With the crew of the International Space Station (ISS) routinely spending six or more months in orbit, it is sometimes forgotten that only a few decades ago the first flights of such length were just being attempted and their effects on the human body were largely unknown. It has taken over a half a century of experience to develop the techniques needed for people to remain healthy and productive in space for months at a time as well as adapt to Earth’s environment after returning.

One of NASA’s earliest “long duration” crewed spaceflights was the mission of Gemini 5 launched on August 21, 1965. The second in a series long duration orbital missions in NASA’s Gemini program, this flight had goal of remaining in orbit for eight days. While very modest by today’s standards, this record-setting spaceflight was just one of the many steps towards NASA’s goal of reaching the Moon as well as developing the means of flying the longer missions common today.

Gemini Program Objectives

The purpose of NASA’s 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. Next is the adapter section which connected the reentry module to the launch vehicle during ascent and housed equipment needed to support the crew while in orbit. 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 called OAMS (Orbital Attitude and Manuvering System), life support, power systems and all other equipment not needed for the return to Earth.

With a typical launch mass of up to about 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). In addition to safety systems added to support crewed flight, the two-stage Titan II required modifications to dampen out longitudinal oscillations known as “pogo”. While not an issue for its role as an ICBM, the pogo effect could become intense enough to cause a problem for a crew. 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.

With the first successful manned test flight of the spacecraft during the brief three-orbit Gemini 3 mission launched on March 23, 1965, NASA was ready to work its way steadily up the learning curve to meet the Gemini program’s objectives (see “The Mission of Gemini 3”). The primary objective of the next flight, Gemini 4 launched on June 3, was to start the step-wise process of increasing the duration of crewed missions by spending four days in orbit (see “The Forgotten Mission of Gemini 4”). A secondary objective was to perform station keeping maneuvers with the spent second stage of its Titan II launch vehicle in preparation of the program’s eventual rendezvous and docking with an Atlas-launched Agena upper stage specially modified to serve as a target vehicle. Although it received the most public attention, an EVA was another secondary objective of this mission. While a simple standup EVA was originally planned for the Gemini 4 mission, a full blown spacewalk with astronaut Ed White completely exiting the spacecraft was performed instead in response to the successful EVA performed during the Soviet Voskhod 2 mission ten weeks earlier (see “The Mission of Voskhod 2”).

The Gemini 5 Mission

The third manned mission of the Gemini program, Gemini 5, would continue pushing the capabilities of the spacecraft and its astronaut crew. In order to meet its primary objectives, Spacecraft Number 5 was the first fully operational Gemini carrying innovative fuel cells required to generate power for longer missions as well as an L-band radar system and a full propellant load to perform an orbital rendezvous. Instead of using an Agena as a target for this mission’s rendezvous exercise, Gemini 5 carried a 34.5-kilogram Rendezvous Evaluation Pod (REP) in its adapter section. Once deployed in orbit, Gemini 5 would practice rendezvousing with the REP which was equipped with a radar transponder and other equipment like an Agena target vehicle which allowed the astronauts to track it out to ranges as great as about 400 kilometers.

Unlike the Gemini 4 mission where these maneuvers were performed only by eye and the intuition of the pilot (unsuccessfully, it should be added, due to the sometimes anti-intuitive nature of orbital mechanics), the Gemini 5 mission would use data from its radar system in conjunction with maneuvers calculated by on-board and ground computers to perform the rendezvous task more accurately. Since the retrorockets on the previous three Gemini flights had operated as intended, the Gemini 5 mission would be the first manned Gemini flight not to use its OAMS to lower its orbit just prior to returning as a “fail safe” measure to guarantee reentry in case of a retrorocket failure. This left significantly more propellant to maneuver in orbit to meet the mission objectives.

During early planning, it was envisioned that one of the Gemini 5 crew would perform an EVA during the mission. Since this goal was accomplished during the Gemini 4 mission and it was felt that a repeat of this feat would be of little additional value, the EVA objective was deleted as development of better equipment for more complex EVAs continued for future missions. Without the need of carrying sufficient consumables to repressurize the Gemini crew cabin after an EVA, mission planners could extend the mission of Gemini 5 from the originally envisioned week in orbit to a full eight days. Twice as long as the Gemini 4 mission, eight days was the minimum mission length required for Apollo to land on the Moon and return to Earth. Secondary objectives included evaluation of the new fuel cells under flight conditions, demonstration of systems to support all phases of orbital rendezvous and a controlled reentry to a predetermined landing point. While in orbit, the two astronauts would conduct 17 experiments to meet various scientific, medical and defense-related objectives.

