[cynest]

Solar with a battery is probably the best for long durations. I imagine gyroscopes might be useful for stabilization. Radiation hardening is fairly simple; most things requiring the shielding can be shielded, with cables connecting them to antennas. To me the biggest issue would be preventing government/RIAA (or equivalent by country) from crippling it electronically from the ground. The server would have to be maintained from the ground, so any malfunction or bug would be the deadliest threat.