Yes, but how common is such self-sacrificing heroism these days? And therein lies the unfathomable sadness that must lie in the hearts of those they leave behind. Such heroes are hard to find (heroism (or what passes for it) today is defined by much flimsier, self-aggrandizing stuff). So those of us who are fortunate enough to have personally known the kind of heroes about which you are speaking can’t help but mourn their passing doubly: once because of the personal loss, and again because there generally are very few who can step in and fill their empty shoes.
Yes, I know there are (and always will be) other astronauts waiting in the wings. But that particular type of courageous, duty-bound, adventurous person is vastly outnumbered (and their proportion is growing smaller by the day) by the type who place no value on such virtues. (And, mark my words, the latter type will be the most vocal in criticism of the mistakes which contributed to today’s tragedy, while really caring very little about the loss of noble human life).