In this age with a permanent human presence in orbit currently provided by the International Space Station (ISS), it seems hard to recall a time when the routine operations needed to maintain it were not so routine. This was certainly the case a half century ago as NASA was still learning the skills needed for Apollo to reach the Moon.

After the early return of NASA’s Gemini 8 mission following a nearly disastrous thruster failure on March 16, 1966 (see “Gemini 8: The First Docking in Space”), NASA still had four more Gemini missions to fly before the first manned Apollo test flight scheduled for the end of that year. While many of the important objectives of the Gemini program had been met, there was still much more to learn and practice before NASA felt confident moving on to the more advanced Apollo flights.

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 subsequently 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. The nose of this module also contained an L-band radar system for orbital rendezvous operations. 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 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 system called OAMS (Orbital Attitude and Maneuvering 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 or more, Gemini needed the largest operational rocket available at the time to get into orbit: a modified Titan II ICBM built by Martin Marietta (which is now part of Lockheed Martin). A number of modifications were made to simplify the operation of this rocket, smooth out its ride and improve its reliability to support crewed missions. With the Gemini spacecraft mounted on top, the Titan II GLV (Gemini Launch Vehicle) was 33 meters tall and had a fully fueled launch mass of about 154 metric tons.

The Gemini 9 Mission Plan

During the first year of manned missions, the Gemini program had made steady progress in meeting its objectives in support of Apollo. A series of long duration missions culminating in the two-week flight of Gemini 7 demonstrated that a crew and its hardware could operate in space for periods of time longer than that needed for Apollo to land on the Moon and return (see “Gemini 7: Two Weeks in the Front Seat of a Volkswagen“). The objectives of the Gemini 9 mission, as well as those that would follow, would center on building experience with rendezvous and docking with an orbiting spacecraft as well as EVAs.

In October 1965, NASA chose the crews that would train for the Gemini 9 mission. The primary crew consisted of Elliot M. See, Jr. as the command pilot and USAF Captain Charles A. Bassett II as the pilot. Before joining NASA’s astronaut corps with the second group selected in September 1962, the 38 year old See had worked as a civilian test pilot for General Electric where he was involved in flight testing of jet engines for various high-performance aircraft. Bassett, who was 34 years old, served as a test pilot at the USAF Fighter Projects Office at Edwards Air Force Base before being selected as an astronaut in October 1963 as part of NASA’s third group of astronauts. Neither man had previously flown in space.

The backup crew for Gemini 9 was USAF Major Thomas P. Stafford as the command pilot and USN Lieutenant Eugene A. Cernan as the pilot. Stafford, who was 35 years old and a graduate of the US Naval Academy, was a pilot who served as the chief of the Performance Branch of the USAF Aerospace Research Pilot School at Edwards before he was selected as an astronaut along with See and seven others in September 1962. He was finishing preparations as pilot for the Gemini 6 mission with Wally Schirra when he was assigned to the Gemini 9 mission. Cernan, who was 31 years old, was a naval aviator with over 1,900 hours of flight experience and was selected for NASA’s third group of astronauts. This was his first flight assignment. All four men of the primary and backup crews also had engineering degrees in addition to being experienced jet aircraft pilots.

The first set of objectives for the Gemini 9 mission centered on orbital rendezvous and docking. The docking target chosen for the Gemini program was a modified Agena D upper stage known as the Gemini Agena Target Vehicle (GATV) launched into orbit using the SLV-3 (Standard Launch Vehicle-3) version of the Atlas booster built by General Dynamics. Built by the Lockheed Missile and Space Company (which is now part of the aerospace giant, Lockheed Martin), the Agena D not only served as an upper stage for use with Thor, Atlas and (by 1966) the Titan IIIB rockets, but could also be integrated into range of Defense Department payloads such as the Corona reconnaissance satellites to provide support functions during these missions. The standardized Agena D, with its modular design, could be easily modified to serve as a docking target for Gemini.

