Gemini XI

Gemini XI conducting a tether experiment using the Agena Target Vehicle
Mission type	Space rendezvous Spacecraft docking Extravehicular activity
Operator	NASA
COSPAR ID	1966-081A
SATCAT no.	02415
Mission duration	2 days, 23 hours, 17 minutes and 9 seconds
Orbits completed	44
Spacecraft properties
Spacecraft	Gemini SC11
Manufacturer	McDonnell Aircraft
Launch mass	3,798 kg (8,374 lb)
Landing mass	1,920 kg (4,230 lb)
Crew
Crew size	2
Members	Charles "Pete" Conrad Jr. Richard F. Gordon Jr.
EVAs	2
EVA duration	2 hours and 41 minutes
Start of mission
Launch date	September 12, 1966, 14:42:26 (1966-09-12UTC14:42:26Z)  UTC (9:42:26 am  EST)
Rocket	Titan II GLV
Launch site	Cape Kennedy, LC-19
End of mission
Recovered by	USS Guam
Landing date	September 15, 1966, 13:59:35 (1966-09-15UTC13:59:36Z) UTC
Landing site	Atlantic Ocean ( 24°15′N 70°0′W / 24.250°N 70.000°W / 24.250; -70.000 (Gemini 11 splashdown))
Orbital parameters
Reference system	Geocentric orbit
Regime	Low Earth orbit
Perigee altitude	298 km (185 mi; 161 nmi)
Apogee altitude	1,374 km (854 mi; 742 nmi)
Inclination	28.8°
Period	101.57 minutes
Epoch	September 14, 1966 [1]
Docking with GATV-5006
Docking date	September 12, 1966, 16:16:00 UTC
Undocking date	September 14, 1966, 16:55:00 UTC
Time docked	2 days and 39 minutes
Mission patch Gordon and Conrad Project Gemini ←  Gemini 10 Gemini 12 →

Gemini 11 (officially Gemini XI) ^[2] was the ninth crewed spaceflight mission of NASA's Project Gemini, which flew from September 12 to 15, 1966. It was the 17th crewed American flight and the 25th spaceflight to that time (includes X-15 flights over 100 kilometers (54 nmi)). Astronauts Pete Conrad and Dick Gordon performed the first direct-ascent (first orbit) rendezvous with an Agena Target Vehicle, docking with it 1 hour 34 minutes after launch; used the Agena rocket engine to achieve a record high- apogee Earth orbit; and created a small amount of artificial gravity by spinning the two spacecraft connected by a tether. Gordon also performed two extra-vehicular activities for a total of 2 hours 41 minutes.

• Clifton C. Williams Jr. (Cape CAPCOM)
• John W. Young (Houston CAPCOM)
• Alan L. Bean (Houston CAPCOM)

• Mass: 3,798 kilograms (8,374 lb)

Highest orbit (followed twice):

• Perigee: 298 kilometers (185 mi; 161 nmi) ^[3]
• Apogee: 1,374 kilometers (854 mi; 742 nmi) ^[4]
• Inclination: 28.85°
• Period: 101.52 min

• Docked: September 12, 1966, 16:16:00 UTC
• Undocked: September 14, 1966, 16:55:00 UTC

• Gordon – EVA 1
  • Start: September 13, 1966, 14:44:00 UTC
  • End: September 13, 1966, 15:17:00 UTC
  • Duration: 33 minutes
• Gordon – EVA 2 (stand up)
  • Start: September 14, 1966, 12:49:00 UTC
  • End: September 14, 1966, 14:57:00 UTC
  • Duration: 2 hours and 8 minutes

• Perform a direct-ascent rendezvous with the Agena Target Vehicle on the first orbit in support of Project Apollo. This would simulate a Lunar Module rendezvous with the Command/Service Module after a lunar landing.
• Use the Agena rocket engine to put the combined craft in a high- apogee elliptical orbit.
• Perform two extra-vehicular activities.
• Demonstrate passive attitude stabilization of the two spacecraft connected by a tether and create artificial gravity by spinning the combined craft. ^[5]
• Perform miscellaneous scientific experiments.
• Perform a computer-controlled atmospheric reentry to a precision splashdown point.

Gemini 11 spacecraft launches on Titan II GLV rocket

Atlas rocket launches Agena target vehicle for the Gemini 11 mission

The direct-ascent rendezvous and docking with the Agena vehicle was achieved approximately 94 minutes after lift-off, depending on the on-board computer and radar equipment with only minimal assistance from ground support. ^[5]

Gemini 11 used the rocket on its Agena target vehicle to raise its apogee to 853 miles (1,373 km), the highest Earth orbit ever reached by a crewed spacecraft at the time. ^[6] The perigee was 179 miles (288 km), and maximum velocity (at perigee) was 17,967 miles per hour (28,915 km/h). ^[5] The apogee record stood until the until Polaris Dawn in 2024; men have achieved greater distances from Earth by flying to the Moon in the Apollo program. ^[7] The maximum operational altitude of the Space Shuttle was much lower, at 386 miles (621 km) for the STS-31 flight in 1990. The September 2021 SpaceX flight of Inspiration4, while having an apogee higher than most Space Shuttle flights, only reached 585 kilometres (364 mi). ^[8]

The crew docked and undocked four times and still had sufficient Gemini maneuvering fuel for an unplanned fifth rendezvous. They did not remain in the high orbit, but changed it back to a near-circular one at 184 miles (296 km). ^[5]

Gordon's first EVA, planned to last for two hours, involved fastening a 100-foot (30 m) tether, stored in the Agena's docking collar, to the Gemini's docking bar for the passive stabilization experiment. Gordon achieved this, but as with previous Gemini EVAs, trying to work for an extended period proved more fatiguing than in ground simulation, and the EVA had to be terminated after only half an hour.

