A bit of feedback regarding this script and my successes and failures with it...
My universe has had a lot of exploration done to it by the 20 or so explorers I have hired over the last five days. Most sectors (except Yaki/Xenon/Pirate) are mapped. Many of the resources in common sectors (asteroids) have been surveyed. For the 2-4 mil I spent hiring their ships, it was probably worth the time.
However (you knew this was coming..), out of those 20 explorers, only two remain alive, and they are new hires. All of the others decided to explore either in dangerous sectors (Terran in my game) or were killed OOS by one hostile ship or another. That doesn't bode well for their survival, and at best makes them a short term investment. At the rate they died, a leveling system means almost nothing at all. And at the rate they die, I probably won't hire any more.
I see their longevity as a big issue, expecially for games with the Terran sectors and their invisible race rep (doesn't show up readily). You might want to consider other options for them, like allowing them to install jumpdrives in their ships and use them to escape. If they currently do, the implementation of it is poor, as most die.
For comparison, using the EST trader script, I have had exactly 1 EST (UT) die in the last six days, and there were 20+ running all the time. That means they have exceptional longevity. I would really like to see explorers with the same level of respect for life that ESTs have.
Other than that, a good script. Unfortunately it is probably time for me to uninstall it, as nearly all my explorers are dead, and there is no leveling up explorers if they can't "find" anything. That means even fixes to their longevity won't make them useful to my game in the future. Sad but true.
Cheers.