In addition to modifications to its primary and secondary propulsion systems to support its role as a docking target, the forward end of the Agena D was fitted with an auxiliary rack holding special rendezvous and telemetry equipment. Also added were strobe lights and an L-band radar transponder to aid in rendezvous operations as well as command equipment to allow the GATV to be controlled from the ground or by the Gemini crew. A cone shaped target docking adapter (TDA), which was under a shroud during launch, was added to the forward end of the stage to allow the nose of the Gemini reentry module to dock with the Agena and mechanically lock the two spacecraft together. Once in orbit, the GATV was 9.7 meters long with a mass of about 3,200 kilograms.

Over the course of the earlier Gemini missions, the crews had worked their way in a step-wise fashion to develop the various skills required to rendezvous and dock with an orbiting spacecraft just as the Apollo Command-Service Module (CSM) and Lunar Module (LM) would have to do during a lunar landing mission. The original objective of the two-day Gemini 6 mission was to rendezvous and dock with the first flight-ready GATV, Agena GATV-5002 (see “The Unflown Mission of Gemini 6”). Unfortunately, the Agena was lost during launch on October 25, 1965 when its main engine failed upon ignition. Without a replacement GATV available, a new “Gemini 6A” mission was quickly devised where the spacecraft would rendezvous with Gemini 7 during its already planned two-week long duration mission. Gemini 6 with Schirra and Stafford at the controls successfully performed its rendezvous with Gemini 7 on December 15 but no docking was attempted because of the lack time to build and qualify an appropriate interface on the crewed target vehicle (see “Rendezvous in Space: Gemini 6 and 7”). The first actual docking in space took place during the Gemini 8 mission on March 16, 1966. Unfortunately plans for additional docking exercises with the Agena GATV-5003 target and an EVA were called off after a Gemini OAMS thruster malfunction forced an early end to the mission.

A number of different rendezvous modes with the GATV had been identified during theoretical studies. The most aggressive and fastest of these, which would be preferred for the Apollo missions when the LM departed the lunar surface, was the “first apogee” method where the active spacecraft would be launched directly into an elliptical orbit that would allow a rendezvous with the passive target spacecraft during the active spacecraft’s first apogee. This method required a fast-paced sequence of precisely timed and executed maneuvers in order to be successful. For the first Gemini dockings, the “coelliptical” method was chosen instead where the active spacecraft would first be placed into a circular orbit below and some distance behind the passive target spacecraft. The active spacecraft would then catch up to its target over the course of several orbits then maneuver to match the target’s orbit in order to perform the actual docking. While this approach took longer, it was much more flexible and allowed more time to plan and execute maneuvers – a desirable characteristic for the first attempts of the untried orbital rendezvous procedure.

For the Gemini 6A and 8 missions, an “M=4” rendezvous profile was followed where the active Gemini rendezvoused with its passive target during the fourth revolution. Now with actual flight experience in hand, Apollo program officials wanted to test more aggressive rendezvous profiles that were closer approximations of what they wished to fly with the LM. After much debate it was decided that Gemini 9 would attempt a “M=3” profile.

In order to rendezvous one orbit sooner than previous missions, Gemini 9 would have to begin its maneuvers immediately after separation from the second stage of its Titan II launch vehicle. The first maneuver with a delta-v of up to 9 meters per second was called IVAR (Insertion Velocity Adjust Routine) which would immediately reduce the inevitable orbit insertion errors using data provided by the spacecraft’s inertial guidance system. At first apogee about a half orbit later, a phase adjustment maneuver would be performed to get proper phasing of the Gemini and Agena orbits. The next big change in the rendezvous profile came one and a half orbits later with a “triple play” maneuver which would correct phase, height and orbital plane errors all at once. The next maneuver two and a quarter revolutions after orbit insertion would circularize Gemini’s orbit 28 kilometers below its target’s circular 298-kilometer orbit. From this point, Gemini 9 would follow the same sequence of maneuvers as the earlier M=4 missions to reach its target for docking but an orbit earlier.

