I believe the biggest issue is that ISS is not built to withstand the higher radiation you are exposed to in higher orbits / between planets. Also the thermal l

I believe the biggest issue is that ISS is not built to withstand the higher radiation you are exposed to in higher orbits / between planets. Also the thermal loads are different when you are in sun 24/7/365 rather than orbiting the earth and spending a significant portion of time in a shadow - though I don't know if that is better or worse.