Fw: [amsat-bb] Optical COmms experiment

From: Gustavo Carpignano (gcarpi@ciudad.com.ar)
Date: Sat Jul 14 2001 - 02:54:53 PDT

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    ----- Original Message -----
    From: "Bob Bruninga" <bruninga@usna.edu>
    To: "Lee Warren M GS-14 AFOTEC/TST" <Warren.Lee@afotec.af.mil>
    Cc: "Joseph Murray" <k0vty@juno.com>; <amsat-bb@AMSAT.Org>
    Sent: Saturday, July 07, 2001 11:39 PM
    Subject: RE: [amsat-bb] Optical COmms experiment
    
    
    > 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
    > APRS LIVE pages     http://web.usna.navy.mil/~bruninga/aprs.html
    > APRS SATELLITES     http://web.usna.navy.mil/~bruninga/astars.html
    > MIM/Mic-E/Mic-Lite  http://www.toad.net/~wclement/bruninga/mic-lite.html
    >
    >
    > ----
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