America’s Second EVA

After docking with its Agena target vehicle, 38½ hours of docked operations would start. On the second day of the mission the next major mission objective would be addressed: an EVA while still docked to the Agena was planned. Up to this time, NASA’s only EVA experience was from Ed White’s brief 20-minute “spacewalk” on June 3, 1965 during the Gemini 4 mission (see “The Forgotten Mission of Gemini 4”). It was not until the Gemini 8 mission that the equipment for more advanced EVA operations was available. Unfortunately, David Scott never had the opportunity to perform his planned EVA after the Gemini 8 mission was cut short. This left a long list of tasks to be accomplished during what was then going to be a record-long 2½ hour EVA by the Gemini 9 pilot.

At a mission elapsed time of 20 hours and 51 minutes, the pilot was scheduled to open his hatch and begin his EVA while attached to the spacecraft using a 7.6-meter umbilical similar to that employed during the Gemini 4 EVA. In addition to the umbilical, life support was also provided by a 19-kilogram, chest mounted Extravehicular Life Support System (ELSS) similar in function to the one worn by White which would allow the astronaut to control his life support and provide 30 minutes of emergency oxygen in case an issue arose with his umbilical-supplied oxygen from Gemini. While standing, the astronaut would recover the experiment called the “S-12 Spacecraft Micrometeoroid Collection” mounted on the Gemini adapter section mounted behind the pilot’s seat and perform some other simple tasks. Next, he would move to the GATV’s Target Docking Adapter (TDA) to remove the similar “S-10 Agena Micrometeoroid Collection” hardware mounted there. With these tasks completed, the astronaut would move across the Gemini adapter section evaluating tether dynamics as well as the usefulness of various handholds and strategically placed Velcro patches on the spacecraft exterior. The pilot would then make his way to the underside of the adapter section where the AMU (Astronaut Maneuvering Unit) was stowed for the Defense Department’s experiment designated D-12.

The AMU was a rectangular backpack measuring 81 by 56 by 48 centimeters with a mass of 76 kilograms. Designed by the USAF, it was meant to provide life support and mobility to an astronaut during an EVA. The unit included a dozen thrusters rated at about five newtons of thrust each to allow the astronaut who wore it to move and change his attitude. The pack carried 11 kilograms of hydrogen peroxide propellant and was capable of a total impulse of about 84 meters per second – far greater than White or Scott had available with their HHMU (Hand Held Maneuvering Units). The AMU also carried 3.3 kilograms of compressed oxygen to provide life support independent of the Gemini spacecraft. The EVA astronaut was suppose to prepare then strap on the AMU with the aid of handholds and foot restraints on the adapter section. The EVA astronaut’s updated G4C spacesuit incorporated new insulation layers including a layer of gray stainless steel fabric called Chromel R in the leg area designed to handle temperatures as high as 700° C from the AMU thruster exhaust.

At the beginning of the second day pass of the EVA, the command pilot would undock from the Agena and move back about 37 meters. The command pilot would then release the AMU and the EVA astronaut, now wearing a 38-meter mechanical tether and using the AMU for life support, would maneuver to a point 12 meters off the nose of Gemini to begin an evaluation of the AMU attitude control system. Afterwards, the command pilot would move the Gemini to pick up the EVA astronaut. After reconnecting his shorter 7.6-meter umbilical, the EVA astronaut would jettison the AMU and complete some last tasks before returning inside. The hatch would be closed after the pilot had spent two hours and 25 minutes outside the spacecraft. The command pilot would then redock with the Agena.

About 3½ hours after the scheduled end of the mission’s EVA, the combined Gemini-Agena would perform the first of three maneuvers with a total delta-v of about 95 meters per second using the Agena’s primary propulsion system. The Agena’s propulsion system was planned to be used in future Gemini missions to perform maneuvers for a second rendezvous with an earlier-used Agena GATV in a storage orbit (as had been done with GATV-5003 used by Gemini 8) as well as boost the combined spacecraft into much higher orbits.

The next two rendezvous exercises to be performed by Gemini 9 were designed to help directly support development of the Apollo rendezvous procedures. In order to cut the total mass of the Apollo spacecraft, the radar system was deleted from the CSM and there was a push to remove it from the LM as well. This would mean that Apollo astronauts would have to rely solely on optical sightings and their computers for rendezvous. In the second rendezvous exercise starting about 45 hours after launch, Gemini 9 would undock and perform a 6.1 meter per second radial maneuver to place itself in a new, elliptical orbit with the same period as before which would carry Gemini up to 21 kilometers from the Agena GATV. This “equi-period rendezvous” would naturally bring Gemini back to the GATV after one orbit approaching from above and ahead of the Agena with only a braking maneuver required to complete the rendezvous. The crew would use only optical sightings and their computer to complete the exercise which would end with a docking at a mission elapsed time of 47 hours and 12 minutes.