On February 8, 1965, NASA officially announced the crew assignments for the Gemini 5 mission. The primary crew consisted of USAF Capt. L. Gordon Cooper as the command pilot and USN Lt. Charles “Pete” Conrad, Jr. as the pilot. The 38-year old Cooper, known as “Gordo” to his colleagues, had a distinguished military career flying jet fighters and as a test pilot before being selected as a member of the original “Mercury 7” astronaut team in 1959 (see “Project Mercury: Choosing the Astronauts & Their Machine“). He was a veteran of the Faith 7 Mercury flight where he spent over 34 hours in orbit in that program’s finale in May 1963. The Gemini 5 mission would make Cooper the first human to fly into orbit twice. Pete Conrad was 35 years old and had been a Navy test pilot before being selected as part of NASA’s second group of astronauts in 1962. This would be his first spaceflight. The backup crew for the Gemini 5 mission was Neil A. Armstrong and Elliot M. See. Both men were civilian pilots who were part of the second group of NASA astronauts and neither had ever flown into space before.

Getting the Mission Off the Ground

The Titan II launch vehicle for the Gemini 5 mission, serial number 62-12560 designated GLV-5, arrived at Cape Kennedy from Martin’s Baltimore, Maryland plant on May 18, 1965. It was erected at Launch Complex 19 (LC-19) on June 7 just four days after the launch of Gemini 4. The 3,605-kilogram Spacecraft No. 5 was shipped from McDonnell’s St. Louis, Missouri facility on June 19 and mated to GLV-5 on July 8. Testing and other preparations continued towards a scheduled August 9 launch date.

As the crew continued its training vying for time on a limited number of increasingly busy simulators supporting an ever faster pace of future Gemini missions, it soon became apparent that more time was required especially to prepare for the untried and complex rendezvous maneuvers. Reluctantly, on July 21, 1965 Gemini program officials pushed back the scheduled launch date by ten days to give the ground and flight crews more time to prepare for the mission. Cooper and Conrad completed a dress rehearsal for the countdown on July 22 which included the simulated launch of an Atlas-Agena from LC-14. Although this mission was not going to use an Agena as a target vehicle, this was a much needed trial run for the Gemini 6 mission which was scheduled to rendezvous with an Agena in late October (see “The Unflown Mission of Gemini 6“). While the longer than expected 14½ hour exercise went well, it was marred by an unsuccessful attempt to raise the erector at LC-19 at its conclusion so that the crew could exit the spacecraft. Cooper and Conrad had to be extracted using a “cherry picker” similar to that employed during the Mercury program and included at Cooper’s insistence as a backup for just this contingency.

Preparations for the launch of Gemini 5 scheduled for August 19 went well up until the day before liftoff. A series of issues with the new fuel cells and associated instrumentation, which were vital for a successful extended mission in orbit, had cropped up eventually forcing an unscheduled hold at 4:00 AM EDT on launch day. With the launch now pushed out to noon, the astronauts were allowed to sleep in late and did not finally enter the spacecraft until 10:35 AM. The countdown proceeded well until T-10 minutes when thunderstorms threatened the launch site. A lightning strike in the vicinity of the pad caused some instrumentation issues forcing the launch to be scrubbed just as torrential rains engulfed LC-19. Later in the day, a minor fire in the tunnel carrying cables from the blockhouse to the launch pad broke out forcing a complete checkout of the facilities including another mock countdown to ensure there were no problems.

The second launch attempt on August 21 would go much better. Cooper and Conrad were woken up at 4:30 AM and had a traditional steak and eggs breakfast after a brief medical examine. Next, they put on their G4C spacesuits which had been originally meant to support an EVA. While the suits no longer included the extra bulky layers and other provisions needed to protect them from the space environment, the crew would be required to wear the suits for the entire eight-day mission despite their best efforts to be allowed to remove them once in orbit.

