At 10:20 pm (22:20:26 UTC) on July 18, 1966, the Gemini 10 space mission launched from Cape Kennedy’s pad LC-19, carrying two astronauts. It was the eighth manned Project Gemini flight, the 16th manned American flight and the 24th spaceflight of all time. This was the first use of the Agena Target Vehicle’s propulsion systems while the spacecraft rendezvoused with the Agena Target Vehicle from Gemini VIII. Astronaut Michael Collins made two spacewalks to retrieve experiments from the Agena. Gemini 10 also established that radiation at high altitude was not a problem. The nearly three-day mission completed 43 orbits.
Project Gemini was NASA’s second human spaceflight program. Conducted between projects Mercury and Apollo, Gemini started in 1961 and concluded in 1966. The Gemini spacecraft carried a two-astronaut crew. Ten Gemini crews flew low Earth orbit (LEO) missions between 1965 and 1966 putting the United States in the lead during the Cold War Space Race against the Soviet Union.
Gemini’s objective was the development of space travel techniques to support the Apollo mission to land astronauts on the Moon. It performed missions long enough for a trip to the Moon and back, perfected working outside the spacecraft with extra-vehicular activity (EVA), and pioneered the orbital maneuvers necessary to achieve space rendezvous and docking. With these new techniques proven by Gemini, Apollo could pursue its prime mission without doing these fundamental exploratory operations.
All Gemini flights were launched from Launch Complex 19 (LC-19) at Cape Kennedy Air Force Station in Florida. Their launch vehicle was the Gemini–Titan II, a modified Intercontinental Ballistic Missile (ICBM). Gemini was the first program to use the newly built Mission Control Center at the Houston Manned Spacecraft Center for flight control.
The astronaut corps that supported Project Gemini included the “Mercury Seven”, “The New Nine”, and the 1963 astronaut class. During the program, three astronauts died in air crashes during training, including the prime crew for Gemini 9. This mission was performed by the backup crew, the only time that had happened in NASA’s history to date.
Gemini was robust enough that the United States Air Force planned to use it for the Manned Orbital Laboratory (MOL) program, which was later canceled. Gemini’s chief designer, Jim Chamberlin, also made detailed plans for cislunar and lunar landing missions in late 1961. He believed Gemini could perform lunar operations before Project Apollo, and cost less. NASA’s administration did not approve those plans. In 1969, McDonnell-Douglas proposed a “Big Gemini” that could have been used to shuttle up to twelve astronauts to the planned space stations in the Apollo Applications Project (AAP). The only AAP project funded was Skylab — which used existing spacecraft and hardware — thereby eliminating the need for Big Gemini.
After the existing Apollo program was chartered by President John F. Kennedy on May 25, 1961, to land men on the Moon, it became evident to NASA officials that a follow-on to the Mercury program was required to develop certain spaceflight capabilities in support of Apollo. Specifically, Jim Chamberlin, the head of engineering at the Space Task Group (STG), was already assigned to start working on a bridge program between Mercury and Apollo in February 1961. He presented two initial versions of Gemini at a NASA retreat at Wallops Island in March 1961. Scale models of Mercury Mark II were shown in July 1961 at McDonnell Aircraft Corporation’s offices in St. Louis. NASA approved Project Gemini on December 7, 1961. The McDonnell corporation was contracted to build it on December 22, 1961.
When it was publicly announced on January 3, 1962, it was formally re-christened Project Gemini. Gemini in Latin means “twins” or “double”, which reflected that the spacecraft would hold two astronauts. Gemini is also the name of the third constellation of the Zodiac and its twin stars, Castor and Pollux.
The major objectives were:
- To demonstrate endurance of humans and equipment in spaceflight for extended periods, at least eight days required for a Moon landing, to a maximum of two weeks
- To effect rendezvous and docking with another vehicle, and to maneuver the combined spacecraft using the propulsion system of the target vehicle
- To demonstrate Extra-Vehicular Activity (EVA), or space-“walks” outside the protection of the spacecraft, and to evaluate the astronauts’ ability to perform tasks there
- To perfect techniques of atmospheric reentry and touchdown at a pre-selected location on land
The two-crew member carrying Gemini capsule was designed by a Canadian, Jim Chamberlin. He was previously the chief aerodynamicist on Avro Canada’s Avro Arrow fighter interceptor program. Chamberlin joined NASA along with 25 senior Avro engineers after cancellation of the Arrow program, and became head of the U.S. Space Task Group’s engineering division in charge of Gemini. The prime contractor was McDonnell Aircraft Corporation, which was also the prime contractor for the Project Mercury capsule.