The third rendezvous exercise, which would commence half an orbit later, was designed to simulate a LM abort from an altitude of 15 kilometers above the lunar surface. The two spacecraft would undock and the Agena would use its secondary propulsion system to maneuver into a lower orbit below and behind Gemini 9. The Gemini would then perform a series of maneuvers to re-rendezvous with the Agena that were timed to have the Sahara Desert as a Moon-like backdrop to test visual sighting procedures under more realistic conditions. The two spacecraft would redock 52 hours and 40 minutes into the mission. After another 53 minutes of docked operations, the two spacecraft would undock and Gemini 9 would perform a separation maneuver to move into a lower 198 by 275 kilometer orbit. With the large number of planned maneuvers, Gemini 9 was budgeted to use 283 kilograms of its 316-kilogram load of OAMS propellants. The last three Gemini missions would have 50% more propellant available for their even more ambitious missions.

After operations with the Agena were completed, the crew of Gemini 9 would then spend their last day performing experiments and preparing for their return home. The mission was scheduled to end with a splashdown in the western Atlantic recovery zone 70 hours and 40 minutes after launch. The GATV would then be maneuvered and used for a number of engineering tests over the following day. With its fuel depleted, it would be left in a circular 407-kilometer storage orbit where, after its orbit had decayed somewhat, it could serve as a passive rendezvous target during a future Gemini mission.

The Birth of the Gemini 9A Mission

After being chosen for the Gemini 9 mission, See, Bassett and Cernan began their training with Stafford finally joining the group after completing his long-delayed Gemini 6A rendezvous mission on December 16, 1965. The first large piece of mission hardware to arrive at Cape Kennedy on February 13, 1966 was the Atlas designated TLV-5303 which would orbit the mission’s Agena target vehicle. But as final preparations for the shipment of Gemini spacecraft no. 9 from McDonnell’s St. Louis plant were being made, the T-38 jet carrying Elliot See and Charles Bassett on a visit to the McDonnell facility crashed as it was coming around to make a landing attempt in St. Louis in poor weather on February 28, 1966. With the tragic loss of the primary crew, the backup crew stepped up to take their place for the first time in the history of spaceflight. Program officials quickly chose USN Lt. Commander James Lovell, who was the pilot on the record-setting Gemini 7 mission, and rookie astronaut USAF Major Edwin “Buzz” Aldrin as the new backup command pilot and pilot, respectively.

As the crews continued their training, preparations for the Gemini 9 mission carried on. The 3,668-kilogram spacecraft no. 9 arrived at Cape Kennedy on March 2 followed two days later by the Agena target vehicle, GATV-5004. As both spacecraft started pre-launch testing, the mission’s Titan II launch vehicle arrived from Martin’s Baltimore plant on March 10. Titan II GLV-9, serial number 62-12564, was erected on the pad at Launch Complex 19 (LC-19) on March 24 – only eight days after the launch of Gemini 8.

The pace of preparations at the Cape quickened as the scheduled May 17 launch date approached. On May 2 GATV-5004 was mated to its Atlas launch vehicle at LC-14. This was followed by a soft mating of the Gemini with its Titan II at LC-19 the next day and hard mating on May 8. After a final Simulated Flight Test (SFT) of both spacecraft on May 11, the mission was declared ready for launch.

Just like the earlier Gemini 6 and 8 missions, the plan was for the Agena to be launched first at 10:00 AM EST. The launch of the Gemini spacecraft would follow at 11:39:09 AM as the Agena GATV-5004 was completing is first orbit with the exact launch time chosen based on the actual orbit the target achieved. Atlas TLV-5303 lifted off from LC-14 on schedule on May 17, 1966. But only 121 seconds into the flight, pitch control was lost on the number 2 booster engine of the Atlas. The ascending rocket pitched hard about until it was travelling backwards and was lost. With the failure of the Agena to reach orbit, the Gemini 9 crew was pulled from their spacecraft as the mission was scrubbed. For the second time, Tom Stafford had lost the primary target vehicle for his rendezvous and docking mission.

