NASA is holding its annual Day of Remembrance today to honor the crew members of Apollo 1 and space shuttles Challenger and Columbia, as well as other NASA employees who have lost their lives while advancing space exploration.

This year marks the 15th anniversary of Columbia’s last space shuttle mission, which suffered a catastrophic and fatal end. The unfortunate event shook the science community and the public, but the lessons taken away from the incident overhauled NASA’s approach to s