After a nearly flawless countdown, Gemini-Titan 5 lifted off from LC-19 at 9:00 AM EDT. All was going well with the ascent until near the end of the first stage burn. The pogo effect set in with the oscillations reaching an uncomfortable peak of 0.38 Gs which exceeded the allowable limit of 0.25 Gs. The ride finally smoothed out just a few seconds before the second stage was suppose to ignite. The rest of the ascent into orbit proceeded as planned with Gemini 5 inserted into an initial 163 by 349 kilometer orbit. A later investigation showed that improper procedures on the ground were responsible for the pogo effect which did not recur for the rest of the Gemini program. The oxidizer tank of the GLV-5 launch vehicle’s first stage was later found afloat in the Atlantic off the coast of Bermuda and was recovered by the US Navy destroyer, USS Dupont (presumably the fuel tank and attached engines broke off and sank).

A Busy First Day

After attaining orbit, the Gemini 5 crew began preparations for their long stay in orbit. Near their first apogee, Cooper fired the OAMS thrusters briefly to raise the perigee to a safer 172 kilometers altitude to ensure orbital decay would not prematurely end the mission. But as the astronauts continued getting ready to deploy the REP, which Conrad had nicknamed “the little rascal”, for the upcoming rendezvous exercise, the first major problem had already cropped up.

As in the future Apollo missions, the long-duration Gemini flights used fuel cells that combined hydrogen and oxygen in a set of specially designed cells to produce electrical power because they were lighter than batteries with the same energy storage capacity. For this mission, which would require an estimated 4,200 amp-hours of electricity, Gemini 5 had been loaded with 10.5 kilograms of liquid hydrogen and 81.5 kilograms of liquid oxygen (LOX). In order to keep the pressure up into the proper operating range as it was emptied, the LOX tank was fitted with an electrical heater to evaporate a small amount of the cryogenic liquid. Unknown to everyone at this time, the heater in the LOX tank had malfunctioned shortly after reaching orbit and the pressure slowly started to drop as a result. Noticing that the pressure in the LOX tank had fallen below the nominal 5,600 kilopascals (kPa) pressure to 3,100 kPa, Conrad manually activated the tank heater. Unfortunately, the malfunctioning heater failed to work and the pressure in the LOX tank continued to slowly declined as the reactant was being used up.

Unaware of the growing problem, the crew continued work for their rendezvous exercise. Two hours and 13 minutes after launch, Cooper yawed the spacecraft 90 degrees to its flight path while passing over the Indian Ocean and ejected the REP target. Cooper then turned to a rear-first attitude and switched on Gemini’s radar. Immediately they were able to detect the REP’s transponder signal which indicated that it was receding at a speed of two meters per second. But just 15 minutes into tracking the REP, the crew noted that the fuel cell’s LOX tank pressure was now only 2,270 kPa and dropping quickly. With a minimum recommended operating pressure of 1,380 kPa, Cooper reluctantly made the decision to power down and abort the rendezvous exercise while out of contact with ground controllers. By the time Gemini 5 had reached the mid-Pacific, the pressure had dropped to only 880 kPa threatening the mission with an early return.

Once back in touch with ground controllers and with the severity of the fuel cell issue realized, engineers at McDonnell set about troubleshooting the problem while at the same time calculations were made to determine how long Gemini 5 could stay aloft on its limited battery power alone. This was done in part to determine not only how much time engineers had to resolve the problem but also to delay Gemini’s return long enough to reach a more favorable recovery zone, if possible. While it was calculated that Gemini could stay in orbit for 13 hours on batteries alone, by the fourth revolution the pressure in the LOX tank had stabilized at 490 kPa. Tests on ground hardware and carefully powering up various spacecraft systems showed that it was possible for the fuel cells to continue operating even at this depressed pressure. Unfortunately, the rendezvous test with the REP was now not possible. A new plan had to be devised to practice rendezvous without the “little rascal”.

In the mean time, the spacecraft was placed into a free drift mode while Cooper and Conrad got some much needed rest on a staggered sleep schedule where one of the astronauts was always awake to monitor spacecraft systems and perform other tasks. Unfortunately, Cooper and Conrad had no better luck getting any sleep than McDivitt and White did during the Gemini 4 mission. Communications with the ground and any activity in the tight confines of the Gemini crew cabin made it difficult for the “off duty” astronaut to get any sleep. The fact that the cabin grew a bit too cool while in the free drift mode only made the situation more uncomfortable. Obviously, changes were needed to keep the crew rested.

