Maintaining very small ecosystems

>
> Why bother with these partial pressure experiments? If we can get the cost of
> space transportation down so we can lift half a bar into orbit, why not wait
> a little while longer so we can lift the whole bar?

As far as I know the problem is more the strength required of
the pressure chamber enclosure, which is proportional to the pressure,
and
the difficulties with entry and exit for EVA's (space suited
excursions); a space suit works much better (esp. the gloves) with 1/2
or 1/4 atmospheric pressure, than with a full atmosphere. If the wearer
has to change atmospheric pressure all the time there's a lot wasted
time there in adjusting. The Space Shuttle and ISS have to deal with
this a lot now; ISS is at a full atmosphere, but the Space Shuttle is at
lower pressure when doing EVA's.

(I notice Mike Combs has now responded similarly to the above)

The other reason for going this way is so we don't have to bring it all
up from Earth. At least in near Earth space, oxygen is likely to be
plentiful (plenty on the Moon) but nitrogen much rarer; adjusting the
atmospheric balance makes a lot of sense as long as it doesn't harm
living things or overly increase fire hazards.

Arthur (apsmith@...