On Jan. 27, 1967, a fire during a test on the launch pad killed three astronauts at the st… . This Tuesday, Jan. 24, 2017 photo provided by NASA shows the Apollo 1 capsule hatch on display in an exhibit at the Kennedy Space Center in Titusville, Fla.

Moonwalkers and dozens of others who took part in NASA’s storied Apollo program paid tribute Thursday to the three astronauts killed in a fire 50 years ago. Gus Grissom, Ed White and Roger Chaffee.

Painted on glass, this artwork represents the Mercury 7 astronauts, NASA’s first class of astronauts: Scott Carpenter, Gordon Cooper, John Glenn, Gus Grissom, Wally Schirra, Alan Shepard, and Deke Slayton.