Because of the schedule impact of the loss of the GATV-5002 target in October 1965 which was meant to be the docking target for the Gemini 6 mission Stafford flew, program officials decided to prepare a backup target vehicle in case of further Agena problems. This backup target, known as the Augmented Target Docking Adapter (ATDA), was basically the forward rack with its rendezvous aids and target docking adapter (TDA) of the standard GATV attached to a Gemini rendezvous and recovery section with a ring of thrusters from the RCS (Reentry Control Section) controlling the craft’s attitude. While the ATDA did not have a propulsion system or the flexibility of a standard GATV, it provided a quick means of creating a backup rendezvous and docking target using flight-ready hardware. ATDA No. 02186 was assembled largely from spare hardware and was tested in short order. It was ready for flight after NASA conducted an acceptance review on February 2, 1966 and placed into storage.

In addition to preparing a backup docking target, NASA officials also made arrangements with General Dynamics to have an Atlas available for launch within two weeks in case of the loss of an Agena target. Atlas TLV-5304, which had been scheduled to support the Gemini 10 mission, was pulled out of storage at the Cape and prepared for a flight initially scheduled for May 31. Since the ATDA had a mass of only 790 kilograms, the Atlas could orbit the new target on its own without the need of an orbit insertion burn as the heavier Agena was required to perform. After the cause of the loss of Atlas TLV-5303 was found to be due to a short in the rocket’s autopilot resulting from a crimped wire, NASA officials gave General Dynamics an extra day to make sure the replacement Atlas did not suffer a similar problem.

With the switch to the ATDA and a launch date now set for June 1, the Gemini 9 mission had to be restructured because of the lack of a target vehicle propulsion system. The new flight with its updated timeline was now officially designated “Gemini 9A” to reflect the modified mission. In case the ATDA was also lost, mission planners examined other mission options for Gemini 9A. For a time, there was consideration given to rendezvousing with the inert GATV-5003 which was used during the Gemini 8 mission. But at an altitude of 402 kilometers, the orbit of this Agena had not decayed enough yet for Gemini 9 to safely reach it with the OAMS propellants available. In the end it was decided that if the ATDA were lost, the Gemini 9A would still be launched anyway but the mission would focus just on Cernan’s EVA and other secondary experiments.

On June 1, 1966 everything was once again ready this time for the modified Gemini 9A mission. Atlas TLV-5304 lifted off from LC-14 on schedule at 10:00:02 AM EST. This time the Atlas worked flawlessly placing the ATDA into a circular 298-kilometer orbit as planned. Aside from a lack of telemetry confirming that the launch shroud covering the docking cone had been jettisoned properly, everything looked good. Meanwhile at LC-19, Stafford and Cernan were preparing for launch already strapped inside Gemini 9. But following a planned three-minute hold so that the Gemini countdown hit zero precisely at the beginning of that day’s 40-second launch window to reach the ATDA, problems developed with the ground launch control equipment when it tried to update the spacecraft’s guidance system with a refined launch azimuth. Unable to resolve the problem in time, the launch was scrubbed and recycled 48 hours to fix the affected equipment. For the fourth time in seven months, Stafford’s Gemini launch had been scrubbed (see “Rendezvous in Orbit: The Gemini 6 Launch Abort”).

For the third attempt to get Gemini 9 off the ground, the backup crew of Lovell and Aldrin were in the spacecraft shortly after 2 AM on June 3 to start preparations for launch. An hour later, Stafford and Cernan were woken up for their prelaunch activities which included breakfast with Deke Slayton who was the MSC Director of Flight Crew Operations. As the crew prepared to enter the spacecraft about four hours after waking up, Tom Stafford jokingly gave the closeout crew a meter-long imitation match to “get the rocket off the pad”. Stafford joked that “Frank (Borman) and Jim (Lovell) may have more flight time”, alluding to his backup’s two weeks spent in Gemini 7, “but nobody has more pad time in Gemini than I did”.

