Laser communications idea

James Rogers (
Sat, 09 May 1998 22:47:59 -0700


I had an idea for long-range (6000+ miles) laser communication system using
(more or less) off the shelf technologies. I am unable to find any obvious
flaw in my idea, so I was hoping for some feedback from people who may be
more knowledgeable about this than I.

Laser targeting/ranging systems, such as those used by the military, mark
their targets by detecting the laser light which is reflected off the
object being illuminated. My idea was to use objects in geosynchronous
orbit as reflective bodies for the purpose of scattering laser light. The
ground stations would use laser pulses to send data by reflecting them off
the geosynchronous object. A passive sensor on the receiving end would
detect the laser light that scatters off the satellite and (hopefully)
discern the bits. In the simplest case scenario, the data communication
would be half-duplex, but more complex arrangements could be developed. I
am unsure of the type of baud rate that could be accomplished this way.

If this worked, it would be an interesting option for
covert/subversive/etc. communications. Lock onto your satellite of choice
and send the data. Encryption would be necessary, but it would probably be
difficult to locate the sender, especially if the laser didn't operate at
visible wavelengths. The problem I see is the possibility that you
wouldn't get a good scatter off the satellite. I know that the
ground-laser-to-geosync works because my mother used to work in a building
where data was transmitted that way, but I am unsure how the downlink worked.


-James Rogers