[Suicide Junkie]

Don't take things too literally.

From what I remember here at work:
- Deadly
- Harsh
- unpleasant
- mild
- good
- optimal

"Optimal" is logically the best possible rating.
All planets can be improved all the way to Optimal.
Climate Control facilities are notoriously slow. If you are not using the level 3 facility, don't expect much. I believe the CC facil works at x% per YEAR, effective each ".0" turn. Deadly = 0%, Optimal = 100%, so a CC3 should take 34 years to turn a hellish, radioactive waste of a planet into an paradise.

Note: You CAN stack these improvement facilities.
By building 5 CC3's you can get your planet jumping up almost a whole rating level each year.


Rather than trying to make all your planets optimal, it may be more efficient to just get a couple optimal, and then use transports to distribute the population to the nastier worlds.