The so-called Day of Remembrance always the last Thursday of January has special meaning this year. Friday marks the 25th anniversary of the shuttle Challenger launch disaster.
Flags flew at half-staff at NASA centers nationwide. In addition, NASA officials laid wreathes at various memorials to honor the dead, including at the Kennedy Space Center Visitor Complex.
NASA's three space-related fatalities occurred within days of one another but years apart. Three astronauts were killed in the Apollo 1 launch pad fire on Jan. 27, 1967. Seven more died aboard Challenger on Jan. 28, 1986. And the seven-member crew of Columbia perished during re-entry on Feb. 1, 2003.
"The legacy of those who have perished is present every day in our work and inspires generations of new space explorers," NASA Administrator Charles Bolden said in a statement. "Every day, with each new challenge we overcome and every discovery we make, we honor these remarkable men and women."
Bolden took part in wreath-laying ceremonies at Arlington National Cemetery in Virginia.