Are you going to rely on a robot like say ... cell phones with battery degradation? Have any laptop computers quit working (outside of the battery)? Refrigerator/freezer/HVAC system go on the fritz? There are also a lot of hazards out there that are hard to program-code and plan for because no one has been over there to see.

A short film I saw years ago and can't remember the name, had a planet that launched millions of tiny almond shaped tiny ships into the universe that landed on far flung planets (and stars and everywhere like seeds do) that if on a habitable planet the ships popped open releasing seeds, bacteria, and fungi to initiate life and kick start terraforming. I remember those being tiny and rocket powered. Similar ships could be like dandelion seeds that float through interstellar space on a solar sail and land indiscriminately, but where conditions are right they flourish and are set up for future colonies.