[Laser] light beacon on balloon

[TWOSIG at aol.com]

This is a project that is not quite a laser project, at least not yet.  
 
There is a local group that sends up balloon packages for fun and education.  
They have sent payloads for radio tracking, telemetry beacons, APRS tracking, 
Amateur TV, and cut down control uplink.  

I spoke to one of the group about a light communication related package.  He 
said that they had tried a strobe light that was unsuccessful in that it did 
not improve the ability to see the balloon with the naked eye.  The group is 
always looking for another experiment to send up so they have another reason to 
have a launch event.  So he encouraged me to come up with a "package design", 
and suggested that it start with a simple beacon to demonstrate light band 
down link and perhaps optical tracking.  They have a microcontroler board that 
could provide a data stream to it.  

I invite suggestions from you for this first beacon project, or for future 
missions.  I was thinking of a hemisphere of bright LEDs flashing at audio 
frequency.  I could use some suggestions on this.  I thought of modulating the 
light beacon with an audio "carrier" modulated with MCW alternating with BPSK 
signals to compare the two modes.  MCW because it could be decoded electronically 
and by eyeball as a flashing light.  PSK31 or PSK64 might be superior for 
electronic decoding.  I still need to select an audio frequency -- any 
recommendations from you?    I am thinking of sendin call sign and a time code that could 
be corelated to the APRS altitude and location tracking that will be the 
primary payload (and used to recover the package).  

A typical simple mission profile would be a launch before 10 AM near 
Hutchinson, Kansas, a two hour climb to about 100,000 feet for balloon burst, then a 1 
hour to return to the ground by parachute.  Ground track would be 30 to 200 
miles depending on winds aloft, eastward or southeastward.  The horizon at peak 
altitude should be about 300 miles away.  
The balloons tend to spin and swing the payload ( ATV pictures often show the 
horizon instead of the Earth below, or full rotations in a few seconds.) so a 
wide field of view is needed.  It will also be in constant motion, vertically 
and horizontally.  

Future experiements that I have though about are: a night launch for improved 
optical tracking, passive retro-reflector,  voice signal instead of digital 
data (AM or 40 kHz subcarrier FM),  radio uplink with the light beacon 
repeating (uplink could be data or voice), a light uplink (requires a wide field of 
view detector array) with a radio repeating downlink, distance measurement (with 
light beam as uplink, downlink, or both), a servo alt-az system to point a 
"narrow" field of view sensor or emmiter.
 
I am still working on how many LEDs and what pattern would give a useable 
transmission pattern, or the duty cycle on the light emitter.  Also if anyone can 
suggest a method of dampening the balloon payload oscillations that does not 
weigh much, it would help.

James
N5GUI