Transposition, docking, and extraction (often abbreviated to transposition and docking) was a maneuver performed during Apollo lunar landing missions from 1969 to 1972, to withdraw the Apollo Lunar Module (LM) from its adapter housing which secured it to the Saturn V launch vehicle 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 (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 docking created a continuous, pressurized tunnel which permitted the astronauts to transfer internally between the CSM and the LM.
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:
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 had trouble getting the capture latches to engage for docking on Apollo 14, and the procedure took two hours and eighteen minutes.
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-orbiting Apollo 7 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), 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.