When space enthusiasts think of the Gemini 4 mission, they automatically remember the historic first American spacewalk by Edward White. While an important achievement, this feat was only a secondary objective of this early mission. Actually, the primary objective of the Gemini 4 mission was for astronauts Jim McDivitt and Ed White to make NASA’s first “long duration” spaceflight lasting four days. In this day when six-month missions to the International Space Station are routine, four days might not seem like much but a half a century ago this was pushing the limits of space medicine and was a necessary step towards the ultimate goal of reaching the Moon.

The Origins of Gemini

The purpose of the Gemini program was to develop the technologies and techniques needed to fulfill President Kennedy’s goal of landing a man on the Moon by 1970. The major objectives of the program were:

– Demonstrate that humans and their equipment can survive up to two weeks in space

– Demonstrate rendezvous and docking techniques in orbit

– Demonstrate the technology and techniques needed to perform EVAs (Extra-Vehicular Activities)

Meeting all of these objectives was necessary if the Apollo lunar program were to be successful.

Gemini was a two-man spacecraft that was roughly conical in shape with a base diameter of 3.3 meters which stood 5.8 meters tall. Built by the McDonnell Aircraft Corporation (which merged with Douglas in 1967 to become McDonnell Douglas which then merged with Boeing 30 years later), it consisted of two major sections. The first section was the reentry module which housed the crew, their equipment, food supplies and so on in orbit as well as the recovery systems needed to safely return them to Earth. Unlike today’s crewed spacecraft, the Gemini crew cabin was pressurized with pure oxygen at about one-third standard atmospheric pressure to save weight. The next section, the adapter section, connected the reentry module to the launch vehicle during ascent. It consisted of a retrograde section which held a set of four solid retrorockets used to start the descent to Earth from orbit and an equipment section which housed the in-orbit propulsion systems, life support, power systems and all other equipment not needed for the return to Earth.

With a typical launch mass of 3,700 kilograms, Gemini needed the largest operational rocket available at the time to get into orbit: a modified Titan II ICBM built by Martin Marietta (which subsequently merged with Lockheed in 1995 to form the aerospace giant, Lockheed Martin). With the Gemini payload attached, the Titan II GLV (Gemini Launch Vehicle) was 33 meters tall and had a fully fueled launch mass of about 154 metric tons.

The Titan GLV was flight tested for the first time on the unmanned Gemini 1 mission launched on April 8, 1964. Since many of the key spacecraft systems were still not ready at this time, the other objectives for this mission were simply to get into orbit to verify Gemini’s structural integrity and provide three orbits’ worth of information on spacecraft performance while remaining attached to the spent second stage of the launch vehicle. No recovery of Gemini 1 was planned or attempted (see “The Launch of Gemini 1”).

The second test flight of the program, Gemini 2, was launched on January 19, 1965. This final unmanned mission successfully tested Gemini’s key systems during an 18-minute ballistic flight which ended with the splashdown of the reentry module 3,422 kilometers downrange (see “The Launch of Gemini 2”). The first manned test flight, Gemini 3, was launched on March 23, 1965 with Virgil “Gus” Grissom and John Young as the crew. The objectives of the Gemini 3 flight were relatively modest: perform a short 4½-hour long mission to verify the performance of the Gemini spacecraft and Earth-based assets in preparation for the more ambitious missions to follow (see “The Mission of Gemini 3”).

Gemini 4 Mission Objectives

With the successful completion of the Gemini 3 mission, NASA was ready to start steadily pushing up the learning curve needed to reach the Moon. The primary objectives for the Gemini 4 mission centered on demonstrating and evaluating the performance of the spacecraft and crew for long duration missions. Originally it was hoped that this would be a week-long mission but there were those who were concerned with flying a mission this long so soon. NASA’s longest manned spaceflight, the Mercury program’s Faith 7 mission, was only 34 hours long and there was little detailed biomedical data available on the Soviet Union’s Vostok missions which lasted as long as five days. There was also the practical matter that the development of the fuel cells needed to power the Gemini spacecraft on longer missions was behind schedule. In the end, Gemini program officials settled on a four-day mission length for Gemini 4 – the maximum mission length practical on battery-power alone. While modest by today’s standards, the flight of Gemini 4 would quadruple NASA’s cumulative number of man-hours in space and be the first step towards meeting the objectives for the Apollo lunar missions.

Secondary objectives for the Gemini 4 mission included further evaluations of the spacecraft’s various systems including the ability to maneuver in orbit. One of the tasks for the Gemini 4 crew upon reaching orbit was to perform station keeping maneuvers with the spent second stage of the Titan II rocket that launched them into orbit. This would be the first small step towards developing rendezvous and docking techniques required for Apollo. Since the propellant load on this mission was just half of that planned for later missions and no radar equipment was being carried, these station keeping maneuvers would be limited in scope and performed by the judgement of the pilot only. Other maneuvers were scheduled at various points of the mission totaling about 24 meters per second to trim the nominal 160-by-290 kilometer orbit and counter the effect of atmospheric drag.