The passive stabilization experiment proved to be troublesome. Conrad and Gordon separated the craft in a nose-down (i.e., Agena-down) position, but found that the tether would not be kept taut simply by the Earth's gravity gradient, as expected. They were able to generate a small amount of artificial gravity, about 0.00015 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of bolas. ^[5]

Gordon successfully performed a second EVA standing up with his head and shoulders out of the hatch to photograph the Earth, clouds, and stars. This was not tiring and lasted more than two hours. ^[5]

The 12 scientific experiments were: ^[9]

• Mass Determination: To test a technique and accuracy of a direct-contact method of determining the mass of an orbiting object, in this case the Agena Target Vehicle.
• Night Image Intensification: To test the usefulness and performance of a low-light-level television system as a supplement to unaided vision in observing surface features primarily when such features are in darkness and spacecraft pilots are not dark-adapted.
• Power Tool Evaluation: To evaluate man's capability to perform work tasks in space, including the comparison of ability to work tethered and untethered, and to evaluate the performance of the minimum-reaction power tool.
• Radiation and Zero G Effects on Blood and Neurospora: To determine whether weightlessness enhances the effects of radiation on human white blood cells and Neurospora crassa fungi. ^[10]
• Synoptic Terrain Photography: To obtain high-quality photographs for research in geology, geophysics, geography, oceanography, and related fields.
• Synoptic Weather Photography: To obtain selective high-quality photographs of clouds to study the fine structure of the Earth's weather system.
• Nuclear Emulsion: To study the cosmic radiation incident on the Earth's atmosphere, to obtain detailed chemical composition of the heavy primary nuclei, and to search for rare particles.
• Airglow Horizon Photography: To measure by direct photography the heights at which atomic oxygen and sodium layers occur in the upper atmosphere.
• Ultraviolet Astronomical Camera: To test the techniques of ultraviolet photography under vacuum conditions and to obtain ultraviolet radiation observations of stars in wavelength region of 2,000 to 4,000  angstroms by spectral means.
• Ion Wake Measurement: To determine and measure the ion and electron wake structure and perturbation of the ambient medium produced by an orbiting vehicle, and to study the changes in the ion flux and wake caused by thruster firings.
• Earth-Moon Libration Region Photography: To investigate the regions of the L4 and L5 libration points of the Earth–Moon system to determine the possible existence of clouds of particulate matter orbiting the Earth in these regions ( Kordylewski clouds).
• Dim-Light Photography and Orthicon: To obtain photographs of various faint and diffuse astronomical phenomena.

The mission ended with the first totally automatic, computer-controlled reentry by the U.S., which brought Gemini 11 down 2.8 miles (4.5 km) from its recovery ship USS Guam, only 1.5 miles (2.4 km) from the planned position. ^[5]

Astronaut recovery was done by Navy Helicopter Squadron HS-3.

The Gemini 11 mission was supported by 9,054 United States Department of Defense personnel, 73 aircraft, and 13 ships. ^[11]

Since Conrad and Gordon were both members of the US Navy, the embroidered mission patch was designed in Navy colors: blue and gold. Stars are used to mark the major milestones of the mission. The first orbit Agena rendezvous is marked by a small gold star just above the Earth, to the left. The Agena docking is marked by a large star on the left. The star at the top marks the record high apogee reached by Gemini 11. Note that the scale is greatly exaggerated; their maximum altitude of 850 miles (1,370 km) is roughly the distance from St. Louis to Cape Kennedy. Finally, the star on the right marks Dick Gordon's spacewalk. The docking, record apogee and spacewalk are also shown on the patch by the Agena, orbital apogee path and spacewalking astronaut.

Gemini 11's record altitude was ultimately the result of an internal race to the Moon. As early as 1961, NASA's Jim Chamberlin and McDonnell Aircraft had advocated using Gemini spacecraft to get to the Moon sooner than Apollo. Their proposals considered using Centaur rockets to boost the Gemini on a circumlunar trajectory (similar to the Soviet's Zond program), lunar orbit missions using Centaur rockets for translunar injection and Agena for lunar orbit insertion, and even lunar landing missions using Gemini in place of the Apollo Command Module and a small open-cockpit Langley Light LM in place of the Apollo Lunar Module. Multiple Titan or Saturn IB rockets, and even the abandoned Saturn C-3 were considered as the launch vehicles.

Pete Conrad liked these ideas and together with McDonnell corporations strongly advocated his Gemini 11 to be circumlunar. Discretely called 'Gemini - Large Earth Orbit', the plan would use a Titan IIIC-launched Transtage. The Gemini 11 crew would be launched with the Titan II GLV as they did in reality, and would dock with the Transtage, which would then boost them to translunar velocity. Conrad managed to stir Congressional interest, but NASA administrator James Webb informed them that any extra funds Congress cared to appropriate for such a project would be better spent accelerating the Apollo program. After further internal struggles, Conrad finally got NASA approval for the Agena on his Gemini 11 flight to boost him onto two record highly elliptical 1,370 km orbits. This high flight was the only remnant of lunar Gemini. ^[12]

The Gemini 11 capsule on display at the California Science Center in Los Angeles

The spacecraft is on display at the California Science Center in Los Angeles, California.

• Agena Target Vehicle
• Extra-vehicular activity
• List of spacewalks
• Splashdown
• Space exploration
• U.S. space exploration history on U.S. stamps
• Space capsule
• Space suit

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

Wikimedia Commons has media related to Gemini 11.

• NASA Gemini 11 press kit - Sep 2, 1966
• The short film Gemini XI is available for free viewing and download at the Internet Archive.
• Spaceflight Mission Patches
• NASA Space Science Data Coordinated Archive
• U.S. Space Objects Registry