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From: eder@ssc-vax.UUCP (Dani Eder)
Newsgroups: talk.politics.misc,sci.misc
Subject: Re: efficiency / greenhouse effect / solar power satellites
Message-ID: <1843@ssc-vax.UUCP>
Date: 7 Apr 88 14:37:53 GMT
Distribution: na
Organization: Boeing Aerospace Corp., Seattle WA
Lines: 41

In article <4086@whuts.UUCP>, sw@whuts.UUCP (WARMINK) writes:
> Just a thought: how much energy does it take to put up one of these
> solar power satellites?
> - extracting raw materials (satellite + lauch vehicle)
> - manufacturing
> - transportation
> - fuel(s) for launch vehicle
> - heating / airconditioning of working enviroments
> 
> How long wil it take to re-coup this initial energy use?
> This is only a half :-) thought...
> 

In the study of SPS made from Lunar Materials that I worked on, we found
that 99% of the mass of an SPS could be made from lunar materials, and
the other 1% was complex enough or had such rare-on-the-Moon materils
that it was better to bring it from the Earth.  You also have to launch
2% of the SPS mass in mining equipment and space factories to manufacture
the other 99%.

The net result is that 3% of the SPS mass must be launched from the
Earth.  The extraction cost of the parts launched from Earth I cannot
give you a number for.  A lot of that is complex equipment, like
computers.  The launch cost (in energy) is  about 100 MegaJoules/kg
for propellant.  This exceeds the energy used in making metals by
one to two orders of magnitude (kind of fuzzy number there).
Let us assume that it takes 200 MJ per kilogram of payload to do
everything on the ground we have to do.

An SPS (large economy size - 5,000 MW) masses 100,000 metric tons
Therefore 3000 tons (3,000,000 kg) must be launched.  If we assume
that 200 MJ are required for each kg, then  600 terajoules are
required on Earth to launch the SPS.  At a power output of
5 gigawatts, the energy payback takes 120,000 seconds, or 1.5 days.

This neglects the considerable energy cost of building the receiving
antenna on the ground, but memory fails at this point as to the
mass of the antenna.

Dani Eder/Boeing/Space Station Program
ssc-vax!eder