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Re: New Projects: Sat Laser Comms

Stan wrote:

> Hello the Net:
> I am thinking of some new satellite projects using LASER communications.
> a few questions for the brain trust:
> 1. are visible laser emitters allowed in space ?    how about non 
> visible IR ?


> 2. any laser spectrum considerations ?   UV, red HeNe, red solid 
> state, IR,

Very high peak power can be generated in a Q-switched Nd:YAG laser at 
1064 nm ... this is what NASA will be testing in the coming years.  
There is lots of very interesting reading in the archives of the DSN ... 
see http://tmo.jpl.nasa.gov/progress_report/index.html or

> 3. how does path loss vary across the laser spectrum ?

Higher frequency = higher loss, same as RF.

> 4. Are other satellites susceptible to laser light  ?


> 5. Since a laser, by itself, is very "pointy" can a scanner be used to 
> cover the footprint
>      much like the grocery checkout scanner  ?

A laser is not necessarily pointy ... diode lasers need lens systems to 
collomate the beam, and you can simply defocus a collomated laser beam 
with , say the beam expander so your pointing requirements go down.  Of 
course, so does your signal to noise ratio.  This would probably be much 
better than a scanner.  The laser beam beam of AO-40 is 1.2 degrees 
FWHM, I think.  I know EME guys with tighter beams than that on L-band!

> 7. Are terrestrial lasers allowed to transmit anywhere into space ?
>     of course with FDA/FAA approvals, as needed.

Yes, you do need approval from the satellite owner, however, to 
illuminate it.

> 8. Are all of the grocery type scanners mechanical in nature, or are 
> there some that electrically steer the beam,
>    for no moving mechanical parts ?  (reliability issues)

They are mechanical, usually rotating mirrors or prisms.

> 9. Possibly a EASYSAT type of standard laser comms module with 
> modulator and scan control.  ??
> 10. How do the pro's use space based lasers for comms ?

Pulse Position Modulation, Q-switched Nd:YAG lasers, Avalanche Photo 
Detectors, big telescopes (10 meter diameter) and very high accuracy 

-Joe KM1P
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