Astronaut Gus Grissom was heavily involved in the development and design of the Gemini spacecraft (the other Mercury astronauts dubbed the Gemini spacecraft the “Gusmobile”). Grissom writes in his posthumous 1968 book Gemini! that the realization of Project Mercury’s end and the unlikelihood of his having another flight in that program prompted him to focus all of his efforts on the upcoming Gemini program.
The Gemini program was managed by the Manned Spacecraft Center, located in Houston, Texas, under direction of the Office of Manned Space Flight, NASA Headquarters, Washington, D.C. Dr. George E. Mueller, Associate Administrator of NASA for Manned Space Flight, served as acting director of the Gemini program. William C. Schneider, Deputy Director of Manned Space Flight for Mission Operations, served as mission director on all Gemini flights beginning with Gemini 6A.
Guenter Wendt was a McDonnell engineer who supervised launch preparations for both the Mercury and Gemini programs and would go on to do the same when the Apollo program launched crews. His team was responsible for completion of the complex pad close-out procedures just prior to spacecraft launch, and he was the last person the astronauts would see prior to closing the hatch. The astronauts appreciated his taking absolute authority over, and responsibility for, the condition of the spacecraft and developed a good-humored rapport with him.
NASA selected McDonnell Aircraft, which had been the prime contractor for the Project Mercury capsule, in 1961 to build the Gemini capsule, the first of which was delivered in 1963. The spacecraft was 18 feet 5 inches (5.61 m) long and 10 feet (3.0 m) wide, with a launch weight varying from 7,100 to 8,350 pounds (3,220 to 3,790 kg).
The Gemini crew capsule (referred to as the Reentry Module) was essentially an enlarged version of the Mercury capsule. Unlike Mercury, the retrorockets, electrical power, propulsion systems, oxygen, and water were located in a detachable Adapter Module behind the Reentry Module. A major design improvement in Gemini was to locate all internal spacecraft systems in modular components, which could be independently tested and replaced when necessary, without removing or disturbing other already tested components.
Many components in the capsule itself were reachable through their own small access doors. Unlike Mercury, Gemini used completely solid-state electronics, and its modular design made it easy to repair.[ Gemini’s emergency launch escape system did not use an escape tower powered by a solid-fuel rocket, but instead used aircraft-style ejection seats. The tower was heavy and complicated, and NASA engineers reasoned that they could do away with it as the Titan II’s hypergolic propellants would burn immediately on contact. A Titan II booster explosion had a smaller blast effect and flame than on the cryogenically fueled Atlas and Saturn. Ejection seats were sufficient to separate the astronauts from a malfunctioning launch vehicle. At higher altitudes, where the ejection seats could not be used, the astronauts would return inside the spacecraft, which would separate from the launch vehicle.
The main proponent of using ejection seats was James Chamberlin, head of the engineering division of NASA’s Space Force Task Group. Chamberlin had never liked the Mercury escape tower and wished to use a simpler alternative that would also reduce weight. He reviewed several films of Atlas and Titan II ICBM failures, which he used to estimate the approximate size of a fireball produced by an exploding launch vehicle and from this he gauged that the Titan II would produce a much smaller explosion, thus the spacecraft could get away with ejection seats.
Maxime Faget, the designer of the Mercury LES, was on the other hand less-than-enthusiastic about this setup. Aside from the possibility of the ejection seats seriously injuring the astronauts, they would also only be usable for about 40 seconds after liftoff, by which point the booster would be attaining Mach 1 speed and ejection would no longer be possible. He was also concerned about the astronauts being launched through the Titan’s exhaust plume if they ejected in-flight and later added that “The best thing about Gemini was that they never had to make an escape.”
