth.

Now we found that rations for field troops or explorers weighed about 2.2
kilos per day (.8 tons per year) and dehydrated could be a lot less. But
over all; 36 tons per person is about 21 years of food mass at their 1.67
tons per year, or 45 food years at our .8 tons per year. I'm not even going
to bother with freeze dried numbers. We won't want to be out that long!
Even if you assume no soil. The mass is still 14 tons per person. Which
comes to 8.38 year of 1.67 tons per year food years, or 17.5 years at our
..8 tons per year. Then I realized that the farm design required doubling
the internal volume of the habitation centrifuge. Which would add another
20 to 230 tons per person! (the latter if you shielded the farm centrifuge
from ambient radiation.)

Any way I ran it, the mass for a transportable, self sustaining farm, wound
up greater than the stored food mass for the duration of our projected
missions. Given that the stored mass would decline as the mission goes on
(a good thing for the return flight), stored food would be simpler and more
reliable than trying to maintain a running farm during a mission, and the
farm would almost double the size of the full g gravitation sections needed
in the ship. I decided to dump the idea and assume ultra frozen and dried
foods stored in the zero g section of the ship. We could have a couple
gardens for fun and fresh Veggies, but I'd assume they were just a couple
plants in the corner of peoples apartments. You might do an analysis to see
if hydroponics for the veggies would weigh less than storing frozen
veggies. I.E. we store the meat, flour, rice, milk, ect.., but grow the
fruits and vegetables. But for my porpoises I assumed the mass numbers
wouldn't show an advantage.

Oh, while on the topic of Mass. The drive system people seem to be going
through hoops to build a huge, high efficiency (relativistic exhaust)
engine to keep the necessary reaction mass amounts down to grams per day. I
would suggest that if we aren't going to recycle our -- ah-- food by
products. The crew will be providing a few tons of usable mass per day.
Dehydrate, incinerate to plasma or ionize, and pump it into the
accelerator. With an electromagnetic accelerator (as apposed to a thermal
rocket) the type of mass used is unimportant, and for ship design purposes
using the same stored mass to feed the crew and drive system is very
elegant and efficient.


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Kelly Starks                       Internet: kgstar@most.fw.hac.com
Sr. Systems Engineer
Magnavox Electronic Systems Company
(Magnavox URL: http://www.fw.hac.com/external.html)

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