Another secondary objective considered in the planning of this mission as early as January 1964 was to perform a simple standup EVA (Extra-Vehicular Activity). For this exercise, one of the crew members would open the hatch of the depressurized crew cabin and standup to expose himself to space for a short period of time. This would be the first of many steps to learn how to perform useful tasks outside the spacecraft as would be required during Apollo missions.

On July 27, 1964, NASA officially announced the crew for the Gemini 4 mission (over ten months before they would eventually fly). The primary crew for the mission consisted of USAF Major James A. McDivitt as the mission’s command pilot and USAF Major Edward H. White, Jr. as the pilot. The 35-year old McDivitt had a distinguished military career that included 145 combat missions during the Korean War and service as an experimental test pilot. White was 34 years old and, like McDivitt, had extensive experience flying experimental aircraft. Both men had known each other since they attended the University of Michigan together where White got a masters in aeronautical engineering and McDivitt received a bachelors graduating first in his class. Both men had also attended the Air Force Test Pilot School together. The backup crew were USAF Major Frank Borman as command pilot and USN Lt. Commander James A. Lovell as pilot. All four men were part of NASA’s second group of astronauts selected in September 1962 and none had previously flown into space.

As the crews continued their training for the Gemini 4 “long duration” mission, there was much debate behind the scenes about the option for White (or his backup, Lovell) to perform an EVA during the mission. As the needed hardware and procedures were being developed for this secondary mission objective, program plans were eventually overcome by events. While high altitude chamber tests for the Gemini 4 crew to practice a standup EVA were officially approved on March 12, 1965, six days later Soviet cosmonaut Alexei Leonov successfully performed the first “spacewalk”, as the press called it, as part of the day-long Voskhod 2 mission (see “The Launch of Voskhod 2”). Spurred on by the Soviet achievement and the apparent lack of any issues encountered by Leonov, there was renewed pressure to include not just a standup EVA on the Gemini 4 mission, but a full-fledged “spacewalk” where Ed White would completely exit the spacecraft. As preparations and debate for an EVA continued, NASA officials gave themselves to as late as the day before the launch to make a final decision on the matter.

The Start of the Mission

The Titan II for the Gemini 4 mission, designated GLV-4, was shipped from Martin’s Baltimore, Maryland plant to Cape Kennedy, Florida (which officially returned to its original name of Cape Canaveral in 1973) on March 29, 1965. GLV-4 was erected on the pad at Launch Complex 19 (LC-19) on March 29 only six days after the successful launch of Gemini 3. The 3,574-kilogram Spacecraft No. 4 was shipped to the Cape on April 4 and was mated with GLV-4 some 19 days later. A series of tests and rehearsals then followed over the next five weeks. After much debate among officials in the Gemini program and at NASA headquarters, NASA Administrator James Webb himself finally approved the EVA option on May 25 – just nine days before the first launch attempt scheduled for June 3.

McDivitt and White were woken up at 4:10 AM EST on June 3 for brief preflight physicals and breakfast. Afterwards, the astronauts were taken to a pre-flight ready room at Launch Complex 16 which had been used for USAF Titan ICBM test flights until 1963 when it was transferred to NASA to support the Gemini program. At LC-16 McDivitt and White donned their new G4C spacesuits that they would wear for the entire four-day mission. White’s spacesuit included additional layers to protect him from the space environment during his EVA that made his suit a bit warmer and stiffer than the one worn by McDivitt. White’s helmet also included a pair of additional removable visors: a clear visor to protect the primary helmet visor from damage and a gold-tinted sun visor to provide protection from the bright unfiltered sunlight. Both men pre-breathed pure oxygen to purge their systems of nitrogen to prevent the bends when the pressure in their suits was eventually dropped to one-quarter of an atmosphere for the EVA scheduled for the second orbit. Other gear needed for the EVA was already stowed onboard the spacecraft.

McDivitt and White arrived at LC-19 at 7:07 AM where Gemini 4 and its Titan II GLV-4 were being prepared for launch. After a ride up the elevator, the crew climbed into their spacecraft at T-100 minutes. With the hatches secured and all other tasks completed, the erector tower that provide access to the rocket and spacecraft was lowered at T-35 minutes. Unfortunately, a incorrectly installed connector prevented the erector from lowering causing a one hour 16 minutes hold as the problem was corrected.

