space as sterilizer
jsut being in space for however many years does a pretty good job of streilizing stuff. imagine, no oxgyn, nogravity, freezing temeperatures. anything that was on the ship is pretty well gone.
however, if we sent humans...humans can not be sterilized, and the spaceship itself would be insulated agaisnt the effects of space as to make it unsteralizable throguh those means.