Gemini was the first astronaut-carrying spacecraft to include an onboard computer, the Gemini Guidance Computer, to facilitate management and control of mission maneuvers. This computer, sometimes called the Gemini Spacecraft On-Board Computer (OBC), was very similar to the Saturn Launch Vehicle Digital Computer. The Gemini Guidance Computer weighed 58.98 pounds (26.75 kg). Its core memory had 4096 addresses, each containing a 39-bit word composed of three 13-bit “syllables”. All numeric data was 26-bit two’s-complement integers (sometimes used as fixed-point numbers), either stored in the first two syllables of a word or in the accumulator. Instructions (always with a 4-bit opcode and 9 bits of operand) could go in any syllable.
Unlike Mercury, the Gemini used in-flight radar and an artificial horizon — devices similar to those used in the aviation industry.
The original intention for Gemini was to land on solid ground instead of at sea, using a Rogallo wing rather than a parachute, with the crew seated upright controlling the forward motion of the craft. To facilitate this, the airfoil did not attach just to the nose of the craft, but to an additional attachment point for balance near the heat shield. This cord was covered by a strip of metal which ran between the twin hatches. This design was ultimately dropped, and parachutes were used to make a sea landing as in Mercury. The capsule was suspended at an angle closer to horizontal, so that a side of the heat shield contacted the water first. This eliminated the need for the landing bag cushion used in the Mercury capsule.
Gemini was equipped with an Orbit Attitude and Maneuvering System (OAMS), containing sixteen thrusters for translation control in all three perpendicular axes (forward/backward, left/right, up/down), in addition to attitude control (pitch, yaw, and roll angle orientation) as in Mercury. Translation control allowed changing orbital inclination and altitude, necessary to perform space rendezvous with other craft, and docking with the Agena Target Vehicle (ATV), with its own rocket engine which could be used to perform greater orbit changes.
Early short-duration missions had their electrical power supplied by batteries; later endurance missions used the first fuel cells in manned spacecraft.
Gemini was in some regards more advanced than Apollo because the latter program began almost a year earlier. It became known as a “pilot’s spacecraft” due to its assortment of jet fighter-like features, in no small part due to Gus Grissom’s influence over the design, and it was at this point where the American manned space program clearly began showing its superiority over that of the Soviet Union with long duration flight, rendezvous, and extravehicular capability. The Soviet Union during this period was developing the Soyuz spacecraft intended to take cosmonauts to the Moon, but political and technical problems began to get in the way, leading to the ultimate end of their manned lunar program.
The Titan II had debuted in 1962 as the Air Force’s second-generation ICBM to replace the Atlas. By using hypergolic fuels, it could be stored for long periods of time and be easily readied for launch in addition to being a simpler design with fewer components, the only caveat being that the propellant mix (nitrogen tetroxide and hydrazine) was extremely toxic compared to the Atlas’s liquid oxygen/RP-1. However, the Titan had considerable difficulty being man-rated due to early problems with pogo oscillation. The launch vehicle used a radio guidance system that was unique to launches from Cape Kennedy.
Deke Slayton, as director of flight crew operations, had primary responsibility for assigning crews for the Gemini program. Each flight had a primary crew and backup crew, and the backup crew would rotate to primary crew status three flights later. Slayton intended for first choice of mission commands to be given to the four remaining active astronauts of the Mercury Seven: Alan Shepard, Grissom, Cooper, and Schirra. John Glenn had retired from NASA in January 1964 and Scott Carpenter, who was blamed by some in NASA management for the problematic reentry of Aurora 7, was on leave to participate in the Navy’s SEALAB project and was grounded from flight in July 1964 due to an arm injury sustained in a motorbike accident. Slayton himself continued to be grounded due to a heart problem.
Titles used for the left-hand (command) and right-hand seat crew positions were taken from the U.S. Air Force pilot ratings, Command Pilot and Pilot. Sixteen astronauts flew on 10 manned Gemini missions.
