RE: [amsat-bb] Optical COmms experiment

[Bob Bruninga <bruninga@xxxxxxxx>]

PCsat will carry 80 stock LEDs (3 Watts input power) on its -Z face which
we may turn on occassionally both as a radiative cooling experiment and
just for fun to see if we can see it.  Previous discussion here resulted
in estimates of a visual magnitude by Lee and/or K0VTY of about 8
(binoculars).  

But those calculations assumed a non-focused beam (or 3 dB).  Now that we
have built it, these LEDS actually have a cone of about 40 degrees or a
"transmit antenna gain" of say 13 dB? or 10 dB greater than originally
assumed, thus raising the possibility to a magnitude of 5.5 just possibly
visible to the naked eye.  The spot will be about 300 miles across..(if it
hits straight down)

We are in the midst of a million other things, so we have not done any
rigorous evaluation of this experiment yet.  If anyone wants to take a
crack at it, they are welcome to contribute! There is nothing special
about these LED's.  We just had a bag of em and decided to do something
with them.  SO assume standard LEDs (whatever that means)...
 
on 3 May 2001, Bob Bruninga wrote:

> Warren Lee and Tony Beresford have both confirmed the 12th magnitude
> visibility for a 3w incandescent bulb at 500 miles.  This now leads me to
> a new CUBESAT design idea:  OPTIsat!
> 
> OPTIsat would be a 4" cube satellite with 225 bright LEDs on the bottom.
> The uplink would be 70 cm CW.  THe downlink would be visual CW.  Peak
> LED power would be about 10w (does anyone know the power efficiency of
> LED's?)
> 
> This would pick up about 4 magnitudes and make it quite visible to
> binoculars...  THink of the fun of kids out on campouts looking for
> OPTIsat and trying their hand at flashing light CW.  And it would be RED.
> Easy to distinguish from stars...
> 
> The transmit duty cycle is 50% CW, 10% HAM pouplation areas, 50% eclipse
> times (only operates in the dark) and half the time no one will be using
> it (50%).  THus the average solar power required to keep it running is
> only 10W * .5 * .1 * .5 * .5 * 1.4 (charging efficiency) or about  200
> miliwatts.  We can do that with just a 2" square solar panel.   Plenty of
> power budget...  
> 
> Actually, then , we could totally cover the bottom 4" panel with 400 LEDs
> for a rated poewr of 20 W and then overdrive them by 100% for 40W peak
> power and gain another magnitude in brightness and still stay within the
> average power budget.
> 
> Of course, the CUBESAT would actually have to be split into two halves,
> with a 6 foot piano wire between them to get gravity gradient
> stabalization.  Then we would have to put a full set of LEDS on the top
> box too, in case it stabalized upside down.  But I would then add a second
> receiver so that one channel drives the "top" and the other drives the
> bottom.  We would only use the one that we could see...
> 
> Wow, sure wish I had funds for a CUBESAT flight...
> Kids would love this one...   (well, this kid would anyway...)
> 
> de WB4APR@amsat.org, Bob

ISS-APRS FAQ:       http://web.usna.navy.mil/~bruninga/iss-faq.html
PCsat Design        http://web.usna.navy.mil/~bruninga/pcsat.html
CUBESAT Designs     http://web.usna.navy.mil/~bruninga/cubesat.html
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