Transposition, docking, and extraction

Transposition, docking, and extraction (often abbreviated to transposition and docking) was a maneuver performed during manned Apollo program missions from 1969 to 1972, and the Apollo-Soyuz Test Project (ASTP) mission in 1975. It involved an astronaut separating the Apollo Command/Service Module (CSM) spacecraft from the adapter which fastened it to its launch vehicle upper stage, turning it around, and docking its nose to the Apollo Lunar Module (LM) (or in the case of ASTP, to a special docking module which enabled docking with the Soyuz spacecraft), then pulling the combined spacecraft away from the upper stage. On the Apollo lunar missions, it was performed shortly after the trans-lunar injection maneuver that placed the Apollo spacecraft on a trajectory towards the Moon, about three days before arrival there.

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 manned Saturn V Apollo flights (starting with Apollo 8), which detached the panels and pushed them away from the S‑IVB with springs.

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