From: dietz@cs.rochester.edu (Paul Dietz)
Subject: Re: Justification for the Space Program
Organization: University of Rochester
Distribution: usa
Date: Fri, 8 Jan 1993 19:00:43 GMT

In article <jfelder-080193105134@latvia.lerc.nasa.gov> jfelder@lerc.nasa.gov (James L. Felder) writes:

> I see societal problems even bigger than those facing the space
> program in siting breeder reactors and the attendent fuel reprocessing
> facilities and waste disposal sites.  The Japanese government is
> already beginning to face severe pressure to slow or halt their
> breeder program.

Ultimately, the reason for this is that breeders are not now competitive.
This is also a significant reason why Britain and Germany are stopping
breeder development.  Fortunately, they aren't needed now.

The Japanese have chosen a breeder cycle that uses large amounts of
plutonium.  Alternate cycles (for example, denatured U-Th) would
produce 2 orders of magnitude less plutonium, and fuel shipments would
be of denatured U-233 with no plutonium, which cannot be used in bombs
without enrichment.  These cycles are more proliferation resistant,
and are compatible with reactors evolved from current commercial
designs, rather than an economy with mostly fast reactors.


> A further problem I
> see is that all the energy conversion to useable form (electricity) occurs
> within the biosphere.  I do not have a feel for how much thermal energy can
> be released into the biosphere before it contributes a significant amount
> directly to global warming (as opposed to CO2's indirect contribution
> through increased solar absorbtion).

I posted a number on that.  Today, direct thermal pollution is
globally insignificant, compared to insolation, or even to the heat
flux from increased greenhouse gases or that caused by human
modification of earth's albedo.  Primary energy use could be pushed up
a couple of orders of magnitude without it becoming unmanagable.
	

>> is very hard to replace with some substitute.  Fossil fuels are
>> an example -- there is no reason why we should not be able
>> to survive indefinitely without them, if some other source of
>> energy is available.

> And no matter what we will have to learn to do without them.  And will
> probably be cursed by future generations for burning such a useful
> commodity simply to heat our homes.

Just like we curse the shortage of whale oil?  Hardly -- they will
view fossil fuel use as a curious historical anomaly, and pity
us for being (so) relatively poor and ignorant that we could not
use cleaner alternatives.


>> In the short term, however, there is no reason why resource use
>> on earth cannot be increased.  There is no reason why we could
>> not supply several times the current population with several times
>> the current US per capita energy consumption indefinitely.

> Yes, but at what cost to the environment?

Nuclear or solar have much lower impacts on the environment than
current energy sources, so the cost would be lower than what we are
already paying.


> No, to unreliable.  Terrestrial solar energy has a problem because of
> intermittent illumination.  Either a large storage capacity must be
> included in the system, or another source must come on-line at night and
> during periods of cloud cover.  The large required land area makes solar
> problematic for large portion of the world.  Plus places like Cleveland
> goes days or weeks with hardly a glimpse of the sun.

Surely, means to move energy in both time and space would be needed.
There are serious economic limits on this today, but there is no
reason to think these limits cannot be extended.

As for land area: current world energy use is only 1/10,000 of the
sunlight hitting earth's surface.  Restricting ourselves to
continents, and assuming a 20% efficieny, we end up using a couple of
percent of the land area of the planet.


> It might be a misconception on my part based on media coverage, but it
> seems that nuclear plants have frequent shut downs for one reason or
> another, often times for days or weeks.  A system that relied on a majority
> of its energy from nuclear power would have to have a significant extra
> capacity included, or a more reliable source ready to come on line at a
> moments notice.

This is a misconception; nuclear plants are usually quite reliable,
and can be made more reliable (and will be more reliable, if we have
experience operating tens of thousands of them).  In a world with more
nuclear reactors, one could even tolerate less reliability, as long as
the failures are independent (and not polluting) and power can be
wheeled.


> Without a track record, though, nothing can be said for powersats, so this
> again probably isn't a compeling argument.  It at least doesn't share the
> intermittent illumination problem of land based solar, plus the power
> source never goes off-line :-).

Powersats as usually described can't hack it as the primary energy
source for earth, since there's not enough room in GEO.  They'd have
to be farther away.  That drives up cost.  I am also not convinced the
orbital debris problem would be managable -- there'd be tens of
thousands of square kilometers of collectors that would be out there
to be hit and breed more debris fragments.  Construction and
maintenance of the powersats would involve billions of tons of
material -- surely some would escape into orbit?


> The price of raw materials in the space program is trivial, but that isn't
> my point.  It is the price of raw materials and energy to the entire
> economy that is the problem. I think that an increasing drag on the ecomomy
> will be felt as these prices go up.

I still don't buy it.  Raw materials prices a small input to the
economy.  The biggest raw material input is energy, but I've argued
that's not going to get scarce.  The high dollar volume non-fuel
minerals will not get scarce either (iron and aluminum, for example),
or can be largely substituted for.  I don't see just what is going to
cause the drag.

	Paul F. Dietz
	dietz@cs.rochester.edu
Newsgroups: sci.space