From: roberts@CMR.NCSL.NIST.GOV (John Roberts)
Newsgroups: sci.space
Subject: Re: SPS
Date: 7 Oct 92 04:41:42 GMT
Organization: National Institute of Standards and Technology
	formerly National Bureau of Standards


-From: ralph.buttigieg@f635.n713.z3.fido.zeta.org.au (Ralph Buttigieg)
-Subject: Re: SPS
-Date: 30 Sep 92 10:25:12 GMT

-Original to: Roberts@Cmr.Ncsl.Nist.Gov
- to roberts@CMR.NCSL.NIST.GOV (John Roberts), via *IXgate 3:713/602

- r> According to Steve Willner, if you choose 10.6um (handy 
- r> because that's what
- r> a CO2 laser put out), then the main absorption is by water vapor, at
-about
- r> 1% per millimeter equivalent. So it wouldn't heat the upper atmosphere
- r> significantly, if you choose a high, dry site for reception there
-wouldn't

- But how do you convert the laser light back into electricity?
- Photovoltics? Does not sound very efficiant to me.

I was referring to the following device (repost):
...............

ELECTROMAGNETICS: "Smallest Antennas Imitate Insect Communication"

"Using tools developed for fabricating electronic integrated circuits, NIST
scientists have produced microantennas the size of a grain of sand and only
60 micrometers across (about the diameter of a human hair). At this tiny size,
these "world's smallest" antennas can capture the extremely short (about 3 to
30 micrometers) wavelengths of infrared radiation. Their development paves
the way for novel infrared detectors that rely on antennas to "see" images
of heat radiating from all warm objects such as people, animals, and buildings.
Such detectors have many applications, including satellite observation of 
Earth, astronomy, medicine, and national defense. There is evidence that 
insects evolved microantennas, similar to the NIST devices, to enhance their
infrared pickup, allow them to see in darkness, and give them a survival 
advantage. The NIST work proves that such tiny insect structures can function
efficiently for infrared wavelengths."

...............

Essentially, the infrared radiation is treated as *very* short wavelength
microwaves. Perhaps the beam needs to be polarized for best results.
The article didn't mention applicability for power reception - that such a
detector might be useful for this is speculation on my part. 

- r> by the greenhouse gases released by fossil fuel. Space-based solar power
- r> would also heat the Earth much less than ground-based 
- r> solar power generation.

- Why? Ground based collectors would use the energy coming to Earth
- already.   I must be missing something.

- Ralph
- * Origin: Vulcan's World-Sydney Australia 02 635-1204 (3:713/635)

I should have said "could". Earth-based photovoltaic power systems greatly
increase the Earth's albedo over a significant area, and only a small portion
of the increased energy absorption goes into power generation. (This would be
at least partially offset by increased radiation at night.) If the IR beam
is much more concentrated than normal sunlight, and if IR power receivers
can be developed with efficiency not too far off from that of microwave
receivers, then there might be a net saving in the heating of the Earth.

John Roberts
roberts@cmr.ncsl.nist.gov

Newsgroups: sci.space