Safety... this is a BIG concern. I would not want to kill any Kerbals, so I have to prepare for my biggest plan: to go to Duna and Ike and return Kerbals back home safely. That's a lot of hard work, but thanks to the probes, I can run experiments without even the needs to kill Kerbals. Now... I did end flight before death for another reason... I think you should watch this video to see why. (I really hate killing Kerbals, so I went persistent editiing to get everyone's ToD value back to 0, and that's behind-the-scene. However the first two attempts are shown and I never did it.)