The Long Haul

With the excitement of the first day behind them, Cooper and Conrad shifted into a routine of performing experiments and monitoring systems on board the spacecraft. On the third day of the mission, Cooper and Conrad performed a rendezvous exercise with a “phantom” Agena target spacecraft. Relying on calculations and commands from ground controllers as well as their on board computer, the crew successfully executed a mock rendezvous that brought them to within 500 meters of their intended target point demonstrating the techniques that would be required for the upcoming Gemini 6 mission to rendezvous and dock with a real target.

After this successful demonstration, Cooper and Conrad powered down the spacecraft once again and entered a free drift mode performing experiments as they could in the days that followed. They executed radar tests with a ground-based transponder, vision tests, observed smoke from a fire in Laredo, Texas and attempted to observe a checkboard pattern target that was laid out for them to support this experiment. Later, the crew observed a Minuteman I launch from LF-06 at Vandenberg Air Force Base in California codenamed “Shuttle Train” sponsored by the Strategic Air Command (SAC). For their third night in orbit, Cooper’s request for uninterrupted sleep was finally granted. That night, Cooper slept for seven hours while Conrad got five hours.

The next day included some more defense-related experiments. The astronauts successfully observed a rocket sled test at Holloman Air Force Base in New Mexico. During the next overpass, they spotted the contrail of a chase plane before they glimpsed the ignition of a second Minuteman I ICBM launched from LF-04 at Vandenberg as part of an SAC test flight known by the code name “Pilot Rock”. Later as they passed over the Atlantic Ocean, they spotted their recovery ship, the aircraft carrier USS Lake Champlain, with a destroyer escort following astern.

In the mean time, other problems were cropping up that were causing concern. While the pressure in the fuel cell LOX tank had actually risen somewhat alleviating concerns about its operation, the cells were producing 20% more waste water than expected. With no way to dump the excess waste water overboard, there were some concerns that it might exceed tank’s storage capacity. Powering down the fuel cells was not an option because of the limited battery life. In addition, excess hydrogen vented from the fuel cell storage tank tended to make the spacecraft tumble which increased OAMS propellant usage. Since the waste water from the fuel cells was being dumped into the same tank that contained the drinking water supply segregated in a separate bladder, the problem was alleviated by the crew increasing their intake of water.

Late during the fifth day of the mission, it was noticed that parts of the OAMS system started growing sluggish with one thruster quitting entirely. After their next sleep period in a free drift mode, Cooper and Conrad awoke to discover that the whole OAMS was acting erratically and that a second thruster had stopped functioning. Fortunately, one of the two redundant rings of attitude thrusters on the reentry module was available for attitude control for what was left of the mission.

Despite the problems, the astronauts were able to accomplish most of their mission objectives. On the morning of August 26, Cooper and Conrad set a new crewed spaceflight endurance record beating the earlier record set by Soviet cosmonaut Valeri Bykovsky who spent just under four days, 23 hours in orbit during the Vostok 5 mission in June 1963. In addition to beating this two year old record, Cooper and Conrad performed all but one of their planned 17 experiments. Only the “D-2 Nearby Object Photography” experiment, which required observing the REP, was not performed because of the fuel cell issues during the first day of flight. All of the other photography experiments were performed as were the other medical, scientific and defense investigations.

Among the medical experiments was the “M-3 In Flight Exerciser” where the astronauts used a bungee cord with foot straps at one end and a handle at the other to perform some simple exercises. With their ship powered down and in free drift mode, Cooper and Conrad exercised frequently during their last few days in orbit to help pass the time. In another experiment, Conrad used inflatable leg cuffs as part of the “M-1 Cardiovascular Conditioning” experiment. While the experiment was running, these cuffs would inflate for two minutes out of every six to put pressure on Conrad’s legs in an effort to prevent deterioration of his cardiovascular system while in orbit. While the results seemed positive if somewhat inconclusive, they were yet another early example of NASA’s desire to address the effects of prolong weightlessness.

