[HCARC] Are Engineers Trying To Make Non Engineers Feel Bad??

Kerry Sandstrom kerryk5ks at hughes.net
Sat Jul 28 08:58:14 EDT 2012


Fred,

I saw this a couple days ago.  I'm not sure what they are really doing.  The 
article I saw talked about experiments to use lasers to communicate from/to 
the earth to/from space.  LEDs flashing Morse code are not what the 
experiment is all about.  I really don't know what the point of the morse 
code is.

As far as using light as the carrier for digital signals, that is just not 
easy.  The stars twinkle becasue of multipath through the atmosphere.  I 
suspect that they will be using a fancy digital modulation scheme with a lot 
of error correction coding on it to get a usable signal to the ground.  Of 
course,  tracking the light source isn't going to be easy either.  This gets 
tried from time to time and the propagation problems always end up 
overwhelming the system.  There is no point in the system unless you can 
carry 100's of Mb/s over the link.  it will be interesting to see how this 
works.

The people who are worried about light polution I don't think will even 
notice!  several decades ago the AF tried to put a belt of X-band (I think0 
dipoles into orbit to reflect signals for communication.  Some people were 
concerned that it would blot out the sky.  I fact, the AF had a real problem 
finding them even at X-band!  Never tried it again.  I think it was called 
Project Westford.

Kerry





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