Weird idea number 2.

You mention "no transmitters" But thinking out of the box a little....If you carried forward your idea of the Laser beacons from your earlier project, then it may be possible to "transmit" something after all. -

How about one of the new Hi power LEDs? 5 Watts to 20W are available now. Just run it at whatever power suits the power budget.

Have the onbard RX activate the LED for a limited period on receipt of a command. Two simple methods of data transfer come to mind. 1) Switch the LED on and off at an audio rate with a 1:1 square wave. Then turn that signal on and off with a CW generated message. Simple but effective. We know that works over 150 miles from recent reports from Australia. Receive using software from weaksignals.com

2) Much nicer. - Switch the LED on / off at some spot frequency between 12 - 20kHz. But arrange for the waveform to be pulse width modulated. Easy ! One comparator and a rectangular wave at 20kHz. - Audio on the other input. You can send anything generated at audio including PSK31 speech, JT65, Domino, etc.

I imagine the sat will be attached to the ISS. Tracking is easy too. Pick a night or early morning when a visible pass will occur. Track the ISS while it is in sunlight then when it reaches the terminator, activate the LED transmitter. Your tracking should be spot on and the signal can be received with very modest equipment.

The receiver on the ground is a magnifying glass lens about 4 - 6inches across. - Or a small telescope. A BPW34 Pin photodiode followed by a low pass filter to remove the 20kHz. What comes out is audio. - That can be fed to a computer soundcard.

73

David