thank for the feedback, BHS. and Lives does't quite fit, i agree. initially, i didn't have the level Star system (or more than 3 planets per level) so Lives became a leftover of the initial "complete 15 levels with 3 lives" notion.
Since adding the level Stars, Lives just means you don't have to return to the menu and click a level to continue play. i've also found myself skimming through levels just to unlock the next and then going back to achieve whatever Stars i hadn't in the first run through.
and i am considering keeping track of "Perfection". ie, all 15 levels in a row, no lives lost and no wasted clicks.
i know i want to make more levels (adding more planets) so, perhaps, "Perfection" = Unlock the next 15 levels?
thanks again, and thanks for playing :)