In late 1963, Slayton selected Shepard and Stafford for Gemini 3, McDivitt and White for Gemini 4, and Schirra and Young for Gemini 5 (which was to be the first Agena rendezvous mission). The backup crew for Gemini 3 was Grissom and Borman, who were also slated for Gemini 6, to be the first long-duration mission. Finally Conrad and Lovell were assigned as the backup crew for Gemini 4.
Delays in the production of the Agena Target Vehicle caused the first rearrangement of the crew rotation. The Schirra and Young mission was bumped to Gemini 6 and they became the backup crew for Shepard and Stafford. Grissom and Borman then had their long-duration mission assigned to Gemini 5.
The second rearrangement occurred when Shepard developed Ménière’s disease, an inner ear problem. Grissom was then moved to command Gemini 3. Slayton felt that Young was a better personality match with Grissom and switched Stafford and Young. Finally, Slayton tapped Cooper to command the long-duration Gemini 5. Again for reasons of compatibility, he moved Conrad from backup commander of Gemini 4 to pilot of Gemini 5, and Borman to backup command of Gemini 4. Finally he assigned Armstrong and Elliot See to be the backup crew for Gemini 5. The third rearrangement of crew assignment occurred when Slayton felt that See wasn’t up to the physical demands of EVA on Gemini 8. He reassigned See to be the prime commander of Gemini 9 and put Scott as pilot of Gemini 8 and Charles Bassett as the pilot of Gemini 9.
The fourth and final rearrangement of the Gemini crew assignment occurred after the deaths of See and Bassett when their trainer jet crashed, coincidentally into a McDonnell building which held their Gemini 9 capsule in St. Louis. The backup crew of Stafford and Cernan was then moved up to the new prime crew of the re-designated Gemini 9A. Lovell and Aldrin were moved from being the backup crew of Gemini 10 to be the backup crew of Gemini 9. This cleared the way through the crew rotation for Lovell and Aldrin to become the prime crew of Gemini 12.
Along with the deaths of Grissom, White, and Roger Chaffee in the fire of Apollo 1, this final arrangement helped determine the makeup of the first seven Apollo crews, and who would be in position for a chance to be the first to walk on the Moon.
In 1964 and 1965, two Gemini missions were flown without crews to test out systems and the heat shield. These were followed by ten flights with crews in 1965 and 1966. All were launched by Titan II launch vehicles. Some highlights from the Gemini program:
- Edward H. White became the first American to make an extravehicular activity (EVA, or “space walk”), on June 3, 1965 during Gemini 4.
- Gemini 5 demonstrated the 8-day endurance necessary for an Apollo lunar mission with the first use of fuel cells to generate its electrical power.
- Gemini 6A and 7 accomplished the first space rendezvous in December 1965, and Gemini 7 set a 14-day endurance record.
- Gemini 8 achieved the first space docking with an unmanned Agena Target Vehicle.
- Gemini 11 set a manned Earth orbital altitude record of 739.2 nautical miles (1,369.0 km) in September 1966, using the propulsion system of its Agena target vehicle. This record still stands as of 2017.
- Edwin “Buzz” Aldrin on Gemini 12 became the first space traveler to prove that useful work could be done outside a spacecraft without life-threatening exhaustion.
Rendezvous in orbit is not a straightforward maneuver. Should a spacecraft increase its speed to catch up with another, the result is that it goes into a higher and slower orbit and the distance thereby increases. The right procedure is to slow down and go to a lower orbit first, and then later to increase speed and go to the same orbit as the other. To practice these maneuvers special rendezvous and docking simulators were built for the astronauts.
The Agena Target Vehicle (ATV), also known as Gemini-Agena Target Vehicle (GATV) was an unmanned spacecraft used by NASA during its Gemini program to develop and practice orbital space rendezvous and docking techniques and to perform large orbital changes, in preparation for the Apollo program lunar missions. Each ATV consisted of an Agena-D derivative upper rocket stage built by Lockheed and a docking adapter built by McDonnell. The Agena was launched from Cape Canaveral Air Force Station Launch Complex 14 on top of an Atlas booster built by the Convair division of General Dynamics. The Agena first burn would occur shortly after shroud jettison and separation from the Atlas over the Atlantic Ocean. Over Ascension Island, a second burn would place the Agena into a low circular orbit.
