Superman's defeat could have been prevented

Couldn't Superman have prevented being killed by Doomsday by traveling back in time, rocketing to the planet nearby Krypton and killing Bertron before he began the Doomsday experiments?

Just when was he going to do that? When Doomsday was on the rampage in Metropolis?

Aside from the risks of messing with time and all the reprecusssions, Superman is virtually never in favour of killing someone as a solution, especially to benefit himself.

It will happen again in one of the sequels and I like it...Doomsday=Cool...part 6 hopefully.