ARLINGTON, Va. (Jan. 31, 2014) -- Fallen astronauts, shuttle commanders and crews were memorialized at multiple sites inside Arlington National Cemetery, Friday, during NASA's day of remembrance.

Crews of the Apollo 1 and Columbia and Challenger space shuttle missions were honored at respective memorials and gravesites, as well as a wreath laying at the Tomb of the Unknowns.

While making remarks at the Challenger and Columbia Memorials at Arlington National Cemetary, or ANC's Section 46, NASA Administrator Charles Bolden called Arlington a "place of hope," while fondly remembering those who gave their lives while attempting to explore space.

"This place is more than just a final resting place for bodies. This is also a place to think about the future," Bolden said in front of the Challenger and Columbia Memorials. "One of the most important things to remember is that the young men and women in the armed forces and members of the NASA family must continue to explore and continue to accept the risks of what we do."

The nearly 100 spectators included family survivors and NASA employees. Present was the widow of Challenger Commander Air Force Lt. Col. Francis Richard "Dick" Scobee, June Scobee Rodgers; Scobee's son, U.S. Air Force Brig. Gen. Richard W. Scobee, daughter Kathie Scobee Fulgham, and the commander's grandchildren.

The final stop of the remembrance was at Section 3 and the gravesites of Apollo 1 astronauts Virgil "Gus" Grissom and Dick Chaffee. Bolden took a moment to speak about the significance of the 1967 mission, which was the opening chapter toward the first manned lunar landing, in July 1969.

"A voyage to the moon without their sacrifices would not have been possible," Bolden said of the Apollo 1 crew. "Our job is to make sure we remain vigilant, and we keep the memory of those we observe today in our hearts."

The third member of the Apollo 1 crew, Edward Higgins White II, is buried at West Point Cemetery, West Point, N.Y.

The Apollo 1 pre-launch training accident occurred Jan. 27, 1967. The space shuttle Challenger exploded 73 seconds after liftoff from central Florida's Kennedy Space Center, Jan. 28, 1986. Space shuttle Columbia disintegrated above Texas and Louisiana, Feb. 1, 2003, while attempting re-entry into the earth's atmosphere.