It's been ages since I've seen it, so I don't know if he explained why it took so long, but the deleted scene might explain a lot. It didn't look that big, no provisions for a 5-year trip, etc. What if the flight to Krypton took only a few hours but when he ran into trouble and smashed his ship up pretty badly, he had to limp back to Earth?
Also, it looks as if the ship had no radiation shielding at all.
And last but not least: IIRC, the content was made up of Kryptonite. And on Krypton, there was this huge, artificial S-emblem in the crust. What if the Kryptonians, in a fit of hubris, decided to use the terraform crystal to create the shield. Only, it had a side effect, causing the spreading of Kryptonite through the planets crust and core, swelling until the planet popped like a water melon hit by an asteroid. And the same thing would have happened to Earth had Superman not removed the continent?
Michael