Finally at 10:15:59 AM EST, Gemini 4 lifted off from LC-19 and towards space. For the first time in history, live television coverage of a manned launch was provided to Europe using the newly commissioned Intelsat I commercial geosynchronous communication satellite. Nicknamed “Early Bird”, this satellite had been launched only two months earlier. Both stages of GLV-4 operated as intended placing Gemini 4 into a 160 by 282 kilometer orbit after the spacecraft had performed its separation burn. For the first time, this manned spaceflight was controlled by the brand new Mission Control Center in Houston, Texas located in what is today called the Johnson Space Center – the same center where American crewed space missions are controlled today.

Once in orbit, McDivitt turned the spacecraft around and began his station keeping exercise with the spent Titan II second stage. Over the course of the next hour, McDivitt attempted to maneuver Gemini 4 closer to the inert Titan stage by pointing the nose of the spacecraft towards the target and firing short bursts of his maneuvering thrusters towards the target. This “eyeball” method of rendezvous only resulted in the distance between the spacecraft and stage increasing over time. In the sometimes counterintuitive world of orbital dynamics, the attempts to close the gap actually resulted in Gemini 4 entering a slightly higher 166 by 290 kilometer orbit where it travelled more slowly relative to its target. Instead of decreasing the distance, the maneuvers only increased it by moving Gemini 4 above and farther behind its target. With 42% of the already limited propellant supply expended and the scheduled EVA approaching, further attempts to rendezvous with the Titan stage were called off. The spent stage would burn up in the atmosphere two days later while Gemini 4 continued on in its mission.

With this first in-orbit task completed, attention now turned towards preparing for White’s EVA. It quickly became apparent that the time allotted to prepare for the EVA was insufficient and McDivitt postponed the EVA from the second to third orbit. Even with the delay, the astronauts still felt rushed and White was getting tired and hot. The crew completed their 54-point pre-EVA checklist with only 15 minutes to spare. McDivitt then depressurized the cabin and White finally opened the spacecraft hatch while passing over Hawaii 4 hours and 18 minutes into the mission. After another 12 minutes, White finally pushed off and exited the spacecraft remaining attached by a gold-wrapped 7.6-meter long umbilical line that supplied him with oxygen and communications.

White remained outside the spacecraft for just 20 minutes as Gemini 4 passed from the Pacific Ocean over the United States. During this time he maneuvered using a Hand Held Maneuvering Unit that used pressurized oxygen as a propellant. While White stated he was able to maneuver easily with the device, he quickly exhausted its limited gas supply and had to rely on tugging on his umbilical line to maneuver. With Gemini 4 approaching orbital sunset, White finally reentered the spacecraft upon the insistence of ground controllers. With some difficulty, White was finally able to close the hatch with the help of McDivitt. Although he was exhausted and the inside of his helmet’s faceplate was becoming fogged, Ed White had completed America’s first EVA. With 36 minutes with the hatch open and 20 minutes actually outside his spacecraft, White now held the EVA duration record beating Leonov’s 12 minutes outside Voskhod 2.

Four Days in Orbit

While Ed White’s EVA captured the most public attention, it was only a secondary objective of the mission. With the EVA completed 4 hours and 54 minutes after launch, literally 95% of the four-day mission still lay ahead of the two astronauts and the ground controllers. Managing a multi-day spaceflight, scheduling activities and responding to changes in real time was new to everyone involved and much was still to be learned on this flight.

In order to conserve fuel and power, the spacecraft was placed into a free drift mode between orbital maneuvers or other tasks requiring a specific spacecraft orientation. McDivitt and White were placed into staggered schedules that allowed one astronaut to rest or sleep while the other performed his assigned tasks. This ensured that there was always an astronaut “on watch” to monitor spacecraft systems and respond if problems cropped up. Unfortunately, in the cramped and sometimes noisy confines of the Gemini crew cabin, it was difficult for the astronauts to get much sleep although White, who was the first scheduled to sleep seven and a half hours after launch, seemed to fare better than McDivitt during the mission.

The astronauts were supplied with a total of 32 meals with four eating periods scheduled during the course of each day. They consisted of ready-to-eat or dehydrated dishes that were prepared for consumption using water injected into their storage bags. A variety of foods and beverages were available to the astronauts including fish dishes for McDivitt who, like other observant Roman Catholics of that time, could not eat meat on Fridays. While there were practical issues with leaky containers, dealing with the buildup of trash and such, the astronauts ate well and noticed a definite increase in energy after each meal.

On the second day of the mission during their 22nd orbit and barely a third of the way through their mission, McDivitt and White were congratulated for exceeding the 34 hour 20 minute American spaceflight record that was set by Gordon Cooper in 1963 during his Mercury-Atlas 9 mission. Between periodic systems checks, dealing with minor malfunctions and orbital maneuvers that raised Gemini’s apogee as high as 296.1 kilometers, McDivitt and White performed a series of experiments during the mission. White periodically used a bungee cord to exercise in orbit. Measurements were also made of the astronauts heart muscle and bone demineralization. Three instruments were carried on the spacecraft exterior monitor static charge, Earth’s magnetic field and the outside radiation environment. Additional sensors throughout the spacecraft monitored radiation exposure of the astronauts and various spacecraft systems.

