It amazes me that they didn't take this into consideration. It's not like windshield wipers are high-tech, they could have provided for this. The "dust" storms on Mars aren't even dust, they're fines (micron size or smaller particles). They ought to have known that with even a mild static charge, they'd clump up on the machine and stay there. It's not as though we didn't know they have these storms. Damned nerds.