Maintaining very small ecosystems

You state that,

" Mining asteroids and transporting their materials back to HEO is likely
to be more expensive than simply shipping them up from the moon. The
operations that are involved in mining and transporting NEA materials are
more complex,..."

I don't think that Mark Prado at www.permanent.com would agree with you.
Carbonaceous chondrite NEAs very well might have reasonable amounts of
water that can be cooked out using very simple solar ovens. A mining
facility a few kilometers away from an NEA would not have to contend with
14 days of darkness, as would be the case on the Moon anywhere other than
the Poles. And a Lunar Polar base would have to have solar power towers
that can track the sun --- more complex than the energy collection system
required a few kilometers away from an NEA where permanent sunlight reins.
And all transportation between L4/L5 and the NEA could be achieved using
safe low-thrust engines, whereas transportation between the Moon and L4/L5
requires either chemical rocketry or complex mass driver/catcher systems.

You also write,

"[NEA resource utilization schemes are] less susceptible to teleoperation
and have much longer
payback times."

I agree with these points being drawbacks to NEAs versus the Moon.

But NEAs do have many advantages over the Moon as well.

Ron Menich

hollroa@...
Please respond to
ssi_list

>>>So you make the walls of the habitat thicker or use stronger material,
you
have a whole asteroid to work with, no need to be miserly with materials.
O'Neill's original Physics Today article did work out the engineering
requirements assuming a full sea-level air pressure, although that was an
assumption that O'Neill later called "naive".>>>

Mining asteroids and transporting their materials back to HEO is likely
to be more expensive than simply shipping them up from the moon. The
operations that are involved in mining and transporting NEA materials are
more complex, less susceptible to teleoperation and have much longer
payback times. It seems highly unlikely to me, that even Lunar mining
systems are going to be able to operate at dirt cheap prices. If we
consider the cost of a simple lunar base, weighing perhaps 100 tonnes, it
becomes clear that materials costs of 25c/kg, delivered to L5, is
hopelessly optimistic: 100,000kg x $10,000/kg to lunar surface = 1 billion
dollars.
Then there is the question of the power source. Do we attempt to
construct a solar power plant out of lunar materials? or do we ship it in
from Earth? A 1-Mw solar power station, with no power storage equipment,
would weigh about 40 tonnes, assuming a 12.5% conversion efficiency. The
mass driver would weigh about 80 tonnes, although only 20 tonnes would need
to be imported from Earth (conductor coils can be produced from lunar
aluminium). Mining equipment, the mass driver, factories for producing
oxygen, fibre glass bags, mass driver conductor coils, are all going to
weigh a lot more, so lets budget 40 tonnes for these. That gives a round
total of 200 tonnes for the lunar base. This is not to say that 200 tonnes
of equipment is the only thing that we are ever going to have to import
from the Earth. The crew that are required to man the station must be
rotated every 2 years or so. Even if we assume that water and air are 100%
recycled, each astronaut will require 0.5 kg of food each and every day. A
4 person crew would consume 1500 Kg of food over the course of 2 years.
This, plus the weight of the vehicle required to transport them to the
moon, would amount to about 25 tonnes, every two years.

So what do we have? 200 tonnes of materials, shipped to the moon
up-front, and 12.5 tonnes per year for the delivery spacecraft. Our 1-mw
power source, assuming that it is capable of tracking the sun, would
produce about 2x10**13 joules per year. Launching 1 kg of material to lunar
escape velocity, requires about 2.8Mj of energy. Assuming a 60% conversion
from direct solar electricity to mass driver momentum, we find that we are
able to transport about 4300 tonnes of material to L2 each year. What would
be the cost, per kg of transported material? The initial investment of 200
tonnes would amount to a cost of $2 billion. Assuming a 10 year payback
time (with zero interest!) that amounts to $200million/year or $46/Kg. Add
in the extra 12.5 tonnes per year for the delivery and return vehicle, and
at $10,000/kg delivery cost to the lunar surface, you find that you need to
charge an extra $29/Kg, just to break even. That's a total of $75/Kg. This
figure does not include development costs of transportation vehicles, mass
drivers, materials processing technology or life support systems. Nor does
it include the cost associated with setting up the space factory that is
required for the construction of space colonies and SPS- satellites It does
not include the costs of shipping all of the required personnel and
materials from Earth to the space factory.

Under these conditions, even Zubrins estimate of $30/kg for material
delivered to L5, is probably over- optimistic A brief examination of all of
the costs involved, indicates that we may be looking at a figure closer to
$100/Kg and more probably $150/Kg, when the cost of the HEO factory is
factored in. This is an enormous improvement over the $10,000/Kg, that we
assumed it would cost in order to deliver the same amount of material to
the lunar surface from the from Earth. It represents a factor of 20-30 drop
in launch costs. But it is much too high for us to even consider the
construction of huge SPS satellites and 3 million tonne, island-one
colonies. More likely, such a plan would concentrate on the manufacture of
communications satellites and orbital hotels. These are potential, low mass
but high revenue objects.

Tony