Back then, people were excited and happy, too. (You can hear people clapping and cheering in the background of some of those launch videos.) But they were also practiced professionals who knew how to keep their emotions in check and control their voice because a national audience was counting on them to describe and explain what was happening. Even the network anchors could be counted on, most of the time, to be sober and measured when reporting important events.
Todays announcers sound like gibbering lunatics by comparison.