>How much more would it have cost them to use a 5 MP one?
Well they'd need to design it, get it built and delivered in time for the whole SLEW of tests that something going into space has to pass. If it failed any one of those since it would have had to be redesigned (and all within the same size/weight as the original chip because other components would have been build around it) then repeat.
Or...you know, they could use a chip they are completely familiar with, that has been tested and used in similar applications and is completely fine for the mission.
Well they'd need to design it, get it built and delivered in time for the whole SLEW of tests that something going into space has to pass. If it failed any one of those since it would have had to be redesigned (and all within the same size/weight as the original chip because other components would have been build around it) then repeat.
Or...you know, they could use a chip they are completely familiar with, that has been tested and used in similar applications and is completely fine for the mission.