Kerbal Space Program has added the new Contract system into the game, as well as updating the client to 64-bit. Both are larg steps for the game and should help with fun and stability.

With the contract system you will have to be careful on how expensive your rocket is, how much fuel you use, and how much of your ship you are able to recover at the end of the mission. Contracts introduce funds into the game as well as a reputation system, so if you loose a lot of Kerbals, you could loose a lot of rep. Some contracts have deadlines, so watch out for those.

If you don't want to use the Contract system, there is a option to continue with the old system without contracts when creating a new game.

The client has also been updated to 64-bit. This means running plugins and mods should run with better stability, and overall performance should improve since the client is not as limited in its memory usage.

This update brings some changes to the UI, new rocket parts, updated parts, and updates to the Tech Tree as well.

Have fun!