By one hour and 40 minutes before launch, Stafford and Cernan were strapped into their seats and the hatches closed. To avoid any last minute problems updating the spacecraft’s guidance system, the ATDA target information was uploaded at 1½ hour and updated again at 15 minutes before scheduled lift off. The updates went off without a hitch and the countdown finally hit zero at 8:39:50 AM EST. With the now familiar roar, the Titan II carrying Gemini 9 was finally on its way.

Rendezvous with an Angry Alligator

With the Titan II accelerating as it pushed Gemini 9 towards orbit, Stafford kept an eye on the spacecraft’s instruments in preparation of the first maneuver immediately after separation. After six minutes of powered flight, Gemini 9 cut loose the last stage of the Titan II and seconds later initiated the IVAR maneuver. With IVAR completed, Gemini 9 was now in a 160 by 267-kilometer orbit about 1,060 kilometers behind the ATDA target.

With no time to enjoy the view, Stafford and Cernan were busy preparing for their next maneuver as they climbed towards their first apogee. As they passed over the Canary Islands tracking station 17 minutes after launch, they got the data they needed for the maneuver based on computer calculations using initial tracking. At 49 minutes into the mission, the OAMS thrusters were fired to add 22.7 meters per second to Gemini’s velocity raising its perigee from 160 to 232 kilometers. During the hour before the “triple play” maneuver, the astronauts took time to check systems, remove their gloves and helmets and prepare their cameras for the rendezvous.

As the time for the next maneuver approached, Stafford pitched the nose of Gemini down 40° and to the left of its flight path by 3°. At two hour and 24 minutes elapsed time, the OAMS thrusters were fired for 51 seconds to change the spacecraft’s velocity by 16.2 meters per second. With the “triple play” maneuver designed to simultaneously correct phase, height and orbital plane errors, Gemini 9 was now in a nearly circular 274 by 276 kilometer orbit 22 kilometers below and 201 kilometers behind the ATDA.

With a radar lock already established at a range of 222 kilometers, Gemini 9 continued to close in towards the ATDA using the same sequence of maneuvers employed successfully during the earlier Gemini rendezvous missions. Three hours and 20 minutes after launch, Stafford and Cernan caught sight of their target at a range of 93 kilometers. As they continued to close in, they could see the flashing of the target’s docking lights raising hopes that the launch shroud had been jettisoned after all. Stafford began slowing his approach at four hours and six minutes elapsed time as he continued to try to get a good look at the target. While they initially thought the shroud may have been jettisoned, soon it became apparent that it was only partially open but still attached to the ATDA blocking access to the docking adapter. When Gemini stopped about 30 meters from the ATDA, the rendezvous was complete but now a docking would be doubtful.

Stafford performed station keeping with the target he described as looking like “an angry alligator” typically staying 9 to 12 meters away as the unstabilized ATDA slowly tumbled. The astronauts provided a detailed description of the situation for the engineers back on the ground. Stafford suggested, half in jest, that it looked like he could just nudge the shroud off using the nose of the Gemini – a proposal ground controllers quickly rejected. It seemed that a lanyard around the shroud had failed to release as it was suppose to do. A later investigation showed that ground crews had taped down the ends of the lanyard because of confusing documentation and the absence of the only member of the team familiar with the undocumented aspects of the lanyard installation as he attended to his pregnant wife. With the ends of the lanyard secured in place, the shroud could not be released.

As ground controllers wrestled with options to jettison the shroud, the decision was made to continue with the next rendezvous exercise. Five hours into the mission, Stafford fired the OAMS thrusters for 35 seconds to change the spacecraft’s velocity by 6 meters per second to start the equi-period rendezvous. As Gemini 9 moved into darkness, Stafford and Cernan were able to track the ATDA using a sextant. The target was exactly where it was suppose to be and Gemini returned to its vicinity as predicted after an orbit. After 75 minutes of drifting away then back towards the ATDA, Stafford began a series of four braking maneuvers to reestablish its position relative to the target. The second rendezvous was now completed.

