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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.followup
Subject: Re: Alternate Energy & Microwaves
Message-ID: <4215@utzoo.UUCP>
Date: Tue, 14-Aug-84 17:10:23 EDT
Article-I.D.: utzoo.4215
Posted: Tue Aug 14 17:10:23 1984
Date-Received: Tue, 14-Aug-84 17:10:23 EDT
References: <4196@utzoo.UUCP>, <369@utastro.UUCP>
Organization: U of Toronto Zoology
Lines: 67

> a) The sun shines 24 hours/day everywhere, not just out in space, but it may
> be difficult to get a satellite far enough away from the earth so it never
> passes through its shadow, particularly if it is in synchronous orbit, which
> means it goes around once in 24 hours, and must therefore be at 25,000 miles
> altitute.

The sun sure doesn't shine 24 hours a day in Toronto!  That statement is
true only if you qualify "everywhere" to mean "all places in empty space,
or without a solid body between themselves and the sun".

The problem of powersats passing through the Earth's shadow is less major
than you might think.  Remember that the Earth's axis, and hence the axis
of the Clarke orbit, is inclined to the ecliptic.  For most of the year,
the Earth's shadow passes "under" or "over" the "back half" of the Clarke
orbit, so powersats are never in shadow.  For short periods during spring
and fall, powersats are in shadow briefly at midnight [assuming rectennas
at about the same longitudes as the satellites themselves].  Midnight is
not a time of high power demand, and this problem could be handled by
backup power sources or by load-sharing among several well-spaced powersats.

> b) If the solar cells aren't there to convert the heat into electricity (i.e.
> make some use of 15% of it) then it will *all* go into the earth's bioshphere
> if it isn't reflected back into space.  The "saved" 15% will presumably get
> converted into work somewhere, which degrades into heat, which enters the
> earth's biosphere.  So where is the "waste?"

Nope.  For the same reasons why the powersats are seldom in the Earth's
shadow, they are seldom between the Earth and the Sun.  Most of the time,
the sunlight they are intercepting would have gone out into interstellar
space.  The only reason this whole thing comes up is that people fuss over
powersats adding heat to the biosphere.  They do, but not as much as (say)
ground-based solar, since the 85% that powersats don't convert successfully
into electricity is radiated into space, not the biosphere.  Ground-based
solar power plants are generally in desert areas, where most solar energy
goes straight back out into space -- until you put a power plant there.

> c) If the Sunsat is put up it will be bright enough to rival the full moon,
> just from reflected light alone (the moon reflects ~8%, is bigger but is
> *much* farther away, and the inverse-square law does a bit of good) ...
> which means ground-based astronomy goes out of business, since most of the
> interesting observations of quasars, distant galaxies, black hole candidates
> and vibrating stellar corpses are confined to "dark time," when the moon is
> nearly aligned with the sun and the night sky is dark.

This is a serious problem.  In the long run, ground-based astronomy is
doomed anyway, both because of increasing volumes of stuff in orbit and
because space is a much better place to do astronomy.  But a ring of
powersats in equatorial orbit may well hasten its demise considerably.
It helps that powersats are designed to *absorb*, not reflect, light.
But it probably doesn't help enough.  The one consolation is that major
powersat construction will involve enough space activity that the costs
of other space activities, e.g. space astronomy, may drop as a side effect.

I agree, this is a painful and undesirable side effect.  I don't see any
way around it, though, and if powersats work as well as people hope, it
may well be worth it.  Perhaps the sale/lease price of a finished powersat
should include a modest "tax" to support space-based astronomy.

> d) If all astronomers become shoe salesmen or zoologists then who will be
> watching when the Klingons come?

Given that "utzoo" is a Zoology-department machine, the prospect of such
job shifts doesn't horrify me as much as you might think.  The Klingons
are unlikely to advertise their presence by occulting quasars anyway.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry