Answer: NASA Engineers

During the 1960s, NASA’s public affairs official for Project Mercury, Lt. Col. John Powers, was fond of using the term A-OK when debriefing the press and public on various missions and the state of affairs in the space program.

At the time, Powers was the first person to use the phrase in a public capacity, but he wasn’t the one who invented it. The first documented use of A-OK was in a memo (in penciled notes on the countdown) from Tecwyn Roberts (a flight dynamics officer) to the flight director of MR-2 (Mercury-Redstone 2).

NASA engineers (where Powers borrowed the phrase from) added the A in the front of the traditional English term OK during transmission tests because the sharp sound of the A cut through radio static better than the softer O sound of the plain term OK.