"Ten, nine, eight…."
For almost 25 years now, you've heard that voice, again and again, softly counting down as another space shuttle stood on the launch pad.
"…seven, six, we have a go for main engine start…."
If you're like most of us, you've never seen him.
"Three, two, one, booster ignition and liftoff -- liftoff for the shuttle Atlantis…."
His name is George Diller, and the countdown for Atlantis is his last for a shuttle. Millions of people have listened to him for a quarter of a century, but sitting in his office here at Launch Complex 39, he confesses he is uncomfortable in the limelight.
"Yes, the last 10 seconds of the count and the liftoff will go down in the history books, and I will have been that voice that announced that," he said. "But for me, just to be in the firing room with the launch team for that last launch -- it's a wonderful love, it's a wonderful feeling."
Diller, a quiet man with sandy hair and round wire-frame glasses, says he ambled into the space business. He grew up near Sarasota, Fla., became a radio reporter for a station in Tampa, and joined NASA in 1979; they needed more public affairs people at the time for the then-newfangled space shuttle.
At launch time he becomes, in effect, a play-by-play announcer for a very high-stakes, high-altitude game. What he says is partly scripted and partly from memory after all these years, but he also needs to be on alert. If something goes wrong he needs to explain it. An unlucky predecessor of his in Houston, describing the ascent of the space shuttle Challenger, kept reading its speed and altitude seconds after it had exploded; he was looking down at his notes instead of up at a television monitor.
"When the main engines light, there's definitely a shot of adrenaline that you can feel. But your mind doesn't wander because you're very intently focused," Diller said.
He's had his share of surprises: engines have shut down, countdowns have been interrupted and restarted at the last minute, and he's had to keep up with it all. On April 29 there was an awkward moment as a launch attempt for the shuttle Endeavour was scrubbed – while the astronauts were on their way to the launch pad. The world was watching, partly because Rep. Gabrielle Giffords' husband, Mark Kelly, was commander; and because President Obama was en route to Florida to watch the launch. Instead they heard Diller calling the whole thing off.
"The only thing certain right now is that we are uncertain," he said as one flight scrubbed.
He says he tries to stay in the background – this is not about him, it's about the shuttle program – and he has shared the countdown duties with younger colleagues. But he has probably done more of them than anyone in history. And he does, by tradition, squeeze in one last "liftoff line" as the shuttle lifts off and control is handed off to the Johnson Space Center in Houston. When Endeavour eventually flew in May, he had pre-written this:
"Three, two, one, booster ignition and liftoff -- liftoff for the final launch of Endeavour, expanding our knowledge, expanding our lives in space."
Does anyone tell him what to say? No, he insists. How does he decide? With difficulty, he says.
"I have to give it some thought, and I struggle with it, and sometimes I maybe get half the line but I don't know how to finish it, and sometimes I'll write the line and sleep on it and come back – and I don't like it.
"Mostly, they come to me when I'm not thinking really hard about it. My lines come to me when I'm in the shower, or thoughts when I'm shaving."
The end of the shuttle era is bittersweet for NASA. Diller said he believes the country will remember the shuttles fondly.
ABC News' Gina Sunseri contributed to this report.