Once the Gemini's hatches were closed and locked just before launch, the busy throng that readied the spacecraft for orbit diminished dramatically--to two men and a machine that smelled slightly of plastic, sitting on top of a 150-ton intercontinental ballistic missile.
Recalling the launcher that powered all 10 manned Gemini spacecraft into orbit, two-time Gemini astronaut Pete Conrad says: "The thing about the Titan that I remember was somewhere in the count, like at T-minus-30 seconds, they open the oxidizer pre-valves. The oxidizer was all the way up in the tank, and that line runs all the way down through the fuel tank down to the base. So when they opened that thing up, you are sitting on top of this thing--you are not that far away--and you can hear it going glah-glah-glah-glah.
"The Saturn V was a great big hulk, you know," he says of the enormous launcher behind the Apollo moon missions, "and the engines are 365 feet away and you don't hear a lot of things happening. But the Titan wasn't that big. You can even feel it sway a little bit in the wind. I'll always remember that oxidizer pre-valve at 30 seconds. When you heard that you knew they were serious about sending you somewhere."
At the time it was chosen for Gemini duty, the Titan II was the most powerful rocket in America's inventory. An improved version of the Air Force's Titan I, it first flew successfully in March 1962. Unlike Project Mercury's Redstones and Atlases, as well as the later Saturn Vs, the Titan used room-temperature propellants called hypergolics, which ignite on contact. At T-minus-0, an electrical signal set things in motion by igniting two small cartridges in the Titan's two first-stage Aerojet engines. The gas from the cartridges started the Titan's turbopumps spinning, which in turn forced both fuel and oxidizer into the engine's combustion chambers. When combined, the hypergolics emitted only a relatively small white flame and a rosy cloud rather than the burst of orange flame and billowing smoke of Mercury and Apollo launches. Four seconds later, if all systems remained go, the bolts that anchored the Titan to the launch pad exploded and the Titan was on its way.
"A light came on in the spacecraft saying we had liftoff," Schirra says. "I heard from the blockhouse that the clock had started, which means we had lifted off. But I knew we had not lifted off. It was a gut feeling. Stafford didn't know what was going on but I had the experience of a Mercury flight and my butt told me we hadn't left the pad."
Schirra's butt was right. A small electrical connector had vibrated loose a split-second before launch, sending a spurious shutdown signal to the Titan's first-stage engines. Had the Titan actually left the pad before engine cutoff, the missile would have toppled over, engulfing Schirra and Stafford in flames. If so, their only chance at survival would have been the Gemini's untried ejection seats.
Recalling the final Gemini mission, Gemini 12, Buzz Aldrin says, "There was no doubt in Jim Lovell's and my mind when we lifted off. Our bodies knew it. We could feel the acceleration straight off. The Saturn V was different. It had a much lower thrust-to-weight ratio and it didn't accelerate as well. When we came back from Apollo  and debriefed, we all agreed that we couldn't identify liftoff except for the instruments and the audio transmissions. But on Gemini we knew."
"Saturn V is an old man's ride," says Dick Gordon, who flew on both Gemini and Apollo missions. "There is a lot more shake-rattle-and-roll going on with the Saturn V because it is so much longer. And it's got three stages and is more flexible in its longitudinal axis. As opposed to the two [stages] on the Titan--which was a young fighter pilot's ride. It's faster. It's dynamic. The forces involved are greater."
Both Schirra and Gemini 5 astronaut Gordon Cooper agreed it was a smoother ride than the liftoff on their previous Mercury flights, which had been launched by Atlas rockets. "The Titan had a thicker skin than the Atlas," Cooper says. "The Atlas was literally a gas bag. Its skin was so thin it had to be pressurized to hold its shape. I remember going up the gantry for my Mercury flight and seeing the skin of the [Atlas] flexing. When you take that flexible skin and you launch it you get more oscillations, kind of like being on the end of a Slinky."
What sticks out in Frank Borman's mind about his ride aboard the Titan that launched him on Gemini 7 was the sound. "The Gemini simulators we trained on were extremely realistic and prepared us for all the sensations of liftoff--except the noise," he says. "Even in our insulated cabin, over 100 feet away from the engines, the sound was almost deafening. It started right off the bat at liftoff and sounded like a large jet in afterburner or a large freight train bearing down on you."
Two and a half minutes after launch, the Gemini-Titan stack was 50 miles high, traveling 6,700 mph, and, with its two first-stage engines gulping 1,600 pounds of propellant every second, had already shed over three-quarters of its launch weight. The crew members were being pressed into their ejection seats by nearly six times the force of gravity when suddenly the acceleration dropped off.
"Staging is really something," says John Young, who flew on Gemini 3 and 10. "It's called "fire in the hole' because you fire the second-stage engine before you get rid of the first stage. [It] blew out everything and fire came all around the vehicle and you could see it. That was a surprise to me. But it is only momentary, and with the second stage firing you get right out of there."
"That second stage surprised me," Dick Gordon says. "On Apollo, the third stage of the Saturn V got to altitude and then chug-chug-chug at about half a G until it got the right velocity and shut down. Well, on Titan both were done simultan-eously. And near the end, you've got 100,000 pounds of thrust pushing an almost empty stage and a lightweight Gemini spacecraft. It was startling how fast the G-forces built up. I said Man, how long is this sucker gonna keep a-running? I tell you I was ready for the second stage to quit about the time it did. And cutoff was a great transition. I mean, you're going from 7 Gs to zero Gs just like that. Soon as that engine cuts you are thrown up against the straps just like on a carrier landing."
At SECO, or Second Stage Cut Off, the Gemini was 100 miles high and 531 miles downrange. Twenty seconds and 90 miles later, the command pilot reached a now-weightless hand toward the left side of the center panel and pressed a button marked SEP SPCFT. In an instant, mini-guillotines fired, severing electrical connections between the Gemini and its booster, while two rings of a flexible charge encircling the base of Gemini's white adapter section detonated, literally ripping the two machines apart.
"I was getting my first view of space," Gordon recalls. "I said, "Holy shit! We just blew up!' Pieces and parts of all the explosive stuff, washers and bolts, were floating in a cloud all around us. It wasn't anything that could puncture the Gemini but it was fascinating to watch all the junk that came out. Pete [Conrad] sees it too, sees me seeing it, and says, "Get to work, Dick.' We didn't have time to look around. We had to go right into our onboard calculations."