----- 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 > > > ---- > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Sat Jul 14 2001 - 03:07:29 PDT