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From: eli@bbn.com (Steve Elias)
Newsgroups: talk.politics.misc,sci.misc
Subject: greenhouse effect / solar power satellites
Message-ID: <22678@bbn.COM>
Date: 28 Mar 88 11:30:59 GMT
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In article <4091@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes:
!In article <22670@bbn.COM! eli@BBN.COM (Steve Elias) writes:
!!In article <2963@sfsup.UUCP! glg@/guest4/glgUUCP (xt1112-G.Gleason) writes:
!:
!:	(regarding solar power satellites)
!
!:!In any case something seems bogus here, because in order to be significant
!:!we would have to be considering SPS's with a total area that is *very*
!:!large (significant relative to the earths total collection are).

	total receiver area is not the only factor which will upset
	thermal equilibrium.  

!:	indeed something is bogus:  the very idea of Solar Power Satellites
!:	being a useful energy source.  they would be enormously expensive
!:	and enormously dangerous (thermally), if enough were built to 
!:	actually provide a decent amount of energy.
!
!If we ever get a lot of energy out of them, we will need a cheaper launch
!system.  We will also use very large thin films to minimize weight and
!cost.  The SPS's will not be built if they are too expensive.  

	regardless of cost or efficiency, the SPS idea is inherently dangerous.
	let me reiterate why this is so... (below)...

!Assuming international cooperation in space (else 
!the SPS is too vulnerable to attack) the SPS is more reliable than other
!systems, and has a greater thermal efficiency on earth.  

	regardless of the efficiency of any of the ground receiver systems,
	solar power satellites would add incredible amounts of energy to
	the earth/atmosphere system, whether in the form of electricity,
	or in the form of waste heat.  this is their function.
	the form the energy takes is not relevant to the global thermal
	considerations.

!If the only criterion for choosing a generator were,
!"what is the danger to man, both short- and long-term", then solar power
!satellites would be a good choice. 

	no way.  they are as dangerous a choice as we could make.
	regardless of efficiency, they would add on the order of the
	same amount of energy flux we receive from the sun now.
	(i recall the order of magnitude -- haven't dug up numbers yet).

!:	energy put into building earthside collectors is not leaving the
!:	earth/atmosphere system, so it doesn't negate the energy sent down
!:	by the power satellites.  reflectivity changes due to the collectors
!:	would have to be considered, as well.  but, regardless of reflectivity
!:	changes, thermal equilibrium would be quite goofed up -- by waste heat
!:	from the microwave receivers...

!You have assumed <= 50% efficiency, others have claimed higher.  Either
!way, this is better efficiency than for a heat engine.  So, it is better
!(if trying to minimize waste heat) to use solar power.

	i wasn't specific enough.  waste heat alone would be dangerous,
	but that isn't the only source of extra thermal energy -- the
	electricity itself is as dangerous as the waste heat.  

	my point isn't that we have to minimize waste heat -- it is that
	we have to minimize the amount of energy that enters the earth
	ecosystem that would not otherwise be there. 

!:	the greenhouse effect can theoretically be kicked off by both CO2
!:	buildup and by large thermal changes -- both factors are 'cause' and
!:	both factors are 'effect'.  that's Frank Drake's point...  

!The effect is far more sensitive to CO2 concentration; present power 
!sources produce more CO2 as a fraction of the total present than they
!do heat.  

	once again:  the greenhouse effect is a theory.  we don't know
	exactly where the 'points of no return' are, on either the CO2 or
	the thermal side.

!By the time we are generating a few % of the solar flux on the earth as
!waste heat, we will have to worry.  By then, I hope we will have moved
!power intensive industry into space (if not, we can produce more power,
!and use the excess to drive a heat pump [perhaps, a large laser] and 
!refridgerate the earth.)

	and:  waste heat is not the problem.  energy that would not 
	otherwise enter the earth/atmosphere system is the problem.

	moving power intensive industry into space would solve the problem
	quite nicely...  (i'm not holding my breath).