Hi,

I am thinking along the lines of K.I.S.S - a simple "bent pipe" linear transponder, with as little to go wrong as possible (the bird will be in GTO for a very long time). Power and link budget permitting (eg a 5 GHz / 10 GHz machine), a wideband transponder would permit ranging experiments, high speed data and video modes in addition to CW & SSB...

Can the attitude of a 1U cubesat in GTO be passively stabilised (gravity gradient?) to keep the antennae pointing towards nadir?

Is a microprocessor (or any digital logic) strictly required? simply having the transponder run whenever the arming pin is out (pulled by ejection from the cubesat canister) and the DC volts are high enough, would eliminate the need for a rad-hard processor. As far as I am aware, the RF circuits in a "rock locked" (no PLL) linear transponder are not as prone to SEU induced latchup as digital circuitry.

73 ZL2WRW Ross Whenmouth