[amsat-bb] Linear Transponder on the ISS.

This is such an obvious question that I think there must be a reason it has not been done.  I would like someone to explain why it is not possible or probable.  I am not seeking to start a flame war.

Why can't we put a SSB/CW linear transponder on the ISS?  It could run whenever the ISS FM station is not being used.  It could use the same antennas.  It would seem to be an easy way to put up another linear transponder with a good signal favoring stations without large antennas.  Could this be a way to bring SSB/CW activity to a larger audience.

I would appreciate hearing from anyone that could shed some light on this.  Thanks,

Doug K9DLP