In the briefing room scene near the end of the first act of “Assignment Earth,” Spock says: "There will be an important assassination today, an equally dangerous government coup in Asia, and, this could be highly critical, the launching of an orbital nuclear warhead platform by the United States, countering a similar launch by other powers."
"Assignment Earth" was first aired on March 29, 1968. Six days later, Martin Luther King, Jr was assassinated by James Earl Ray. On that same day (April 4, 1968), NASA launched the unmanned Apollo 6 rocket, which suffered a serious mishap in flight and flew wildly off-course, just like the Saturn V featured in the episode.