The McDonnell Gemini spacecraft would then be launched from Launch Complex 19, as soon as 90 minutes later. Both countdowns would proceed in parallel and required close synchronization. The Gemini would rendezvous and dock with the Agena as soon as Gemini’s first orbit toward the end of the program.
The Gemini astronauts would then fly the combined spacecraft in a stabilized mode and perform a number of experiments:
- Using the Agena’s attitude control system to stabilize the combination, which saved the Gemini’s propellants
- Extra-vehicular activity to perform practice work on a tool panel. This required installing handrails on later flights to prevent excessive astronaut exertion.
- Refiring the Agena engine to raise the spacecraft’s apogee. Gemini 11 reached a record of 739.2 nautical miles (1,369.0 km). The modified Bell 8247 engine was qualified for up to 15 restarts.
- Undocking, unreeling a 50-foot (15 m) nylon tether between the capsule and the Agena and flying in a “dumbbell” configuration with the Agena below the astronauts, to check the gravitational effect on the formation stability in uncontrolled mode. This technique is now known as Gravity-gradient stabilization.
- Using a similar tether and a few thruster bursts to rotate the two craft around each other as an early test of artificial gravity.
- After rendezvous with its own ATV, Gemini 10 performed a second rendezvous with the ATV from Gemini 8.
After the Gemini capsule separated for the last time, the Agena remained in orbit for a short time and was used to verify the command system.
The first Gemini-Agena Target Vehicle (GATV) was launched on October 25, 1965 while the Gemini 6 astronauts were waiting on the pad. While the Atlas performed normally, the Agena’s engine exploded during orbital injection. Since the rendezvous and docking was the primary objective, the Gemini 6 mission was scrubbed, and replaced with the alternate mission Gemini 6A, which rendezvoused (but could not dock) with Gemini 7 in December.
Gemini 10 was designed to achieve the objectives planned for the last two missions — rendezvous, docking and EVA. As well as this, it was also hoped to dock with the Agena Target Vehicle from the Gemini 8 mission. This Agena’s battery power had failed many months earlier and this would demonstrate the ability to rendezvous with a passive object. It would be also the first mission to fire the Agena’s own rocket, allowing them to reach higher orbits.
The Gemini 10 mission patch was simple in design but highly symbolic. The main feature is a large X with a Gemini and Agena orbiting around it. The two stars have a variety of meanings: the two rendezvous attempts, Castor and Pollux in Gemini or the two crew members. This is one of the few crew patches without the crew’s name. It is able to be displayed “upside down” but is correctly shown with the spacecraft to the right. It was designed by Young’s first wife, Barbara.
The Agena Target Vehicle for Gemini 10, GATV-5005, was launched on July 18, 1966 at 20:39:46 UTC with a mass of 7,000 pounds (3,200 kg). The Agena launched perfectly for the second time, after problems had occurred with the targets for Gemini 6 and 9. Gemini 10 followed 100 minutes later at 22:20:26 UTC and entered a 86.3-by-145.2-nautical-mile (159.9 by 268.9 km) orbit. They were 970 nautical miles (1,800 km) behind the Agena.
Two anomalous events occurred during the launch. At liftoff, a propellant fill umbilical became snared with its release lanyard. It ripped out of the LC-19 service tower and remained attached to the second stage during ascent. Tracking camera footage also showed that the first stage oxidizer tank dome ruptured after staging and released a cloud of nitrogen tetroxide. The telemetry package on the first stage had been disabled at staging, so visual evidence was the only data available. Film review of Titan II ICBM launches found at least seven other instances of post-staging tank rupture, most likely caused by flying debris, second stage engine exhaust, or structural bending. NASA finally decided that this phenomenon did not pose any safety risk to the astronauts and no corrective action had to be taken.
