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From: eder@ssc-vax.UUCP (Dani Eder)
Newsgroups: sci.research
Subject: Re: Microwave power beaming (was 'art imitates life')
Message-ID: <1266@ssc-vax.UUCP>
Date: Fri, 29-May-87 19:13:15 EDT
Article-I.D.: ssc-vax.1266
Posted: Fri May 29 19:13:15 1987
Date-Received: Tue, 2-Jun-87 01:40:34 EDT
References: <6693@allegra.UUCP> <1115@oliveb.UUCP> <5893@brl-smoke.ARPA>
Organization: Boeing Aerospace Corp., Seattle WA
Lines: 52
Summary: safety of SPS

In article <5893@brl-smoke.ARPA>, gwyn@brl-smoke.ARPA (Doug Gwyn ) writes:
> In article <1115@oliveb.UUCP> gnome@oliveb.UUCP (Gary) writes:
> -Well, according to the May 7 MACHINE DESIGN, Lockheed-Georgia has entered
> -a proposal to create a smaller version of "Project Flashlight".
> -Their idea is to beam 2MW of power (as microwaves) at their unmanned planes
> -in order to keep them in a figure-8 watchdog position over an area for
> -60 to 90 days.
> 
> I really think this (as well as similar ideas for beaming power
> to Earth from solar-collector satellites) is extremely dangerous.
> What is to keep someone (even a poor little bird) from flying
> through the beam by accident?

I was part of a study in 1984 that looked at design of a Solar Power
Satellite made from lunar materials (the report is published as
volume 6 #1 of the journal 'Space Power', 1986).  The direct answer
to your question is 'nothing'.  At least in the space-based power
supply scenario we looked at, the maximum beam intensity was required
to be no more than 300 watts per square meter.  This is 30% of peak
desert noonday sunlight intensity.  Unless the receiving antenna were
located in a desert area, the combined sunlight+microwave intensity will
be well within tolerable limits for humans and animals.

Now, an SPS will not likely be located in a desert, since you generally
want to get power to where people are.  As for airplanes, the beam area
will probably be marked as a keep out zone, to prevent long-term low
level exposure to passengers and crew.  Of course, an airplane could
stray into the beam by accident, but the metal skin of the plane will
reduce the interior intensity to only a few watts per square meter, and
the plane will generally be through the beam in less than a minute.

As for someone wandering into the beam on the ground, they would have
to climb two fences, then hike about two miles to the center of the
beam.  Then they would have to climb up on the receiving antennas to
get the full beam intensity.  Standing underneath doesn't get you much.
So, it is physically possible, but it makes about as much sense as
intentionally walking into the firebox of a coal-fired power plant.

As for the beam itself wandering, the beam is produced by a phased
array of microwave transmitters in space.  The control signal is
coming from a transmitter located in the center of the receiving
antenna on the ground, and is powered by the incoming beam.  So, if
the beam wanders, the control signal turns off, and the phased
array loses phase lock, spreading its' beam over the entire earth,
where it becomes a harmless intensity (less than TV intensity in
most areas).

I do not know of the microwave powered airplane design rules, so I
cannot comment on it's safety.  If there is anything more you would
like to know about Solar Power Satellites, let me know.

Dani Eder/Advanced Space Transportation/Boeing/ssc-vax!eder