Shielding adds significant weight, which isn't good for space-bound components.
I would guess they just use RAID, do round-trip data verification before writes succeed, and then reinitialize and scrub any storage module behaving improperly.
For bits stored on SSDs which already rely on error correction, if they were willing to make custom hardware rather than use something off-the-shelf, they could add more chips and scale up the error correcting code to deal with more errors.