Gemini 10 established that radiation at high altitude was not a problem. After docking with their Agena booster in low orbit, Young and Collins used it to climb temporarily to 412.4 nautical miles (763.8 km). After leaving the first Agena, they then met with the dead, drifting Agena left over from the aborted Gemini 8 flight — thus executing the program’s first double rendezvous. With no electricity on board the second Agena, the rendezvous was accomplished with eyes only — no radar. After the rendezvous, Collins spacewalked over to the dormant Agena at the end of a 50-foot (15 m) tether, making Collins the first person to meet another spacecraft in orbit. He retrieved a cosmic dust-collecting panel from the side of the Agena, but was not able to take any pictures; in the complicated business of keeping his tether clear of the Gemini and Agena, his Hasselblad camera worked itself free and drifted away.
Collins discovered that he was unable to use the sextant for navigation as it did not seem to work as expected. At first he mistook airglow as the real horizon when trying to make some fixes on stars. Then the image didn’t seem right. He tried another instrument that they had on board but this was not practical to use as it had a very small field of view.
They fortunately had a backup in the form of the computers on the ground. They made their first burn to put them into a 143-by-147-nautical-mile (265 by 272 km) orbit. However Young didn’t realize that during the next burn, he had the spacecraft turned slightly, which meant that they introduced an out-of-plane error. This meant two extra burns were necessary, and by the time they had docked with the Agena, 60% of their fuel had been consumed. It was decided to keep the Gemini docked to the Agena as long as possible, as this would mean that they could use the fuel on board the Agena for attitude control.
The first burn of the Agena engine lasted 80 seconds and put them in a 159-by-412-nautical-mile (294 by 763 km) orbit. This was the highest a person had ever been, although the record was soon surpassed by Gemini 11, which went to over 540 nautical miles (1,000 km). This burn was quite a ride for the crew. Because the Gemini and Agena docked nose-to-nose, the forces experienced were “eyeballs out” as opposed to “eyeballs in” for a launch from Earth. The crew took a couple of pictures when they reached apogee but were more interested in what was going on in the spacecraft — checking the systems and watching the radiation dosage meter.
After this, they had their sleep period which lasted for eight hours and then they were ready for another busy day. The crew’s first order of business was to make a second burn with the Agena engine to put them into the same orbit as the Gemini 8 Agena. This was at 20:58 UTC on July 19 and lasted 78 seconds and took 340 feet per second (105 m/s) off their speed, putting them into a 159-by-206-nautical-mile (294 by 382 km) orbit. They made one more burn of the Agena to circularize their orbit to 203.9 nautical miles (377.6 km).
It was now time for the first of two EVAs on Gemini 10. This was to be just a standup EVA, where Collins would stand in the open hatch and take some photographs of stars as part of experiment S-13. They used a 70 mm general purpose camera to image the southern Milky Way in ultraviolet. After orbital sunrise, Collins then photographed a color plate on the side of the spacecraft (MSC-8) to see whether film reproduced colors accurately in space. They reentered the spacecraft six minutes early when they both found their eyes were irritated, which was caused by a minor leak of lithium hydroxide in the astronauts’ oxygen supply. After repressurizing the cabin, they ran the oxygen at high rates and flushed the environment system.
After the exercise of the EVA Young and Collins slept in their second ‘night’ in space. The next ‘morning’ they started preparing for the second rendezvous and another EVA.
After undocking from their Agena, the crew thought they sighted the Gemini 8 Agena. It however turned out to be their own Agena 3.0 nautical miles (5.5 km) away, while their target was 95 nautical miles (176 km) away. It wasn’t until just over 16 nautical miles (30 km) away that they saw it as a faint star. After a few more correction burns, they were station-keeping 10 feet (3.0 m) away from the Gemini 8 Agena. They found the Agena to be very stable and in good condition.
At 48 hours and 41 minutes into the mission, the second EVA began. Collins’ first task was to retrieve a Micrometeorite Collector (S-12) from the side of the spacecraft. This he accomplished with some difficulty (similar to that encountered by Eugene Cernan on Gemini 9A). However, the collector floated out of the cabin some time later during the EVA and was lost.
He next traveled over to the Agena and tried to grab onto the docking cone but found this impossible as it was smooth and had no grip. Collins used a nitrogen-propelled Hand-Held Maneuvering Unit (HHMU) to move himself towards the Gemini and then back to the Agena. This time he was able to grab hold of some wire bundles and retrieved the Micrometeorite Collector (S-10) from the Agena. He decided against replacing it as he could lose the one he had just retrieved.
