Transposition, docking, and extraction

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Transposition, docking, and extraction, often shortened to transposition and docking, was a maneuver used on Apollo lunar missions to free the Lunar Module from its adapter on the Saturn V and prepare it for flight. The command module pilot separated the Command and Service Module from the adapter, turned the CSM around, and docked its nose to the Lunar Module, then pulled the two together away from the upper stage. This created a continuous, pressurized tunnel that let the crew transfer between the CSM and the LM without space suits. The docking happened soon after the trans-lunar injection that sent the spacecraft on a three-day trip to the Moon. A similar docking was used in 1975 on the Apollo–Soyuz Test Project to connect with a special docking module that linked the Apollo CSM to the Soyuz.

The maneuver was usually performed by the Command Module Pilot, though the Commander and the Lunar Module Pilot were trained as backups. It typically took about an hour, but could take longer if problems occurred; for example, on Apollo 14 Stuart Roosa’s trouble engaging the docking latches extended the time to about 2 hours and 18 minutes. Transposition and docking occurred on all Apollo missions carrying both the CSM and LM, starting with Apollo 9. The concept was first tested in Earth orbit on Apollo 7, which used a docking target in the SLA but carried no LM. The early Block I SLA on the Saturn IB had panels that opened but didn’t move away, preventing docking; this was fixed with the Block II SLA used from Apollo 8 onward, which detached the panels and pushed them away with springs. The last mission to use the maneuver was Apollo–Soyuz, which docked to a specially designed adapter compatible with Soyuz 19.