Substitution Cipher Puzzle

These words were spoken by American astronaut Neil Armstrong on July 20, 1969, as he became the first human to set foot on the Moon during the Apollo 11 mission. Armstrong had intended to say "one small step for a man," and the missing article has been the subject of debate for decades, with some audio analyses suggesting it was spoken but lost in transmission.

The moment was watched by an estimated 600 million people worldwide, making it one of the most witnessed events in human history. The Apollo 11 mission represented the culmination of the Space Race between the United States and the Soviet Union, and Armstrong's words captured the magnitude of human achievement in exploring beyond our own planet.