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Use reflected sunlight to communicate from space

Space probe - use reflected sunlight to communicate
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Ok, as far as I understand it, current space probes use solar panels and radioactivity to generate electricity which can power their radios....(and other equipment obviously).

To save electricity, could we not miss out the radio, by having a device - say based on a LCD in front of a mirror, which would darken/lighten to interrupt the sunlight to stream digital data back to Earth? (A bit like using mirrors / slats to send morse code between boats)

Assumptions:

1. The LCD device would use less power than a radio...

2. It's possible from Earth to detect this light signal amongst all the background light from other places...

3. That probe is going to be able to 'see' the Earth and sun for suitable periods of time....

(If visible light is to difficult to detect, doesn't the sun kick out a whole load of other electromagnetic radiation that would be suitable ?- and then we would need an analogous device to a mirror)

monojohnny, May 28 2006

Sunlight to Power Laser http://www.nrel.gov...ess/1995/solar.html
[TIB, May 30 2006]

[link]






       I think this is a solution waiting for a problem. The radio devices currently used don't use much power, and (as you point out) don't need a direct line of site with us in order to work.
neilp, May 28 2006
  

       Take the point about line-of-sight.... but I would say any power-saving would be an advantage on a space probe.....
monojohnny, May 29 2006
  

       Some power would be needed to orientate the mirror. Could be a viable system for communication between satellites which are stationary relative to each other. +
7ennyn, May 29 2006
  

       If an optic system was employed to concentrate the light through a focus, then the switching system need only be arranged at that point. A small mirror could easily deviate the path of the beam elsewhere (a fraction of a degree would send the light to the moon instead). But the switching would be mechanically based (or use physical properties at least) and might have quite a low bit-rate.
Ling, May 29 2006
  

       Couldn't we get rid of the mechanical-system to orient the mirror, by using a dome-shaped LCD screen, which could be used to direct the outgoing beam ? (by switching one pixel to transparent whilst the others would be 'on') ?
monojohnny, May 29 2006
  

       Good effort. Given that LCD screens have only recently been able to switch fast enough to simulate motion (25Hz) bandwidth would be limited, but the basic idea still holds up. They (the JPL 'they', I think) have been looking into using laser instead of radio - it focusses better.
wagster, May 29 2006
  

       A flat mirror acts like a pinhole camera--it projects an image of the sun. The reflected light from the sun will be spreading out in a cone, not travelling in a tight beam like a laser. Making sunlight into a narrow beam of light will take some serious technology, which will have to adapt for the angle between the sun and the target.   

       Current practices allow the accumulation of energy for stronger signals. The uses for a sunlight system are going to be limited. Still, an interesting idea.
baconbrain, May 29 2006
  

       OR... use sunlight to run a laser directly + (see link)
TIB, May 30 2006
  
      
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