Before they returned home, the Gemini 5 crew participated in a unique communications experiment. Cooper and Conrad briefly talked with former Mercury astronaut Scott Carpenter who was living in Sealab II at the time. Sealab II was the second in a series of underwater habitats developed by the US Navy to prove the viability of saturation diving and humans living in isolation for extended periods of time – issues not unlike those being addressed by NASA’s crewed space program. With a crew of four other “aquanauts”, Carpenter, who was technically still on NASA’s astronaut roster, was spending 30 days at a depth of 62 meters off the coast of La Jolla, California while his fellow aquanauts rotated through two-week stays in Sealab II (for a US Navy documentary on Sealab II, see the Related Video section below). The conversation of these two Mercury veterans exploring two different alien frontiers was surely one of the more unusual moments in the history of the Gemini program.

Returning Home

As the Gemini mission approached its end on the morning of August 29, Cooper and Conrad began preparing for their return to Earth. With neither man being described as particularly tidy, the cramped cabin of their spacecraft had filled up with trash and assorted clutter prompting the often witty Conrad to characterize their mission as “eight days in a garbage can”. This was not too surprising given that a team of specialists had efficiently packed as much as possible into the limited storage space available on the small spacecraft so it was inevitable that better trash management strategies would need to be developed for future long space flights.

But as the astronauts stowed their gear and prepared their spacecraft for landing, ground controllers were concerned about the weather in the planned recovery zone in the Atlantic Ocean 800 kilometers southwest of Bermuda. Early on August 27, a tropical depression had formed over the Atlantic about 560 kilometers east southeast of Barbados and began gaining strength as it drifted more or less towards the north over the Windward Islands. By the morning of August 29, what would become Hurricane Betsy was located east of Puerto Rico and had already strengthened to become a tropical storm. As a result, conditions in the primary recovery zone were quickly worsening. Although the conditions still had not exceeded established safety requirements for landing, the decision was made to bring Gemini 5 back home one orbit early with enough time for the USS Lake Champlain to reposition itself to the alternate recovery zone to the east and farther from the intensifying tropical storm.

While making their final pass over Hawaii 190 hours, 27 minutes and 43 seconds after launch, Gemini 5 fired its four retrorockets in succession to begin the descent back to Earth. With the reentry taking place in complete darkness, the descent was made on instruments only. Cooper held the reentry module in a full lift attitude until an altitude of 120 kilometers and then rolled to a bank angle of 53 degrees. Based on the prediction of the on-board computer, it quickly became apparent that they were going to overshoot their planned landing point. Cooper changed the bank angle to 90 degrees to increase the drag with the G-load quickly shooting up from 2½ to 7½ Gs. Unknown to Cooper and Conrad at the time, human error had resulted in the wrong rotation rate of the Earth being entered into the ground computer guidance program (360 degrees per day instead of 360.98 degrees) which caused a navigation error.

At an altitude of 20 kilometers, Cooper manually deployed the drogue chute followed later by the main parachute. The Gemini 5 reentry module splashed down in the Atlantic 170 kilometers from its planned landing point at 7:55 AM EDT after a flight that lasted a record 7 days, 22 hours, 55 minutes and 14 seconds. Because of the navigation snafu, the demonstration of a precision landing would have to wait for another Gemini flight. Despite coming down far from the recovery ship, the Gemini 5 reentry module was quickly spotted by a Navy helicopter which dispatched three divers to secure the capsule 43 minutes after splashdown. While the seas were calm at the landing site and Cooper initially wanted to wait for the USS Lake Champlain to recover them, he quickly changed his mind when he discovered how far away the carrier actually was and opted for a helicopter recovery instead.

Once on board the carrier, Cooper and Conrad, who were walking fairly well despite eight days in a weightless state, were greeted by the crew and whisked off for the first in a series of post-flight medical examines. While the astronauts’ blood plasma and calcium levels were somewhat low, they survived their eight-day spaceflight in good condition and seemed back to normal after just a couple of days after returning Earth. With 640 man-hours of cumulative experience in space, the American manned space program seemed to have finally turned a corner and was overtaking the Soviet space effort which had become quiet after the Voskhod 2 mission. While there were still more Gemini missions planned to learn what was needed about working and living in space, NASA seemed well on its way to getting Apollo to the Moon.

Follow Drew Ex Machina on Facebook.

Related Video

Here is a US Navy educational film about Sealab II entitled “Man in the Sea: The Story of Sealab II”.

﻿

Related Reading

“The Forgotten Mission of Gemini 4”, Drew Ex Machina, June 3, 2015 [Post]

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

Gemini 5 Press Kit, NASA Press Release 65-262, August 12, 1965