Primary objectives: Evaluate effects of prolonged space flight. Demonstrate and evaluate performance of spacecraft and systems in 4-day flight. Evaluate procedures for crew rest and work cycles, eating schedules, and real-time flight planning. Secondary objectives: Demonstrate and evaluate EVA and control by use of HHMU and tether. Station-keep and rendezvous with second stage of GLV. Evaluate spacecraft systems. Make in-and-out-of plane manoeuvres. Further test OAMS retro backup capability. Perform 11 experiments.

At 10:16 a.m., Thursday, 3 June 1965, millions of people throughout the world looked and listened while Gemini IV lunged spaceward. The Gemini IV spacecraft had no name, official or otherwise (such as "Molly Brown" for Gemini 3), nor did its pilots wear a distinctive patch on their suits, as did all later Gemini crews. A few of the newsmen called the ship "Little Eva," to symbolize the extravehicular activity. Television coverage of the launch for the first time had an international audience, as the scene was broadcast to 12 European nations via the Early Bird satellite. Heightened by the prospect of EVA and the first use of the new Mission Control Centre in Houston, interest in Gemini IV reached levels never again matched in the program.

In the spacecraft, James McDivitt and Ed White had no doubts about lift-off, as they felt their vehicle pick up speed. There was very little noise. The hush was broken only when the launch vehicle bounced like a pogo stick for a few seconds. Then everything smoothed into near silence again. Pyrotechnic shattered the illusion of quiet at stage 1 and, later, at stage 2 separation. The spacecraft entered an elliptical orbit of 163 kilometres at the low point (perigee) and 282 kilometres at the high point (apogee).

The plan to fly in formation with the spent Titan 2 second stage was a real learning experience in orbital dynamics. The manoeuvring toward another object in orbit proved to be far different from what flight engineers expected. To catch something in Earth's atmosphere, one simply moves as quickly as possible in a straight line to the place where the object will be at the right time. Gemini IV showed, that will not work in orbit.

When the astronauts tried to fly toward the target, the craft got farther and farther away. Adding speed also raises altitude, moving the spacecraft into a higher orbit than its target. The paradoxical result is that the faster moving spacecraft has actually slowed relative to the target, since its orbital period, which is a direct function of its distance from the center of gravity, has also increased. They discovered that, to catch up with an object ahead of you, you must drop down, and then rise back up after you catch up, rather than speed up, because speeding up puts you into a higher, and therefore slower, orbit.

As a result, the crew, like everyone else at MSC, got a whole lot smarter and really perfected rendezvous manoeuvres, which Apollo had to use. Gemini IV's problem was compounded by its limited fuel supply; the Spacecraft 4 tanks were only half the size of later models, and the fuel had to be conserved for the fail-safe manoeuvres. For this flight, they had to give up the effort after burning half their fuel.

Over the Indian Ocean, White was ready for America's first EVA - hoses hooked up, umbilical ready, zip gun in hand, and chest-pack in place - and they again rested and chatted. Nearing Carnarvon, Australia, they began to depressurize the cabin. Then a mechanical problem arose - the door would not unlatch because a spring had failed to compress. After much yanking and poking around the hatch ratchet, the door suddenly cracked open. White found the hatch as hard to push up in zero g as it had been on the ground.

White rose slowly through the hatch and installed a camera to record his movements as he swam in space, with the zip gun, tethered to his right arm. floating freely by his side. White triggered a burst from the gun, rose above the hatch, and, without imparting any motion to the spacecraft, propelled himself away. He saw the thrusters firing, expelling plumes of flaming as, as McDivitt steadied the spacecraft. White propelled himself away from the danger - across the top of the spacecraft and out beyond its nose.

While he was floating freely, White had paid no attention to the time; and, since they were on the internal spacecraft communications link, Flight Control could not break in on them. Radio listeners had a chance to hear an American human satellite broadcast his views of the spectacle of Earth. White told McDivitt and the world how beautiful it all was, of the pictures he was taking, and how well he was feeling - no vertigo or disorientation whatever.

Finally, after 15 minutes 40 seconds, McDivitt broke off to ask the ground if they wanted anything. "Yes," Kraft chuckled, "Tell him to get back in." And when McDivitt had to tell White it was time to come back inside, Mission Control and the whole world heard him sigh, "It's the saddest moment of my life."

McDivitt heard boots thumping atop the spacecraft and White came back to the hatch as Gemini IV was passing over the Atlantic. White closed the hatch and reached for the handle to lock it. When it failed to catch, he knew it was going to be as hard to close as it had been to open. Pushing on the handle lifted White out of his seat, so McDivitt pulled on him to give him some leverage. Finally White felt a little torque in the handle and yelled for McDivitt to yank harder. The door was latched.

While White relaxed, McDivitt began powering down some of the spacecraft systems to save electrical power and control fuel, intending to drift for the next two and a half days. Seven and a half hours after lift-off, White went to sleep. He and McDivitt had intended to sleep alternate periods of four hours each, but this was hard to do. The constant crackle of radioed information and orders and the occasional automatic thruster firings kept them awake. Whoever was on duty frequently bumped the sleeper in this uncommonly small bedroom.

The crew used the bungee exerciser more than had been planned, but White later said that his desire to do strenuous work dwindled during the flight; although, as McDivitt suggested, this might have been caused by lack of sleep. Both agreed that a systematic exercise program would be needed for long missions. The bone demineralization experiment did show a greater mass loss in the small finger and heel than that experienced by Earthbound, bed-rested patients. To this day, bone demineralization is a matter of concern that has yet to be resolved.

After 48 revolutions, covering 75 hours of flight, the spacecraft computer was updated during a stateside pass. Told to turn the computer off, McDivitt flipped the switch and discovered that he could not. On the ground, efforts to solve the problem began at once. For the next few revolutions, the crew received instructions for trying different switch positions, but the computer finally quit entirely. Now they would have to resort to a rolling Mercury-type re-entry, rather than the lifting bank angle the computer was supposed to help them achieve.

In revolution 62, at 97 hours 28 minutes, they fired their manoeuvring thrusters in the proper retro-attitude for 2 minutes 41 seconds. Afterward they jettisoned the equipment adapter. Bang! bang! bang! bang! went the retrorockets. Gemini IV was returning to Earth. Without the computer, McDivitt and White suspected, they would land short of the planned Atlantic landing point. The spacecraft was getting some lift, but they were sure it would not be enough.

At 27,000 meters, McDivitt slowed the roll rate and stopped it completely at 12,000 meters. Shortly, he punched out the drogue parachute. When it deployed, the spacecraft gyrated instead of stabilizing. At 3,230 meters, the main parachute deployed and unfurled with a comforting shock. The splashdown - at 97 hours 56 minutes 12 seconds after launch - was rough, slamming them against the water. But they were down and safe.

Gemini IV missed its mark by 80 kilometres; but several of the recovery ships had begun moving toward its landing site, and one helicopter crew watched the spacecraft descend to the ocean. Within a few minutes, swimmers jumped into the water and attached a flotation collar. Then the pilots were hoisted into the helicopter. Fifty-seven minutes after touchdown, the crew stepped onto a triumphal red carpet on the deck of the aircraft carrier Wasp to be greeted by the ship's crew.