Joe Strout wrote in message ...

Yes, I know, I'm not saying that artificial lighting is better than
natural lighting when natural lighting is available. My point is that,
when natural lighting is not available or practical for whatever reason,
you don't give up on the whole idea and conclude that crops can only be
grown on Mars or some such. Instead, you put in artificial lights, and
this is a perfectly reasonable thing to do.

Basically I'm trying to debunk claims I hear bandied about, from Zubrin
and others, that growing crops under artificial light is thoroughly
impractical due to energy requirements. I believe that's a
politically-motivated load of crap, and I'd like to demonstrate that.

-Joe

That depends on what you mean by thoroughly impractical. From NASA's
closed cycle experiments, we've determined that it takes about 5 acres
of crops to fully support a single human being (for both staple food
and CO2 scrubbing). However, if you're willing to scrub your CO2
elsewhere and just look to plants for food, it still takes about 1.5
acres of well chosen plants to support that human. That means if
you've got a colony of 20 people, you already require 30 acres of
producing crops to fully support them. If you have to provide that
light artifically, you really are talking about a damn lot of energy.

Of course, in all likelihood in the beginning of space colonization
only 10% of food would actually be fresh produce grown in situ. This
is more than enough for most people to feel healthy, and for a colony
of 20 people would only require a modest 3 acres--more reasonable,
really.

The fault in Zubrin's logic lies not in the analysis of how much light
is required to fully support a human, but in the assumption that fully
supporting a human with in situ crops would be reasonable at an early
stage of exploration/conolization. Clearly it would not be.

No matter that day/night cycles on Mars are similar to earth's--the
first group of 10 colonists/explorers are not going to be able to
erect 15 acres of sun lit habitable volume/soil for their life
support. The primary driver will not be sunlight anyway but habitable
volume. Zubrin's own analysis of Martian conditions concluded that
solar power was not sufficient for a two year stay--some sort of
nuclear power would be required for life support. If you already have
to have a 500KW nuclear reactor, it makes little difference in weight
or volume if you quadruple the power to 2 MW and allow most of that
for growing crops.

Zubrin conveniently forgets the scaleability of nuclear power when he
argues for 'natural' crop growing on Mars, not considering that it
would be an extreme burden to erect a greenhouse with even one acre of
soil, especially one with a transparent top. Far more likely for early
colonists are volume saving stacks of hydroponic crops, with solar
collectors and light diffusers providing the majority of light and
some help from articial light for light-intensive crops.

Tom Merkle