Transposition, docking, and extraction (often abbreviated to transposition and docking) was a maneuver performed during
Apollo
Apollo is one of the Twelve Olympians, Olympian deities in Ancient Greek religion, ancient Greek and Ancient Roman religion, Roman religion and Greek mythology, Greek and Roman mythology. Apollo has been recognized as a god of archery, mu ...
lunar landing missions from 1969 to 1972, to withdraw the
Apollo Lunar Module
The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed sp ...
(LM) from its
adapter housing which secured it to the
Saturn V launch vehicle
A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...
upper stage and protected it from the
aerodynamic stresses of launch. The maneuver involved the command module pilot separating the
Apollo Command and Service Module
The Apollo command and service module (CSM) was one of two principal components of the United States Apollo (spacecraft), Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functi ...
(CSM) from the adapter, turning the CSM around, and
docking its nose to the Lunar Module, then pulling the combined spacecraft away from the upper stage. It was performed shortly after the
trans-lunar injection maneuver that placed the
Apollo spacecraft on a three-day trajectory to the
Moon
The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
. The docking created a continuous, pressurized tunnel which permitted the astronauts to transfer internally between the CSM and the LM.
The same maneuver was performed on the 1975
Apollo–Soyuz Test Project (ASTP) mission to extract a special docking module used to connect the Apollo Command Module with the
Soyuz spacecraft.
Procedure
Transposition and docking was performed by the
Command Module Pilot (CMP) (although, as a backup, the Commander and
Lunar Module Pilot (or ASTP Docking Module Pilot) were also trained to perform the maneuver), and involved the following steps:
#A "CSM/LV Sep" button on the control panel was pressed, which ignited
detonating cord and separated the CSM from the
Spacecraft–lunar module adapter (SLA), and the four adapter panels from each other and the
S-IVB upper stage. This exposed the
LM.
#The CSM's
translation
Translation is the communication of the semantics, meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The English la ...
thrusters were used to move it a safe distance away.
Rotation
Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...
thrusters were then used to
pitch up the CSM 180° and
roll it to the proper alignment angle for
docking. Translation thrusters were then used to move it back to the LM. A T-shaped docking target on the top of the LM aligned optically with a reticle pattern on the CMP's left-hand docking window to ensure proper spacecraft alignment.
#A soft dock was achieved when a probe at the top of the CSM was inserted into a hole in the center of a cone-shaped drogue at the top of the LM and three small capture latches closed. Hard dock was achieved by activating a mechanism which retracted the probe and caused twelve more capture latches to close around the command module's docking flange.
#A pressure equalization valve in the CM forward hatch was opened to allow oxygen to fill the LM through a similar valve in its hatch that was left open at launch. When the pressure equalized, the pilot removed the CM hatch, removed the probe and drogue, inspected the capture latches, and connected two
umbilical cables which electrically connected the CM and LM. He then replaced the CM hatch.
#The LM hold-down attachments and umbilical connection to the S-IVB
Instrument Unit were released, and the CSM's translation thrusters were used to pull the CSM/LM stack a safe distance away from the
S-IVB, which would then be steered by ground control either to a
heliocentric orbit
A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun ...
, or to a deliberate crash landing on the Moon.
The astronauts were in no hurry to complete this maneuver, which nominally took about an hour. It would take longer if problems were encountered; for instance,
Stuart Roosa
Stuart Allen Roosa (August 16, 1933 – December 12, 1994) was an American aeronautical engineer, smokejumper, United States Air Force pilot, test pilot, and NASA astronaut, who was the Command Module Pilot for the Apollo 14 mission. The mis ...
had trouble getting the capture latches to engage for docking on
Apollo 14
Apollo 14 (January 31February 9, 1971) was the eighth crewed mission in the United States Apollo program, the third to Moon landing, land on the Moon, and the first to land in the Geology of the Moon#Highlands, lunar highlands. It was the las ...
, and the procedure took two hours and eighteen minutes.
Missions

Transposition and docking was performed on all Apollo missions which carried both the CSM and the LM, from
Apollo 9 onward. Transposition and a mock LM-docking approach was first simulated on the
Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
-orbiting
Apollo 7
Apollo 7 (October 11–22, 1968) was the first crewed flight in NASA's Apollo program, and saw the resumption of human spaceflight by the agency after the fire that had killed the three Apollo 1 astronauts during a launch rehearsal test ...
flight (which carried a docking target in the SLA, but no LM). The "Block I" SLA used on the early
Saturn IB launch vehicles had panels that opened at a 45° angle but did not separate from the S‑IVB. One of the panels did not open the full angle, preventing the crew from approaching the S‑IVB for fear they might strike this panel. This was corrected with the "Block II" SLA design used on all crewed
Saturn V Apollo flights (starting with
Apollo 8
Apollo 8 (December 21–27, 1968) was the first crewed spacecraft to leave Sphere of influence (astrodynamics), Earth's gravitational sphere of influence, and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times ...
), which detached the panels and pushed them away from the S‑IVB with springs.
The last mission to use the maneuver was the
Apollo–Soyuz Test Project mission, in which the Apollo CSM docked to a specially designed adapter module which carried docking equipment compatible with the
Soyuz 19 spacecraft.
See also
*
Manned Venus flyby – a transposition and docking maneuver would have been required on this mission
References
{{reflist
External links
Apollo 15 Flight Journal: Transposition, Docking and Extraction
Astrodynamics
Orbital maneuvers
Apollo program
Articles containing video clips