His last task on this EVA was to test out the HHMU. However this stopped working and meant they finished the EVA after only 39 minutes. During this time, it took the crew eight minutes to close the hatch as they had some difficulty with the 50-foot (15 m) umbilical. It was jettisoned along with the chestpack used by Collins an hour later when they opened the hatch for the third and final time.
There were ten other experiments that the crew performed during the mission. Three were interested in radiation: MSC-3 was the Tri-Axis Magnetometer which measured levels in the South Atlantic Anomaly. There was also MSC-6, a beta spectrometer, which measured potential radiation doses for Apollo missions, and MSC-7, a bremsstrahlung spectrometer which detected radiation flux as a function of energy when the spacecraft passed through the South Atlantic Anomaly.
S-26 investigated the ion and electron wake of the spacecraft. This provided limited results due to the lack of fuel for attitude control, but found that electron and ion temperatures were higher than expected and it registered shock effects during docking and undocking.
The S-5 and S-6 experiments were performed, which were previously carried on Gemini 9A; these were Synoptic Terrain and Synoptic Weather photography respectively. There was also S-1 which was intended to image the Zodiacal light. All of these experiments were of little use as the film used was only half as sensitive as Gemini 9A and the dirty windows lowered the transmission of light by a factor of six.
The crew also tried to perform D-5, a navigation experiment. They were only able to track five stars, with six needed for accurate measurements. The last experiment, D-10, was to investigate an ion-sensing attitude control system. This experiment measured the attitude of the spacecraft from the flow of ions and electrons around the spacecraft in orbit. The results from this experiment showed the system to be accurate and responsive.
The last day of the mission was short and retrofire came at 70 hours and 10 minutes into the mission. They landed at 21:07:05 UTC on July 21, 1966, only 3.0 nautical miles (5.6 km) away from the intended landing site — 26°44.7′N 71°57′W — and were recovered by USS Guadalcanal. The Gemini 10 mission was supported by a total of 9,067 U.S. Department of Defense personnel, 78 aircraft and 13 ships. The Agena Target Vehicle reentered on December 29, 1966.
For many years the spacecraft was the centerpiece of a space exhibition at Norsk Teknisk Museum, Oslo, Norway. It was returned on request in 2002. It is currently on display at the Cosmosphere in Hutchinson, Kansas. When the restoration of the Gemini 6A spacecraft is completed, then Gemini 10 will be restored in full view of the public. At the end of this restoration it will be put back on full display at the Cosmosphere. One of the hatches is displayed at Virginia Air and Space Center in Hampton, Virginia.
On September 29, 1967, a pair of se-tenant stamps were issued at Kennedy Space Center, Florida, to salute America’s space accomplishments. The 5-cent stamps were designed by Paul Calle of Stamford, Connecticut. The left stamp, Scott #1331, depicts Astronaut Ed White, the first American astronaut to perform a spacewalk. White and two other astronauts died earlier in 1967 (the year this stamp was issued) when the Apollo I space capsule caught fire on the launching pad. White’s famous spacewalk occurred on June 3, 1965. The spacecraft depicted on the right-hand stamp, Scott #1332, is Gemini 4, the mission for which lasted from June 3 to 7, 1965. An unseparated pair of stamps is catalogued as Scott #1332b.
Lithographed and engraved, the stamps were printed using the Giori press and perforated 11 in panes of 50. On the upper left and lower left panes, the astronaut stamp was the first, third, and fifth stamps; the spaceship was the second and fourth. This arrangement was reversed on the upper right and lower right panes. In these positions, the spaceship was the first, third, and fifth stamps, with the astronaut on the second and fourth.
Offset and intaglio were combined to produce the stamp, which had one horizontal plate number. Offset printed the red stripes in the flags on the astronaut’s spacesuit and capsule and light blue sky areas, as well as the inscription on the astronaut stamp. The Giori press printed dark blue sky areas, the aqua earth, and black tones on the capsule and astronaut. The inscription on the spaceship stamp was white. An initial printing of 120,000,000 was authorized with 60,432,000 of each stamp ultimately released.