Navigation experiments using a sextant to measure the position of celestial objects were performed along with two-color photography of the Earth’s limb to assess its future use for navigation. Finally, a pair of photography experiments using a 70mm Hasselblad 500C camera were performed. One centered on obtaining high quality images of the Earth especially of well mapped areas to aid in the interpretation of future space-based photography. A complementary experiment focused on photographing various weather phenomena with better quality than was possible with the first generation TIROS weather satellites (see “The First Weather Satellite”).

During the long mission, the astronauts even had an opportunity to talk with their wives in Mission Control to get updates about news from home. Pat White commented about how wonderful Ed’s spacewalk looked and reminded him to drink his water. Pat McDivitt asked Jim “Are you being good?” to which he replied “Don’t have much choice. All I can do is look out the window.”

The Return Home

By the morning of June 7, 1965, the four-day mission of Gemini 4 was finally winding down and the astronauts prepared for their return. The primary recovery zone was located in the Atlantic Ocean about 640 kilometers south of Bermuda where the Essex-class aircraft carrier, the USS Wasp, was stationed. During a computer update the day before the scheduled return, it was discovered that the computer was not operating properly. Efforts by ground controllers and McDivitt to diagnose and fix the problem were ultimately unsuccessful. While the nature of the problem did not require an early end of the mission, it meant that the computer was not going to be available to navigate the reentry module during the return to Earth. As a result, Gemini 4 would be forced to fly a more punishing 8-g ballistic reentry manually with the spacecraft rolling during descent to cancel out its lift.

At a mission elapsed time of 97 hours and 28 minutes, Jim McDivitt turned Gemini 4 to fly tail first and fired the equipment section’s maneuvering thrusters for 2 minutes and 41 seconds. This “fail safe” maneuver dropped the perigee of Gemini 4 down from 159 to 77 kilometers ensuring that the spacecraft would come down even if the retrorockets failed to fire. After the equipment section was jettisoned, the four solid retrorocket motors fired in succession as planned. After the retrograde section was cut loose, McDivitt set the spacecraft rolling at an altitude of 120 kilometers. After the worse of the reentry was over, McDivitt started slowing the roll at 27 kilometers and stopped it completely at 12 kilometers altitude followed by the drogue chute deployment. The main chute deployed at 3,230 meters and, learning from the experience of Grissom and Young during Gemini 3, the astronauts braced themselves for the transition to a two-point suspension. Fortunately, the astronauts’ helmets did not hit anything during the jarring transition.

Gemini 4 finally splashed down at 12:12:12 PM EST on June 7, 1965 about 81 kilometers from the aim point owing to the lack of computer guidance. The flight lasted a total of 97 hours, 56 minutes and 12 seconds – a new American record that was still just over 21 hours shy of the world record set in 1963 by Soviet cosmonaut Valery Bykovsky during the Vostok 5 mission. Although Gemini 4 had come down short of the landing zone, its descent was observed by one of the helicopters deployed for the recovery. Divers were in the water a few minutes after splashdown and were able to secure the capsule. McDivitt opted for a helicopter pickup and the two astronauts were on the deck of the USS Wasp 57 minutes after splashdown.

Subsequent medical exams showed that Jim McDivitt and Ed White had come through their four-day mission in excellent condition and without any major problems. With the successful completion of this first step, the way was now clear to attempt a second long duration mission this time for eight days – the absolute minimum flight length required for an Apollo lunar landing. This next mission, Gemini 5, would fly in just two and a half months bringing America one step closer to the Moon (see “Eight Days or Bust: The Mission of Gemini 5“).

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Related Video

Here is a classic NASA documentary on the mission of Gemini 4 entitled The Four Days of Gemini 4:

Related Reading

“The Launch of Voskhod 2”, Drew Ex Machina, March 18, 2015 [Post]

“The Mission of Gemini 3”, Drew Ex Machina, March 23, 2015 [Post]

“The Launch of Gemini 2”, Drew Ex Machina, January 19, 2015 [Post]

“The Launch of Gemini 1”, Drew Ex Machina, April 8, 2014 [Post]

General References

David Baker, The History of Manned Space Flight, Crown Publishers, 1981

Barton C. Hacker and James M. Grimwood, On the Shoulders of Titans: A History of Project Gemini, SP-4203, NASA History Division, 1977

David J. Shayler, Gemini: Steps to the Moon, Springer-Praxis, 2001

Steve Whitefield (ed.), Gemini 4: The NASA Mission Reports, Apogee Books, 2011