After about another hour of station keeping, it was time for the first burn to set up the final rendezvous exercise. At an elapsed time of 7 hours and 15 minutes, Stafford fired the OAMS thrusters for a 1.1 meter per second delta-V which lowered Gemini’s orbit to 289 by 296 kilometers. This would allow the two satellites to slowly drift apart over the hours which followed. In the mean time, Stafford and Cernan chatted with controllers about the ATDA issue as they performed systems checks, ate and then tried to get some sleep.

After a fitful night’s sleep, the astronauts were ready to start work for the second day in orbit. With Gemini 9 now 111 kilometers ahead of its target, Stafford started the first in a set of maneuvers for the mission’s final rendezvous exercise 18 hours and 23 minutes after launch. After just a half an hour, Gemini 9 had maneuvered into a higher 307 by 309-kilometer orbit which allowed the ATDA, which was now 155 kilometers away, to start closing in from behind and below. In a rehearsal of a no-radar rendezvous following a LM abort, Stafford and Cernan attempted to visually track their target as they closed in. Over the Atlantic Ocean and then the Sahara Desert, the astronauts had much difficulty spotting their target. It was not until the distance had closed to six kilometers that the ATDA was spotted looking “like a pencil dot on a sheet of paper”, as described by Stafford. After three hours and 19 minutes, Gemini 9 completed its final rendezvous with the ATDA. The astronauts concluded that they would have failed to rendezvous with the target without the radar and that a visual-only rendezvous did not seem feasible. The LM would ultimately keep its rendezvous radar after all.

With three rendezvous exercises completed in under 24 hours, only one major objective of the Gemini 9A mission remained: Cernan’s EVA. When it was decided that it would be too dangerous for Cernan to attempt freeing the ATDA’s stuck launch shroud because of fears that sharp edges of the lanyard could puncture his suit, it was decided to leave the ATDA in order to conserve Gemini’s dwindling OAMS propellant supply. With the crew being so fatigued by their activities so far, Stafford insisted that Cernan’s EVA should be postponed until the following day. Eventually ground controllers agreed with CAPCOM Neil Armstrong later saying that Stafford’s decision reflected “exceptionally good judgment”.

After Stafford had maneuvered to within 8 centimeters of the ATDA as part of a Defense Department experiment to simulate the inspection of a tumbling satellite, the OAMS thrusters were briefly fired to change Gemini’s velocity by a meter per second and the ATDA was left behind for the final time. The astronauts concentrated on conducting various medical and scientific experiments in addition to the usual routines of monitoring their spacecraft’s systems, eating and resting.

The Snake and the Return Home

At 5:30 AM EST on June 5, 1966, Stafford and Cernan, who had already been awake for some time, began preparations for the EVA about 4½ hours before it was scheduled to commence. Alternating between periods of activity then resting as they unstowed and set up their equipment in the cramped confines of Gemini’s cabin, the two worked through an 11-page check list and were ready a few minutes ahead of schedule. At a mission elapsed time of 49 hours and 22 minutes, Cernan’s hatch was opened for what was planned to be a 167-minute EVA.

Standing on his seat, Cernan discarded a trash bag then set about some simple tasks. These included retrieving the S-10 Micrometeoroid Collection experiment from the adapter section after 16 hours of exposure and setting up a rearview mirror to provide Stafford with a view of the adapter section. But as he was working through his list, Cernan was discovering how each task seemed to take longer than he had rehearsed during zero-g training on aircraft. When he finally fully exited the spacecraft to test tether dynamics, Cernan found that every movement he made seemed to cause a reaction that set his body tumbling in an undesired direction. The umbilical, which Cernan referred to as “the snake”, made every motion more difficult especially since he had no HHMU (Hand Held Maneuvering Unit) like White had during his EVA a year earlier to counteract its effects.

After making his way back to the spacecraft, Cernan started moving over the adapter section. He found that his mobility was greatly reduced as he fought against his pressurized spacesuit which was made even stiffer by its extra protective layers. The handholds set up for the EVA also proved to be inadequate and the Velcro patches were not strong enough to hold Cernan in place especially as he struggled with “the snake”. While the view was simply amazing, all of this intense physical effort taxed Cernan’s strength and tired him. After reaching the lower edge of the adapter section, Cernan carefully moved passed a jagged edge left from stage separation and towards the AMU stowed beneath.

