Uh... that's your first thought, really? You honestly think, out of the combined force of Japan, the US, the US military, and plenty of brilliant engineers across the globe, that that HASN'T crossed their mind?

Try radiation hardening electronics + battery life + hardening optics/sensors + control range + reliability/safety + size of areas involved = a 1,200lb flying robot that probably won't work, or only work for a few minutes, nevermind will probably crash and break open the pressure casing.

...

Godamnit...