Physical conditioning would prove crucial for Ed White’s survival on the United States’ first spacewalk, as fellow astronaut Gene Cernan would discover on his own excursion a year later. During training, White spent a total of 60 hours in vacuum chambers, rehearsing opening the hatch, pushing himself outside and moving around in a mockup of the space suit that he would wear, all at simulated altitudes of up to 55 km. The suit itself weighed 14 kg, cost over $30,000 to construct and comprised no fewer than 22 layers to provide protection from the intense heat of direct sunlight to the frigid cold of orbital darkness and, Time magazine told its readers, ‘‘as a pressure force to keep White’s body from exploding in the near-vacuum of space’’. Estimates that the suit could be punctured by a high-velocity micrometeorite were placed at about 10,000 to one, although tests blasted it with splinters of plastic fired at speeds of 7.6 km per second – and it held its own. The hand-held manoeuvring unit, which White would position just below his midriff, consisted of two cylinders of compressed oxygen, belted to a handle which also acted as a trigger to send jets of air through a pair of hollow tubes. White would position it as necessary to aim its impulse through his centre of mass in order to make a specific movement.

As the launch drew nearer and information about the forthcoming spacewalk trickled out, some sections of the media expressed scepticism that it had been a long – planned exercise and felt it was a hastily-concocted stunt to catch up with the Russians. Chris Kraft, the lead flight director for Gemini IV, angrily suppressed such talk. “We’re not playing Mickey Mouse with this thing,” he snapped. “We’re trying to carry out flight operations. I don’t think it’s very fair to suggest we’re carrying out a propaganda stunt.’’

In spite of the doubts, the media response to the mission was enormous. All 800 seats in the MSC’s main auditorium proved woefully inadequate for the 1,100 journalists who requested accreditation before the launch and NASA was forced to lease a nearby building at a total cost of $96,165 per year, plus $181,000 for modifications, television monitors and chairs, to handle the overspill. This ‘Gemini News Center’ would track each mission over the next 17 months and provide a base for over a thousand newspaper, magazine, radio and television representatives, as well as five dozen public relations groups from industry.

Twelve hours before liftoff, a Martin team began the lengthy effort to fuel the Titan II, while the backup crew of Frank Borman and Jim Lovell oversaw checks inside the capsule itself – flipping switches to their launch positions, testing communication circuits and handling routine chores for McDivitt and White. The prime crew was duly awakened at 4:10 am on 3 June 1965 and marched crisply through their medical checks, steak-and-eggs breakfast, suited-up and were at the foot of Pad 19 by 7:07 am. Among the procedures put into place in support of White’s EVA – which would necessitate the depressurisation of the entire cabin, thus exposing McDivitt to vacuum, too – was prebreathing pure oxygen to flush nitrogen from their bloodstreams and avoid attacks of the bends.

Once aboard the spacecraft, White’s faceplate fogged, but he quickly cleared the problem by switching on his suit fan. Then, barely half an hour before the scheduled launch, as the erector was being lowered, it stuck at a 12-degree angle from the Titan. A second attempt was made to raise then lower it, but it stuck again. Eventually, engineers discovered an improperly-fitted connector in a junction box, replaced it and the erector lowered. After a 76-minute delay, Gemini IV speared for the heavens at 10:16 am, to the synchronised yells of ‘‘Beautiful!’’ from both McDivitt and White. Despite initial pogo effects, which caused the astronauts to stutter their words over the communications link, the Titan quickly calmed down and gave them a perfect ride to orbit. They would later describe it as exhibiting little noise, but stressed that the near-perfect silence was shattered abruptly when pyrotechnics jettisoned the first stage and the second stage ignited.

Monitoring the ascent and, indeed, the entire mission, were 300 flight controllers, technicians, engineers, physicians, and scientists supervised by Chris Kraft in the new MOCR. In the Real Time Computer Complex, five IBM 7094-11 computers each processed 50,000 bits of telemetry per second from the vehicle. Also watching the launch, thanks to live television coverage from the Intelsat 1 (‘Early Bird’) satellite in geostationary orbit, were citizens of a dozen European nations.

Within minutes, Gemini IV had entered an initial elliptical orbit of 163-282 km and, almost immediately, McDivitt set to work on the first task of the mission: to station-keep with the Titan II’s second stage. It was whilst attempting this manoeuvre that they encountered problems. Firstly, despite having been outfitted with flashing, 2.5 million-candlepower lights, the stage had not been designed as a rendezvous target and when the capsule entered orbital nighttime, it was rendered almost invisible to them. Moreover, it was tumbling and the astronauts were cautious about getting too close. Difficulty in judging distances by eyesight alone complicated matters yet further.

When they first spotted the booster, propellant streaming from its nozzle, McDivitt estimated it to be 120 m from them, whereas White felt it was 70 m away. McDivitt cancelled the motion imparted by the separation manoeuvre and thrusted towards the target, but after two OAMS burns he was surprised to observe that the Titan seemed to move ‘away’ and ‘downward’. A few minutes later, he pitched the spacecraft nose-down and pulsed the thrusters again, with no success. Approaching orbital nighttime by this point, he reported that he could see the flashing lights, but that the gap seemed to have increased, he guessed, to around 600 m. For a while, circumstances improved and McDivitt felt he was gaining on the stage, but with the early streaks of dawn its lights dimmed and vanished from view. At length, realising that he was wasting precious propellant, McDivitt asked Chris Kraft which objective was more important – rendezvous or EVA – and was assured that the latter was the mission’s main task.

Their biggest obstacle of all, as rendezvous expert (and fellow astronaut) Buzz Aldrin would explain after the flight, was a lack of understanding of basic orbital mechanics. ‘‘When they emerged into daylight, the booster was below and ahead of Gemini IV,’’ wrote Tom Stafford, who was following the mission closely in anticipation of his own rendezvous on Gemini VI. ‘‘Jim’s instinctive move was to thrust toward it, as though he were flying formation in a jet airplane. By doing so, of course, he increased the speed – and moved into a higher orbit even further behind the booster. The only way to get even close to the Titan, in these circumstances, would have been to fire thrusters retrograde – against the direction of travel – slowing the Gemini and dropping its orbit.’’ It was an early lesson: adding speed raises altitude, moving a spacecraft into a higher orbit than its target. However, paradoxically, the faster-moving spacecraft actually slows in comparison to the target, since its orbital period – a direct function of its distance from the centre of gravity – also increases. To catch up with a target ahead, future crews would drop into a lower orbit, then rise back up to meet it.

It was an early lesson, admittedly, but not an easy one. ‘‘It’s a hard thing to learn,’’ wrote Deke Slayton, ‘‘since it’s kind of backward from anything you know as a pilot.’’ Added engineer Andre Meyer: ‘‘We just didn’t understand or reason out the orbital mechanics involved. As a result, we all got a whole lot smarter and really perfected rendezvous manoeuvres.’’