This week, NASA is celebrating the 50th anniversary of Apollo 11, the first crewed mission to the moon. However, as its name implies, the Apollo 11 mission was just one small part of various missions to send humans to the moon.

The United States Apollo program began in the mid-1960s, shortly after President John F. Kennedy’s call to send a man to the moon in 1961, with the intent of sending a crew to orbit the Earth in February 1967. However, the mission never made it off the ground due to a tragedy during a launch rehearsal test.

READ MORE: A brief history of NASA's Apollo program

On Jan. 27, 1967, all three crew members taking part in a launch rehearsal test at Cape Kennedy Air Force Station Launch Complex 34 in Cape Canaveral, Fla. were killed in a cabin fire that destroyed the command module. Command Pilot Virgil I. “Gus” Grissom, Senior Pilot Edward H. White III and Pilot Roger B. Chaffee, who were all intended for the orbital mission, died in the fire.

Reports by a NASA accident review board and the U.S. Congress deemed the accident an electrical fire which spread rapidly due to the high pressure and oxygen in the cabin, as well as highly combustible materials in the cabin. The men could not escape via the door hatch because of the high pressure in the cabin. Reports also deemed “inadequate emergency preparedness” as a partial cause of the astronauts’ deaths — since the launch rehearsal was not considered a dangerous mission, the report cited a lack of emergency equipment and emergency teams onsite as a partial reason the accident became fatal.

QUIZ: Test your Apollo 11 knowledge

After the January 1967 tragedy, it would take more than a year and a half for NASA to send another crewed mission into space. Though there was some inconsistency in naming the Apollo missions, the first crewed Apollo mission into space was Apollo 7 in October 1968. The mission to the moon was finally successful in July 1969, when Neil Armstrong, Michael Collins and Edwin “Buzz” Aldrin landed on the surface of the moon.

How to experience the Apollo 11 mission as it happened, no time or space travel required