Apollo 9 was the first Apollo mission to include an EVA, a spacewalk conducted from the LM Spider orbiting the Earth to simulate external transfer rescue techniques from the LM to the CSM and test the spacesuit (Extravehicular Mobility Unit or EMU) to be worn on the lunar surface by future moonwalkers.

On the fourth day of the mission, McDivitt and Schweickart entered the LM Spider in preparation of the EVA. Because of space sickness, Schweickart’s scheduled two hour EVA was scrubbed and then rescheduled for a more classic spacewalk from the porch of the LM Spider when Schweickart felt better. Apollo 9 was the only mission in history with a spacewalk conducted from the LM.

APOLLO 9 EVA PRACTICE Test subject John B. (Jack) Slight, MSC Flight Crew Support Division, is seen transferring from Lunar Module trainer to Command Module trainer during Apollo 9 extravehicular activity practice under zero-gravity conditions aboard a US Air Force KC-135 Jet Aircraft from Ellington Air Force Base. Slight is wearing the Extravehicular Mobility Unit (EMU). [NASA caption]