Once again, Cernan struggled to prepare the AMU with every task taking four or five times longer than expected. The handholds and foot restraints that were provided were found to be inadequate as the astronaut struggled to maintain position as he performed even the simplest of tasks. By the 67-minute mark of the EVA, the faceplate of Cernan’s improved helmet started fogging as moisture built up in his suit. As Cernan worked through his 35-point checklist to prepare the AMU, his heart rate hit 155 beats per minute. Tired and sweating profusely, Cernan was finally able to switch his air supply from the Gemini to the AMU completing this objective. Cernan rested a while but his vision was still limited by the faceplate fogging up. In the mean time, Cernan’s struggles had ripped open the seams on the outer insulation layers of his spacesuit subjecting his back to high temperatures. Garbled communications and Stafford’s inability to see his crewmate only worsen the situation.

With flight doctors concerned about Cernan becoming overheated and too exhausted, the decision was finally made to cancel the AMU free flight exercise. Cernan’s fatigue, his fogged faceplate and the inevitable struggle that was yet to come when discarding the AMU made deployment unwise. Bitterly disappointed, Cernan disconnected himself from the AMU with much effort and made his way back to the hatch with his view restricted to a gap he had created in the fog on his faceplate using his nose. After some difficulty moving back inside due to suit mobility issues, the hatch was finally closed with Stafford’s help. Cernan had spent only two hours and 8 minutes outside the Gemini spacecraft – 39 minutes less than planned. Despite the early return inside, the record-setting EVA was still considered a success. All in all it was chalked up as a learning experience with Cernan’s unexpected difficulties revealing a number of shortcomings in EVA equipment, training and techniques that would have to be addressed during the remaining three Gemini flights.

About an hour and a half after the EVA was completed and with the cabin repressurized, Stafford fired Gemini’s thrusters to adjust the orbit one last time to optimize the orbit for retrofire the next day. With the EVA completed, the astronauts rested and ate before moving on to performing experiments, stowing gear for their return home and other duties for the balance of their last day in orbit day.

The astronauts woke up from their third “night” in orbit just under four hours before their scheduled return to the Earth. Their final objective of the mission was to perform a precision landing using inputs from their computer to steer the Gemini reentry module during descent. After the retro-rockets were fired at 8:26:17 AM EST on June 6 at 71 hours, 46 minutes and 44 seconds after launch, Gemini 9 was predicted to come down 102 kilometers from its intended aim point. Despite the initial aiming error, the Stafford and Cernan were able to guide their capsule to splashdown only 704 meters from their intended target point in the west Atlantic recovery zone just past 9:00 AM EST. The Gemini 9A mission had ended with a total flight time of 72 hours, 20 minutes and 50 seconds.

Having come down so close to the aircraft carrier the USS Wasp which was tasked with their recovery, Stafford and Cernan opted to stay in their ship until it was hoisted aboard 53 minutes after splashdown. With the mission of Gemini 9A now completed, efforts now turned towards the remaining three flights of the Gemini program. In addition to practicing various rendezvous options in preparation for the Apollo lunar missions, the crews of these last flights would also have to overcome the issues uncovered during Cernan’s EVA if astronauts were expected to perform useful tasks outside of their spacecraft. Despite the issues, Gemini 9 was very successful and brought the US one step closer to its lunar landing goal with 3½ years remaining in the decade.

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Related Reading

“The Unflown Mission of Gemini 6”, Drew Ex Machina, October 25, 2015 [Post]

“Rendezvous in Space: The Launch of Gemini 7”, Drew Ex Machina, December 4, 2015 [Post]

“Rendezvous in Space: The Gemini 6 Launch Abort”, Drew Ex Machina, December 12, 2015 [Post]

“Rendezvous in Space: Gemini 6 and 7”, Drew Ex Machina, December 15, 2015 [Post]

“Gemini 8: The First Docking in Space”, Drew Ex Machina, March 16, 2016 [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 9 Press Kit”, NASA Press Release 66-97, May 10, 1966