S-IVb secondary payloads

Found and photographed at the NASA-HQ historical archive was this painting depicting work being done upon an orbiting S-IVb stage. What’s happening is that small secondary payloads were to be installed in the Instrument Unit which ringed the top of the S-IVb stage below the conical main payload shroud, and they could be accessed by astronauts for use or retrieval. This is described in the Saturn V Payload Planner’s Guide (available HERE).