From NASA:

“Every year at this time, we take a moment to reflect as the NASA Family on the very broad shoulders on which we stand: the shoulders of those women and men of NASA who gave their lives so that we could continue to reach for new heights for the benefit of all humankind.”

Exploration on a frontier is risky business, worth appreciating, when that line is pushed further by brave people, so the rest of us can follow in their footsteps.